Search

The UV/Cl2 process (also known as chlorine photolysis, which is the combination of chlorine and simultaneous irradiation of UV light) is conventionally applied at acidic mediums for drinking water treatment and further treatment of wastewater effluents for secondary reuse. This is because the quantum yield of HO• from HOCl (ϕHO•, 254 = 1.4) is greater than the one from OCl- (ϕHO•, 254 = 0.278) by approximately 5 times. Moreover, chlorine photolysis in acidic mediums also tends to have lower radical quenching rates than that of their alkaline counterparts by up to 1000 times. The aim of this research is to investigate the applicability of the UV/Cl2 process by assessing its efficacy on the removal of trimethoprim (TMP) at not only acidic to neutral conditions (pH 6-7), but also alkaline mediums (pH 8-9). At alkaline pH, free chlorine exists as OCl- and since OCl- has a higher molar absorption coefficient as compared to HOCl at higher wavelengths, there would be higher reactive chlorine species (RCS) formation and contribution. TMP removal followed pseudo-first order kinetics and depicted that a maximum fluence based constant (kf′ = 0.275 cm2/mJ) was obtained using 42.25 μM (3 mg/L) of chlorine at pH 9, with an irradiation of 275 nm. At alkaline conditions, chlorine photolysis performance followed the trend of UV (275)/Cl2 > UV (265)/Cl2 > UV (310)/Cl2 > UV (254)/Cl2. RCS like Cl•, Cl2−• and ClO• contributed to the degradation of TMP. When the pH was increased from 6 to 8, contribution from hydroxyl radicals (HO• ) was decreased whilst that of RCS was increased. Application of UV (310)/Cl2 had the highest HO• generation, contributing to TMP removals up to 13% to 48% as compared to 5% to 27% in UV (254, 265, 275)/Cl2 systems at pH 6-9. Artificial neural networks modelling was found to be able to verify and predict the contribution of HO• and RCS conventionally calculated via the general kinetic equations in the UV/Cl2 system at 254, 265, 275 and 310 nm.

The management of contaminants of emerging concern (CECs) in water bodies is particularly challenging due to the difficulty in detection and their recalcitrant degradation by conventional means. In this review, CECs are characterized to give insights into the potential degradation performance of similar compounds. A two-pronged approach was then proposed for the overall management of CECs. Light-driven oxidation processes, namely photo/Fenton, photocatalysis, photolysis, UV/Ozone were discussed. Advances to overcome current limitations in these light-driven processes were proposed, focusing on recent trends and innovations. Light-based detection methodology was also discussed for the management of CECs. Lastly, a cost–benefit analysis on various light-based processes was conducted to access the suitability for CECs degradation. It was found that the UV/Ozone process might not be suitable due to the complication with pH adjustments and limited light wavelength. It was found that EEO values were in this sequence: UV only > UV/combination > photocatalyst > UV/O3 > UV/Fenton > solar/Fenton. The solar/Fenton process has the least computed EEO < 5 kWh m−3 and great potential for further development. Newer innovations such as solar/catalyst can also be explored with potentially lower EEO values.

Nature-based solutions or Green infrastructure (GI) used for managing stormwater pollution are growing in popularity across the globe. Stormwater GI models are important tools to inform the planning of these systems (type, design, size), in the most efficient and cost-effective manner. MUSIC, an example of such a tool, uses regression and first order decay models. Studies validating MUSIC model performance are, however, scarce, hindering future model development and transferability of the model for systems operating under different design and climatic conditions. To close this gap, this paper evaluates MUSIC for a field scale bioretention system, stormwater wetland and vegetated swale operating under Singapore tropical climate. The treatment modules were able to simulate outflows and effluent pollutant concentrations reasonably well for cumulative event volumes (mostly within ±25%) and cumulative TP and TN loads (within ±30%). Outflow TSS loads were significantly under-estimated as a result of greater variability in measured TSS concentrations across events. The findings indicate that simple empirical models such as MUSIC can be transferred to different regions provided that management decisions are based on long-term modelling efforts. The modules generally simulated the outflow hydrographs and pollutographs of the different inflow and drying/wetting conditions relatively poorly.

Water is a limited and valuable resource. Singapore has four national sources of water supply, one of which is natural precipitation. Pollutants collected in stormwater runoff are deposited into drainage systems and reservoirs. Major nutrient pollutants found in local stormwater runoff include nitrate and phosphate, which may cause eutrophication. Bioretention systems are efficient in removing these pollutants in the presence of plants. This paper discusses plant traits that can enhance the phytoremediation of nutrient pollutants in stormwater runoff for application in bioretention systems. The plant species studied showed variations in chlorophyll florescence, leaf greenness, biomass production, and nitrate and phosphate removal. In general, dry biomass was moderately correlated to nitrate and phosphate removal (r = 0.339–0.501). Root, leaf, and total dry biomass of the native tree species showed a moderate to strong correlation with nitrate removal (r = 0.811, 0.657, and 0.727, respectively). Leaf dry biomass of fast-growing plants also showed a moderate to strong relationship with the removal of both pollutants (r = 0.707 and 0.609, respectively). Root dry biomass of slow-growing plants showed a strong relationship with phosphate removal (r = 0.707), but the correlation was weaker for nitrate removal (r = 0.557). These results are valuable for choosing plants for application in bioretention systems. Keywords: Nitrogen, Phosphorus, Plant traits, Bioretention system, Stormwater, Tropical plant, Nutrient pollutant, Native plants

Stormwater runoff management is challenging in a highly urbanised tropical environment due to the unique space constraints and tropical climate conditions. A modular bioretention tree (MBT) with a small footprint and a reduced on-site installation time was explored for application in a tropical environment. Tree species used in the pilot studies were Talipariti tiliaceum (TT1) and Sterculia macrophylla (TT2). Both of the MBTs could effectively remove total suspended solids (TSS), total phosphorus (TP), zinc, copper, cadmium, and lead with removal efficiencies of greater than 90%. Total nitrogen (TN) removal was noted to be significantly higher in the wet period compared to the dry period (p &lt, 0.05). Variation in TN removal between TT1 and TT2 were attributed to the nitrogen uptake and the root formation of the trees species. A field study MBT using Talipariti tiliaceum had a very clean effluent quality, with average TSS, TP, and TN effluent EMC of 4.8 mg/L, 0.04 mg/L, and 0.27 mg/L, respectively. Key environmental factors were also investigated to study their impact on the performance of BMT. It was found that the initial pollutant concentration, the dissolved fraction of influent pollutants, and soil moisture affect the performance of the MBT. Based on the results from this study, the MBT demonstrates good capability in the improvement of stormwater runoff quality.

Chemical oxygen demand (COD) is one of the most important water quality parameters that quantifies the amount of oxygen needed to oxidize oxidizable pollutants (mainly organics) in water samples. However, erroneous COD results were commonly observed for bromide-rich industrial wastewater samples using standard COD test. Bromide in water sample is known to seriously interfere with COD test. However, there is no satisfactory approach to effectively eliminate bromide interference thus far. In this study, two strategies, namely masking and correction, were investigated for their effectiveness to suppress bromide interference. For the masking strategy, silver ion was assessed for its effectiveness to neutralize bromide in water samples through precipitation and complex formation reactions. Silver ion offered only partial masking effect on bromide, while the residue bromide can still cause significant interference on COD determination. For the correction strategy, an equivalent redox reaction reflecting bromide interference mechanism was proposed, and a theoretical correction factor of 0.1 g COD/g Br− was found based on stoichiometry. The effectiveness of the proposed correction factor for bromide interference under different wastewater pollutant matrix was evaluated using different types of wastewater samples (synthetic wastewater, domestic wastewater and bromide-rich industrial wastewater) with varying amounts of bromide (from 0 to 2000 mg L−1) added to the samples. The findings showed that with bromide concentration up to 600 mg L−1, the correction factor of 0.1 g COD/g Br− was applicable to all the tested wastewater samples, suggesting that this correction strategy could be practically used to eliminate bromide interference in standard COD test.

Ozonation is a well-known and widely applied advanced oxidation process (AOP) for industrial wastewater treatment, while the ozonation efficiency might be limited by low mass transfer, poor solubility, and rapid decomposition rate of ozone molecules in the aqueous phase. The present study aims to investigate the feasibility of combined microbubble-catalytic ozonation process (M-O3/Fe/GAC) for improving the ozonation efficiency during treatment of petrochemical wastewater (PCW). M-O3/Fe/GAC process optimization was carried out with different pH conditions, ozone dosages and catalyst loadings. The optimum operating conditions were identified as 50 mg L−1 ozone dosage, real PCW pH (7.0–7.5) and 4 g L−1 catalyst loading. Among different ozonation processes, M-O3/Fe/GAC process achieved the highest chemical oxidation demand (COD) removal efficiency of 88%, which is 18% and 43% higher than those achieved by the microbubble and macrobubble ozonation processes, respectively. Phenolic compounds presented in PCW could be reduced by 63% within 15 min in M-O3/Fe/GAC treatment process. Long-term continuous flow studies suggested M-O3/Fe/GAC process to be the most cost-effective technology for PCW treatment with an operating cost of S$0.18 kg−1 COD and S$0.4 m-3 with good catalyst stability. Liquid size exclusion chromatography with organic carbon detection (LC-OCD) data suggested humic substances to be the dominant organic species in PCW, M-O3/Fe/GAC could achieve significant humic substances removal and biodegradability enhancement in PCW. Kinetics and mechanism studies revealed that organics removal in M-O3/Fe/GAC was 1.8 times higher than that in microbubble ozonation process, and hydroxyl radical (●OH) was the dominant oxidant specie for organics removal in M-O3/Fe/GAC process.

Forward osmosis (FO) has been postulated as a potential viable alternative to conventional pressure-driven membrane treatment processes for water treatment, wastewater reclamation and desalination. Nevertheless, FO suffers from inherent drawbacks such as internal concentration polarization (ICP) and membrane fouling. Its practicality is further limited by the operational dilemma of either experiencing a more severe dilutive ICP in active-layer-facing-feed-solution (AL-FS) orientation or suffering a higher fouling propensity in active-layer-facing-draw solution (AL-DS) orientation, especially with the conventional asymmetric single-skinned FO membranes. Aiming at alleviating the problem of internal fouling while still exploiting the lower ICP and higher water flux of the AL-DS orientation, this study has demonstrated the fabrication of a flat-sheet mesh-incorporated double-skinned substrate membrane for thin-film composite (TFC) FO membrane. Through a progressive substrate membrane surface modification via polydopamine (PDA) deposition, this study explicitly correlates the increment of substrate membrane surface hydrophilicity to the improved fouling resistance and fouling reversibility of resultant TFC-FO membrane in the AL-DS orientation. The effects of foulant types (i.e., alginate and silica), cross-flow rates (i.e., high flow and low flow) and membrane orientations (i.e., AL-DS and AL-FS) have also been systematically studied to better understand FO operation characteristics and enhance its practical applications. The PDA modified double-skinned membrane developed in this study, e.g., TFC-Psf-6, has demonstrated more than 93.0% of water flux recovery in the AL-DS orientation after cleaning as well as significantly surpassing the performance over unmodified double-skinned TFC-Psf-0 (81.7%) and single-skinned TFC-Psf-S (61.7%) under the same testing condition.

A novel bio-entrapped salt marsh sediment membrane reactor (BESMSMR) was evaluated for treating high-salinity pharmaceutical wastewater, and membrane fouling behaviour was also assessed. The BESMSMR was operated in parallel with a conventional membrane bioreactor (CMBR), and a salt marsh sediment membrane bioreactor (SMSMBR) as well as an entrapped biomass MBR (bio-entrapped membrane reactor, BEMR) to facilitate a meaningful comparison of performance characteristics obtained in these reactor systems. Two hydraulic retention times (HRTs) of 60 and 40 h with organic loading rates (OLRs) varied from 7.0 to 11.9 kg COD/m 3 d were tested. The pharmaceutical wastewater used has an average total chemical oxygen demand (TCOD) of 17,931 ± 1851 mg/L and total dissolved solids (TDS) of 20,881 ± 2030 mg/L. The BESMSMR demonstrated the highest removal efficiencies of TCOD (78.4–81.3%), due to the ability of the marine sediment microorganisms seeded from coastal shores to thrive in the hyper-saline environment and degraded recalcitrant organic matter present in the pharmaceutical wastewater. The anoxic zone presented in the inner part of bio-carriers could have triggered the denitrification reaction, and thus improved the TN removal rate by 15–20%. Membrane fouling was reduced with lower concentrations of mixed liquor suspended solids (MLSS), extracellular polymeric substance (EPS), and soluble microbial products (SMP) in the entrapped biomass MBRs. Proteins rather than carbohydrates were the main component of EPS and SMP in the MBR systems. The novel BESMSMR possesses the benefits of salt marsh sediment and an entrapped biomass technique that offered effective organic removal for the high-salinity pharmaceutical wastewater and reduced membrane fouling.

The effect of hydraulic retention time (HRT) on the membrane fouling behavior of submerged ceramic membrane photobioreactors (SCMPBRs) fed with effluent from a submerged ceramic membrane bioreactor (SCMBR) was investigated. The effluent from a SCMBR was continuously fed to three SCMPBRs operated at different HRTs (72, 24, and 6.5 h) for a period of 100 d. Results of the effect of mixed liquors characteristics on fouling showed that mixed liquor suspended solids (MLSS), zeta potential and extracellular polysaccharides (EPS) were not the key factors leading to various fouling behaviors for the SCMPBRs. Membrane fouling rates increased with lower operating HRTs through increased production of carbohydrates in soluble microbial product (SMP). The transmembrane pressure (TMP) value of SCMPBR6.5h exceeded 30 kPa after 68 d of operation, while the TMP of SCMPBR72h and SCMPBR24h were relatively constant throughout the 100 d. Different membrane fouling phenomena were observed at different HRTs. It was noted that biological reactions (e.g., hydrolysis) were induced on the biofilm/biocake layer formed on the membrane surface when operating SCMPBR at long HRT (i.e., 72 h). For SCMPBR operating at short HRT (i.e., 6.5 h), fouling layer and active layer developed on the membrane surface facilitated sieving of colloidal particles and organics. The detailed composition of the organic compounds on membrane foulants in the SCMPBR6.5h showed that carbohydrates and proteins were the major foulants. The finding of much higher organic in non-filtered membrane foulant samples as compared to filtered samples together with the findings from membrane fouling resistance distribution, molecular weight distribution (MWD) and particle size distribution (PSD) indicated that macromolecular compounds contributed more to membrane fouling than those small molecular compounds or soluble compounds.

In this study, the removal of ibuprofen (IBP), a pharmaceutical compound, from aqueous media by Money plant (Epipremnum aureum) was investigated. The effect of ferrous iron (Fe(2+)) on enhancing the IBP removal rate was also analyzed. The first-order removal rate constants showed higher values for lower IBP initial concentrations in the range of 0.20-0.28 d(-1) for an initial concentration of 125 μg L(-1) to 0.03-0.13 d(-1) for an initial concentration of 1000 μg L(-1). Introducing ferrous iron to the aqueous media enhanced the first-order removal rate constant up to 6.5 times in a 3 d time period. Along with the removal of IBP from the media, the endogenous concentration of H2O2 also decreased presumably by the production of hydroxyl radical (·OH). Reduction in the endogenous H2O2 concentration was recorded to be 38% and 98% in the absence and presence of Fe(2+) respectively in the first day and the H2O2 level remained considerably low until day 7 which then gradually increased slightly. Simultaneous reduction of IBP and endogenous H2O2 concentration could be due to the reaction of IBP with ·OH and presumably ·OH production itself accelerated via Fenton reaction. In addition, presence of sodium bicarbonate (NaHCO3) as ·OH scavenger in the system showed reduction of first-order removal rate constant from 1.30 d(-1) to 0.07 d(-1) which could be a possible evidence of biological advanced oxidation process which is believed to play an important role in phytoremediation.

Pharmaceutical and personal care products (PPCPs) and artificial sweeteners (ASs) are emerging organic contaminants (EOCs) in the aquatic environment. The presence of PPCPs and ASs in water bodies has an ecologic potential risk and health concern. Therefore, it is needed to detect the pollution sources by understanding the transport behavior of sewage molecular markers in a subsurface area. The aim of this study was to evaluate transport of nine selected molecular markers through saturated soil column experiments. The selected sewage molecular markers in this study were six PPCPs including acetaminophen (ACT), carbamazepine (CBZ), caffeine (CF), crotamiton (CTMT), diethyltoluamide (DEET), salicylic acid (SA) and three ASs including acesulfame (ACF), cyclamate (CYC), and saccharine (SAC). Results confirmed that ACF, CBZ, CTMT, CYC and SAC were suitable to be used as sewage molecular markers since they were almost stable against sorption and biodegradation process during soil column experiments. In contrast, transport of ACT, CF and DEET were limited by both sorption and biodegradation processes and 100% removal efficiency was achieved in the biotic column. Moreover, in this study the effect of different acetate concentration (0–100 mg/L) as an easily biodegradable primary substrate on a removal of PPCPs and ASs was also studied. Results showed a negative correlation ( r 2 > 0.75) between the removal of some selected sewage chemical markers including ACF, CF, ACT, CYC, SAC and acetate concentration. CTMT also decreased with the addition of acetate, but increasing acetate concentration did not affect on its removal. CBZ and DEET removal were not dependent on the presence of acetate.

Nanofiltration (NF), as a cost-efficient pre-concentrating process, has been incorporated into Zero Liquid Discharge (ZLD) treatment system to improve economic feasibility. However, NF is required to operate with an extremely high recovery rate to achieve ZLD, which could cause severe and complex membrane fouling. Understanding the variation of fouling behavior with increase in recovery rate is crucial for the development of effective fouling control strategy. Spatial variation of fouling behavior in a 3-stage NF used for industrial RO brine treatment towards ZLD was investigated in present study. Distinctive fouling characteristics were observed in each operation stage. Membrane fouling was dominated by organics at lead stage, which could be completely removed via simple base cleaning. Scaling by deposition of bulk crystallization occurred on fouling layer at middle stage, which required a combination of acid and base cleaning for its removal. At the tail stage, more refractory scaling by surface crystallization accompanied by irreversible silica and ferric fouling led to the formation of fouling layer that was resistant to conventional chemical cleaning. Significant humics in preformed fouling layer could have facilitated the occurrence of surface crystallization. Minor elements present in the feed such as silica, humics and iron could cause significant fouling and alter preformed fouling layer that induced more complex and refractory fouling/scaling as recovery rate increased.

While reverse osmosis (RO) technology is playing an important role in industrial wastewater reclamation, safe and cost-effective RO concentrate (ROC) disposal becomes challenging due to high levels of organic pollutants. The present study assessed the feasibility of combined advanced oxidation – biological process for organics removal in real ROC. Four advanced oxidation processes (AOPs) were evaluated for ROC pre-treatment, including UV/H2O2, UV/Persulfate (PS), Fenton and Fluidized bed reactor (FBR)-Fenton processes. Based on the results of process optimization and cost evaluation, FBR-Fenton was identified as the most cost-effective pre-treatment technology with a chemical cost of S$0.519/m3. Under the optimum operating conditions with 10 mM H2O2, 1.25 mM Fe2+, pH 3 and HRT of 1 h, continuous FBR-Fenton process increased the BOD5/COD ratios in ROC by 4.2–10.0 times, while the COD removal efficiency was in the range of 30.9–59.8%. A biological activated carbon (BAC) column with EBCT of 120 min was combined with FBR-Fenton for continuous treatment of ROC. Over the 120-day operation, the combined system performed consistent organics removal in ROC with an average COD removal efficiency of 69%. The average effluent COD level in ROC was observed to be 26 mg/L. Both LC-OCD data and fluorescence EEM spectra suggested humic substances to be the dominant organic species in ROC, FBR-Fenton could achieve significant humic substances removal and biodegradability enhancement in ROC. High-throughput sequencing demonstrated Planctomycetes to be top dominant phylum in BAC media with high salinity influent, and FBR-Fenton process promoted its proliferation for higher COD removal efficiency in ROC.

In recent years, many studies have been conducted on using different filter media in bioretention systems for stormwater runoff treatment. This critical review paper provides a comprehensive review on the current state of water treatment residual (WTR), a recycled material that can be used as bioretention filter media for removals of key stormwater runoff pollutants (especially phosphorus) and future perspectives with innovative modification on WTR applied for pathogen removal from stormwater runoff. This review paper comprised (i) a brief summary of the reported WTR characteristics, (ii) a thorough evaluation of WTR performance on major pollutants removal from stormwater runoff (iii) a discussion on phosphorus removal mechanisms by WTR applied in the stormwater runoff treatment, and (iv) a review of the future perspectives of WTR for pathogen removal and other potential practical application in the field of stormwater treatment. As outlined in this review, WTR in stormwater runoff treatment has yet to be fully explored. The possible enhancements, especially metal surface modification on WTR are reviewed to bring about the widespread use of WTR in stormwater reuse practices.

This study deals with the feasibility and practicality to recover water and nutrients from fresh urine by means of evaporation/condensation. The evaporation process generated two distinct fractions: a condensate and a concentrate. The optimal percentage of evaporation (in volume) was found to be 80%, resulting in optimal condensate quality. Higher percentages of evaporation resulted in a deterioration of water quality, as urea decomposed into ammonia, followed by volatilization of the ammonia which ended up in the condensate. Following evaporation, struvite was recovered from the concentrate at an optimal Mg/N ratio of 1/1. The condensate was purified by filtration into two layers of soil and sand, followed by zeolites. Complete removal of N-NH3 and 91% removal of chemical oxygen demand (COD) could be achieved throughout this process. Finally, the condensate was disinfected by sodium hypochlorite, achieving over 6-log inactivation of MS2 bacteriophage at a dose of 1,200 mg min/L. In conclusion, this study shows that there exist some potential benefits to the production of high-quality water and fertilizer from urine. The value of struvite recovered from the concentrate was found to be equivalent to that of the water from the condensate, showing that both streams deserve equal attention.

Aluminum-based water treatment residue (Al-WTR) generated during the drinking water treatment process is a readily available recycled material with high phosphorus (P) adsorption capacity. The P adsorption capacity of Al-WTR generated from Singapore’s water treatment plant was evaluated with reference to particle size range, adsorption pH and temperature. Column tests, with WTR amendments in sand with and without compost, were used to simulate the bioretention systems. The adsorption rate decreased with increasing WTR sizes. Highest P adsorption capacity, 15.57 mg PO43−-P/g WTR, was achieved using fine WTR particles (&gt, 50% particles at less than 0.30 mm). At pH 4, the contact time required to reduce effluent P concentration to below the detectable range was half compared with pH 7 and 9. The adsorption rate observed at 40 ± 2 °C was 21% higher compared with that at 30 ± 2 °C. Soil mixes amended with 10% WTR and compost were able to maintain consistently high (90%) total phosphorus (TP) removal efficiency at a TP load up to 6.45 g/m3. In contrast, TP removal efficiencies associated with columns without WTR amendment decreased to less than 45% as the TP load increased beyond 4.5 g/m3. The results showed that WTR application is beneficial for enhanced TP removal in bioretention systems.

Microalgae in three submerged ceramic membrane photobioreactors (SCMPBRs) with different hydraulic retention times (HRTs) were fed with permeate of a submerged ceramic membrane bioreactor for a period of 3 months to investigate the lipid content and also the biodiesel quality produced at different HRTs. The lipid content, lipid productivity and fatty acid compositions for all three SCMPBRs were not significantly different at the 95% confidence level. These results suggested that insignificant change in the amount of fatty acids was observed at different HRTs that supplied varying concentration of nitrate in the medium. Among the fatty acids, palmitic acid, palmitoleic acid, oleic acid and linoleic acid were the main components, whereas stearic acid was a minor fatty acid. Since there was insignificant effect of HRT on lipid content, lipid productivity and fatty acid compositions, the optimum HRT for SCMPBRs can then be designed based on optimum nutrient removal performance and low membrane fouling propensity.

Three types of nanosilver materials, which were commercial, chemically-synthesized and biologically-synthesized, respectively, were compared in terms of the disinfection efficiencies against Escherichia coli and MS2 coliphage in order to pinpoint promising material with the best performance. Disinfection results showed biologically-synthesized silver nanoparticles (referred to hereafter as ‘bio-AgNPs’) had the best disinfection performance, 10 mg/L of which was able to inactivate all the E. coli in 1 min (>6 log removals) and achieved 4 log removals of MS2 coliphage. Bio-AgNPs were therefore selected for further study in terms of effects of the concentration and contact time as well as the impacts of environmental conditions on the viral inactivation. Given the viral inactivation profile of bio-AgNPs shown in this study, it could be concluded that viral inactivation by bio-AgNPs could be inhibited by total organic carbon (TOC) (10 mg/L as humic acid) and chloride ion (5 mg/L) to a large extent while Ca2+/Mg2+/ionic strength only had minor effects on the viral inactivation at high concentrations (188 mg/L as CaCO3 of hardness or 5.6 mM of ionic strength, respectively). This part of the study may help enlighten further mechanism studies on viral inactivation by nanosilver.

In the present study, the sorption and biodegradation characteristics of five pharmaceutical and personal care products (PPCPs), including acetaminophen (ACT), carbamazepine (CBZ), crotamiton (CTMT), diethyltoluamide (DEET) and salicylic acid (SA), were studied in laboratory-batch experiments. Sorption kinetics experimental data showed that sorption systems under this study were more appropriately described by the pseudo second-order kinetics with a correlation coefficient (R2) > 0.98. Sorption equilibrium data of almost all target compounds onto soil could be better described by the Freundlich sorption isotherm model. The adsorption results showed higher soil affinity for SA, following by ACT. Results also indicated a slight effect of pH on PPCP adsorption with lower pH causing lower adsorption of compounds onto the soil except for SA at pH 12. Moreover, adsorption of PPCPs onto the soil was influenced by natural organic matter (NOM) since the higher amount of NOM caused lower adsorption to the soil. Biodegradation studies of selected PPCPs by indigenous microbial community present in soil appeared that the removal rates of ACT, SA and DEET increased with time while no effect had been observed for the rest. This study suggests that the CBZ and CTMT can be considered as suitable chemical sewage indicators based on their low sorption affinity and high resistance to biodegradation.

Uptake of two widely studied microcystins (MCs), microcystin-LR (MCLR) and microcystin-RR (MCRR), by peat was investigated under various environmental conditions. MCRR showed better removal (98.6 μg/g) compared to MCLR (87.8 μg/g) in a binary system. The uptake was very rapid with 90% of the toxins being removed from the aqueous phase in initial 15 min of contact. Acidic pH was slightly favorable for the uptake, but removal of MCLR and MCRR can also be achieved in neutral pH. Adsorption isotherm and kinetic modelling provided insights into the simultaneous sorption of MCLR and MCRR onto peat. The influence of various counter ions in the aqueous solution on the adsorptive removal of MCs by peat was investigated under different environmental conditions. Leaching studies showed about 50% of the toxins get desorbed at high alkaline pH. Temperature did not have much effect on either the uptake or the leaching process. The potential of peat to sequester MCs from real reservoir waters was studied to validate the optimized sorption process.

The generation of brine solutions from dense membrane (reverse osmosis, RO or nanofiltration, NF) water reclamation systems has been increasing worldwide, and the lack of cost effective disposal options is becoming a critical water resources management issue. In Singapore, NEWater is the product of a multiple barrier water reclamation process from secondary treated domestic effluent using MF/UF-RO and UV technologies. The RO brine (concentrates) accounts for more than 20% of the total flow treated. To increase the water recovery and treat the RO brine, a CDI based process with BAC as pretreatment was tested. The results show that ion concentrations in CDI product were low except SiO2 when compared with RO feed water. CDI product was passed through a RO and the RO permeate was of better quality including low SiO2 as compared to NEWater quality. It could be beneficial to use a dedicated RO operated at optimum conditions with better performance to recover the water. BAC was able to achieve 15–27% TOC removal of RO brine. CDI had been tested at a water recovery ranging from 71.6 to 92.3%. CDI based RO brine treatment could improve overall water recovery of NEWater production over 90%. It was found that calcium phosphate scaling and organic fouling was the major cause of CDI pressure increase. Ozone disinfection and sodium bisulfite dosing were able to reduce CDI fouling rate. For sustainable operation of CDI organic fouling control and effective organic fouling cleaning should be further studied.

Boron removal by reverse osmosis (RO) membranes has been improved through raised pH and its removal mechanism was suggested as either charge repulsion or size exclusion. In the present study, boron removal by different RO membranes at different salinities was investigated along with their respective zeta potentials. While the impact of salinity on zeta potential of RO membranes was similar, its impact on boron removal by brackish water reverse osmosis (BWRO) membranes was different from that by SWC4+ and ESPAB membranes. RO membranes used in this study showed negative zeta potential value at high pH. However, at pH 9 and with higher salinity, their zeta potentials shifted to positive values. Boron removal by BWRO membranes decreased with increasing salinity at pH 9. The shift of zeta potential towards positive values at higher salinity suggested that charge repulsion mechanism became less dominant. Boron removal by ESPAB and SWC4+ decreased initially when NaCl concentration was increased towards 2000 mg/L at pH 9. However, removal increased slowly when NaCl was beyond 2000 mg/L. This observation suggested that boron removal by these membranes at low salinity was partially contributed by charge repulsion mechanism. At higher salinity, size exclusion could be the dominant factor for boron removal by SWC4 and ESPAB.

Despite considerable research effort undertaken by the scientific community, membrane fouling is still a major technical hurdle that needs to be addressed to enhance the cost-effectiveness of operating reverse osmosis (RO) system for wastewater reclamation. In this study, fouling behaviors (i.e. the rate and extent of flux decline and fouling reversibility) of a laboratory-scale RO system fed with ultrafiltration (UF) prefiltered secondary effluent were studied at two operationally important permeate recovery levels. The associated fouling mechanisms were delineated with the aid of microscopic analysis of the fouling layer characteristics (i.e. composition, morphology and the fouled membrane surface properties). There was a remarkable correlation between the different fouling behaviors observed and the characteristics of fouling layers developed. Organic fouling by carbohydrates and protein-like matters was found to be primarily responsible for the flux loss observed at the first-stage RO with a recovery of 55%. More severe organic fouling together with inorganic precipitation of calcium phosphate and calcium carbonate which resulted in a more drastic and irreversible flux loss was observed at the second-stage RO with a higher recovery of 70%. The membrane fouling potential of effluent organic matter (EfOM) was found to increase greatly with increasing permeate recovery. When permeate recovery was increased to 75% which corresponds to a feed water concentration factor of 4, the fouling potential was increased to 10 times its original value. This study identified the need for more effective organic fouling control at the second-stage RO.

Effluent organic matter (EfOM) has been considered by many to play an important role in fouling of RO membranes used for wastewater reclamation. However, due to their heterogeneous composition, which is a mixture of structurally complex aquatic humic substances (AHS), soluble microbial products (SMP) or extracellular polymeric substances (EPS) and other poorly defined organic compounds, the fractional component(s) or physical–chemical properties responsible for the fouling phenomenon are still not well understood. This study aims to obtain a better understanding of interactions between fractional components of EfOM and RO membranes and attempts to identify the most influential fraction(s) or physical–chemical properties governing the fouling process. Four EfOM fractions were isolated and fractionated from UF prefiltrated treated effluent based on hydrophobicity and charge characteristics. EPS was extracted from the biological treatment stage to assess their fouling potential on RO membranes via well-controlled laboratory-scale experiments. The individual organic fractions were rigorously characterized in terms of physico-chemical properties. A clear correlation was observed between the physico-chemical properties of EfOM fractions and their fouling potential. Under hydrodynamic and chemical conditions typical of commercial applications, the hydrophilic neutral fraction, mainly composed of small size carbohydrates, resulted in the highest flux decline and exhibited highest affinity towards the membrane. EPS biopolymers, to which great importance has been associated with regard to causing RO organic fouling, resulted in less fouling than hydrophilic carbohydrates. Although EPS biopolymers tended to accumulate on the membrane in much higher quantities, the cake layer formed was found to constitute a much lower resistance towards filtration and has a much lower membrane affinity, probably due to their large molecular sizes. The contribution of AHS and other hydrophilic fractions to membrane fouling was found to be much lower as compared to hydrophilic carbohydrates and EPS biopolymers.

The interactions of complex organic matters in reclaimed water were studied for the rejection mechanisms for organics removal by nanofiltration (NF) membrane. Rejection study on single organic fractions showed that base fractions are the most difficult ones to be removed, with the removal efficiencies of 40.08–47.73% for hydrophobic-base (Hpo-B) and 75.51–79.14% for hydrophilic-base (Hpi-B), respectively. Experimental results for interaction studies showed that with the presence of hydrophilic-acid (Hpi-A) and hydrophobic-acid (Hpo-A) at a concentration ratio of 1, the average rejections for acid + base fractions were 11–30% and 9–26% higher than those for the two corresponding single fractions, respectively. It was noted that after the ratio reaches a certain range (>2 for Hpo-A in our case) the beneficial effects become less significant since the saturation of opportunities for interactions. With presence of acid and base fractions, the neutralization reactions and hydrophilic interactions would be the major beneficial interaction among different components. With the presence of hydrophobic-neutral (Hpo-N) at a concentration ratio of 1, the average rejections for neutral + base fractions were improved by 9–35% and when at a ratio of 2, the rejections only increased 2.28–8.87% more. The interaction between neutral organics and base organics would be due to the effect of coupling of different permeable components.

The application of immunofluorescent labeling using quantum dots for detection of inactivated Cryptosporidium parvum oocysts in spiked water samples (reservoir water, treated wastewater effluent, permeate of a membrane bioreactor, and tap water) provided more consistent results compared with the organic fluorophores label. The varying degree of particles present in the different water samples (with turbidity ranging from 0.2 to 6.1 NTU) in nonconcentrated water samples had insignificant interference on the labeled counts (2-sample t-tests, p > 0.236) using the quantum dot label, while the quantum dot label provided an advantage of approximately 50% lower interference in concentrated water samples compared with the organic fluorophores label.

The effect of mean cell residence time (MCRT) (5, 8.3, 16.7, and 33.3d) on domestic wastewater treatment performance had been investigated using four bench-scale pre-denitrification submerged membrane bioreactors (MBR) operated in parallel. The 33.3-d MCRT MBR had the lowest microbial activities in terms of specific oxygen uptake rate, specific denitrification rate and observed sludge yield. Excellent COD removal efficiency (more than 95%) and nitrification (more than 97%) were observed in all the four MBRs investigated. Even though high nitrification can be achieved in all the MBRs, total nitrogen (TN) removal efficiency was found to be affected by MCRT with a maximum of 77% at 33.3-d MCRT. Better TN removal efficiency achieved in the 33.3-d MCRT MBR was due to the combined effect of high mixed liquor concentration and lower dissolved oxygen concentration in the recycled mixed liquor. A comparison of terminal-restriction fragment length polymorphisms (T-RFLP) fingerprints based on 16S rRNA and nirS gene revealed that the microbial communities of 5- and 8.3-d MCRT are grouped under the same branch while 16.7- and 33.3-d MCRT are grouped in another branch. T-RFLP based on amoA gene shows that members from the Nitrosomonas genus were more dominant under shorter MCRT operating environment. Clustering analysis did not show any correlation with the organic and nitrogen removal performance obtained in this study.

The objective of this study was to investigate the rejection of steroid hormone estrone by NF membranes as a function of feed water chemistry. Experimental results indicated that estrone rejection by NF membranes in electrolyte background solution decreased continuously during first 10 h and then stabilized. A clear pH-dependency was observed for estrone rejection. DL membrane exhibited a better performance in terms of estrone rejection at pH 10.4 because the electrostatic repulsion between the dissociated estrone molecules and highly negative-charged DL membrane reduced the proximity of estrone to the membrane surface. The presence of HA in feed solution appeared to improve both of estrone adsorption on membrane and estrone rejection. The lower the solution pH value, the higher amount of HA adsorbed on DL membrane and the greater the increment in adsorption of estrone on membrane by addition of HA. More importantly, it was found that, the presence of HA could enhance the rejection of estrone under all the pH conditions investigated in this study, with the greatest “enhancement effect” on estrone rejection at pH 4.

A series of gold zinc oxide catalysts have been prepared using a coprecipitation procedure and selective oxidation of CO in hydrogen-rich mixtures was investigated in a fixed-bed reactor in the temperature range from 313 to 393 K. The results showed that the suitable content of Au in ZnO was about 1.5 wt.% and calcined at 573 K, shortened as Au (1.5)/ZnO-573. Stability investigation, performed at 353 K and lasted for 500 h, indicated Au (1.5)/ZnO-573 catalyst activity was slightly deteriorated as time on stream was over 350 h. Investigation indicated little addition of platinum into Au (1.5)/ZnO-573 catalyst could definitely improve its stability. However, further study showed that the selectivity of removal of CO from hydrogen-rich mixtures for Au (1.5)-Pt/ZnO-573 catalyst would be decreased with increasing content of Pt on the catalyst when Pt content was over 1.0 wt.%, which indicates that the suitable content of Pt would be 1.0 wt.% and the catalyst was indicated as Au (1.5)-Pt (1.0)/ZnO-573. Kinetic experiments performed on it were carried out in an isothermal fixed-bed microreactor under intrinsic conditions.

This study is intended to develop a stopgap coagulation protocol for immediate health protection of residents exposed to high arsenic from drinking water. The results of a simulated manual jar-test showed that ferric sulfate can maintain a satisfactory arsenic removal efficiency (>95%), and be relatively independent of water conditions. Combining with effective sand filtration, 20, 30, 60 mg/L of ferric sulfate were suitable for removing

In this study, four similar bench-scale submerged Anoxic/Oxic Membrane Bioreactors (MBR) were used simultaneously to investigate the effects of solids retention time (SRT) on organic and nitrogen removal in MBR for treating domestic wastewater. COD removal efficiencies in all reactors were consistently above 94% under steady state conditions. Complete conversion of NH4+-N to NO3--N was readily achieved over a feed NH4+-N concentration range of 30 to 50 mg/L. It was also observed that SRT did not significantly affect the nitrification in the MBR systems investigated. The average denitrification efficiencies for the 3, 5, 10 and 20 days SRT operations were 43.9, 32.6, 47.5 and 66.5%, respectively. In general, the average effluent nitrogen concentrations, which were mainly nitrate, were about 22.2, 27.6, 21.7 and 13.9 mg/L for the 3, 5, 10 and 20 days SRT systems, respectively. The rate of membrane fouling at 3 days SRT operation was more rapid than that observed at 5 days SRT. No fouling was noted in the 10 days and 20 days SRT systems during the entire period of study.

An integrated membrane process (IMP) comprising a membrane bioreactor (MBR) and a reverse osmosis (RO) process was developed for water reclamation. Wastewater was treated by an MBR operated at a sludge retention time (SRT) of 20 days and a hydraulic retention time (HRT) of 5.5 h. The IMP had an overall recovery efficiency of 80%. A unique feature of the IMP was the recycling of a fraction of RO concentrate back to the MBR. Experimental results revealed that a portion of the slow- and hard-to-degrade organic constituents in the recycle stream could be degraded by an acclimated biomass leading to an improved MBR treatment efficiency. Although recycling concentrated constituents could impose an inhibitory effect on the biomass and suppress their respiratory activities, results obtained suggested that operating MBR (in the novel IMP) at an F/M ratio below 0.03 g TOC/g VSS.day could yield an effluent quality comparable to that achievable without concentrate recycling. It is noted in this study that the novel IMP could achieve an average overall TOC removal efficiency of 88.94% and it consistently produced product water usable for high value reuse applications.

To accurately simulate concentration polarization in spiral wound reverse osmosis modules and quantitatively study the effects of the spacer on this phenomenon, a 2-D streamline upwind Petrov/Galerkin (SUPG) finite element model was developed by numerically solving the coupled convection–diffusion equation and Navier–Stokes equations in the feed channel. The model was verified with published experimental data of permeate flux in an empty channel. The numerical simulation results agreed well with the experimental data. The model was then used to simulate the velocity profile and concentration polarization in a segment (5 cm long) of a reverse osmosis feed channel with single filament attached to a membrane or submerged in the feed channel. It was found that velocity and concentration profiles in the regions near the filament were dramatically affected by the filament. In the regions immediately in front of and behind the filament which was attached to a membrane surface, salt concentration increased compared with those in an empty channel under the same operating conditions. This simulation study also showed that the wall concentration would be underestimated if flow direction transition (from crossflow direction to the direction approaching membrane surfaces) regions near the membrane surface were not adequately represented in the simulations. This could be one of the criteria for accurate simulation of concentration polarization. Numerical simulations suggest that the model could be a reliable tool for quantitative study of concentration polarization in spiral wound modules and for spacer design and optimization.

A two-stage sequencing batch reactor (SBR) system was used for treatment of oily wastewater with COD and oil and grease (O&G) concentrations ranging from 1,722–7,826 mg/L and 5,365–13,350 mg/L, respectively. A suitable start-up protocol was developed using gradual increase in oily wastewater composition with methanol as the co-substrate. This strategy enabled a short acclimation period of 12 days for the sludge in the two-stage SBR to adapt to the oily wastewater. After acclimation, the 1st stage and 2nd stage SBRs were able to achieve COD removals of 47.0 ± 2.4% and 95.3 ± 0.5%, respectively. The 1st stage SBR was able to achieve 99.8 ± 0.1% of O&G removal and effluent O&G from the 1st stage SBR was only 6 ± 2 mg/L. The 2nd stage SBR was used to further remove COD in the effluent from the 1st stage SBR. The final effluent from the 2nd stage SBR had a COD concentration of 97 ± 16 mg/L with no detectable O&G content. Thus, a two-stage SBR system was shown to be feasible for treating high strength oily wastewater to meet the local discharge standards.

The bacterial community involved in removing nitrogen from sewage and their preferred DO environment within an anoxic/oxic membrane bioreactor (A/O MBR) was investigated. A continuously operated laboratory-scale A/O MBR was maintained for 360 d. At a sludge age of 150 d and a C/N ratio of 3.5, the system was capable of removing 88% of the influent nitrogen from raw wastewater through typical nitrogen removal transformations (i.e. aerobic ammonia oxidation and anoxic nitrate reduction). Characterization of the A/O MBR bacterial community was carried out using fluorescence in situ hybridization (FISH) techniques. FISH results further showed that Nitrosospira spp. and Nitrospira spp. were the predominant groups of ammonia and nitrite oxidizing group, respectively. They constituted up to 11% and 6% of eubacteria at DO below 0.05 mg/l (low DO), respectively, and about 14% and 9% of eubacteria at DO between 2–5 mg/l (sufficient DO), respectively, indicating preference of nitrifiers for a higher DO environment. Generally low counts of the genus Paracoccus were detected while negative results were observed for Paracoccus denitrificans, Alcaligenes spp, and Pseudomonas stutzeri under the low and sufficient DO environments. The overall results indicate that Nitrosospira spp., Nitrospira spp. and members of Paracoccus spp. can be metabolically functional in nitrogen removal in the laboratory-scale A/O MBR system.

Columnar packed-bed (PB) reactors with a specific surface area of 127 m 2 /m 3 were investigated in this study for treating nitrate wastewater. This study demonstrated that a single-stage packed bed was able to achieve total nitrogen (TN) and chemical oxygen demand (COD) removal efficiencies higher than 83 and 75%, respectively. The highest achievable TN and COD removal rates were 47.2 g N/m 2 .d and 158.0 g COD/m 2 .d, respectively. The substrate removal rate in the PB column was found to follow half-order reaction kinetics, with a reaction coefficient, k, of 53.62 (mg/L) 1/2 /d. A dual-stage PB system was capable of achieving TN and COD removal efficiencies greater than 99 and 98%, respectively. Effluent TN and COD concentrations less than 6.5 mg NO 3 - -N/L and 50.0 mg COD/L, respectively, were obtained when the dual PB system was used.

This research was part of a study of filamentous growth and control in an ultracompact biofilm reactor (UCBR). Morphologies of biofilm and filamentous bacteria in the UCBR were investigated. Ethanol was used as a substrate and sodium hypochlorite was applied as a toxicant to control filamentous growth. The results indicated that factors such as chemical oxygen demand, surface loading rate, pH, and dissolved oxygen could initiate filamentous overgrowth in the UCBR. Different biofilm and filamentous morphologies in the UCBR were observed under different operational conditions. Chlorination was an effective approach to control filamentous growth during and after biofilm formation. Proper chlorine dosing had no effect on biofilm, but killed filaments. Overdose of chlorine damaged biofilm and caused adverse effects such as low treatment efficiency, media clogging and washout, and biofilm color change in the reactor. Frequent monitoring of the morphologies of filaments and biofilm was needed during chlorination to prevent chlorine overdose.