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Long-term inhibitory effect of free ammonia (FA) on the catabolic and anabolic activities of an enriched Nitrosomonas culture was investigated. Ammonia oxidizing bacteria (AOB) was inhibited at FA concentration of 34.34 ± 6.85 mg NH3-N/L while threshold inhibitory FA concentration was likely 23.64 ± 4.51 mg NH3-N/L. Below the latter, cell-specific ammonia oxidation rate (AOR), cell number and extracellular polymeric substances (EPS) increased. The calculated yield showed AOB had tended to increase cell mass under FA inhibition. Nitrite concentration increased by 58.6% 12 days after FA decreased to 8.89 ± 0.95 mg NH3-N/L. However, AOB cells became more sensitive to free nitrous acid (FNA) after 70 days of FA inhibition. Long-term FA inhibition changed AOB cell morphology and this could have increased AOB vulnerability to FNA. This study indicated FA inhibited catabolic and anabolic activities, and that long-term FA inhibition had adverse impact on process recoverability and subsequent failure threshold.

Summarization: Municipal solid waste incineration (MSWI) generates bottom ash, fly ash (FA), and air pollution control (APC) residues as by-products. FA and APC residues are considered hazardous due to the presence of soluble salts and a high concentration of heavy metals, and they should be appropriately treated before disposal. Physicochemical characterization using inductively coupled plasma mass spectroscopy (ICP-MS), X-ray diffraction (XRD), and X-ray fluorescence (XRF) have shown that FA and APC have potential for reuse after treatment as these contain CaO, SiO2, and Al2O3. Studies conducted on treatment of FA and APC are categorized into three groups: (i) separation processes, (ii) solidification/stabilization (S/S) processes, and (iii) thermal processes. Separation processes such as washing, leaching, and electrochemical treatment improve the quality and homogeneity of the ash. S/S processes such as chemical stabilization, accelerate carbonation, and cement solidification modify hazardous species into less toxic constituents. Thermal processes such as sintering, vitrification, and melting are effective at reducing volume and producing a more stable product. In this review paper, the treatment processes are analyzed in relation to ash characteristics. Issues concerning mixing FA and APC residues before treatment, true treatment costs, and challenges are also discussed to provide further insights on the implications and possibilities of utilizing FA and APC as secondary materials. Presented on

Cellulose is the most abundant biomass resource and use of cellulose in the synthesis of novel nanomaterials like carbon dots (CDs) has gained attention over the years. However, the photoluminescence yield of cellulose-based CDs is low in the absence of modification additives. Durian shell waste (DSW) is a cellulose rich source and is used for the first time in a one-pot process without any modification agent to produce CDs. The presence of carboxylic acids, esters and amino compounds in durian shell was crucial to improving the CD surface and resulting in a mass yield of 13.9% and quantum yield of 6.2%. This was two times higher compared to that of CDs derived from pure cellulose precursors. The blue-green emitting CDs showed stability over a wide range of pH and chloride concentration and was resistant to photobleaching. Further, the CDs showed high selectivity towards Fe3+ by forming a non-fluorescent ground complex with the oxygen functional groups. Based on the linear relationship between normalized fluorescence intensity and concentration of Fe3+ ions, the synthesised CDs may be used as a fluorescent probe to detect Fe3+ over a concentration range of 0–20 μM with a detection limit of 128 nM. The method was successfully applied in sensing Fe3+ in actual water systems. Nanyang Technological University The authors would like to thank the Interdisciplinary Graduate school of Nanyang Technological University and Nanyang Environment & Water Research Institute for the financial and technical support extended to this study. We would like to acknowledge the Facility for Analysis, Characterization, Testing and Simulation, Nanyang Technological University, Singapore, for use of their transmission electron microscopy facilities.

Kandy City is a UNESCO world heritage site. Being the second largest city in Sri Lanka and host to the annual Esala Perahara festival, it has a floating population two to three times its 120,000 permanent residents. Among the city's key landmarks is Kandy Lake, a culturally, environmentally, and economically significant ornamental lake. Nevertheless, inadequate urban development regulation has resulted in serious pollution of the lake. An integrated remedial measure was needed to improve the urban lake's water quality sustainably, for the Kandy community and their cultural heritage. A project was initiated by the University of Peradeniya (UOP), Sri Lanka, and the Nanyang Environment and Water Research Institute (NEWRI), Singapore. It started with modelling of Kandy Lake and community surveys, demonstrated implementation of wastewater management technologies (floating wetlands and an aerobic sequencing batch reactor (SBR)), and initiated community outreach with schools. The project also involved local authorities and government agencies in Kandy, and provided an informal cooperation platform. After project handover on July 10, 2014, further developments were observed in Kandy, including implementation of sewerage and centralised wastewater treatment, rehabilitation of Kandy Lake and the Mid-Canal, and integration of Kandy Lake into the city's development plan and regulations.

In the operation of biological wastewater treatment processes, fast sludge settling during liquid-solids disengagement is preferred as it affects effluent quality, treatment efficiency and plant operation economy. An important property of fast settling biological sludge is the ability to spontaneously form big and dense flocs (flocculation) that readily separates from water. Therefore, there had been much research to study the conditions that promote biological sludge flocculation. However, reported findings have often been inconsistent and this has possibly been due to the complex nature of the biological flocculation process. Thus, it has been challenging for wastewater treatment plant operators to extract practical information from the literature. The aim of this review is to summarize the current state of understanding of the factors that affect sludge flocculation so that evaluation of such information can be facilitated and strategize for intervention in the sludge flocculation and deflocculation process.

Ultrasound (ULS), sodium hydroxide (NaOH) and combined ultrasound/NaOH pre-treatment were applied to pre-treat waste activated sludge and improve the subsequent anaerobic digestion. Synergistic effect was observed when NaOH treatment was coupled with ultrasound treatment. The highest synergistic Chemical Oxygen Demand (COD) solubilization was observed when 0.02M NaOH was combined with five minutes ultrasonication: an extra 3,000 mg/L was achieved on top of the NaOH (1,975 mg/L) and ultrasonication (2,900 mg/L) treatment alone. Further increase of NaOH dosage increased Soluble Chemical Oxygen Demand (SCOD), but did not increase the synergistic effect. Nine minutes and 18 minutes ultrasonication led to 20% and 24% increase of methane production, respectively; Whereas, 0.05M NaOH pre-treatment did not improve the sludge biodegradability. Combined ultrasound/NaOH (9min+0.05M) showed 31% increase of methane production. A stepwise NaOH addition/ultrasound pre-treatment (0.02M+ULS for 5 min + 0.02M+ULS for 4 min) was tested and resulted in 40% increase of methane production using 20% less chemicals.

This study proposes a new path to utilize thermal hydrolyzed sludge (TH sludge) as fertilizer given high value chemical compounds that can promote plant growth were identified in the liquid fraction of TH sludge (TH liquor). Together with micro- and macro-nutrients released/synthesized during thermal hydrolysis, the feasibility of using TH liquor as organic fertilizer was evaluated. Besides high contents of N, P and K, total free amino acids (FAAs) and plant-growth-promoting FAAs (including glutamic acid, leucine and cystine) also presented in high concentration (4.98–6.48 and 1.12–2.73 g/100 g) in the TH liquor. For the first time, phytohormone compound, indole-3-acetic acid, was observed and the content was the highest in TH liquor with 165 °C treatment (165 °C TH liquor). Meantime, 165 °C TH liquor did not have negative impact on the growth of soil microbes, and this product, instead, demonstrated stimulating effect on the plant growth. These results suggest that 165 °C TH liquor has a great potential to be an organic fertilizer. The remaining solids of TH sludge could be converted to valuable biochar. The holistic approach of using TH liquor as organic fertilizer and producing biochar could realize nearly zero-waste discharge in sludge management.

Absence of sludge deflocculation under prolonged (24 h or longer) conditions with dissolved oxygen (DO) less than 0.5 mg L⁻1 was recently reported. The reduced aerobic microbial activity, was speculated, had been compensated by the activity of other bacterial (i.e. facultative) communities. To assess such a compensation mechanism and to better evaluate impact of overall microbial activity on the flocculation process, SBR sludge samples were inhibited by using sodium azide under various DO conditions. Sludge deflocculated only in the presence of sodium azide, regardless of DO conditions. This was linked to sodium azide’s inhibitory effects on the microbes as indicated by the reduced ammonium and DOC removals. Extracellular potassium level in the mixed liquor of azide spiked samples also indicated simultaneous cell lysis. Fluorescence excitation emission matrix (FEEM) analysis of the extracted bound EPS and fluorescence quenching based interaction studies indicated sodium azide had interacted with the EPS components, and especially with the bound EPS proteins. The impact of such interactions on reduced floc stability needs consideration. This study confirmed the importance of overall microbial activity in the biological flocculation process and the role of bacterial communities, other than the aerobes, in mitigating deflocculation under low DO conditions.

Anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) offers the possibility of a clean and renewable energy source – i.e. biogas. However, OFMSW lacks certain characteristics that may limit its efficacy as such a resource. Bio-resources such as sewage sludge and animal wastes have these characteristics and so may be used to enhance OFMSW's digestion. Anaerobic co-digestion (AcoD) of OFMSW with sewage sludge has been extensively studied and applied successfully at full-scale. Pre-treatments can increase substrate biodegradability and so biogas yield, but these may need further investigation to determine economic viability. Mathematical modeling has been shown useful in aiding selection of appropriate combinations of substrates and pretreatment for co-digestion (e.g. substrate type and mix ratio). This review also considers the fate of the digestate following such anaerobic co-digestion. The difficulties in implementation of the co-digestion approach need not necessarily be technical in nature but can be due to management issues.

The anaerobic digestion process is a multi - step reaction dependent on concerted activities such as exchange of metabolites among physiologically different microbial communities. This study investigated the impact of iron oxide nanoparticles on the anaerobic sludge microbiota. It was shown there were three distinct microbial phases following addition of the nanoparticles: microbial stress and cell death of approximately one log order of magnitude, followed by microbial rewiring, and recovery. Furthermore, it was noted that cellular stress led to the establishment of intercellular nanotubes within the microbial biomass. Intercellular nanotube - mediated communication among genetically engineered microorganisms and ad hoc assembled co - cultures have been previously reported. This study presents evidence of intercellular nanotube formation within an environmental sample – i.e., anaerobic sludge microbiota subjected to stress. Our observations suggested a mode of microbial communication in the anaerobic digestion process not previously explored and which may have implications on bioreactor design and microbial functions.

Host defense cationic Antimicrobial Peptides (AMPs) can kill microorganisms including bacteria, viruses and fungi using various modes of action. The negatively charged bacterial membranes serve as a key target for many AMPs. Bacterial cell death by membrane permeabilization has been well perceived. A number of cationic AMPs kill bacteria by cell agglutination which is a distinctly different mode of action compared to membrane pore formation. However, mechanism of cell agglutinating AMPs is poorly understood. The outer membrane lipopolysaccharide (LPS) or the cell-wall peptidoglycans are targeted by AMPs as a key step in agglutination process. Here, we report the first atomic-resolution structure of thanatin, a cell agglutinating AMP, in complex with LPS micelle by solution NMR. The structure of thanatin in complex with LPS, revealed four stranded antiparallel β-sheet in a ‘head-tail’ dimeric topology. By contrast, thanatin in free solution assumed an antiparallel β-hairpin conformation. Dimeric structure of thanatin displayed higher hydrophobicity and cationicity with sites of LPS interactions. MD simulations and biophysical interactions analyses provided mode of LPS recognition and perturbation of LPS micelle structures. Mechanistic insights of bacterial cell agglutination obtained in this study can be utilized to develop antibiotics of alternative mode of action. MOE (Min. of Education, S’pore) NMRC (Natl Medical Research Council, S’pore) Published version

Recycled paper mill effluent (RPME) contains high levels of organic and solid compounds, causing operational problems for anaerobic biological treatment. In this study, a unique modified anaerobic inclining-baffled reactor (MAI-BR) has been developed to treat RPME at various initial chemical oxygen demand (COD) concentrations (1000–4000 mg/L) and hydraulic retention times (HRTs) (3 and 1 day). The COD removal efficiency was decreased from 96 to 83% when the organic loading rate (OLR) was increased from 0.33 to 4 g/L day. Throughout the study, a maximum methane yield of 0.25 L CH4/g COD was obtained, while the pH fluctuated in the range of 5.8 to 7.8. The reactor performance was influenced by the development and distribution of the microbial communities. Based on the next-generation sequencing (NGS) analysis, the microbial community represented a variety of bacterial phyla with significant homology to Euryarchaeota (43.06%), Planctomycetes (24.68%), Proteobacteria (21.58%), Acidobacteria (4.12%), Chloroflexi (3.14%), Firmicutes (1.12%), Bacteroidetes (1.02%), and others (1.28%). The NGS analysis showed that the microbial community was dominated by Methanosaeta concilii and Candidatus Kuenenia stuttgartiensis. This can be supported by the presence of filamentous and spherical microbes of different sizes. Additionally, methanogenic and anaerobic ammonium oxidation (ANAMMOX) microorganisms coexisted in all compartments, and these contributed to the overall degradation of substances in the RPME.

This study investigated the feasibility of using ultrasonic (ULS), ozone assisted ultrasonic (ULS-Ozone) and alkaline assisted ultrasonic (ULS + ALK) post-treatment to target the persistent organic fraction in anaerobically digested sludge in order to increase methane recovery. Synergistic COD solubilization in digested sludge was observed when ozone (0.012 g O 3 g −1 TS) and alkaline (0.02 M for 10 min) treatment was combined with ULS treatment. The digested sludge Soluble Chemical Oxygen Demand (SCOD) increased from 200 mg/L to 1500, 2600 and 2650 mg/L after the ULS, ULS-Ozone and ULS + ALK treatments, respectively. Different compounds were, however, solubilized after the ULS-Ozone and ULS + ALK treatments as indicated by size exclusion chromatography (SEC). ULS + ALK treatment primarily solubilized macromolecules with molecular weight (MW) over 500 kDa; while, the ULS-Ozone treatment solubilized macromolecules with MW higher than 500 kDa and also organics with MW around 103 kDa. The methane production from “re-digestion” of the treated digested sludge increa s ed by 28.3%, 48.3% and 39.5% after the ULS, ULS-Ozone and ULS + ALK treatments, respectively.

Bioretention, as a popular low impact development practice, has become more important to mitigate adverse impacts on urban stormwater. However, there is very limited information regarding ensuring the effectiveness of bioretention response to uncertain future challenges, especially when taking into consideration climate change and urbanization. The main objective of this paper is to identify the cost-effectiveness of bioretention by assessing the hydrology performance under future scenarios modeling. First, the hydrology model was used to obtain peak runoff and TSS loads of bioretention with variable scales under different scenarios, i.e., different Representative Concentration Pathways (RCPs) and Shared Socio-economic reference Pathways (SSPs) for 2-year and 10-year design storms in Singapore. Then, life cycle costing (LCC) and life cycle assessment (LCA) were estimated for bioretention, and the cost-effectiveness was identified under different scenarios. Our finding showed that there were different degree of responses to 2-year and 10-year design storms but the general patterns and insights deduced were similar. The performance of bioretenion was more sensitive to urbanization than that for climate change in the urban catchment. In addition, it was noted that the methodology used in this study was generic and the findings could be useful as reference for other LID practices in response to climate change and urbanization.

Heavy metal pollution in natural water environment is always a concern in both human and ecosystem health. All current systems available in the market for detecting heavy metal ions have common drawbacks such as bulky size, expensive set-up and costly maintenance. This paper presents an optical microfiber sensor functionalized with chelating agent to detect the existence of specific heavy metal ions of low concentration. To the best of our knowledge, coating of chelating agent on silica microfiber of very small diameter (3.9 μm) is the first such report. A clear spectral shift was observed when the sensor was immersed into metal ion solution of concentration 10 ppb.

Agriculture waste can be a significant issue in waste management as its impact can be felt far from its place of origin. Post-harvest crop residues require clearance prior to the next planting and a common practice is burning on the field. The uncontrolled burning results in air pollution and can adversely impact the environment far from the burn site. Agriculture waste can also include animal husbandry waste such as from cattle, swine, and poultry. Animal manure not only causes odors but also pollutes water if discharged untreated. However, agricultural activities, particularly on a large scale, are typically at some distance from urban centers. The environmental impacts associated with production may not be well recognized by the consumers. As the consumption terminal of agricultural produce, urban areas in turn generate food waste, which can contribute significantly to municipal solid wastes. There is a correlation between the quantity of food waste generated and a community’s economic progress. Managing waste carries a cost, which may illustrate cost transfer from waste generators to the public. However, waste need not be seen only as an unwanted material that requires costly treatment before disposal. The waste may instead be perceived as a raw material for resource recovery. For example, the material may have substantial quantities of organic carbon, which can be recovered for energy generation. This offers opportunity for producing and using renewable and environment-friendly fuels. The “waste” may also include quantities of recoverable nutrients such as nitrogen and phosphorus.

Development of metallic and nonmetallic heteroatom doped carbon dots have gained attention due to their enhanced physicochemical and photoluminescence properties. In this study, a facile one pot hydrothermal carbonisation approach was taken to synthesise nitrogen, aluminum co-doped carbon dots (N/Al-CDs) with a photoluminescence quantum yield of 28.7%. Durian shell, a cellulose biomass waste, was used as the primary carbon source and compared to previously reported cellulose based carbon dots, this study presents one of the highest quantum yields. The structural and fluorescent properties of the synthesised N/Al-CDs were characterized through X-ray photoelectron spectroscopy (XPS), fluorescence spectra, and Fourier transform infrared spectroscopy (FTIR). The maximum emission was at 415 nm upon excitation at 345 nm. The synthesised N/Al-CDs were resistant to photobleaching and highly photostable within the pH, ionic strength and temperature variations investigated. The transmission electron microscopy (TEM) images showed particles were quasi-spherical and well dispersed with an average diameter of 10.0 nm. Further, the N/Al-CDs was developed as a fluorescence sensor for highly selective and sensitive detection of Mn (VII) ions. A linear relationship was developed over a concentration range of 0-100 μM while the limit of detection was 46.8 nM. Application of the sensor for detection of Manganese (VII) to two real water samples showed relative standard deviation was less than 3.9% and 1.3%, respectively. Nanyang Technological University The authors would like to thank the Interdisciplinary Graduate School of Nanyang Technological University and Nanyang Environment & Water Research Institute for the financial and technical support extended to this study. We would like to acknowledge Dr. Pan Chaozhi from Environmental Bio-innovations Group for the insights that improved the manuscript quality and finally the Facility for Analysis, Characterization, Testing and Simulation, Nanyang Technological University, Singapore, for use of their transmission electron microscopy facilities.

In the published literature, deflocculation of aerobic biological flocs under low dissolved oxygen (DO) (< 0.5 mg/L) conditions is typically reported as occurring as early as after 1 h of oxygen deficiency. However, results of this study involving aerobic sludge from three different sources repeatedly indicated a lack of deflocculation after 24 h of low DO conditions. This finding has led to the conclusion that low DO might not be a direct cause of deflocculation. In addition to the low DO conditions, the sludge samples were not re-fed throughout the experiment, but deflocculation was still not observed. An analysis of the soluble microbial products (SMP) and loosely and tightly bound extracellular polymeric substances (EPS) was performed to improve understanding of the sludge’s behavior in response to low DO conditions. Results indicated no increase in SMP content or change in the tightly bound EPS content upon extended periods of low DO. It was concluded that high proteins concentration in the bound EPS improved flocs stability, and so contributed to the maintenance of floc integrity during extended periods of low DO conditions. This project was supported by funding from Grundfos Holdings through project Understanding and Mitigation of Sludge Deflocculation During Nitrogen Removal Process.

This study investigated the initiation and maintenance of nitritation in a membrane bioreactor (MBR) with long solids retention time (SRT) of 43.8 days. Nitritation was initiated within 65 days in the MBR via dissolved oxygen (DO) limitation (70 days. Quantitative polymerase chain reaction (qPCR) results showed that cell abundances of Nitrospira and Nitrobacter decreased by between 50.0 to 68.9% and 60.6 to 96.4%, respectively following the FNA shocks. The maximum ammonium loading rate achieved was 1.81 kg N/(m3 day) with ammonium removal ratio and nitrite accumulation ratio of over 0.97 and 0.96, respectively. Average emission rate of N2O from the MBR was 2.1 ± 0.72% of ammonium removed. FNA shock on day 195 reduced the N2O emission by 13.6%. The strategy developed in this study verified that spiked FNA shock together with DO limitation can be used for maintaining nitritation in MBRs with long SRTs. This method can potentially allow for maintaining nitritation at relatively low capital and operating expenditure when treating high concentration ammonium wastewater. Ministry of Education (MOE) This study was funded by Academic Research Fund Tier 2, Ministry of Education, Singapore, grant number MOE2014-T2-1-029.

The introduction of glyphosate, found in herbicides, to waterbodies is of concern due to its toxicity and hence potential threat to public health and ecological systems. The present study has compared glyphosate removal from aqueous solution with activated carbon and biochar. Box–Behnken design, and percent contribution with Pareto analysis techniques were used in surface response and efficiency calculations modelled the process conditions and their effects. The adsorption data better fitted the Freundlich isotherm model than the Langmuir model. The rate of glyphosate adsorption was found to follow a pseudo-second-order model. pH of the solutions was regulated by buffering during the adsorption process. Higher efficacy of glyphosate removal was obtained by optimising parameters such as operating pH, initial glyphosate concentration, temperature, adsorbent dose, and contact time. The conditions yielding the best removals were pH 8.0, 0.2 mg/L, 50.0 °C, 11.4 g/L, 1.7 h for activated carbon and pH 5.0, 0.7 mg/L, 50.0 °C, 12.3 g/L, 1.9 h for biochar, for the aforementioned parameters respectively. The maximum removal capacity and efficiency were 0.0173 mg/g and 98.45% for activated carbon, and 0.0569 mg/g and 100.00% for biochar. The test results indicated biochar could be important from the perspective of performance and affordability.

Antimicrobial peptides (AMPs) are potentially vital as the next generation of antibiotics against multidrug resistant bacterial pathogens. Thanatin, an insect derived pathogen inducible 21-residue long antimicrobial peptide, demonstrates antimicrobial activity toward broad range of pathogens. Thanatin is an excellent candidate for antibiotics development due to potent in vivo activity in animal model and low toxicity to human cells. Recent studies indicated mode of action of thanatin could be intriguing and may comprise bacterial membrane permeabilization and interactions with periplasmic proteins. In order to better understand selectivity and membrane disruption, here, we determined 3-D structure of the thanatin in zwitterionic DPC-d38 micelle by NMR spectroscopy. The depth of insertion of thanatin into micelle structure was investigated by spin labelled doxyl lipids, 5-DSA and 16-DSA. DPC-bound structure of thanatin is defined by a -hairpin structure and an extended and turn conformations, for residues G1-I8, at the N-terminus. The -hairpin structure is delineated by two antiparallel -strands, residues I9-C11 and residues K17-R20, which is connected by loop consisted of residues N12-G16. There are cross -strands sidechain-sidechain packing interactions among hydrophobic and aromatic residues. Spin labelled lipid studies revealed a set of spatially proximal residues V6, I8, Q19, R20 and M21 may be deeply inserted into the hydrophobic core of the DPC micelle. Whilst, residues including those at the turn/loop are merely surface localized. The atomic resolution structure and orientation of thanatin in zwitterionic DPC micelle may be utilized for understating mode of action in lipid membrane and further development of non-toxic analogs. Ministry of Education (MOE) Accepted version This work has been supported by the research grant ARC18/13 from the Ministry of Education (MOE), Singapore. The pdb coordinates of the DPC bound structure of thanatin are deposited to RCSB Protein Data Bank with accession number 6AAB. NMR chemical shifts are deposited to BMRB database with accession code 36201.

A biosorption column and a settling tank were operated for 6 months with combined municipal and industrial wastewaters (1 m3/hr) to study the effect of dissolved oxygen (DO) levels and Fe3+ dosage on removal efficiency of dissolved and suspended organics prior to biological treatment. High DO (>0.4 mg/L) were found to be detrimental for soluble chemical oxygen demand (COD) removals and iron dosing (up to 20 ppm) did not improve the overall performance. The system performed significantly better at high loading rate (>20 kg COD.m−3.d−1) where suspended solids and COD removals were greater than 80% and 60%, respectively. This is a significant improvement compared to the conventional primary sedimentation tank, and the process is a promising alternative for the pre-treatment of industrial wastewater.

This study investigated the biosorption process kinetics and the associated microbial community. Seed sludge from the aeration tank of a wastewater treatment plant in Singapore was acclimated with synthetic wastewater formulated to contain colloidal (ca. 40%) and dissolved COD (Chemical Oxygen Demand). The COD removal kinetics and the individual mechanisms involved were determined by subjecting the acclimated sludge to increasing organic loadings (0.1, 0.5, 1.0, and 2.5 g COD per g suspended solid) of synthetic wastewater. Under pH 7, sorption capacity of the acclimated sludge increased with organic loading. Comparison between live and azide-inactivated sludge revealed that under organic loading of 1.0 g COD/g SS, a level similar to a typical contact tank for carbon capture, at least 74% of the biosorption capacity was contributed by carbon storage. Kinetics data suggested that carbon storage was the predominant mechanism in the first 20–30 min of the carbon capture biosorption process. The removal kinetics of dissolved COD can be represented by a pseudo-second-order model and intraparticle diffusion model. These suggested the rate-limiting steps could include chemisorption and intraparticle diffusion. On the other hand, colloid COD removal can be described as a first order process with respect to initial organic loading. Taxa capable of carbon-storage which include Chloroflexi, Thiobacillus sp., Xanthobacter sp., Mycobacterium sp., and Nakamurella sp., were uniquely detected in the acclimated sludge. NRF (Natl Research Foundation, S’pore) Accepted version

This study investigated the behaviour and characteristics of soluble microbial products (SMP) in two anoxic-aerobic membrane bioreactors (MBRs): MBRcontrol and MBRpharma, for treating municipal wastewater. Both protein and polysaccharides measured exhibited higher concentrations in the MBRpharma than the MBRcontrol. Molecular weight (MW) distribution analysis revealed that the presence of pharmaceuticals enhanced the accumulation of SMPs with macro- (13,091 kDa and 1,587 kDa) and intermediate-MW (189 kDa) compounds in the anoxic MBRpharma, while a substantial decrease was observed in both MBR effluents. Excitation emission matrix (EEM) fluorescence contours indicated that the exposure to pharmaceuticals seemed to stimulate the production of aromatic proteins containing tyrosine (10.1-32.6%) and tryptophan (14.7-43.1%), compared to MBRcontrol (9.9-29.1% for tyrosine; 11.8-42.5% for tryptophan). Gas chromatography - mass spectrometry (GC-MS) analysis revealed aromatics, long-chain alkanes and esters were the predominant SMPs in the MBRs. More peaks were present in the aerobic MBRpharma (196) than anoxic MBRpharma (133). The SMPs identified exhibited both biodegradability and recalcitrance in the MBR treatment processes. Only 8 compounds in the MBRpharma were the same as in the MBRcontrol. Alkanes were the most dominant SMPs (51%) in the MBRcontrol, while aromatics were dominant (40%) in the MBRpharma. A significant decrease in aromatics (from 16 to 7) in the MBRpharma permeate was observed, compared to the aerobic MBRpharma. Approximately 21% of compounds in the aerobic MBRcontrol were rejected by membrane filtration, while this increased to 28% in the MBRpharma.

In this study, a fed-batch acidogenic reactor was operated at a 3 d hydraulic retention time (HRT) and fed with alkaline pre-treated sludge to investigate salinity effects on methanogens' abundance, activities and their consumption of produced acetic acid (HAc) and total volatile fatty acids (VFAs). The salinity concentration was increased step-wise by adding sodium chloride. At 3‰ (parts per thousand) salinity, the average produced volatile fatty acids (VFAs) concentration was 2410.16 ± 637.62 mg COD L(-1) and 2.70 ± 0.36 L methane was produced daily in the acidogenic reactor. Further batch tests indicated methanogens showed a HAc degradation rate of 3.81 mg COD g(-1) VSS h(-1) at initial HAc concentration of 1150 mg COD L(-1), and showed tolerance up to 16‰ salinity (3.76 g Na(+) L(-1)) as indicated by a constant HAc degradation rate. The microbiological study indicated this can be related to the predominance of acetate-utilizing Methanosarcinaceae and Methanomicrobiales in the reactor. However, with salinity increased to 20‰ and 40‰, increases in VFAs and HAc production and decreases in methane production, methanogens population, acidogenic bacteria population and acidification extent were observed. This study demonstrated presence of acetate-utilizing methanogens in an acidogenic reactor and their high tolerance to salinity, as well as their negative impacts on net VFAs production. The results would suggest the presence of methanogens in the acidogenic reactor should not be ignored and the recovery of methane from the acidogenic reactor needs to be considered to avoid carbon loss.

In light of global warming mitigation efforts, increasing sludge disposal costs, and need for reduction in the carbon footprint of wastewater treatment plants, innovation in treatment technology has been tailored towards energy self-sufficiency. The AB process is a promising technology for achieving maximal energy recovery from wastewaters with minimum energy expenditure and therefore inherently reducing excess sludge production. Characterization of this novel sludge and its comparison with the more conventional B-stage sludge are necessary for a deeper understanding of AB treatment process design. This paper presents a case study of a pilot-scale AB system treating municipal wastewaters as well as a bio- (biochemical methane potential and adenosine tri-phosphate analysis) and physico-chemical properties (chemical oxygen demand, sludge volume index, dewaterability, calorific value, zeta potential and particle size distribution) comparison of the organic-rich A-stage against the B-stage activated sludge. Compared to the B-sludge, the A-sludge yielded 1.4 to 4.9 times more methane throughout the 62-week operation.

A 16S rRNA gene multiplex 454 pyrosequencing approach was used to characterize the structure of the bacterial community in subsurface flow constructed wetlands planted with Typha angustifolia and unplanted wetland mesocosms receiving ibuprofen-enriched wastewater at a concentration of 250 μg L −1 . The removal efficiency of ibuprofen (IBP) in the planted beds (78.5%) was significantly higher than that in the unplanted beds (57.9%) ( P ≤ 0.05). The presence of ibuprofen significantly ( P ≤ 0.05) reduced the diversity of the bacterial community. In total, 20 phyla comprising 265 genera were identified. The most predominant phyla were Firmicutes (27.6%), Actinobacteria (26.0%) and Proteobacteria (24.9%), making up 57–95% of the 16S rDNA sequences. Other dominating phyla in wetland soils were Chloroflexi (7.3%), Bacteroidetes (2.7%), Synergistetes (2.1%), and Acidobacteria (2.0%). A distinct profile of bacterial community in the wetland mesocosms was observed after IBP enrichment. IBP-enrichment enhanced the relative abundance of Actinobacteria, Bacilli and γ-Proteobacteria at class level. The efficient ibuprofen removal observed in this study suggested that the IBP-enriched wetland systems may have selected a restricted group of bacteria that was able to survive best in the disturbed condition and participate in the IBP biodegradation. Our findings also indicated that the presence of macrophytes may have a vital impact on the microbial community and planted wetlands may be more robust and buffered against significant shifts in microbial composition in response to IBP-disturbance.

This study investigated the degradation and production of volatile fatty acids (VFAs) in the acidogenic phase reactor of a two-phase anaerobic system. 20 mmol/L bromoethanesulfonic acid (BESA) was used to inhibit acidogenic methanogens (which were present in the acidogenic phase reactor) from degrading VFAs. The impact of undissociated volatile fatty acids (unVFAs) on “net” VFAs production in the acidogenic phase reactor was then evaluated, with the exclusion of concurrent VFAs degradation. “Net” VFAs production from glucose degradation was partially inhibited at high unVFAs concentrations, with 59%, 37% and 60% reduction in production rates at 2190 mg chemical oxygen demand (COD)/L undissociated acetic acid (unHAc), 2130 mg COD/L undissociated propionic acid (unHPr) and 2280 mg COD/L undissociated n-butyric acid (unHBu), respectively. The profile of VFAs produced further indicated that while an unVFA can primarily affect its own formation, there were also unVFAs that affected the formation of other VFAs. NRF (Natl Research Foundation, S’pore)

This manuscript presents a comparison of the A-stage and B-stage sludges in terms of anaerobic biodegradability and low molecular weight compounds present in the supernatant using Gas Chromatography-Mass Spectrometry (GC-MS). The GC-MS analysis of A-stage and B-stage supernatants identified respectively 43 and 19 organic compounds consisting mainly of aromatics (27.9% and 21%), alcohols (25.6% and 15%) and acids (30.2% and 15%). The methane potential was found to be 349±1 mL CH4/g VS and 238±12 mL CH4/g VS, respectively. After anaerobic digestion of these sludges, a greater proportion of aromatics (42% and 58%) and a lower proportion of acids (10% and 10%) and alcohols (16% and 10%) was observed.

Transitional metal oxides are promising anode materials for sodium ion batteries (SIBs) due to their high theoretical capacities and material abundance; however, their sodium storage capability is significantly hindered by the sluggish sodiation/desodiation reaction kinetics. Herein, towards achieving fast and durable sodiation/desodiation reaction, Fe 3 O 4 and Co 3 O 4 nanocrystals encapsulated in carbon micro-spheres are synthesized via a biochemistry approach using recombinant elastin-like polypeptides containing hexahistidine tag (ELP16-His) followed by annealing. Fe 3 O 4 and Co 3 O 4 nanocrystals of approximately 5 nm in size, which are uniformly dispersed in a carbon matrix, are obtained. The carbon-encapsulated metal oxides exhibit encouraging sodium storage capacities (657 and 246 mA h g −1 at 0.1 and 2 A g −1 , respectively, for carbon-encapsulated Fe 3 O 4 ; 583 and 183 mA h g −1 at 0.1 and 2 A g −1 , respectively, for carbon-encapsulated Co 3 O 4 ), and have a high capacity retention after 100 cycles at 0.5 A g −1 . The superior electrochemical properties of the carbon-encapsulated metal oxide nanocrystals demonstrate their potential for use as anode materials for high-capacity, high-rate and durable sodium storage.

Recent research has shed light on utilization of carbon storage microorganisms in the A-stage of AB process for higher methane generation and resource recovery potential. Typically, organic matters are entrapped into biomass in the A-stage and subsequently channeled to the anaerobic digester for energy/resource recovery. In the following B-stage, nitrite shortcut strategy is often implemented to achieve low energy nitrogen removal. In this study, an enriched glycogen accumulating organism (GAO) culture was deployed as the A-stage carbon storage microorganisms to enhance the removal of soluble COD. This study aimed (1) to address the challenge arising from incidental nitrite leakage into the A-stage tank, leading to free nitrous acid (FNA) inhibition; and (2) to evaluate the continued (henceforth referred to as ‘accumulated’) inhibitory effects on GAOs’ carbon metabolisms under the subsequent FNA-free condition. Upon FNA exposure, dynamics in carbon storage mechanisms were obtained and could be linked to higher cellular energy expenditure for detoxification activity. The inhibition on carbon transformation, however, was found to be reversible, suggesting the robustness of GAO towards FNA inhibition and its potential application in the nitrite-shortcut AB process. NRF (Natl Research Foundation, S’pore) Accepted version

This study investigates alkali-solubilized dissolved organic matter (DOM) and its fate in the anaerobic treatment process. DOM was fractionated into high molecular weight (HMW) protein-like substances (PL), HMW saccharide-like substances (SL), low molecular weight (LMW) PL, LMW SL, and humic acid-like substances (HAL). The results indicate alkali-solubilized DOM is primarily composed of LMW PL, HMW SL, and HAL. Alkaline pretreatment improved the overall anaerobic degradability of DOM in sludge (removal efficiency of total DOM increased by 28.4%). However, certain DOM fractions (mainly HMW PL and HAL) exhibited low degradability during anaerobic treatment, primarily caused by the low degradability of aromatic groups (such as aromatic amine groups from tryptophan-like PL). Alkaline pretreatment also resulted in an increase of residual DOM, which is mainly composed of HAL (52.9%) and HMW SL (49.9%).

A pilot-scale landfill and a two-phase (acidogenesis and methanogenesis) anaerobic sequencing batch reactor (anSBR) system was setup to treat leachate collected from the simulated landfill cell which had leachate recirculation (at

This study investigated an alkaline two-stage enhanced anaerobic sludge digestion system, which simultaneously combined biological and chemical mode of degradation. The alkaline enhanced mesophilic stage-1 was operated at pH 8 with 3 days hydraulic retention time (HRT), while the mesophilic stage-2 was without pH adjustment at 17 days HRT. The system achieved higher chemical oxygen demand (COD) removal, volatile solids (VS) reduction, and methane yield than the conventional 20 days HRT single-stage system. Further enhancement was obtained by moving the stage-1 from 35 to 55 °C, but it did not yield better energy balance with the 3 + 17 days HRT configuration implemented in this study. 454 pyrosequencing revealed the acclimation of specialized communities in the alkaline two-stage system. Methanosarcina, Methanobrevibacter and Methanothermobacter could survive at pH 8 in the alkaline enhanced stage-1 and contributed to regulating the potentially inhibitory volatile fatty acids (VFA) or hydrogen levels under the enhanced sludge solubilization and acidogenesis condition. Various fermentative populations, distinct to those in the single-stage system, were also enriched in the stage-1s. These populations could grow at pH 8, were transferred into the stage-2, and ensured continuity of the biochemical reactions under mild alkaline condition, leading to the enhanced sludge digestion process.

The sequential combination of ultrasonication and ozonation as sewage sludge treatment prior to anaerobic digestion was investigated. Synergistic volatile suspended solids (VSS) solubilization was observed when low energy ultrasonication ( 500 kDa) were found to be the main solubilization products when sludge was only ozonated. However, solubilization products by ozone were mainly in the form of low MW components (MW < 27 kDa) when sludge was pre-ultrasonicated. The high MW products generated by ultrasound were effectively degraded in the subsequent ozonation. Anaerobic biodegradability increased by 34.7% when ultrasonication (9 kJ g−1 TS) and ozonation (0.036 g O3 g−1 TS) were combined sequentially. The maximum methane production rate increased from 3.53 to 4.32, 4.21 and 4.54 mL CH4 d−1 after ultrasonication, ozonation and ultrasonication–ozonation pre-treatments, respectively. Accepted version

Photoluminescent carbon dots have gained increasing attention in recent years due to their unique optical properties. Herein, a facile one-pot hydrothermal process is used to develop nitrogen-doped carbon dots (NCDs) with durian shell waste as the precursor and Tris base as the doping agent. The synthesized NCDs showed a quantum yield of 12.93% with a blue fluorescence under UV-light irradiation and maximum emission at 414 nm at an excitation wavelength of 340 nm. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy showed the presence of nitrogen and oxygen functional groups on the NCD surface. The particles were quasi-spherical with an average particle diameter of 6.5 nm. The synthesized NCDs were resistant to photobleaching and stable under a wide range of pH but were negatively affected by increasing temperature. NCDs showed high selectivity to Tetracycline as the fluorescence of NCDs was quenched significantly by Tetracycline as a result of the inner filter effect. Based on sensitivity experiments, a linear relationship (R2 = 0.989) was developed over a concentration range of 0-30 μM with a detection limit of 75 nM (S/N = 3). The linear model was validated with two water samples (lake water and tap water) with relative recoveries of 98.6-108.5% and an RSD of

2-Phase anaerobic digestion (AD), where the acidogenic phase was operated at 2 day hydraulic retention time (HRT) and the methanogenic phase at 10 days HRT, had been evaluated to determine if it could provide higher organic reduction and methane production than the conventional single-stage AD (also operated at 12 days HRT). 454 pyrosequencing was performed to determine and compare the microbial communities. The acidogenic reactor of the 2-phase system yielded a unique bacterial community of the lowest richness and diversity, while bacterial profiles of the methanogenic reactor closely followed the single-stage reactor. All reactors were predominated by hydrogenotrophic methanogens, mainly Methanolinea. Unusually, the acidogenic reactor contributed up to 24% of total methane production in the 2-phase system. This could be explained by the presence of Methanosarcina and Methanobrevibacter, and their activities could also help regulate reactor alkalinity during high loading conditions through carbon dioxide production. The enrichment of hydrolytic and acidogenic Porphyromonadaceae, Prevotellaceae, Ruminococcaceae and unclassified Bacteroidetes in the acidogenic reactor would have contributed to the improved sludge volatile solids degradation, and ultimately the overall 2-phase system's performance. Syntrophic acetogenic microorganisms were absent in the acidogenic reactor but present in the downstream methanogenic reactor, indicating the retention of various metabolic pathways also found in a single-stage system. The determination of key microorganisms further expands our understanding of the complex biological functions in AD process. NRF (Natl Research Foundation, S’pore) Published version

Urban stormwater runoff is both a significant pollution source and a potentially valuable resource. This study compares stormwater management in two cities: Singapore and Berlin, Germany. In comparing the strategies for stormwater management, we illustrate how differences in geography (e.g., land and water availability), urban infrastructure, regulatory regimes, legislation and intensives between the two cities have led to different solutions for stormwater management. Singapore, faced with a serious issue of water scarcity, has placed an increasing emphasis on stormwater management through developing a comprehensive network of drains and canals, mainly with the aim of controlling flooding and potable water supply. In contrast, in Berlin, concerns for the protection of surface water quality and non-potable water supply in the urban areas have resulted in a shift in management goals towards a low impact solution based on source control. The cost analysis indicated that the decentralized rainwater h...

The effects of temperature on nitrous oxide (N2O) accumulation during denitrification and denitritation were investigated. Batch experiments were performed to measure N2O accumulation at 25 and 35 °C. More N2O accumulation was observed during denitritation at the higher temperature as compared with full denitrification and low temperature tests. The highest nitrite concentration tested in this study (25 mg/L NO2−N and pH 8.0) did not show inhibitory effect on N2O reduction. It was found that the major cause of more N2O accumulation during denitrification at higher temperature was due to higher N2O production rate and lower N2O solubility. Specific nitrate, nitrite, and N2O reduction rates increased 62, 61, and 41 %, respectively, when temperature rose from 25 to 35 °C. The decrease of N2O solubility in mixed liquor at 35 °C (when compared to 25 °C) resulted in faster diffusing rate of N2O from liquid to gas phase. It was also more difficult for gas phase N2O to be re-dissolved. The diffused N2O was then accumulated in the headspace, which was not available for denitrification by denitrifiers. The results of this study suggest higher temperature may worsen N2O emission from wastewater treatment plants (WWTPs). Accepted version

Three horizontal subsurface flow constructed wetlands and three sand filters (without plants) were set up at the campus of Nanyang Technological University, Singapore. Eight pharmaceuticals including carbamazepine, naproxen, diclofenac, ibuprofen, caffeine, ketoprofen, salicylic acid, and clofibric acid were enriched in the wetland inflow. Three factors, namely, with/without the presence of vegetation, operational modes (batch and continuous), and hydraulic residence time were investigated by a polynomial regression model with analysis of variance, including factorial design, to find the relationships between contaminant removal and the affecting factors, as well as to determine the dominant variables and how each of them interact for each parameter. The objective of this study was to compare the removal efficiencies of selected pharmaceuticals under different wetland retention times, planted versus unplanted modes, and feeding strategies.

Metal vanadium phosphates (MVP), particularly Li3V2(PO4)3 (LVP) and Na3V2(PO4)3 (NVP), are regarded as the next-generation cathode materials in lithium/sodium ion batteries. These materials possess desirable properties such as high stability, theoretical capacity, and operating voltages. Yet, low electrical/ionic conductivities of LVP and NVP have limited their applications in demanding devices such as electric vehicles. In this work, a novel synthesis route for the preparation of LVP/NVP micro/mesoporous 3D foams via assembly of elastin-like polypeptides is demonstrated. The as-synthesized MVP 3D foams consist of microporous networks of mesoporous nanofibers, where the surfaces of individual fibers are covered with MVP nanocrystallites. TEM images further reveal that LVP/NVP nanoparticles are about 100-200 nm in diameter, with each particle enveloped by a 5 nm thick carbon shell. The MVP 3D foams prepared in this work exhibit ultrafast rate capabilities (79 mA h g(-1) at 100C and 66 mA h g(-1) at 200C for LVP 3D foams; 73 mA h g(-1) at 100C and 51 mA h g(-1) at 200C for NVP 3D foams) and excellent cycle performance (almost 100% performance retention after 1000 cycles at 100C); their properties are far superior compared to current state-of-the-art active materials.

The rapid development of nanotechnology will inevitably result in an increasing release of engineered nanoparticles (NPs) to wastewaters. In this study we investigated the fate and toxicity of ZnO NPs in aquatic plant mesocosms, as well as the potential for root accumulation and root-to-shoot translocation of these Zn NPs in the wetland plant Schoenoplectus tabernaemontani exposed to ZnO NPs. The growth of S. tabernaemontani in these hydroponic mesocosms was significantly inhibited by ZnO NPs (1000 mg L(-1)) compared to a control. Levels of Zn in the plant roots for the ZnO NP treatment ranged from 402 to 36513 μg g(-1), while values ranged from 256 to 9429 μg g(-)(1) (dry weight) for Zn(2+) treatment, implying that the uptake of Zn from ZnO NPs was substantially greater than that for Zn(2+). The root uptake (of the initial mass of Zn in the solution) for ZnO NP treatment ranged from 8.6% to 43.5%, while for Zn(2+) treatment they were 1.66% to 17.44%. The low values of the translocation factor for both ZnO NP (0.001-0.05) and Zn(2+) (0.05-0.27) treatments implied that the potential for translocation of Zn NPs from roots to shoots was limited. ZnO NP distribution in the root tissues of S. tabernaemontani was confirmed by scanning electron microscopy (SEM). Transmission electron microscopy (TEM) demonstrated that ZnO NPs could pass through plant cell walls, and were present within the plant cells of S. tabernaemontani.

The feasibility of manipulating operating parameters, i.e. Food-to-microorganisms (F/M) ratio, SRT, and residual DO, to enhance biosorption performance was investigated. It was observed that lower F/M and longer SRT resulted in sludges which captured carbon mainly through carbon storage. Surface sorption, however, was the dominant mechanism for sludges grown under the higher DO condition. Generally, biosorption was optimal at pH 7. Sorption kinetic studies revealed that sludge cultivated under the low F/M ratio of 0.15 (Sludge S1) showed the best overall biosorption performance. Determination of calorific value revealed that Sludge S1 was able to capture energy as much as 0.9 kJ/g SS within 15 min contact time. About 66.3% of the overall biosorption capacity was attributed to carbon storage. Sludge S1 was able to accumulate organic substrate and stored this as polyhydroxyalkanoates (PHA). Culture-independent microbial community analysis through DGGE revealed the presence of strains capable of PHA-accumulation, e.g. Rhodobacter sp., and Thauera sp. While different dominating mechanisms resulted from different cultivation conditions, the best biosorption performance was significantly contributed by carbon storage activity. Accepted version