Performance analysis of a stormwater green infrastructure model for flow and water quality predictions.

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 treatment residual: A critical review of its applications on pollutant removal from stormwater runoff and future perspectives.

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.

Sorption and biodegradation characteristics of the selected pharmaceuticals and personal care products onto tropical soil.

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.

Biodiesel production by microalgae cultivated using permeate from membrane bioreactors in continuous system.

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.

Peroxydisulfate-based Non-radical Oxidation of Rhodamine B by Fe-Mn Doped Granular Activated Carbon: Kinetics and Mechanism Study.

While numerous persulfate-based advanced oxidation processes (AOPs) have been studied based on fancy catalysts, the practical combination of Fe or Mn modified granular activated carbon (GAC) has seldom been investigated. The present study focused on a green and readily synthesized Fe-Mn bimetallic oxide doped GAC (Fe-Mn@GAC), to uncover its catalytic kinetics and mechanism when used in the peroxydisulfate (PDS)-based oxidation process for degrading Rhodamine B (RhB), a representative xenobiotic dye. The synthesized Fe-Mn@GAC was characterized by SEM-EDS, XRD, ICP-OES and XPS analyses to confirm its physicochemical properties. The catalytic kinetics of Fe-Mn@GAC+PDS system were evaluated under varying conditions, including PDS and catalyst dosages, solution pH, and the presence of anions. It was found Fe-Mn@GAC exhibited robust catalytic performance, being insensitive to a wide pH range from 3 to 11, and the presence of anions such as Cl-, SO4 2-, NO3 - and CO3 2-. The catalytic mechanism was investigated by EPR and quenching experiments. The results indicated the catalytic system processed a non-radical oxidation pathway, dominated by direct electron transfer between RhB and Fe-Mn@GAC, with singlet oxygen (1O2) playing a secondary role. The catalytic system also managed to maintain a RhB removal above 81 % in successive 10 cycles, and recover to 89.5 % after simple DI water rinse, showing great reusability. The catalytic system was further challenged by real dye-containing wastewater, achieving a decolorization rate of 84.5 %. This work not only provides fresh insight into the kinetics and mechanism of the Fe-Mn@GAC+PDS catalytic system, but also demonstrates its potential in the practical application in real dye-containing wastewater treatment.

Disinfection by-products control in wastewater effluents treated with ozone and biological activated carbon followed by UV/Chlor(am)ine processes.

Sequential utilization of ozone (O3) and biological activated carbon (BAC) followed by UV/chlor(am)ine advanced oxidation process (AOP) has drawn attention in water reuse. However, the formation of disinfection by-products (DBPs) in this process is less evaluated. This study investigated the DBP formation and the relevant toxicity during the O3-BAC-UV/chlor(am)ine treatment of sand-filtered municipal secondary effluent. DBP formation in UV/chlorine and UV/dichloramine (NHCl2) processes were compared, where the impact of key operational parameters (e.g., UV wavelength, pH) on DBP formation were comprehensively evaluated. O3-BAC significantly reduced DBP formation potential (DBPFP) (58.2 %). Compared to UV/chlorine AOP, UV/NHCl2 AOP reduced DBP formation by 29.7 % in short-time treatment, while insignificantly impacting on DBPFP (p > 0.05). UV/NHCl2 AOP also led to lower calculated cytotoxicity (67.7 %) and genotoxicity (55.9 %) of DBPs compared to UV/chlorine AOP. Compared to 254 nm UV light, the utilization of 285 nm UV light decreased the formation of DBPs in wastewater treated with the UV/chlorine AOP and UV/NHCl2 AOP by 31.3 % and 19.2 %, respectively. However, the cytotoxicity and genotoxicity in UV/NHCl2 AOP using 285 nm UV light increased by 83.4 % and 58.5 %, respectively, compared to 254 nm. The concentration of DBPs formed in the UV/NHCl2 AOP at pH 8 was 54.3 % lower than that at pH 7, suggesting a better control of DBPs at alkaline condition. In the presence of bromide, UV/NHCl2 AOP tended to generate more brominated DBPs than UV/chlorine AOP. Overall, UV/NHCl2 AOP resulted in lower concentration and toxicity of DBPs compared to UV/chlorine AOP.

Analyzing disinfection by-products yield and mechanisms in UV/Cl2 using response surface methodology and quantitative structure-activity relationship models.

The study aimed to investigate the formation of halogenated disinfection byproducts (DBPs) during applying UV/chlorine (UV/Cl2) and unravel the interactive impacts of critical operational parameters and the mechanisms behind DBPs formation. Response surface methodology and quantitative structure-activity relationship models were developed to evaluate the contribution of electrophilic, nucleophilic, and free radical reactions to the formation of DBPs in UV/Cl2. The study found that Cl2 and its interactions dominated the total DBPs and non-Br-DBPs formation, while Br- and the Cl2-Br- interaction played a decisive role in the Br-DBPs formation. The study also observed significant interactions of Br, Cl2, and pH on chloroform, bromodichloromethane, dichloroacetonitrile, 1,1-dichloro-2-propanone, trichloroactic acid, and chlorodibromoacetic acid formations, while no evident interaction on chloral hydrate, dibromochloromethane, trichloroacetone, dibromoacetic acid, and bromodichloroacetic acid formations. The electrophilic substitution of HOBr mainly controlled the formation of trihalomethanes, and the contribution of nucleophilic, electrophilic, and free radical (•OH, Cl•, Cl2•- and ClO•) reactions depended on the molar ratio of Cl2 to Br, and pH-determined hydrolysis rate constants of DBPs and the types of free radicals. Overall, the response surface methodology and quantitative structure-activity relationship models provided a reference for revealing DBPs formation mechanisms in other disinfection processes.

Cu(II) assisted peroxymonosulfate for antibiotic resistant bacteria inactivation: A potential disinfection technology in swimming pool.

Alternative disinfection technology to chlorination is required to control the risk of antibiotic resistance in swimming pools. In this study, copper ions (Cu(II)), which often exist in swimming pools as algicides, were used to activate peroxymonosulfate (PMS) for the inactivation of ampicillin-resistant E. coli. Cu(II) and PMS showed synergistic effects on E. coli inactivation in weak alkaline conditions, obtaining 3.4 log inactivation in 20 min with 10 µM Cu(II) and 100 µM PMS at pH 8.0. Quenching experiments indicated that radicals (i.e., OH and SO4-) were not the main disinfectors for E. coli inactivation. Based on the structure of Cu(II) and density functional theory calculations, the Cu(II)-PMS complex (Cu(H2O)5SO5) was recommended as the active species for E. coli inactivation. Under the experimental conditions, the PMS concentration had a greater influence on E. coli inactivation than the Cu(II) concentration, possibly because increasing PMS concentration accelerates ligand exchange reaction and facilitates active species generation. By forming hypohalous acids, halogen ions could improve the disinfection efficiency of Cu(II)/PMS. The addition of HCO3- concentration (from 0 to 1.0 mM) and humic acid (0.5 and 1.5 mg/l) did not significantly inhibit the E. coli inactivation. The feasibility of adding PMS to waters containing Cu(II) for the inactivation of antibiotic-resistant bacteria was validated in actual swimming pool waters, where 4.7 log inactivation of E. coli was achieved in 60 min.

Performance of an ultra-compact biofilm reactor treating domestic and synthetic wastewaters.

The performance of an ultra-compact biofilm reactor (UCBR) treating domestic wastewater (DWW) collected from a local water reclamation plant; and gradually shifting to a mono-type carbon source synthetic wastewater (SWW) combined with DDW (CWW) and finally SWW; was investigated in this study. The total COD concentrations of influent DWW and CWW/SWW were 413.6 ± 80.8 mg/L and 454.9 ± 51.3 mg/L, respectively. The UCBR was able to achieve average total COD removal efficiencies of 70 ± 10% and 80 ± 4% for DWW and SWW respectively. The total COD concentrations of the effluent of DWW and CWW/SWW were 122.5 ± 44.4 mg/L and 89.7 ± 10.3 mg/L, respectively. These observations suggested that heterotrophs in the UCBR system were able to better assimilate and remove carbon of mono-type SWW compared to diverse carbon sources such as DWW; although the influent soluble COD concentrations of the SWW were higher than those of the DWW. However, the effluent NH(4)(+)-N concentrations for both types of wastewater were rather similar, <3.0 mg/L; although the influent NH(4)(+)-N concentrations of the DWW were 1.5 times those of the SWW.

Investigation of the efficacy of the UV/Chlorine process for the removal of trimethoprim: Effects of operational parameters and artificial neural networks modelling.

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.

RO brine treatment and recovery by biological activated carbon and capacitive deionization 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.

Efficient bio-refractory industrial wastewater treatment with mitigated membrane fouling in a membrane bioreactor strengthened by the micro-scale ZVI@GAC galvanic-cells-initiated radical generation and coagulation processes.

Micro-scale ZVI@GAC-based iron-carbon galvanic-cells (ZVI@GACs) were prepared with the Ca-Si-H/Ca-H formation process and first applied to initiate radical generation and coagulation processes in MBR for treating bio-refractory industrial wastewater (IWW). Batch tests revealed the H2O2 production (0.19-0.28 mg/L) and •OH generation (p-CBA decay, k1 = 0.040 min-1) in ZVI@GACs-dosed system (packing volume of 5%) under aeration. Adoption of ZVI@GACs into aerobic activated sludge process (ZVI@GACs/AS) enhanced TOC degradation (k2) and phenolic compounds (PHENs) destruction (k3). ZVI@GACs/AS at ZVI@GACs packing volume of 5%, 10% and 20% improved k2 from 0.11 h-1 (bare AS) to 0.17, 0.21 and 23 h-1 and k3 from 0.24 h-1 to 0.36, 0.49 and 0.57 h-1, respectively. The oxygen uptake rate (OUR) and 15-min acute bio-toxicity demonstrated that the bio-toxicity of IWW was reduced and the activity of biomass was enhanced in the ZVI@GACs/AS system. In MBR, ZVI@GACs at packing volume of 10% enhanced COD and PHENs removal by 14% and 22%, respectively. Membrane fouling cycle was prolonged by 71%. The accumulations of EPS-proteins, EPS-polysaccharides, SMP-proteins and SMP-polysaccharides were reduced by 6%, 67%, 27% and 60%, respectively. Fourier transform infrared spectroscopy (FTIR) confirmed the oxidation of SMP-polysaccharides in ZVI@GACs-MBR. The iron ions released from ZVI@GACs showed inhibition on the secretion of SMP-/EPS-proteins. Floc particle size distribution (PSD) and X-ray diffraction (XRD) spectrum confirmed that the coagulation effects of Fe(OH)3 and FeOOH triggered by Fe3+ increased the sludge floc size and contributed to membrane fouling mitigation. Genus Enterococcus was enriched in MBR with the destruction of PHENs by the ZVI@GACs-initiated radical generation process. The findings of this study confirmed successful development and adoption of ZVI@GACs into MBR for bio-refractory IWW treatment. It also provided an in-depth understanding on the mechanisms of ZVI@GACs-MBR system.

FeOx@GAC catalyzed microbubble ozonation coupled with biological process for industrial phenolic wastewater treatment: Catalytic performance, biological process screening and microbial characteristics.

Phenolic compounds are common ccontaminants in industrial effluents. In this study, a combined catalytic microbubble ozonation and biological process was developed and applied for efficient industrial phenolic wastewater (PWW) treatment. Catalytic activity of an iron-oxides (FeOx) doped granular activated carbon (GAC) catalyst (FeOx@GAC) in microbubble ozonation for PWW treatment was investigated. The results demonstrated that the FeOx@GAC catalyzed microbubble ozonation (O3/FeOx@GAC) obtained significantly higher reaction rate constant (k1 = 0.023 min-1) in TOC removal compared to the bare GAC catalyzed microbubble ozonation (O3/GAC, k1 = 0.013 min-1) and ordinary microbubble ozonation (k1 = 0.008 min-1). Destruction rate constant of phenolic compounds (k2) was improved from 0.014 min-1 (ordinary microbubble ozonation) to 0.025 min-1 (O3/FeOx@GAC). The 60-min pretreatment of PWW by O3/FeOx@GAC process enhanced BOD5/COD ratio from 0.31 to 0.76 and reduced the acute bio-toxicity by 79.2%. Screening and characterization of biological post-treatment processes were conducted among activated sludge process (ASP), up-flow anaerobic sludge blanket (UASB) and membrane bioreactor (MBR). UASB and ASP showed limited phenolic compounds removal of 35.4% and 57.0% with lower bio-toxicity resistance than MBR (94.9% phenolic compounds removal). The combined process O3/FeOx@GAC-MBR was thus developed and achieved high COD removal (98.0%) and phenolic compounds degradation (99.4%). PWW pretreatment by O3/FeOx@GAC process decreased membrane fouling rate of MBR by 88.2% by reducing proteins/polysaccharides accumulation in both extracellular polymeric substances and soluble microbial products. 16S rRNA high-throughput sequencing revealed the predominance of phylum Proteobacteria, class Alphaproteobacteria and genera Mycobacterium, Gordonia, Pedomicrobium & Defluviimonas in biological PWW treatment bio-systems. Pearson correlation coefficient and ANOVA analysis verified that Mycobacterium possessed high bio-toxicity resistance and was the main contributor to the biodegradation of phenolic compounds.

Effects of phosphorus on biofilm disinfections in model drinking water distribution systems.

Drinking water biofilm development is affected by the available nutrient levels and the presence of disinfectants. Phosphorus is recognized as another important limiting nutrient besides organic carbon. In this study, drinking water biofilms were developed in annular reactors to examine the effects of phosphorus on the biofilm disinfections with free chlorine and monochloramine. Phosphorus addition was found to increase the biofilm cell number but decrease the exopolysaccharides (EPS) production. The disinfection efficacies of both free chlorine and monochloramine were increased when phosphorus was added into the reactor systems. At the same disinfection dosages, monochloramine showed greater biofilm removal efficiency than free chlorine. Monochloramine could be a better choice than free chlorine in biofilm disinfection when phosphate-based corrosion inhibitors are applied.

Treatment of industrial brine using capacitive deionization (CDI) towards zero liquid discharge - challenges and optimization.

Thermal-based Zero Liquid Discharge (ZLD) process has been used for managing industrial brine. However, conventional thermal ZLD process is very energy intensive. In view of this, pre-concentration techniques have been applied prior to thermal process to reduce energy consumption of ZLD systems. Capacitive Deionization (CDI) is an emerging desalination technique and has yet to be extensively explored for the treatment of industrial brine especially for ZLD applications. High concentration of total dissolved solids (TDS) and high fouling potential of industrial brine are two major challenges in CDI process. This paper reviews the possible factors for optimizing CDI process in industrial brine treatment, namely, cell architectures, strategies in operation and fouling control. Cell architectures of membrane CDI (MCDI) and flow-electrode CDI (CDI) are preferred options for treating industrial brine compared with classic CDI in terms of energy consumption and fouling propensity. There are other operational strategies that could enhance the feasibility of using CDI process for ZLD application. These include reversed voltage desorption, multi-stage operation, brine recirculation and fouling control. Fouling control methods comprise pretreatment, antifouling modification, antiscalant and chemical cleaning. These methods could be integrated to optimize fouling mitigation. In addition to providing insights on feasibility of using CDI to concentrate industrial brines, this review also proposed guidelines for optimizing CDI process applied to treat industrial brines for ZLD applications.

A method to eliminate bromide interference on standard COD test for bromide-rich industrial wastewater.

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.

Performance and fouling characteristics of different pore-sized submerged ceramic membrane bioreactors (SCMBR).

The membrane bioreactor (MBR), a combination of activated sludge process and the membrane separation system, has been widely used in wastewater treatment. However, 90% of MBR reported were employing polymeric membranes. The usage of ceramic membranes in MBR is quite rare. Four submerged ceramic membrane bioreactors (SCMBRs) with different membrane pore size were used in this study to treat sewage. The results showed that the desirable carbonaceous removal of 95% and ammonia nitrogen removal of 98% were obtained for all the SCMBRs. It was also showed that the ceramic membranes were able to reject some portions of the protein and carbohydrate, whereby the carbohydrate rejection rate was much higher than that of protein. Membrane pore size did not significantly affect the COD and TOC removal efficiencies, the composition of EPS and SMP or the membrane rejection rate, although slight differences were observed. The SCMBR with the biggest membrane pore size fouled fastest, and membrane pore size was a main contributor for the different fouling potential observed.

Role of metal modified water treatment residual on removal of Escherichia coli from stormwater runoff.

Extensive studies have been conducted on bioretention filter media applied in best management practices for stormwater runoff treatment. To date, more reported studies are focused on pollutants elimination such as suspended solids and nutrients. There has been limited research on pathogen removal from stormwater runoff. More focused studies on pathogen removal are therefore required if the intended stormwater is harvested for indirect potable use. In this study, water treatment residuals (WTR), a recycled biofilter media was surface-modified with metals to assess its potential for E. coli removal from stormwater runoff. To achieve this goal, four types of modified WTRs, prepared using iron, copper, platinum, and silver as antibacterial agents, were tested in parallel batch tests. After the cost-effectiveness evaluation among the four modified WTRs for bacterial removal, Fe2O3- and CuO-WTRs were shortlisted for further mechanism and stability studies. Stable antibacterial performances (E. coli log removal of 0.58 ±â€¯0.04 and 0.90 ±â€¯0.04, respectively) were achieved using the Fe2O3- and CuO-WTRs under intermittent synthetic and natural stormwater runoff conditions. No significant metal leaching was observed over prolonged continuous treatment. The experimental results showed the bio-adsorption onto the surface modified Fe2O3- and CuO-WTR was a key mechanism for E. coli removal followed by E. coli inactivation at solid-liquid interface caused by the antibacterial effect of metal coatings (where CuO was reported to have higher biotoxicity than Fe2O3). These findings clearly suggested the potential of CuO-modified WTR for pathogen removal in stormwater treatment practices.

Effect of mean cell residence time on the performance and microbial diversity of pre-denitrification submerged membrane bioreactors.

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.

Alternative immunofluorescent labeling of Cryptosporidium parvum in water samples using semiconductor quantum dots.

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.