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The East Asian Monsoon (EAM) impacts storms, freshwater availability, wind energy production, coal consumption, and subsequent air quality for billions of people across Asia. Despite its importance, the EAM's long‐term behavior is poorly understood. Here we present an annually resolved record of EAM variance from 1584 to 1950 based on radiocarbon content in a coral from the coast of Vietnam. The coral record reveals previously undocumented centennial scale changes in EAM variance during both the summer and winter seasons, with an overall decline from 1600 to the present. Such long‐term variations in monsoon variance appear to reflect independent seasonal mechanisms that are a combination of changes in continental temperature, the strength of the Siberian High, and El Niño–Southern Oscillation behavior. We conclude that the EAM is an important conduit for propagating climate signals from the tropics to higher latitudes. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Published version

With the popularity of swimming activities across the world, the responsibility of the pool operators and managers to ensure the microbial and chemical safety of the pool participants becomes extremely significant. Disinfection by-products (DBPs) in swimming pool waters (SPWs) have attracted considerable public attentions due to their high frequency of occurrence, considerable concentrations and potent toxicity. This study explored the appropriateness of novel approaches for the control and treatment of DBPs. Chlorine/bromine stabilized disinfectants have been attempted to fulfil the dual requirements of sufficient disinfectants and less DBP formation. Reverse osmosis and nanofiltration have been used to remove haloacetic acids (HAAs, a group of prevalent DBPs) and the mechanism governing the rejection has been well interpreted. The effect of calcium ion (a ubiquitous species in SPWs) on HAA rejection has been systematically investigated. The fundamental understanding of these DBP control protocols offers good theoretical basis for future practical applications. Doctor of Philosophy (IGS)

Due to increasing threats from terrorism in the past decades, progressive collapse modeling of buildings is gaining popularity with objective of simulating collapse process of the whole or partial structural system, in order to give useful insight to improve existing design for the structure against progressive collapse. In this thesis, a novel modeling framework for progressive collapse of reinforced concrete (RC) frame structures is proposed. A set of damage assessment criteria to identify and quantify flexural, shear and axial damages and failures of RC members is suggested. This set of damage criteria incorporates axial-shear-flexural interactions of the structure during the analysis and it is capable of tracing cracking and crushing of concrete, yielding and fracture of reinforcement as well as final failures of cross-sections within RC members. Direct member removal algorithm is developed to simulate the process of collapse at member level, based on combined flexural/shear/axial failures of RC members. With developing a specially designed searching scheme, a new algorithm to monitor substructure collapse is also proposed. Locations and magnitudes of impact loads of the collapsed partial structure are also identified and calculated, according to rigid-body kinematics and energy principle. In addition, inelastic and oblique impact effects are properly considered. To efficiently simulate progressive collapse of large-scale buildings, superelement technique which separates the structure into linear and nonlinear zones is employed to reduce the computational time. As buildings in progressive collapse may undergo large rigid-body rotations of the structure, a rigid-body rotation correction to improve conventional superelement formulation is proposed for a more accurate large deformation analysis using superelement. Further, in order to consider nonlinearity spread during progressive collapse analysis, an adaptive superelement algorithm to automatically identify the propagation of nonlinear zone and then update the definition of superelement is proposed. By incorporating direct member removal algorithms as well as model regeneration procedure, an efficient adaptive superelement modeling procedure is developed for progressive collapse of RC frame structures. Numerical examples are given to show the advantages and effectivity of the suggested damage criteria and modeling procedures, through comparison with the results obtained from physical tests or standard nonlinear finite element analysis. Doctor of Philosophy (CEE)

Increasing use of nanomaterials (NMs) in a wide range of consumer products has raised concerns about their impacts on natural and engineered ecosystems. NMs released into the ecosystems will potentially influence organisms at all levels of the food chain. Microorganisms are at a low trophic level and play critical roles in maintaining the health of ecosystems. Hence, the impacts of NMs on microorganisms have attracted great interests. However, majority of the toxicological studies of NMs have focused on their bactericidal (killing) and bacteriostatic (growth-inhibiting) effects. Although the concentration of NMs in the environments is expected to be much lower than those used in most nanotoxicity studies, little is known about the influences of NMs at sublethal concentrations on critical functions of microorganisms. The objective of this study was to elucidate the impact of NMs on microbial functions. Specifically, the focus was on the influence of NMs at sublethal levels on bacterial social behaviours including production of communal resources, intercellular communication, and collective antibiotic tolerance. Cells of Pseudomonas species often produce siderophores, a group of organic compounds that facilitate iron uptake for the producers and their neighboring non-producers in microbial communities. Pyoverdine (PVD) is one of the most important siderophores produced by Pseudomonas aeruginosa and it is an important communal resource in environmental microbial communities and also a key virulence factor in establishing infections in medical settings. Tellurium nanorods (TeNRs) produced using a metal-reducing bacterium Shewanella oneidensis and physicochemically synthesized single-wall carbon nanotubes (SWCNTs) significantly inhibited PVD production in P. aeruginosa. Quantitative polymerase chain reaction (qPCR) and RNA-sequencing based transcriptomics analyses revealed that the inhibition was at transcriptional level. Quorum sensing (QS) is one of the most important signalling systems that bacteria use to coordinate cooperative behaviours. QS signalling has been shown to play a critical role in various natural and engineered bioprocesses. The acylated homoserine lactones (AHLs) is one of the predominant QS signals used by most Gram-negative bacteria. Using Pseudomonas syringae and Pantoea stewartii as model organisms, the key AHLs produced by these two organisms were identified and quantified the influences of silver nanoparticles (AgNPs) and single-wall carbon nanotubes (SWCNTs) on the production of different AHLs. P. syringae mainly produced 6 short-chain AHLs, while P. stewartii produced 11 short- and long-chain AHLs. The presence of AgNPs in P. syringae cultures resulted in overall reduction of AHLs. Intriguingly, the production of most AHLs in P. stewartii was not significantly affected by either 0.5 µg/ml AgNPs or 20 µg/ml SWCNTs. This study reports the differential effects exhibited by NMs on the production of different signals. The impact of AgNPs on collective antibiotic tolerance of a sludge wastewater community in terms of live/active community composition was also evaluated. There was no significant change in the community structure in response to the nanomaterial treatment. Moreover, treatment with tetracycline followed by AgNPs treatment did not result in significant change in the antibiotic tolerance profile under the testing conditions. Taken together, these findings provide a novel insight into environmental impacts of NMs. This study will aid in comprehensive understanding the effect of NMs on various aspects of cell-cell interactions in microbial communities that often play critical roles in maintaining the health of ecosystems in various natural and engineered ecosystems. Doctor of Philosophy (CEE)

This study investigates production scaling up of MgO cement synthesized from reject brine and evaluates the mechanical properties and microstructures of the resulting MgO cement. Hydration process and carbonation degree of the resulting MgO mortar were investigated and compared with commercial MgO cement. Compressive strength, scanning electron microscopy (SEM), X-ray powder diffraction (XRD), particle size analysis, acid reactivity, and thermogravimetric and differential thermal analysis (TG/DTA) were engaged for sample characterization. Results showed that MgO cement synthesized from reject brine possesses higher mechanical strength of 32.5 MPa at the age of 28 days as compared to the commercial MgO cement (20.1 MPa). This is mainly attributed to the high reactivity of the synthesized MgO cement as revealed by the microstructure study. Master of Engineering (CEE)

With the prevailing green skepticism, consumers tend to devalue firms' environmental claims and raise concerns on service fairness of green offerings. Applying theoretical insights from fairness literature to the context of green consumerism, this study examines the antecedents, consequences, and moderators of fairness perceptions in consumers' response to green service offerings. A scenario-based experiment is conducted (n 1⁄4 600) for data collection and the data are analyzed using Structural Equation Modelling (SEM). It is found that consumers' inferred relative profit (PRO) of the firm negatively influences their perceived fairness (FAI), whereas a positive inference on firms' motives (MOT) leads to a fairer perception by consumers. Furthermore, to a certain extent, firms' commitment to environment (F-ENV) and con- sumers' personal environmental commitment (C-ENV) serve as effective moderators that enhance consumers' fairness perception. However, multi-sampling moderation tests suggest that PRO remains as a persistent source of the unfairness perception regardless of the levels of C-ENV. It is only when F-ENV is present then consumers' unfairness perception would be attenuated. This study contributes to literature with a unique theoretical perspective of service fairness in examining consumers' behavioral response to green service offerings. Also, it provides practical insights to managing the effectiveness of firms' green initiatives by placing consumers’ fairness as a critical concern. Accepted version

International audience; Understanding how loss of biodiversity affects ecosystem functioning, and thus the delivery of ecosystem goods and services, has become increasingly necessary in a changing world. Considerable recent attention has focused on predicting how biodiversity loss simultaneously impacts multiple ecosystem functions (that is, ecosystem multifunctionality), but the ways in which these effects vary across ecosystems remain unclear. Here, we report the results of two 19-year plant diversity manipulation experiments, each established across a strong environmental gradient. Although the effects of plant and associated fungal diversity loss on individual functions frequently differed among ecosystems, the consequences of biodiversity loss for multifunctionality were relatively invariant. However, the context-dependency of biodiversity effects also worked in opposing directions for different individual functions, meaning that similar multifunctionality values across contrasting ecosystems could potentially mask important differences in the effects of biodiversity on functioning among ecosystems. Our findings highlight that an understanding of the relative contribution of species or functional groups to individual ecosystem functions among contrasting ecosystems and their interactions (that is, complementarity versus competition) is critical for guiding management efforts aimed at maintaining ecosystem multifunctionality and the delivery of multiple ecosystem services.

Locating suitable caves and stalagmites for palaeoenvironmental and palaeoclimatic studies can be challenging. Isotopic geochemical analyses, albeit commonly performed for palaeoclimatic reconstruction, are also time consuming and costly. Therefore, petrographic and non‐destructive morphological studies on speleothems are desirable to facilitate sample selection for further analysis. In this study, 20 caves were surveyed in Ban Rai district, Uthai Thani province in western Thailand. After external physical observations in the field, three stalagmite samples were collected from Tham Nam Cave to test their potential for palaeoclimatic research. Firstly, the stalagmites were scanned by X‐ray computed tomography (CT scanning) and subsequently the CT images were compared with petrographic inspections. Columnar fabrics show the highest density, whereas closed and open dendritic fabrics have medium and the lowest densities, respectively. Layers near the top and bottom of the three stalagmites were dated by U‐Th mass spectrometric techniques. All three samples were deposited between c. 87 and c. 105 ka ago; therefore, they are probably the oldest stalagmites that have been reported so far from mainland Southeast Asia. However, their physical features indicate that all the samples have suffered from postdepositional dissolution, and are unlikely to be suitable for palaeoclimatic research. The internal dissolution feature of stalagmites, however, cannot be identified by visual inspection of uncut samples. We hereby argue that CT images are useful to characterize stalagmite petrography, in particular fabric, porosity and density. Such features can be used to select the ideal plane of a stalagmite for sectioning, to maximize the chances of robust climatic reconstruction. NRF (Natl Research Foundation, S’pore) Accepted version

A microgrid system, be it connected to the utility grid or an independent system, usually consists of a mix of generation - renewable and non-renewable; loads - controllable or non-controllable and Energy Storage Systems (ESSs) such as batteries or flywheels. In order to determine how much power is utilized from the controllable resources such as ESS, diesel generators, micro-turbines or gas turbines, we first need to determine how much the demand is or how much the renewable energy sources are generating is which is accomplished using forecasting techniques. Due to the intermittent nature of renewable resources such as wind energy or solar energy, it is difficult to forecast wind power or solar power accurately. These forecasts are highly dependent on weather forecasts. It is evident that forecast of any data based on forecast of other parameters would lead to further inaccuracy, even if the relation between the inputs and output maybe predetermined through regression methods. Therefore, this paper illustrates an approach to use historical power data instead of numerical weather predictions to produce short-term forecast results. The concept is based on persistence method presented in [1]. This method uses the “today equals tomorrow” concept. From [2], we know that persistence technique produces results that are more accurate as compared to other forecasting techniques for a look-ahead time of 4-6 hours. Both [1] and [2] were based on wind power forecasting. In this paper, we investigate persistence method for short-term electrical demand, solar PV (Photovoltaic) power and wind power forecasting. Since the forecasts are dependent on historical averages of the data in the ‘near’ past, the accuracy is inversely proportional to the variation of power between the historical data and the actual data. Published version

As the free field geological condition is usually complex, the conventional wave attenuation law established for the homogeneous open field may not be applicable for actual field situations. Thus, to understand the impact of the attenuation law and the geological features on the blast wave propagation, a field rock blasting test is conducted and the ground vibration is carefully monitored. To better understand the phenomenon, a numerical model considering the field geological features is established using the finite difference method. The field test results are then used to calibrate the numerical model. From the calibration, the parameters involved in the general form of peak particle velocity have been determined. It is demonstrated that the blast wave propagation in the free field is significantly governed by the field geological conditions, especially the interface between rock and soil layers. Published version

The mixing of turbulent jets can be applied in a wide variety of fields. For the sake of effective mixture, the jets configuration needs to be properly addressed. From an environmental aspect, it is vital to design a jets configuration so that the efflux flows can mix rapidly and effectively with the ambient fluid. Previous studies have suggested that jets interactions with inclination configuration to be an optimal scheme in terms of improving mixture. However, most previous studies only concern the side jets as zero mass flux compared to the central jet, i.e.,1~5%, which might not be suitable for most engineering applications. In this study, the writer investigated the behaviour of three submerged round jets injecting convergingly to stationary recipient water in the laboratory. The three jets are set in the same vertical plane and have intersectant axes. Four parameters were investigated in this investigation: the inclined (converging) angle of the side jets with respect to the central jet, the momentum coefficient (velocity ratio) of the side jets, the Reynolds number of the central jet and the jet spacing ratio. Two incline angles (30° and 45°), four momentum coefficients (1⁄16, 1⁄9, 1⁄4 and 1⁄1), three Reynolds numbers (4240, 6400 and 8000) and three jet spacing ratios (2, 3 and 4) were applied. The complex interactions had been investigated by employing the advanced laser diagnostic techniques of particle image velocimetry (PIV). With the PIV system, both ensemble-averaged and instantaneous characteristics of the complex flow fields were acquired. Geometric features and gross mixing characteristics were addressed by the ensemble-averaged (long time average) results, e.g., the location of the merging point, combining point and necking point. The mixing behaviour of the converging jets was also investigated through the analysis of the longitudinal and cross-sectional velocity distributions. The cross sectional distribution of the mean streamwise and lateral velocity on both the X-Y and X-Z planes, respectively,were found to attain self-similarity after the flow was fully developed and the merging processes were complete. The jet boundary was elucidated by the jet half-width based on the cross-sectional velocity distribution. The converging jets were observed to grow linearly on the X-Y plane and shaped like a parabola curve with open rim on the X-Z plane. The growth rate of the jet half width for converging jets was marginally enhanced than that of a single pipe jet on the X-Y plane but significantly enlarged on the X-Z plane. Based on the experimental results, the cross-sectional profiles of the streamwise velocities were found to show strong resemblance on both the central planes and the parallel offset planes. The mean streamwise velocity for converging jets might be prescribed by the corresponding values on the two central planes (X-Y and X-Z).It was also demonstrated by the velocity measurements that the entrainment (mixture) from ambient fluid to the jets were enhanced when suitable parameters had been chosen based on jets spreading and the lateral velocity gradient near the jets edges. The dynamic processes in the interactions among the three converging jets are revealed by time series of instantaneous flow fields. Galilean decomposition of the velocity vectors and calculation of λ_2(complex eigenvalues) in conjunction with the vorticity fields are used to discriminate the swirling and the shearing in the evolution of the flow.The free outer shear layers of the side jets depict the standard K-H roll-ups similar with that of a single pipe jet flow in the merging region. These K-H structures become unstable gradually and the instability is characterized by “sinuous” flow motions. The two shear layers interact with each other, forming large-scale discrete vortices. The periodic nature of the interactions between the negative and positive Karman-like vortices enhances mixing among three converging jets. The translational velocity of these discrete vortices is estimated to be about 60~80% of the average efflux velocity〖 U〗_0. Based on the experimental results in the present study, it has been found that the large-scale mixing of jets would be maximised when the jets momentum flux is matched (1:1:1). The geometrical features of the flow field are altered at different jet spacing ratios and inclination angles. The merging and combining of the coplanar jets take place earlier with smaller jet spacing ratios or bigger inclination angles. In these situations, the 45° jets at jet spacing ratios of 3 are found to be more receptive to the influence from the side jets because the side jets penetrate the central jet at a location close enough to the nozzle where the central jets’ instabilities have not yet developed, but not so close as in those cases with smaller jet spacing where there are still sufficient room of the evolution of the mixing layer for the jets. Doctor of Philosophy (CEE)

Forward osmosis (FO) process has been gaining popularity in recent years as a potential alternative to pressure-driven membrane processes such as reverse osmosis (RO) for water desalination and wastewater reclamation. However, the main drawback of FO system is permeate flux decline due to internal concentration polarization (ICP) when conventional RO membranes are used. The only commercially available FO flat sheet membrane developed by Hydration Technologies Inc (HTI) presented low water permeation flux. Therefore, the development of novel FO membranes with optimized structure to reduce ICP has become a critical issue to facilitate FO practical applications. In this study, single layer asymmetric microporous hollow fiber membranes were fabricated using Torlon polyamide-imide (PAI) material as the porous support followed by a simple polyelectrolyte cross-linking using polyethyleneimine (PEI) to produce hollow fiber membranes with a positively charged nanofiltration (NF)-like selective layer. The newly developed PAI hollow fiber membranes show a pure water permeability of 2.19-2.25 l/m2.h.bar and reasonable NaCl and MgCl2 rejections of 49% and 94% at 1 bar, respectively. It is also found that in FO processes, when using 0.5 M MgCl2 as a draw solution and de-ionized (DI) water as the feed in the active layer facing feed water (AL-FW) configuration at 23C, the water fluxes of two PAI FO hollow fiber membranes are 8.36 and 9.74 l/m2.h, respectively, and the salt to water flux ratio (Js/Jv) of the two membranes is smaller than 0.4 g/l, which is lower than the data of 0.85 g/l for commercial HTI FO membrane. Different from a neutral membrane, the positively charged FO membrane provides double electric repulsions to the salt transfer through the membrane in the AL-FW configuration, leading to a reduction of salt penetration, while in the active layer facing draw solution (AL-DS) configuration, the positive charges facilitate salt transportation. This study provides a simple and effective approach to make hollow fibers with a NF-like skin suitable for FO applications. An improvement for the single layer PAI hollow fiber membranes has been carried out by incorporating a negatively charged polyelectrolyte layer on the selective skin, aiming to enhance membrane antifouling property. This new type of PAI FO membrane possesses pure water permeability of 3.7-4.3 l/m2.h.bar and Na2SO4 rejection up to 85% at 1 bar. In the FO process, the membranes can achieve water flux of 17 and 12 l/m2.h for the AL-DS and AL-FW configurations, respectively, using a 2000 ppm Na¬2SO4 aqueous solution as the feed and 0.5 M Na2SO4 as the draw solution. When the feed contained 1000 ppm bovine serum albumin (BSA) and 2000 ppm Na2SO4, a steady water flux of 11 l/m2.h can be maintained using 0.5 M Na2SO4 as the draw solution at ambient temperature of 23 °C. The approach of making FO membranes developed in this study offers the advantages of simple fabrication process, tailorable selective layer and promising membrane performance for protein-contained wastewater treatment by FO process. Doctor of Philosophy (CEE)

This study focuses on the synthesis of hierarchical TiO2 nanorod spheres for photocatalytic clean water and energy production. TiO2 nanorod spheres were firstly synthesized by developing a facile template-free low-temperature hydrothermal method. In order to overcome the drawbacks of hydrothermal method for practical engineering applications, facile novel calcination method was developed to scale-up fabricate TiO2 nanorod spheres via deliberately adding TiCl3 into resorcinol and formaldehyde reaction. Hydrothermally synthesized TiO2 nanorod spheres were applied for concurrent photocatalytic membrane filtration for water purification via a “win-win” strategy to maximize the advantages of photocatalysis and membrane filtration. Calcined TiO2 nanorod spheres were used for simultaneous photocatalytic H2 generation and Cu2+ recovery. The formation mechanisms of TiO2 nanorod spheres were elaborated and the detailed influencing factors were investigated systematically. It is of great significance not only in promoting the scale-up fabrication of hierarchical TiO2 nanorod spheres but also in broadening their applications in clean water and energy production. Doctor of Philosophy (CEE)

Due to increasing complexity of the infrastructure in urban living environment, the determination of geotechnical parameters such as soil stiffnesses (shear and Young’s moduli) and damping ratio at different strains are becoming increasingly important in geotechnical engineering. However, derivation of these parameters requires additional resources and time to conduct advanced geotechnical testing. One such advanced geotechnical test is the wave propagation test which can be incorporated into various tests to determine the parameters simultaneously. It is the intention of this study to further develop the capabilities of the wave propagation test in order to realise its full potential of determining both the soil stiffness and damping ratio. The versatility of the wave propagation test will be demonstrated through its incorporation into a cyclic triaxial test to determine both the dynamic and mechanical properties of geo-materials. Despite recent popularity, the wave propagation test has yet to be standardised. Furthermore damping ratio was seldom determined using the wave propagation test. Hence, concerted effort was expended to develop proper procedures for the determination of damping ratio. This study was separated into four test series supplemented by numerical modelling.Test Series I investigates three different configurations of transducers used for wave propagation test: ultrasonic, bender/extender element and the hybrid bender element – ultrasonic system. Despite the non-invasive nature of the ultrasonic system, it was unable to provide accurate and reliable S-wave velocity, hence shear stiffness, due to poor transducer design. Development of the hybrid bender element – ultrasonic system provided better understanding of the ultrasonic system and its limitations. The bender element test system was eventually selected due to its stronger signal. Prior to subsequent tests, it was further improved with better waterproofing.Test Series II can be separated into two parts. The first part evaluates the different techniques used to determine the material damping ratio from the P- and S-wave signals. The Hilbert transform method (HTM) was shown to be the most reliable and robust method to determine damping ratio. As the HTM has never been applied in the field of geotechnical test, it is verified experimentally by comparing the results derived for Ottawa 20-30 sand with those reported in the literature. Numerical simulations were further conducted using a simplified viscoelastic material model to verify the HTM. Meanwhile, the study of the numerical model revealed the discrepancy in the analytical solution which is used to obtain Young’s modulus E from the flexure natural frequency. A correction factor χm was introduced to account for the discrepancy caused by the Timoshenko beam effect and to reconcile the difference in actual and calculated E. The study allowed better understanding of the input parameters of the viscoelastic model. The establishment of the testing framework allows the investigation of the effects of changing net confining pressures and degrees of saturation (Sr) on P- and S-wave velocities and damping ratios (Vp, Vs, ξp and ξs, respectively). The relationship of Vp with Skempton pore pressure parameter B, matric suction and Sr were examined. The limitation of using B-value to determine full saturation was highlighted and Vp was proposed as a better proxy for Sr as it was found to increase sharply when Sr is greater than about 80 - 90% to about 1500 m/s at full saturation. The experiments also showed that the effect of matric suction on Vs is not isotropic compared with isotropic effective confining stress. Trends of ξp and ξs with Sr were shown to exhibit significant variability. However, values of ξp and ξs were generally close to each another. The damping ratios were also shown to decrease with increasing confining pressure and to increase with increasing Sr. Test Series III demonstrated the robustness of the testing framework through tests on soil-rubber mixtures – an engineered material where changes in stiffness and damping characteristics can be controlled and varied significantly. Results of Vs and ξ obtained were compared with those obtained from the resonant column test reported in the literature. The rubber can also be treated as a third phase to observe the response of wave propagating through a material with different phases. In Test Series IV, undisturbed residual soil specimens were tested in a cyclic triaxial set-up equipped with bender elements, local displacement transducers (LDT) and proximity sensors. Both dynamic and mechanical properties were determined. Dynamic parameters (E and Poisson’s ratio ν) determined using the LDT was found to be inaccurate due to slippage between the rubber membrane and the soil specimens. Results of the dynamic soil properties (G/Gmax and ξ) with shear strain were shown to agree with the literature. The residual soil specimens were sheared under consolidated undrained condition and constant water content condition for the saturated and unsaturated specimens, respectively. The effective shear strength parameters (ϕ’ and c’) were observed to fall within the range shown in the literature. The effective cohesion intercept was shown to increase with depth as the deeper specimens have a higher density. The total cohesion was also shown to increase with both the matric suction and depth. Doctor of Philosophy (CEE)

It is the behaviour of velocity distribution and turbulent intensity structure in a 3-D flow that forms the focus and objective of the present study. MASTER OF ENGINEERING (CEE)

Most of the approaches to the studies of microbial populations in environmental engineering systems have presumed that a microbial population comprises cells with the same physiological properties. However, it is known that individual cells within a microbial population have different physiological states. The purpose of this study was to investigate physiological heterogeneity in the eukaryotic population of Saccharomyces cerevisiae and prokaryotic population of Escherichia coli, and also within microbial community (e.g., microbial granules) found in environmental engineering systems. The first objective was to identify different subpopulations of S. cerevisiae and E. coli populations using flow cytometry analysis of membrane integrity, membrane potential and respiratory activity. The second objective was to examine sensitivity of different subpopulations of bacterial cells to chlorine disinfectant. The third objective was to analyse spatial distribution of viable and dead cells within bacterial granule of Pseudomonas veronii. Fluorescent probes such as propidium iodide (PI), DiBAC4(3) and CTC in combination with flow cytometry and confocal laser scanning microscope were used for the assessment of physiological states of microbial cells at single-cell level. This study revealed that for the assessment of cell viability of eukaryote S. cerevisiae, the most practical method was the determination of membrane integrity using PI. Two subpopulations with high and low activities of alcohol dehydrogenase were detected in the growing population of S. cerevisiae. The share of respiratory active cells of E. coli population under long-term starvation dropped to 5%, whereas approximately 50% of cells maintained the membrane potential. The results of cell viability determination by PI in combination with flow cytometry indicated that CT values required for 2-log inactivation (CT99) for E. coli cell populations with µ=0.9 h-1 and µ=0.2 h-1 were 0.06 and 0.09 mg min l-1, respectively. A thin stratum of dead cells (

Forward osmosis (FO) is an emerging membrane separation technology. It is different from the well-studied pressure-driven membrane separation processes. The FO process is based on water transport under an osmotic pressure difference across a semi-permeable membrane. The distinct operating conditions lead to unique technical challenges during the exploitation of FO technology. According to a comprehensive literature investigation, one of the stringent barriers is lacking of effective FO membranes. The objectives of this research were to develop high performance FO membranes, and furthermore, to systematically study the mass transport and the governing mechanisms in FO process. Thin film composite (TFC) FO membranes with a tailored support structure were developed in this study. The membranes consisted of a highly porous substrate with finger-like pore structure, which was prepared via phase inversion, and a polyamide rejection layer synthesized by interfacial polymerization. The TFC FO membranes had small structural parameters due to the thin cross-section, low tortuosity, and high porosity of the substrates. The membrane rejection layers exhibited superior separation properties (higher water permeability and excellent selectivity) relative to commercial FO membranes. Under FO testing conditions, these membranes achieved high water flux while maintaining relatively low solute reverse diffusion. Comparison of the synthesized TFC FO membranes with commercial FO and reverse osmosis (RO) membranes revealed the critical importance of the substrate structure, with a straight finger-like pore structure preferred over a spongy pore structure to minimize internal concentration polarization (ICP), a unique and critical problem resulting in low water flux in the osmotically driven membrane processes. In addition, membranes with high water permeability and excellent selectivity are preferred to achieve both high FO water flux and low solute flux. The results proved that TFC membranes with a tailored porous substrate and rejection layer are promising for FO applications. In the study of polyamide rejection layer synthesis, the influence of monomer concentrations (i.e., m-phenylenediamine (MPD) and trimesoyl chloride (TMC) concentrations) on the membrane separation properties as well as the FO performance was systematically investigated. A strong trade-off between the water permeability and salt rejection of the membranes was observed, where reducing the MPD concentration or increasing the TMC concentration may result in a higher membrane permeability but a lower salt rejection. In FO tests, membranes with poor salt rejection had severe solute reverse diffusion, which enhanced the severity of ICP. It was found that the FO water flux was governed by both the membrane water permeability and solute rejection. For a membrane with higher water permeability but lower solute rejection, the reduced membrane frictional resistance was compensated simultaneously by the more severe solute-reverse-diffusion-induced ICP. The net effect on the FO water flux depends on the competition of these two opposing mechanisms. Under conditions where solute reverse diffusion may cause severe ICP (e.g., high draw solution concentration and high water flux level), membranes need to be optimized to achieve a high salt rejection even if this is at the expense of lower water permeability. In view of the importance of the water permeability and salt permeability on FO performance, a systematic comparison study of prevailing semi-permeable FO membranes with nanofiltration (NF)-like and RO-like separation properties in terms of flux performance and fouling behavior was conducted. Due to the crucial influence of solute reverse diffusion on FO water flux, the high-rejection RO-like FO membranes generally performed better than the NF-like counterparts in sodium chloride based FO tests. On the other hand, the high permeability of NF-like FO membranes could achieve higher water flux, when proper draw solutes were used to minimize draw solute leakage. Fouling tests suggested that the NF-like TFC FO membranes tended to be more fouling resistant due to their relatively smooth membrane surface. This work further elucidated the major mechanisms that govern the FO performance. These mechanisms were summarized as a frictional resistance loss mechanism (MR), solute-reverse-diffusion-induced ICP (MICP-Js), concentration of feed solutes (concentrative ICP or MICP-feed in the active-layer-facing-draw-solution orientation) and dilution of draw solutes (dilutive ICP or MICP-draw in the active-layer-facing-feed-solution orientation). These mechanisms are related to the properties of membrane, draw and feed solutions. This work led to a set of systematic criteria for the selection of FO membranes, draw solution and optimization of other operating conditions, of which the practicability was demonstrated in potential FO applications. Doctor of Philosophy (CEE)

Aerobic granulation is a process to form dense and spherical aggregates through cell-to-cell self-immobilization without addition of biocarriers. Recently, intensive research efforts have been dedicated to the development of aerobic granules and their applications for wastewater treatment. However, the microbiological origin of this phenomenon is still largely unknown and very little information is currently available regarding the mechanisms of aerobic granulation at levels of energy metabolism and cellular communication. This study, therefore, attempts to address a basic question: Are adenosine triphosphate (ATP) and cellular communication required in the formation and maintenance of aerobic granules? In the first phase of this study, the possible roles of ATP and cellular communication in the formation of aerobic granules were investigated. For this purpose, three sequencing batch reactors (SBRs) inoculated with synthetic wastewater-acclimated activated sludge were operated in the absence and presence of a chemical uncoupler, 3,3’,4’,5-tetrachlorosalicylanilide (TCS), which has the ability to dissipate the Proton Motive Force (PMF) and subsequently inhibit ATP synthesis. Results showed that aerobic granules were successfully cultivated in the control reactor free of TCS, while aerobic granulation was completely inhibited with the addition of 2 and 4 mg L-1 TCS. It was found that cellular ATP content in the control reactor increased along granulation process, meanwhile, the increase in the production of signaling molecules, i.e., autoinducer-2 (AI-2) and N-acylhomoserine lactones (AHLs), as well as, extracellular polymeric substances (EPS) was also observed. However, in the presence of TCS, the production of AI-2, AHLs and EPS was significantly inhibited due to the suppressed ATP synthesis, which ultimately resulted in the failure of aerobic granulation. It was, therefore, demonstrated that ATP and cellular communication played important roles in the development of aerobic granules. Doctor of Philosophy (CEE)

Lakes in the Hindu Kush-Himalaya-Tibetan (HKHT) regions are crucial indicators for the combined impacts of regional climate change and resultant glacier retreat. However, they lack long-term systematic monitoring and thus their responses to recent climatic change still remain only partially understood. This study investigated lake extent fluctuations in the HKHT regions over the past 40 years using Landsat (MSS/TM/ETM+/OLI) images obtained from the 1970s to 2014. Influenced by different regional atmospheric circulation systems, our results show that lake changing patterns are distinct from region to region, with the most intensive lake shrinking observed in northeastern HKHT (HKHT Interior, Tarim, Yellow, Yangtze), while the most extensive expansion was observed in the western and southwestern HKHT (Amu Darya, Ganges Indus and Brahmaputra), largely caused by the proliferation of small lakes in high-altitude regions during 1970s−1995. In the past 20 years, extensive lake expansions (~39.6% in area and ~119.1% in quantity) were observed in all HKHT regions. Climate change, especially precipitation change, is the major driving force to the changing dynamics of the lake fluctuations; however, effects from the glacier melting were also significant, which contributed approximately 31.9−40.5%, 16.5−39.3%, 12.8−29.0%, and 3.3−6.1% of runoff to lakes in the headwaters of the Tarim, Amu Darya, Indus, and Ganges, respectively. We consider that the findings in this paper could have both immediate and long-term implications for dealing with water-related hazards, controlling glacial lake outburst floods, and securing water resources in the HKHT regions, which contain the headwater sources for some of the largest rivers in Asia that sustain 1.3 billion people.

The parasitic marine dinoflagellate Amoebophrya is the first known eukaryote with aerobic mitochondria without a genome., Dinoflagellates are microbial eukaryotes that have exceptionally large nuclear genomes; however, their organelle genomes are small and fragmented and contain fewer genes than those of other eukaryotes. The genus Amoebophrya (Syndiniales) comprises endoparasites with high genetic diversity that can infect other dinoflagellates, such as those forming harmful algal blooms (e.g., Alexandrium). We sequenced the genome (~100 Mb) of Amoebophrya ceratii to investigate the early evolution of genomic characters in dinoflagellates. The A. ceratii genome encodes almost all essential biosynthetic pathways for self-sustaining cellular metabolism, suggesting a limited dependency on its host. Although dinoflagellates are thought to have descended from a photosynthetic ancestor, A. ceratii appears to have completely lost its plastid and nearly all genes of plastid origin. Functional mitochondria persist in all life stages of A. ceratii, but we found no evidence for the presence of a mitochondrial genome. Instead, all mitochondrial proteins appear to be lost or encoded in the A. ceratii nucleus.

Magnetotactic bacteria biomineralize intracellular magnetic nanocrystals surrounded by a lipid bilayer called magnetosomes. Due to their unique characteristics, magnetite magnetosomes are promising tools in Biomedicine. However, the uptake, persistence, and accumulation of magnetosomes within mammalian cells have not been well studied. Here, the endocytic pathway of magnetite magnetosomes and their effects on human cervix epithelial (HeLa) cells were studied by electron microscopy and high spatial resolution nano-analysis techniques. Transmission electron microscopy of HeLa cells after incubation with purified magnetosomes showed the presence of magnetic nanoparticles inside or outside endosomes within the cell, which suggests different modes of internalization, and that these structures persisted beyond 120 h after internalization. High-resolution transmission electron microscopy and electron energy loss spectra of internalized magnetosome crystals showed no structural or chemical changes in these structures. Although crystal morphology was preserved, iron oxide crystalline particles of approximately 5 nm near internalized magnetosomes suggests that minor degradation of the original mineral structures might occur. Cytotoxicity and microscopy analysis showed that magnetosomes did not result in any apparent effect on HeLa cells viability or morphology. Based on our results, magnetosomes have significant biocompatibility with mammalian cells and thus have great potential in medical, biotechnological applications. Published version

The primary goal of this study is to investigate the classification capability of several artificial intelligence techniques, including the decision tree (DT), multilayer perceptron (MLP) network, Na&iuml, ve Bayes, radial basis function (RBF) network, and support vector machine (SVM) for evaluating spatial and temporal variations in water quality. The application case is the Song Quao-Ca Giang (SQ-CG) water system, a main domestic water supply source of the city of Phan Thiet in Binh Thuan province, Vietnam. To evaluate the water quality condition of the source, the government agency has initiated an extensive sampling project, collecting samples from 43 locations covering the SQ reservoir, the main canals, and the surrounding areas during 2015&ndash, 2016. Different classifying models based on artificial intelligence techniques were developed to analyze the sampling data after the performances of the models were evaluated and compared using the confusion matrix, accuracy rate, and several error indexes. The results show that machine-learning techniques can be used to explicitly evaluate spatial and temporal variations in water quality.

Strong cold surge events (CSEs) are some of the most distinct winter weather events in East Asia, impacting natural ecosystems and over 100 million individuals. The impact of such extreme CSEs as driven by synoptic systems is direct and immediate. Changes in large-scale synoptic patterns as potentially affected by changes in the Arctic are further expected to influence CSE occurrences in East Asia. Defying a straightforward analysis, semi-permanent atmospheric systems such as the Siberian High (SH), influencing large-scale synoptic patterns, make the atmospheric circulation highly variable and assessment of CSE onset difficult. Rather varied region-specific metrics are currently adopted for predicting CSE occurrence locally but the fundamental understanding of the onset of CSEs continues to be a major challenge. Based on an analysis of monthly synoptic patterns for three unusual CSEs in East Asia and further extended for eight strong to extreme CSEs, we propose a new coupling framework for an improved understanding and interpretation of the atmosphere dynamics driving CSE onset. The coupling framework involves linkages between the Siberian High, Aleutian Low, and Jet Stream. We also present the first meteorological scale for categorizing the intensity of such unusual CSEs. Published version

The tiny green algae belonging to the Chloropicophyceae play a key role in marine phytoplankton communities; this newly erected class of prasinophytes comprises two genera (Chloropicon and Chloroparvula) containing each several species. We sequenced the plastomes and mitogenomes of eight Chloropicon and five Chloroparvula species to better delineate the phylogenetic affinities of these taxa and to infer the suite of changes that their organelle genomes sustained during evolution. The relationships resolved in organelle-based phylogenomic trees were essentially congruent with previously reported rRNA trees, and similar evolutionary trends but distinct dynamics were identified for the plastome and mitogenome. Although the plastome sustained considerable changes in gene content and order at the time the two genera split, subsequently it remained stable and maintained a very small size. The mitogenome, however, was remodeled more gradually and showed more fluctuation in size, mainly as a result of expansions/contractions of intergenic regions. Remarkably, the plastome and mitogenome lost a common set of three tRNA genes, with the trnI(cau) and trnL(uaa) losses being accompanied with important variations in codon usage. Unexpectedly, despite the disappearance of trnI(cau) from the plastome in the Chloroparvula lineage, AUA codons (the codons recognized by this gene product) were detected in certain plastid genes. By comparing the sequences of plastid protein-coding genes from chloropicophycean and phylogenetically diverse chlorophyte algae with those of the corresponding predicted proteins, we discovered that the AUA codon was reassigned from isoleucine to methionine in Chloroparvula. This noncanonical genetic code has not previously been uncovered in plastids.

Background Short-read sequencing technologies have long been the work-horse of microbiome analysis. Continuing technological advances are making the application of long-read sequencing to metagenomic samples increasingly feasible. Results We demonstrate that whole bacterial chromosomes can be obtained from an enriched community, by application of MinION sequencing to a sample from an EBPR bioreactor, producing 6 Gb of sequence that assembles into multiple closed bacterial chromosomes. We provide a simple pipeline for processing such data, which includes a new approach to correcting erroneous frame-shifts. Conclusions Advances in long-read sequencing technology and corresponding algorithms will allow the routine extraction of whole chromosomes from environmental samples, providing a more detailed picture of individual members of a microbiome. Electronic supplementary material The online version of this article (10.1186/s40168-019-0665-y) contains supplementary material, which is available to authorized users.

Hospital wastewater contains pharmaceutical residues, chemicals, and pathogens that cause coloration and nourish pathogenic microorganisms. The objective of the study was to evaluate the effectiveness of a medical wastewater treatment system at Military Hospital 175 (Ho Chi Minh City, Vietnam) that combined a membrane bioreactor (MBR) system with nanofiltration (NF). The influent of the system was the wastewater discharged from the operating rooms of the hospital. The system has a capacity of 50 L/day and operates at three organic load rates (OLR) of 0.5, 1.5 and 2.5 kgCOD/m3day (COD: Chemical oxygen demand), in which each load rate operates for 40 days. The results showed that most nutritional criteria generally achieved positive results. Specifically, the average COD removal was shown to be consistently high throughout the three phases at 94%, 93.3%, and 92.7%, respectively. For removal of nitrogen, the system demonstrated efficiencies of 75%, 79%, and 83%, respectively, to three phases. The log removal value (LRV) for Escherichia coli and coliform bacteria were higher than four throughout the study period. The average removal efficiency for color and total iron was approximately 98% and 99%, respectively. The water quality after treatment, especially after NF, meets the Vietnamese standard of grade A. The arrangement in which the MBR preceded NF was also found to limit the amount of soil and solids entering subsequent treatment, which therefore improved the efficiency of NF, as demonstrated by the stability of post-NF transmembrane pressures throughout three cycles renewed by two backwashes.

Comamonas is often reported to be one of the major members of microbial communities in various natural and engineered environments. Versatile catabolic capabilities of Comamonas have been studied extensively in the last decade. In contrast, little is known about the ecological roles and adaptation of Comamonas to different environments as well as the virulence of potentially pathogenic Comamonas strains. In this study, we provide genomic insights into the potential ecological roles and virulence of Comamonas by analysing the entire gene set (pangenome) and the genes present in all genomes (core genome) using 34 genomes of 11 different Comamonas species. The analyses revealed that the metabolic pathways enabling Comamonas to acquire energy from various nutrient sources are well conserved. Genes for denitrification and ammonification are abundant in Comamonas, suggesting that Comamonas plays an important role in the nitrogen biogeochemical cycle. They also encode sophisticated redox sensory systems and diverse c-di-GMP controlling systems, allowing them to be able to effectively adjust their biofilm lifestyle to changing environments. The virulence factors in Comamonas were found to be highly species-specific. The conserved strategies used by potentially pathogenic Comamonas for surface adherence, motility control, nutrient acquisition and stress tolerance were also revealed. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Published version

4-Chlorophenol (4-CP) oxidation plays an essential role in the detoxification of 4-CP. However, oxidative regulation of 4-CP at the genetic and biochemical levels has not yet been studied. To explore the regulation mechanism of 4-CP oxidation, a novel gene cluster, cphRA2A1, involved in biodegradation of 4-CP was identified and cloned from Rhodococcus sp. strain YH-5B by genome walking. The sequence analysis showed that the cphRA2A1 gene cluster encoded an AraC-type transcriptional regulator and a two-component monooxygenase enzyme, while quantitative real-time PCR analysis further revealed that cphR was constitutively expressed and positively regulated the transcription of cphA2A1 genes in response to 4-CP or phenol, as evidenced by gene knockout and complementation experiments. Through the transcriptional fusion of the mutated cphA2A1 promoter with the lacZ gene, it was found that the CphR regulator binding sites had two 15-bp imperfect direct repeats (TGCA-N6-GGNTA) at −35 to −69 upstream of the cphA2A1 transcriptional start site. Notably, the sub-motifs at the −46 to −49 positions played a critical role in the appropriate interaction with the CphR dimer. In addition, it was confirmed that the monooxygenase subunits CphA1 and CphA2, which were purified by His-tag affinity chromatography, were able to catalyze the conversion of 4-CP to 4-chlorocatechol, suggesting that strain YH-5B could degrade 4-CP via the 4-chlorocatechol pathway. This study enhances our understanding of the genetic and biochemical diversity in the transcriptional regulation of 4-CP oxidation in Gram-positive bacteria. Published version

To identify novel inhibitors of Mycobacterium tuberculosis cell envelope biosynthesis, we employed a two-step approach. First, we screened the diverse synthetic small molecule 71,544-compound Enamine library for growth inhibitors using the non-pathogenic surrogate Mycobacterium bovis BCG as screening strain and turbidity as readout. Second, 16 confirmed hits were tested for their ability to induce the cell envelope stress responsive promoter piniBAC controlling expression of red fluorescent protein in an M. bovis BCG reporter strain. Using a fluorescence readout, the acetamide E11 was identified. Resistant mutant selection and whole genome sequencing revealed the mycolic acid transporter Mmpl3 as a candidate target of E11. Biochemical analysis using mycobacterial spheroplasts and various membrane assays suggest that E11 indirectly inhibits MmpL3-facilitated translocation of trehalose monomycolates by proton motive force disruption. E11 showed potent bactericidal activity against growing and non-growing M. tuberculosis, low cytotoxic, and hemolytic activity and a dynamic structure activity relationship. In addition to activity against M. tuberculosis, E11 was active against the non-tuberculous mycobacterium M. abscessus, an emerging opportunistic pathogen. In conclusion, we identified a novel bactericidal anti-mycobacterial lead compound targeting MmpL3 providing an attractive starting point for optimization. MOE (Min. of Education, S’pore) NMRC (Natl Medical Research Council, S’pore) MOH (Min. of Health, S’pore) Published version

Advanced treatment of reclaimed water prior to potable reuse normally results in the inactivation of bacterial populations, however, incremental treatment failure can result in bacteria, including pathogens, remaining viable. Therefore, potential microorganisms need to be detected in real-time to preclude potential adverse human health effects. Real-time detection of microbes presents unique problems which are dependent on the water quality of the test water, including parameters such as particulate content and turbidity, and natural organic matter content. In addition, microbes are unusual in that: (i) viability and culturability are not always synonymous, (ii) viability in water can be reduced by osmotic stress, and (iii) bacteria can invoke repair mechanisms in response to UV disinfection resulting in regrowth of bacterial populations. All these issues related to bacteria affect the efficacy of real-time detection for bacteria. Here we evaluate three different sensors suitable for specific water qualities. The sensor A is an on-line, real-time sensor that allows for the continuous monitoring of particulates (including microbial contaminants) using multi-angle-light scattering (MALS) technology. The sensor B is a microbial detection system that uses optical technique, Mie light scattering, for particle sizing and fluorescence emission for viable bacteria detection. The last sensor C was based on adenosine triphosphate (ATP) production. E. coli was used a model organism and out of all tested sensors, we found the sensor C to be the most accurate. It has a great potential as a surrogate parameter for microbial loads in test waters and be useful for process control in treatment trains.

The transcription factor NF-E2 Related Factor-2 (NRF2) is an important drug target. Activation of NRF2 has chemopreventive effects in cancer and exerts beneficial effects in a number of diseases, including neurodegenerative diseases, inflammatory diseases, hepatosteatosis, obesity and insulin resistance. Hence, there have been great efforts to discover and characterize novel NRF2 activators. One reported NRF2 activator is the labdane diterpenoid andrographolide. In this study, we identified the mechanism through which andrographolide activates NRF2. We showed that andrographolide inhibits the function of KEAP1, a protein that together with CUL3 and RBX1 forms an E3 ubiquitin ligase that polyubiquitinates NRF2. Andrographolide partially inhibits the interaction of KEAP1 with CUL3 in a manner dependent on Cys151 in KEAP1. This suggests that andrographolide forms Michael acceptor dependent adducts with Cys151 in KEAP1 in vivo, leading to inhibition of NRF2 ubiquitination and consequently accumulation of the transcription factor. Interestingly, we also showed that at higher concentrations andrographolide increases NRF2 protein expression in a Cys151 independent, but likely KEAP1 dependent manner, possibly through modification of other Cys residues in KEAP1. In this study we also screened secondary metabolites produced by endophytes isolated from non-flowering plants for NRF2-inducing properties. One of the extracts, ORX 41, increased both NRF2 protein expression and transcriptional activity markedly. These results suggest that endophytes isolated from non-flowering or other plants may be a good source of novel NRF2 inducing compounds. Published version

Enterobacter sp. strain EA-1 is an electrochemically active bacterium isolated from tropical sediment in Singapore. Here, the annotated draft genome assembly of the bacterium is reported. Whole-genome comparison indicates that Enterobacter sp. EA-1, along with a previously sequenced Enterobacter isolate from East Asia, forms a distinct clade within the Enterobacter genus.

Particle fluidization is a promising unsteady-state shear means of mitigating membrane fouling. It has the potential to lower energy requirement and prolong membrane lifespan in membrane-based wastewater treatment processes. In particular, the particles facilitate back-transport in the polarization layer and also play the role of mechanical scouring agents, the latter of which is dominant for millimeter-sized particles. In this study, an accelerometer was first successfully used to unveil the dynamics of GAC particles with three particle diameters (namely, 1.20 mm, 1.85 mm, and 2.18 mm). The energy contained in the accelerometer signal representing the solid phase was consistent with the extent of fouling mitigation in the filtration tests. The smallest GAC particle with a particle diameter of 1.20 mm conferred the least scouring efficiency, while both the larger particles with diameters of 1.85 mm and 2.18 mm provided similar scouring efficiency. The impact of particle diameter is due to the balance between particle inertia, and the difference between superficial liquid velocity and minimum fluidization velocity. Furthermore, in a practical pilot-scale AnFMBR with wastewater, the accelerometer was shown to be able to diagnose the de-fluidization of the GAC particles due to severe clogging issues, which thereby eliminated the fouling mitigation capacity. Trends in the trans-membrane pressure (TMP) and flux data did not indicate de-fluidization of the GAC particles. In order to further improve this technique in terms of scouring efficiency and energy requirement, the hydrodynamics of the fluidized GAC particles, and correspondingly the relationship between the particle behavioural characteristics and the extent of membrane-fouling mitigation were investigated. Directly correlating particle behavior with membrane fouling trends showed that higher particle velocities, particle concentration and particle momentum generally all showed a negative correlation with dTMP/dt. Of the three characteristics (namely, particle velocity, concentration and momentum), the negative correlation between dTMP/dt and particle momentum was most pronounced, which suggests that momentum transfer between the GAC particles and the membrane represents a key mechanism effecting the scouring to diminish membrane fouling. More in-depth studies of the improvement of micrometer-sized particulate (namely, polystyrene foulant) critical flux in the presence of fluidized GAC particles was studied, whereby a Direct Observation Through the Membrane (DOTM) technique was used to measure the membrane critical flux locally and overall. It was found that (i) the fluidized GAC particles increased critical flux by an order-of-magnitude relative to that with tangential liquid shear alone; (ii) the overall critical flux increased with the increase of GAC particle diameter or power input; and (iii) a higher power input was required for sufficient bed expansion to enable more consistent critical flux values over the whole membrane height. Accordingly, the impact of different overall GAC concentrations, which give different expanded bed heights, on the extent of fouling mitigation was investigated in this study. The results indicate that the highest overall concentration was advantageous in terms of enabling (i) higher membrane fouling mitigation at a lower power required per unit permeate (Pp) for the polystyrene foulant but not bentonite foulant; and (ii) more similar local critical flux values over the three heights along the membrane investigated, which implies more uniform fouling mitigation across the membrane. The relative benefits of adjusting overall GAC concentration versus the particle diameter of the GAC media were also critically assessed. Finally, the effect of the sphericity (φ) of the fluidized media on the extent of fouling mitigation was studied. Three types of millimeter-sized rice media were used as the fluidized media. Relative to GAC media, the rice media had similar particle densities and similar particle diameters, but offered much lower sphericities (lowest sphericity in this study was 0.54) due to the greater aspect ratios. The results indicate that the correlation between sphericity of the fluidized media and hydrodynamics (and the attendant fouling mitigation) was not straightforward, likely tied to the influence of drag on the countering effects of media-membrane contact and particle rotation. In conclusion, this thesis gave a deep understanding of the fluidized GAC particle behavioral characteristics and the correlation with the extent of membrane-fouling mitigation in solid-liquid fluidization membrane filtration systems. The parameters investigated included GAC particle diameter (dp),overall GAC concentration, fluidized particle sphericity (φ), superficial liquid velocity (Ul) thereby the power requirement (Pr), and height along the vertically aligned membrane. The findings are expected to be valuable in the optimization of membrane fouling mitigation towards more energy-efficient in a solid-liquid fluidization membrane filtration system. Doctor of Philosophy (IGS)

Highlights • A pilot microbial electrolysis cell (MEC) was tested for H2O2 production. • Passive air diffusion to a carbon electrode successfully produced H2O2. • The highest H2O2 conversion was only 7.2%. • Catholyte pH over 11 can mitigate H2O2 loss in MECs., A pilot-scale dual-chamber microbial electrolysis cell (MEC) equipped with a carbon gas-diffusion cathode was evaluated for H2O2 production using acetate medium as the electron donor. To assess the effect of cathodic pH on H2O2 yield, the MEC was tested with an anion exchange membrane (AEM) and a cation exchange membrane (CEM), respectively. The maximum current density reached 0.94–0.96 A/m2 in the MEC at applied voltage of 0.35–1.9 V, regardless of membranes. The highest H2O2 conversion efficiency was only 7.2 ± 0.09% for the CEM-MEC. This low conversion would be due to further H2O2 reduction to H2O on the cathode or H2O2 decomposition in bulk liquid. This low H2O2 conversion indicates that large-scale MECs are not ideal for production of concentrated H2O2 but could be useful for a sustainable in-situ oxidation process in wastewater treatment.

This thesis deals with the challenge of dispatching taxis to passenger booking requests. The main contribution is the methodology which assigns and re-assigns groups of taxis to groups of passenger booking requests and reflects the interest of not just taxis but also passengers, and which produces stable assignments. The proposed methodology is de-signed for a centralized system that assigns and re-assigns the bookings simultaneously in decision epochs in real-time. The solution to the stable marriage algorithm, originally designed for matching men and women according to their preferences, is applied to dis-patching taxis to passenger booking requests. The proposed methodology is evaluated in a custom-made taxi simulation model. The results indicate that the proposed taxi dis-patching strategies outperform a commonly used first-come, first-served dispatching strategy in a number of performance indicators (e.g. passenger waiting time and taxi distance) as well as for various combinations of advance and immediate booking requests. Doctor of Philosophy

Biogas is a clean and renewable energy source in a carbon-constrained world. Carbon dioxide (CO2) capture is essential for upgrading biogas to increase energy density. The gas-liquid membrane contactor (GLMC) has been proposed and investigated as a promising alternative to conventional CO2 absorption techniques such as packed towers and bubble columns. Owing to its desirable properties such as hydrophobicity, suitable pore size, high porosity, good mechanical strength, and high thermal stability, polyvinylidene fluoride (PVDF) membrane has been extensively used in GLMC processes. However, PVDF membrane is vulnerable to wetting, swelling and degradation by solvents under long-term operations, thus restricting its application for CO2 removal in membrane contacting processes. Therefore, developing novel membranes to improve the durability in the GLMC process is of significant importance. To achieve this goal, an inorganic-organic fluorinated titania-silica (fTiO2-SiO2)/PVDF composite membrane was fabricated via facile in-situ vapor-induced hydrolyzation method followed by hydrophobic modification. This low mass-transfer-resistance membrane, composing of a mesoporous layer deposited onto macroporous substrate, was designed for biogas upgrading in GLMC application. Surface hydroxylation was introduced to facilitate the bridging of TiO2-SiO2 nanoparticles and PVDF substrate, which resulted in a more coherent deposition of fTiO2-SiO2 layer onto the substrate. The surface microstructure was fine-tuned by controlling the amount of doped Si precursor, forming an integrated mesoporous fTiO2-SiO2 layer. The resultant fTiO2-SiO2/PVDF composite hollow fiber membrane exhibited a tighter pore size of ~25 nm and a desired water contact angle of ~124°, which effectively prevented membrane wetting. The high CO2 absorption fluxes were achieved due to lower mass transfer resistance, by using 1 M of monoethanolamine (MEA) and sodium taurinate as absorbents, respectively. The long-term stability test showed a good integrity between the fTiO2-SiO2 layer and the PVDF substrate after 31 days of GLMC operation. The main benefit is the robust fluorinated inorganic layer that exhibited strong chemical resistance and high hydrophobicity, thus preventing membrane damage and pore wetting. This study provides an insight into the preparation of high-performance inorganic/organic composite hollow fiber membranes for CO2 removal in GLMC applications. Considering the high corrosion and energy-intensity of using traditional amine-based absorbents for CO2 capture in GLMC processes, it is more appropriate to use environmentally-benign solvents for CO2 capture. A highly efficient biocatalytic carbonic anhydrase (CA)-polydopamine (PDA)/polyethylenimine (PEI)-PVDF composite membrane was designed and fabricated for CO2 conversion and capture using water as absorbent. The co-deposition of PDA/PEI with amino functional groups was employed to amine-functionalize a PVDF substrate as support for subsequent in-situ CA immobilization by cross-linking with glutaraldehyde. This enhances the enzyme stability and prolongs its lifespan, thus facilitating CO2 removal efficiency in the GLMC process due to the superb catalysis of CA enzyme for CO2 hydration. By using water as absorbent with a liquid velocity of 0.25 m·s−1 in a bench-scale GLMC setup, a high-efficiency CO2 absorption flux (2.5 × 10−3 mol·m−2·s−1) of the proposed biocatalytic membrane was obtained, which was ~165% higher than that of the non-biocatalytic membrane. A good long-term stability in terms of enzyme activity for CO2 hydration of the biocatalytic composite membranes was also achieved during 40 days of test duration. Overall, the results achieved in this work could provide promising insights into the development of biocatalytic membranes for extended GLMC applications using environmentally-benign absorbents to achieve a high-efficiency CO2 removal. Inspired by better gas selectivity along with tunable pore size and facile functionalization of metal-organic frameworks (MOFs), a highly efficient aminosilane-modified zeolitic imidazolate framework-8 (mZIF-8) based composite hollow fiber membrane with a dense skin layer was successfully fabricated for biogas upgrading in the GLMC process by dispersing mZIF-8 into dense polydimethylsiloxane (PDMS) matrix and depositing on a porous PVDF substrate. (3-aminopropyl)triethoxysilane was introduced to modify the ZIF-8 nanocrystals in order to cross-link with PDMS chains for further hydrophobicity enhancement. Compared with the pristine PVDF membrane, the newly developed composite membranes with a dense skin exhibited competitive hydrophobicity with a contact angle of 130°, ensuring its anti-wetting ability. The mZIF-8 based composite membrane realized a higher CO2 mass transfer efficiency as well as a higher selectivity of CO2/CH4 using water or aqueous amine absorbents in GLMC processes. A robust long-term stability of mZIF-8 based composite membrane was also achieved in a 15-day operation. This work provides a new strategy to improve the biogas upgrading performance using dense composite membranes with modified MOFs in GLMC applications. Doctor of Philosophy

In this study, monthly time series of precipitations and temperatures from 1024 controlled and homogeneous meteorological stations located in the Emilia-Romagna region (northern Italy) are processed in order to assess potential climate changes that occurred during the period 1961–2015. Normal period as baseline between 1961 and 1990 (1990s) and recent period between 1991 and 2015 (2010s) were adopted in this study to analyse the possible effect of climate change on water availability during long-term period. Based on monthly and annual temperature (TT), precipitation (PP), and potential (ET0), the actual evapotranspiration (AET0) and water availability (WA) were computed at high spatial resolution. Between the two analysed periods, during the 2010s, it was found an increase in the maximum mean annual temperature by 1.08°C while the maximum mean annual precipitation saw a slight decrease (from 2222 mm to 2086 mm). The precipitation decrease is more intense in the South and West sectors of area (8%) and mainly depends on negative changes taking place during the winter and the beginning of spring (from December to March). The maximum mean annual ET0 and AET0 reached values of 663 mm and 565 mm during the 1990s, while during the 2010s, the found values were 668 mm and 572 mm, respectively. Because of the decrease in precipitation and increase in the ET0 and AET0, the WA (the proportion of precipitation that is available at the soil surface for subsequent infiltration and runoff processes) shows a reduction (about 10–20%) in the whole region, with exception of the North-East part of the Emilia-Romagna region. The decrease in the mean annual water availability induces severe issues concerning the water resources management across the whole Emilia-Romagna region. Published version

Biofilm formation, one of the primary causes of biofouling, results in reduced membrane flux or increased transmembrane pressure and thus represents a major impediment to the wider implementation of membrane bioreactor (MBR) technologies for water purification. Most studies have focused on the role of bacteria in membrane fouling as they are the most dominant and best studied organisms present in the MBR. In contrast, there is limited information on the role of the archaeal community in biofilm formation in MBRs. This study investigated the composition of the archaeal community during the process of biofouling in an MBR. The archaeal community was observed to have lower richness and diversity in the biofilm than the sludge during the establishment of biofilms at low transmembrane pressure (TMP). Clustering of the communities based on the Bray–Curtis similarity matrix indicated that a subset of the sludge archaeal community formed the initial biofilms. The archaeal community in the biofilm was mainly composed of Thermoprotei, Thermoplasmata, Thermococci, Methanopyri, Methanomicrobia and Halobacteria. Among them, the Thermoprotei and Thermoplasmata were present at higher relative proportions in the biofilms than they were in the sludge. Additionally, the Thermoprotei, Thermoplasmata and Thermococci were the dominant organisms detected in the initial biofilms at low TMP, while as the TMP increased, the Methanopyri, Methanomicrobia, Aciduliprofundum and Halobacteria were present at higher abundances in the biofilms at high TMP. Published version

Microbially mediated biogeochemical processes are crucial for climate regulation and may be disrupted by anthropogenic contaminants. To better manage contaminants, we need tools that make real‐time causal links between stressors and altered microbial functions, and the potential consequences for ecosystem services such as climate regulation. In a manipulative field experiment, we used metatranscriptomics to investigate the impact of excess organic enrichment and metal contamination on the gene expression of nitrogen and sulfur metabolisms in coastal sediments. Our gene expression data suggest that excess organic enrichment results in (i) higher transcript levels of genes involved in the production of toxic ammonia and hydrogen sulfide and (ii) lower transcript levels associated with the degradation of a greenhouse gas (nitrous oxide). However, metal contamination did not have any significant impact on gene expression. We reveal the genetic mechanisms that may lead to altered productivity and greenhouse gas production in coastal sediments due to anthropogenic contaminants. Our data highlight the applicability of metatranscriptomics as a management tool that provides an immense breadth of information and can identify potentially impacted process measurements that need further investigation.

Bus transportation is one of the most important means of public transportation in today’s world. All major transit regulators intend to improve the bus operation such that the system functions sustainably with respect to all stakeholders involved viz. authority, operators and the commuters. On a day-to-day basis, several improvements are implemented using consumer satisfaction indices or parameters that are critical and need immediate attention. However, a systematic bus transit system design requires an analytical framework for rational decision making such that the transit network serves the maximum number of commuters at their desired level of service while being financially sustainable for the operators and the regulator. In this study, the mathematical modelling technique is employed to propose strategies for a financially and socially sustainable bus transportation system using the mathematical programming (optimization) approach. A set of problems addressing two important aspects of bus transit operation viz. service/network design and regulatory framework design involving different stakeholders are discussed which represent a diverse range of analytical problems faced by the bus transit industry today. In the first section of the thesis, problems relating to transit network design are discussed which act as analytical interfaces between the operators and the commuters; helping the operator to come up with optimal strategies in terms of service network design and tackle issues of congestion. Specifically, a comprehensive design of limited stop service is proposed using the deterministic and stochastic user equilibrium. Further, a bus transit network design problem is proposed to include congestion effects and derive optimal strategies of travel on common lines out of a set of lines serving the transit network. In the second section of the thesis, problems relating to transit network and regulatory framework design of bus transit are discussed with respect to the government contracting regime. A few major bus transit friendly cities recently adopted this regime wherein the government/authority owns all infrastructure and tenders out transit route packages (sets of routes) to private transit players through competitive tendering only for routine operation and maintenance. This thesis presents a detailed mathematical modelling framework of the government contracting regime based on two aspects (i) bus transit route packaging and (ii) competitive tendering of transit route packages to contesting operators. For each of the mathematical models developed, detailed solution algorithms are developed in order to reformulate, linearize and subsequently convexify the formulation to solve it to global optimality. Various mathematical techniques including linearization for the product of binary variables, reformulation-linearization technique, single and multi-dimensional piecewise linearization method and linear piece-wise approximation method are used in the thesis to propose the solution methodology. Thereafter, the mathematical models are validated on real-time transit networks, and results obtained are discussed with some more discussions. To conclude, all the model formulations developed in this thesis present a comprehensive decision making framework for a sustainable bus transit system in the long run. Addressing transit network design and the transit regulatory /policy issues, the proposed framework of analytical models in totality would certainly provide transit planners with a good insight into equitable methods of transit operation to promote social welfare. Doctor of Philosophy (CEE)

Copyright © 2017 Techno-Press, Ltd. The interdisciplinary research area of small scale energy harvesting has attracted tremendous interests in the past decades, with a goal of ultimately realizing self-powered electronic systems. Among the various available ambient energy sources which can be converted into electricity, wind energy is a most promising and ubiquitous source in both outdoor and indoor environments. Significant research outcomes have been produced on small scale wind energy harvesting in the literature, mostly based on piezoelectric conversion. Especially, modeling methods of wind energy harvesting techniques plays a greatly important role in accurate performance evaluations as well as efficient parameter optimizations. The purpose of this paper is to present a guideline on the modeling methods of small-scale wind energy harvesters. The mechanisms and characteristics of different types of aeroelastic instabilities are presented first, including the vortex-induced vibration, galloping, flutter, wake galloping and turbulence-induced vibration. Next, the modeling methods are reviewed in detail, which are classified into three categories: the mathematical modeling method, the equivalent circuit modeling method, and the computational fluid dynamics (CFD) method. This paper aims to provide useful guidance to researchers from various disciplines when they want to develop and model a multi-way coupled wind piezoelectric energy harvester.

It is known that the turbulence can significantly influence the membrane fouling performance. At the same time, many underlying mechanisms and operating parameters have not been scrutinized in details. This is mainly due to the complexities in doing so. In particular, the effect of turbulence on the membrane fouling behavior is rarely reported. In the present study, it was found that increasing turbulence kinetic energy and eddy length scale generally reduced the fouling rate. However, the fouling reduction with integral length scale was limited to an optimal value. The statistical analysis indicated that the fouling rate is cross dependent on both factors. The experiments on the impact of jets on the fouling control of hollow fiber membrane filtration showed that the fouling rate was lower with a higher jet velocity due to higher shear rate that led to a higher critical flux. Doctor of Philosophy (CEE)

The use of Titanium Dioxide (Ti02) nanostructures for photocatalytic environmental applications has received significant attention due to a growing emphasis on sustainability. Against this backdrop, this study proposes the use of nano-crystallised carbon composite one-dimensional Ti02 nanostructure with improved photocatalytic activity in the visible light region for such applications. Amongst the studied one-dimensional nanostructures, nanofibrous anatase Ti02 provided a better medium for photocatalytic reactions. Thus a Bb Ti401 t/Ti02 composite nanofiber was assembled through electrospinning. First, it was observed from the experimental results that the formation of the bismuth titanate (B b Ti4011) phase on the anatase Ti02 nanofiber enhanced its photocatalytic performance in the degradation of A07 as well as H2 generation under visible light. The enhanced photocatalytic activity is attributed to the presence of the BbTi4011 which narrowed the band-gap and allowed for improved charge suppression. Moreover, after the formation of the nano-crystallised carbon layer which doped itself into the composite nanofiber, the appearance of the composite nanofiber changed from cream to black. It was observed that there was a significant reduction to the optical band gap which narrowed to 2.55eV (-480nm). Furthermore, through the characterisation study using TEM it demonstrated that the carbon has fully crystallised into the lattice of the composite nanofiber. This indicates that the crystallisation process was a result from the substitution of anions and cations with C-elements into the lattice of the composite nanofiber which triggered the formation of a -2.5nm thick disorder lattice along the fringes. The H2 evolution tests under sacrificial conditions showed that the nano-crystallised carbon composite nanofiber demonstrated excellent ability to generate H2 under visible light irradiation. The introduction of the nano-crystallised carbon dopant not only improved the visible light absorption capability of the composite nanofiber but also created more reaction sites to facilitate the access of reactant. Furthermore it is proposed that the formation of the nano-crystallised carbon layer permitted for an enhanced electrons transfer process through a sequential electron flow. As such, the combination of these factors enriches the photocatalytic performance of the synthesised complex nanofiber. These finding presents the tremendous potential of the complex nanofiber as it is of great importance and promise to utilise solar energy for water purification and energy harvesting applications. Doctor of Philosophy (IGS)

Concerning the rapid increase in global energy consumption and severe environmental issues, sustainable energy is being increasingly investigated as an alternative to fossil fuels. Osmotic energy, as one form of sustainable energy, can be harnessed by pressure retarded osmosis (PRO) technology, and the semi-permeable membrane is employed as an essential element in the PRO process. However, it is challenging to achieve highly efficient PRO operations due to internal concentration polarization (ICP) effect, mechanical deformation and fouling issues regarding the PRO membranes. Developing membranes that could maintain continuous energy generation with various feed and draw streams is critical for the real-world PRO applications. The objectives of this thesis are to design and fabricate novel PRO membranes with stable power output using various feed and draw solutions. Firstly, this thesis covers the study of substrate structure design and performance evaluation of a novel thin film composite (TFC) flat sheet PRO membrane with excellent mechanical stability under high hydraulic pressures. Subsequently, a TFC membrane in the configuration of hollow fiber with excellent performance was synthesized, which could be applied in a mild fouling environment and maintain the energy output after a low-fouling surface modification. Finally, a specially-designed integral membrane that could be operated in active layer facing feed (AL-FS) orientation under high pressure was fabricated and could produce stable energy generation in a severe fouling environment. To begin with, TFC polyetherimide (PEI) flat sheet membranes were fabricated and characterized. Firstly, three substrates with various morphologies were developed, and subsequently, an interfacial polymerization method was conducted on top of the substrates to form a thin-film selective skin layer for solutes rejection. The membrane performance was evaluated in terms of water flux, power density and reverse solute flux, and these factors were found to vary with the substrate structure. Among three as-prepared TFC membranes, TFC-PEI#2 membrane was chosen for subsequent stability tests due to its relatively high performance as well as satisfactory mechanical strength. The membrane intrinsic properties in terms of water and salt permeability altered with hydraulic pressure were studied for two ascending and descending pressure cycles. Both the intrinsic properties and PRO performance could reach similar values at each applied pressure within the two cycles, which indicated a reversible deformation within 0~17.2 bar. With a 300-min period of PRO test performed at 17.2 bar, a stable 12.8 W·m-2 power density was achieved. In the second study, thin-film composite polyetherimide (TFC-PEI) hollow fiber membranes with excellent performance were synthesized by phase inversion and interfacial polymerization method. The resultant membranes consisted of small-dimension fibers which bestowed excellent mechanical properties to withstand high pressure without any supporting spacers. The membrane surface facing feed stream was modified by depositing polyelectrolytes to increase surface negative charge and hydrophilicity. The introduction of this method was then proven to be effective in reducing protein and poly-alginate fouling while maintaining mechanical properties and intrinsic separation properties of the membranes. The modified TFC-PEI-M membranes resulted in almost no flux reduction at 15 bar with alginate as feed foulants. It demonstrated that osmotic power generation of TFC membranes could be well maintained after polyelectrolytes-deposited low-fouling modification with a feed stream containing organic foulants. Finally, a novel integral polyamide-imide (PAI) membrane was designed and fabricated in order to maintain performance using a feed stream consisting of a complex fouling system. Two PAI substrates with various morphologies were acquired by adjusting the internal coagulant solution during the spinning process. Subsequently, a surface cross-linking post-treatment using poly(allylamine hydrochloride) (PAH) was conducted to synthesize the selective layer. The PRO performances of the two resultant integral membranes were evaluated in the active layer-facing-feed (AL-FS) orientation. The membrane with a sponge-like substrate could produce higher power output using deionized water (DI) as feed, and 1 M MgCl2 as the draw stream compared to that with the other substrate structure and was selected for further optimization. The NaCl rejection of this membrane was then further improved by a secondary cross-linking procedure using glutaraldehyde (GA). The as-prepared integral membrane was characterized by a series of protocols to investigate the pore size and functional groups on the surface. Fouling tests were conducted with a real wastewater reverse osmosis (RO) retentate adopted as the feed. With 1 M NaCl as the draw stream, the membrane could produce a stable power density 4.3 W·m-2 at 12~13 bar hydraulic pressure. Although the AL-FS orientation has been recognized as the orientation with low fouling occurrence, the mechanical robustness of traditional TFC membranes is weak in this orientation and impossible to be operated under high pressures. Fabricating an integral membrane with promising performance and stability in AL-FS mode demonstrated great potential for this low-fouling strategy in PRO process. The future work for the next stage includes four parts. Firstly, the effect of mono and divalent ions in the feed solution will be studied for the low-fouling modified thin film composite membrane Secondly, the PRO performance of the integral membrane is recommended to be further improved by exploring different cross-linking chemicals and conditions. Thirdly, the stability tests of the integral cross-linking membranes and long-term fouling tests will be conducted to further study the viability in real-world applications. Fourthly, the substrates with low cost and suitable for chemical cross-linking will be investigated to explore the possible applications. Doctor of Philosophy (CEE)

The current water quality guidelines intended to protect people from gastrointestinal disease resulting from the recreational use of water bodies solely rely on counts of indicator bacteria in the water phase. However previous studies have indicated that sediments in aquatic bodies could harbour pathogenic microorganisms. Sediments could deteriorate the water quality if there is sediment resuspension into overlying water column in an aquatic body. Compared to water, little is known about microbial quality of sediments in aquatic environment. Potential risks associated with sediment resuspension to recreational users is not well studied. Hence, determining the microbial quality of sediments in the water bodies is important. In this thesis, microbial quality of sediments in two aquatic bodies WB1 and WB2 was investigated. WB1 and WB2 are two important urban water bodies serving as sources of potable water. Currently WB2 is open to public for various non-swimming water recreation activities such as boating, canoeing and kayaking. In future, authorities may open WB1 for recreational purposes as part of Active beautiful clean (ABC) waters programme initiated by Public Utilities Board (PUB) of Singapore. WB1 and WB2 have different land use type. The microbial quality investigation in the present study focussed on the (i) occurrence of conventional bacterial indicators (E.coli and enterococci) and potential enteric viral indicators (FRNA coliphages) in the sediments of WB1 and WB2 and (ii) Survival and adsorption of enteric viral indicators in tropical sediments (sediments of WB1 and WB2 as well as a marine clay sediment). As there is no microbial guideline requirement of permissible levels for indicator bacteria in sediments for recreational purposes, a quantitative microbial risk assessment (QMRA) was done. Quantitative microbial risk assessment based on the enterococci concentration showed that the maximum single event risk for WB1 was within the USEPA (United States Environmental Protection Agency) acceptable freshwater illness rate of 3.6%. In WB2, even though there was a very low probability (0.012) that the maximum risk was above the guideline requirement, 98.8% of the time the risk was below the guideline requirement. F-specific RNA coliphages (FRNA) are potential candidates of human enteric viruses responsible for gastroenteritis illness. However, information regarding the genetic diversity and distribution of these phages in sediments, especially from a tropical climate is not available. Since the concentration of FRNA phages in the sediments of WB1 and WB2 was low, enrichment method (USEPA method 1601) was necessary to detect FRNA phages. Molecular techniques were used to detect and characterise the FRNA phages from the aquatic sediment samples. The two-step enrichment method coupled with quantitative PCR (qPCR) used in this study was shown to be a reliable method for genotyping FRNA coliphages, especially when concentrations of phages are low in the environmental samples. Genotyping of FRNA coliphages has been used to differentiate between animal and human faecal pollution. Genogroups II and III are typically associated with human excreta and genogroups I and IV with animal faeces. In the present study, G II was the most prevalent group with a detection rate of 29% followed by GI (19%) and GIII (16%). Genotype IV was not detected in any of the samples. The low indicator virus titre observed in the sediments of WB1 and WB2, led to the survival and adsorption study of two model viruses (MS2 and phiX174) in tropical sediment suspensions using laboratory microcosms. The effect of electrostatic and hydrophobic forces in viral adsorption to sediments was assessed through adsorption data analysis. In addition, it was found that presence of indigenous microbes had an obvious effect on virus survival in sediments. There are some previous studies indicating that sediments have protective effect on virus survival by which sediment associated viruses are protected from inactivation. In this study the protective effect of sediments for the virus survival was not observed. Doctor of Philosophy (CEE)

Despite the great microbial diversity nature has to offer, a relatively small group of electrochemically-active microorganisms (EAM) has been discovered. This work aimed to explore the use of a three-electrode set-up to enrich and isolate novel EAM. The approach was chosen as an alternative to the conventionally used microbial fuel cell. A three-electrode set-up using a carbon felt working electrode was developed and optimised with a pure culture of Pseudomonas aeruginosa, a species not conventionally tested using this type of system. The platform was sensitive enough to detect current generation using phenazines as redox mediator. Furthermore, simultaneous, real-time electrochemical detection of the redox-active metabolites Pseudomonas quinolone signal and pyocyanin was achieved in live cultures using voltammetry, with implications for diagnostic devices in healthcare settings. After this validation, the platform was then used to characterise a complex microbial community, during long-term electrochemical enrichment. Tropical climate sediment was chosen as inoculum source, as it is currently under-explored in this context which frequently focuses on enrichment from waste water. Specifically, sediments from a canal system and a mangrove region of Singapore were chosen and enriched separately for EAM. Comparison revealed the enriched community from canal sediment was superior to that from the mangrove sediment in terms of electrogenic activity when evaluated by chronoamperometry, and was chosen for further characterisation. Voltamperometric techniques and electrochemical impedance spectroscopy, performed over a wide range of potentials, dynamically characterised extracellular electron transfer (EET) over the four month enrichment. Metagenomics and metatranscriptomics analysis revealed that Geobacter metallireducens was heavily enriched on the electrodes, a species not typically associated with a lactate-fed system such as this. Chlorobium, Clostridium and Rhodopseudomonas were also abundant, indicating tropical climate sediments are host to a range of microorganisms capable of EET. Two novel isolates were grown in pure culture from the enrichment, identified to be from the genera Enterobacter and Aeromonas. Both isolates were capable of EET in defined media on carbon felt and screen-printed electrodes. Both could avail of acetate and lactate as electron donor. Additionally, the Enterobacter isolate could perform mediated electron transfer using the soluble redox shuttle 2- hydroxy-1,4-naphthoquinone (HNQ), indicating it may have availed of this mode of EET during the initial enrichment. This work outlines a comprehensive methodology for characterising and isolating novel EAM from unconventional inocula. It also highlights the applicability of this set-up for monitoring a wide range of EAM, in both mixed communities and pure culture. Specific genera characterised range from high current generators such as Geobacter to more modest performers such as Pseudomonas, Enterobacter and Aeromonas. In addition to characterising EAM, such technology can be used for biosensors, as demonstrated by the detection of redox-active metabolites of the pathogen Pseudomonas aeruginosa. Doctor of Philosophy (IGS)

Bacteria of the Comamonas genus are often present in various engineered and natural ecosystems, in particular, the aromatic compounds-contaminated and denitrifying environments. Intriguingly, they are usually found to be associated with surface or interface as multicellular aggregates known as biofilms. Extensive previous research efforts have been focused on the versatile catabolic capabilities of Comamonas; in contrast, little is known about their biofilm lifestyle and biofilm-mediated environmental processes. The objective of this study was to understand the biofilm lifestyle of Comamonas in environmental processes and the influence of environmental conditions. Specifically, using C. testosteroni as a model organism, this thesis work focuses on elucidating the influences of (i) a model aromatic pollutant 3-chloroaniline (3-CA), (ii) nitrate, and (iii) extracellular biomacromolecules in wastewater on the biofilm lifestyle of Comamonas and their environmental implications. Bioaugmentation of C. testosteroni has been frequently proposed in wastewater and soil treatment to remove toxic aromatic compounds. The performance of bioaugmentation is affected by a number of biological and environmental factors including the interaction between the target pollutant and the augmented bacterial cells. The first part of this thesis work explored the influence of a toxic aromatic pollutant 3-CA on the biofilm lifestyle of C. testosteroni capable of degrading the aromatic compound toward a better understanding of cell-pollutant interaction in bioaugmentation. The results showed that the exposure to 3-CA greatly reduced the retention of C. testosteroni cells in packed-bed bioreactors, which could be attributed to the altered bacterial motility and cell surface hydrophobicity. Through an integrated genomic and transcriptomic analysis, we found that exposure to 3-CA reduced the intracellular c-di-GMP level by downregulating the expression of genes encoding c-di-GMP synthases and induced massive cell dispersal from the biofilms. As the reduced c-di-GMP caused biofilm dispersal, we attempted to develop robust biofilm processes by elevating c-di-GMP level. To achieve this objective, the C. testosteroni strain was constructed which constitutively expressing a c-di-GMP synthase YedQ. Under batch growth conditions with a high surface to volume ratio, an elevated c-di-GMP concentration in C. testosteroni significantly increased the contribution of biofilms in 3-CA biodegradation. In continuous submerged biofilm reactors, C. testosteroni with an elevated c-di-GMP level exhibited an enhanced 3-CA biodegradation and a decreased cell detachment rate. In microbial communities driving domestic wastewater treatment, bacteria of the Comamonas genus were often reported to be among the most abundant microorganisms. In addition, a high abundance of Comamonas was also found in nitrate-removing microbial communities presented in river wetlands, soil, and constructed wetlands. However, why they are there and what roles they may play remain largely unknown. In this thesis work, we demonstrated the involvement of Comamonas biofilms in denitrification under bulk aerobic conditions and elucidated the influence of nitrate respiration on its biofilm lifestyle. Our results showed that C. testosteroni could use nitrate as sole electron acceptor for anaerobic growth. Under bulk aerobic condition, biofilms of C. testosteroni were capable of reducing nitrate and, intriguingly, nitrate reduction significantly enhanced viability of the biofilm-cells and reduced cell detachment from the biofilms. Nitrate respiration was further shown to play an essential role in maintaining high cell viability in the biofilms. RNA-seq analysis, quantitative polymerase chain reaction (qPCR), and liquid chromatography-mass spectrometry (LC-MS/MS) revealed a higher level of bis-(3’-5’)-cyclic dimeric guanosine monophosphate (c-di-GMP) in cells respiring on nitrate than those grown aerobically (1.3×10-4 fmol/cell vs. 7.9×10-6 fmol/cell; P < 0.01). C-di-GMP is one universal signaling molecule that regulates the biofilm mode of life and a higher c-di-GMP concentration reduces cell detachment from biofilms. Taken together, this study reveals that nitrate reduction occurs in mature biofilms of C. testosteroni under bulk aerobic conditions and the respiratory reduction of nitrate is beneficial to the biofilm lifestyle by providing more metabolic energy to maintain high viability and a higher level of c-di-GMP to reduce cell detachment. Wastewater bacteria of the Comamonas genus were often found to form cell aggregates in activated sludge-based wastewater treatment. However, the isolates rarely form flocs in synthetic wastewater, a chemically defined medium that is formulated based on key physicochemical characteristics of real wastewater, e.g., pH, ionic strength, chemical oxygen demand (COD), and total nitrogen/phosphorus (NH4-N and PO4-P). The discrepancy observed for bacterial floc formation in real wastewater and synthetic wastewater suggests an important role of neglected, unknown components, i.e., “dark matter”, in real wastewater. In this study, using C. testosteroni as a model organism, we examined the effect of microfiltered (pore size of 0.22 µm) and ultrafiltered (molecular weight cut-off (MWCO) of 225 kDa) wastewater on bacterial floc formation. Combing the floc formation observations with the Fourier Transform Infrared Spectroscopy (FTIR) analyses and enzymatic treatment, we report for the first time that high molecular weight fraction of the soluble EPS, in particular, proteins and extracellular DNA, are the major floc-forming inducers in wastewater. The underlying mechanism was further characterized by using the DLVO theory. In the presence of soluble EPS, cell surface was found to become more hydrophobic and the energy barrier disappeared, leading to irreversible attachment and floc formation. Therefore, the physicochemical effect of soluble EPS in real wastewater should not be neglected in wastewater biofilm processes which facilitated the initial biofilm formation. Doctor of Philosophy (CEE)

Changes in climate because of global warming during the 20th and 21st centuries have a direct impact on the hydrological cycle as driven by precipitation. However, studying precipitation over the Western Maritime Continent (WMC) is a great challenge, as the WMC has a complex topography and weather system. Understanding changes in precipitation patterns and their groupings is an important aspect of planning mitigation measures to minimize flood and drought risk as well as of understanding the redistribution of precipitation arising from climate change. This paper employs Ward’s hierarchical clustering on regional climate model (RCM)-simulated monthly precipitation gridded data over 42 approximately evenly distributed grid stations from the years 2030 to 2060. The aim was to investigate spatial and temporal groupings over the four major landmasses in the WMC and to compare these with historical precipitation groupings. The results showed that the four large-scale islands of Java, Sumatra, Peninsular Malaysia and Borneo would experience a significant spatial redistribution of precipitation over the years 2030 to 2060, as compared to historical patterns from 1980 to 2005. The spatial groups were also compared for two future forcing scenarios, representative concentration pathways (RCPs) 4.5 and 8.5, and different groupings over the Borneo region were observed. Published version

Smart grid technology development progression has created a possibility for the end users’ participation in the electricity market possible. Recently, the Singapore government has changed the rule for participation in the wholesale market. The Smart Community project, developed by NTU, DNV GL and Green Koncepts, will look into critical factors that will help retail consumers to participate in the demand responses (DR) program and time of use (TOU) pricing. This study reviews benefits for current retail consumer, the impact of DR and TOU on real-time energy consumption of the users, the impact of user experience-focus application toward smart grid participation program on participation reliability and contribution in power reduction during curtailment period. The DR program allows the users to become an active participant in the energy market. It also allows the government to plan better on the limited and costly energy resources, improve system reliability, and reduce transmission and distribution congestion, check and balance on the market power generation. A mobile-based user-experience focus on convenience application is to be developed for consumers to actively participate in the demand-side management programme, which make Singapore Wholesale Energy Market more resilient and reducing market power by introducing competition. Published version

Pseudomonas aeruginosa is an opportunistic pathogen that causes severe airway infections in humans. These infections are usually difficult to treat and associated with high mortality rates. While colonizing the human airways, P. aeruginosa could accumulate genetic mutations that often lead to its better adaptability to the host environment. Understanding these evolutionary traits may provide important clues for the development of effective therapies to treat P. aeruginosa infections. In this study, 25 P. aeruginosa isolates were longitudinally sampled from the airways of four ventilator-associated pneumonia (VAP) patients. Pacbio and Illumina sequencing were used to analyse the in vivo evolutionary trajectories of these isolates. Our analysis showed that positive selection dominantly shaped P. aeruginosa genomes during VAP infections and led to three convergent evolution events, including loss-of-function mutations of lasR and mpl , and a pyoverdine-deficient phenotype. Specifically, lasR encodes one of the major transcriptional regulators in quorum sensing, whereas mpl encodes an enzyme responsible for recycling cell wall peptidoglycan. We also found that P. aeruginosa isolated at late stages of VAP infections produce less elastase and are less virulent in vivo than their earlier isolated counterparts, suggesting the short-term in vivo evolution of P. aeruginosa leads to attenuated virulence.