Conventional water resources in many regions are insufficient to meet the water needs of growing populations, thus reuse is gaining acceptance as a method of water supply augmentation. Recent ...advancements in membrane technology have allowed for the reclamation of municipal wastewater for the production of drinking water, i.e., potable reuse. Although public perception can be a challenge, potable reuse is often the least energy-intensive method of providing additional drinking water to water stressed regions. A variety of membranes have been developed that can remove water contaminants ranging from particles and pathogens to dissolved organic compounds and salts. Typically, potable reuse treatment plants use polymeric membranes for microfiltration or ultrafiltration in conjunction with reverse osmosis and, in some cases, nanofiltration. Membrane properties, including pore size, wettability, surface charge, roughness, thermal resistance, chemical stability, permeability, thickness and mechanical strength, vary between membranes and applications. Advancements in membrane technology including new membrane materials, coatings, and manufacturing methods, as well as emerging membrane processes such as membrane bioreactors, electrodialysis, and forward osmosis have been developed to improve selectivity, energy consumption, fouling resistance, and/or capital cost. The purpose of this review is to provide a comprehensive summary of the role of polymeric membranes and process components in the treatment of wastewater to potable water quality and to highlight recent advancements and needs in separation processes. Beyond membranes themselves, this review covers the background and history of potable reuse, and commonly used potable reuse process chains, pretreatment steps, and advanced oxidation processes. Key trends in membrane technology include novel configurations, materials, and fouling prevention techniques. Challenges still facing membrane-based potable reuse applications, including chemical and biological contaminant removal, membrane fouling, and public perception, are highlighted as areas in need of further research and development.
•Colloidal particles in membrane feed monitored using a light scattering technology.•Colloidal particle levels in the membrane feed water followed a diurnal pattern.•Correlation developed between ...colloidal particle level and optimum coagulant dose.•Real time “targeted” coagulant release reduced 80 to 96% membrane fouling.•This technique lowered irreversible fouling with no coagulant leakage in filtrate.
Fouling of microfiltration (MF)) membranes during water/wastewater treatment is predominantly caused by colloidal particles (size <1 µm) in the feed water. Until recently no online technology was available to directly measure the occurrence of colloidal particles in these waters. This study evaluated the viability of a novel online light scattering technology (Nanoparticle Tracking Analysis) to continuously monitor colloidal particles in the membrane feed water (a secondary-treated wastewater) for targeted removal by injecting coagulant at a dosage proportional to the measured concentration of colloidal particles. A diurnal variation was observed in the colloidal particle concentration in the feed water with the lowest concentration occurring at approximately 6 am and the highest concentration occurring after mid-day. The peak colloidal particle concentrations were 4 to 6 times higher than the lowest concentrations measured on the same day. Bench-scale studies were performed to develop a relationship between colloidal particle concentration and the optimum coagulant dosage required for their removal. Subsequently, a pilot-scale study was performed using two MF pilot units operated in parallel, one receiving targeted coagulant dosing and the other with no coagulant dosing, to demonstrate the effectiveness of targeted coagulant dosing in preventing membrane fouling. The pilot unit that received targeted coagulant dose experienced only 4 to 20% of the transmembrane pressure increase of the increase experienced by the pilot unit that received no coagulant. Evaluation of fouling resistance indicated that targeted coagulation improved flux by predominantly lowering the irreversible fouling. The filtrate water quality measured by colloidal particle concentration, chemical oxygen demand (COD), and turbidity were very similar for the two pilot units. This suggests that although the efficiency of particle and organic materials removal does not change with coagulant addition, the particles filtered by the membrane in the control unit contributed to membrane irreversible fouling, while in the coagulant-treated unit, the coagulated colloidal particles were removed away from the membrane into the backwash stream during the frequent backwash/air scour procedures.
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Advanced oxidation using UV/free chlorine and UV/chloramines are being considered as alternatives to UV/H2O2 for treatment of reverse osmosis (RO) permeate in treatment trains for the potable reuse ...of municipal wastewater. This pilot-scale comparison of the three advanced oxidation processes (AOPs) evaluated three factors important for selecting among these alternatives. First, the study characterized the speciation of oxidants serving as the source of radicals within the AOPs to facilitate process modeling. Kinetic modeling that included consideration of the chloramines occurring in RO permeate accurately predicted oxidant speciation. Modeling of the UV/free chlorine AOP indicated that free chlorine is scavenged by reactions with ammonia and monochloramine in RO permeate, such that oxidant speciation can shift in favor of dichloramine over the short (∼30 s) timescale of AOP treatment. Second, the order of efficacy for degrading the target contaminant, 1,4-dioxane, in terms of minimizing UV fluence was UV/free chlorine > UV/H2O2 ≫ UV/chloramines. However, estimates indicated that the UV/chloramines and UV/H2O2 AOPs could be similar on a cost-effectiveness basis due to savings in reagent costs by the UV/chloramines AOP, provided the RO permeate featured >3 mg/L as Cl2 chloramines. Third, the study evaluated whether the use of chlorine-based oxidants within the UV/free chlorine and UV/chloramines AOPs enhanced disinfection byproduct (DBP) formation. Even after AOP treatment and chloramination, total halogenated DBP formation remained low at <15 μg/L for all three AOPs. DBP formation was similar between the AOPs, except that the UV/free chlorine AOP promoted haloacetaldehyde formation, while the UV/H2O2 and UV/chloramines AOPs followed by chloramination increased chloropicrin formation. However, total DBP formation on a toxic potency-weighted basis was similar among the AOPs, since haloacetonitriles and haloacetamides were the dominant contributors and did not differ significantly among the AOPs.
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•Mixtures of oxidants occur in AOPs at potable reuse facilities.•A kinetic model could predict oxidant speciation in these AOPs.•The order of efficacy for 1,4-dioxane loss was UV/HOCl > UV/H2O2 ≫ UV/chloramines.•Halogenated DBP concentrations were similar for these AOPs.
An epoxy treatment was applied to a pipeline used to convey advanced treated recycled water from a purification facility to a recharge site. The epoxy treatment was applied to prevent further ...deterioration (corrosion) of the interior cement mortar lining (CML). A soil column study was conducted to evaluate the effect of the epoxy liner on the clogging potential of water before and after conveyance. The clogging potential was represented by differences in the column's relative hydraulic conductivity and water quality, between the treatment plant and injection site, before and after epoxy lining. Hydraulic conductivity of columns at the injection well site declined rapidly before epoxy and improved considerably after epoxy application. Total suspended solids (TSS) and cellular adenosine triphosphate (cATP) median concentrations improved significantly. Before epoxy, TSS increased with pipeline transit from 0.005 to 0.053 (mg/L) compared with 0.009 mg/L after epoxy. Before epoxy, cATP increased from 0.14 to 1.6 pg/ml across pipeline transit compared with 0.37 pg/ml after epoxy. Aluminum and nitrate followed similar trends. Results indicate that epoxy liner reduced the clogging potential of high purity recycled water, likely due to a decrease in particle and biomass load (clogging constituents) accumulated during pipeline transit.
Practitioner Points
Clogging potential of advanced treated recycled water increases with pipeline transit.
Epoxy lining the pipeline used for conveyance reduces the particulate and microbial loading of the highly purified water.
Applying epoxy to pipelines used to convey advanced treated recycled water has the dual benefit of infrastructure protection and improving water quality.
Reducing particle and microbial load in the advanced treated recycled water can reduce maintenance frequencies and elongate production periods for MAR applications.
Clogging potential of advanced treated recycled water increases with pipeline transit, which is reduced by coating the inside of the pipeline with epoxy. Application of epoxy to pipelines decreases particle and microbial loading of highly purified water produced with advanced treatment.
Selected perfluorinated surfactants were irradiated in aqueous hydrogen peroxide solutions using artificial sunlight to study transformation under aquatic environmental conditions. Indirect ...photolysis mediated by hydroxyl radical was observed for N-ethyl perfluorooctane sulfonamidoethanol (N-EtFOSE), N-ethyl perfluorooctane sulfonamido acetate (N-EtFOSAA), N-ethyl perfluorooctane sulfonamide (N-EtFOSA), and perfluorooctane sulfonamide acetate (FOSAA). An upper limit for the bimolecular reaction rate constant for reaction of •OH and N-EtFOSAA was determined to be (1.7 ± 0.7) × 109 M−1s−1. A proposed reaction pathway for degradation of the parent perfluorochemical, N-EtFOSE, to the other perfluoroalkanesulfonamides and perfluorooctanoate (PFOA) was developed and includes oxidation and N-dealkylation steps. As they did not undergo additional degradation, perfluorooctane sulfonamide (FOSA) and PFOA were the final degradation products of hydroxyl radical-initiated oxidation. UV−visible absorption spectra for the perfluorochemicals, showing absorbance in the UV region below the range of natural sunlight, are also reported. In sunlit environments, indirect photolysis of perfluorochemicals is likely to be important in the determination of their environmental fate given the slow rates expected for biotransformation and weak sorption. Photolytic conversion of perfluorochemicals into refractory perfluorinated acids, mainly PFOA, could mean that a significant fraction of these compounds will accumulate in the world’s oceans.
N-nitrosodimethylamine (NDMA) is a probable human carcinogen found in ng/l concentrations in chlorinated and chloraminated water. A method was developed for the determination of ng/l levels of NDMA ...using liquid chromatography–tandem mass spectrometry (LC–MS/MS) preceded by sample concentration via solid-phase extraction with activated charcoal. Recoveries were greater than 90% and allowed a method reporting limit as low as 2
ng/l. Using this method, the removal of NDMA was determined for the Interim Water Purification Facility (IWPF), an advanced wastewater treatment facility operated by the Orange County Water District (OCWD) in Southern California. The facility treats effluent from an activated sludge treatment plant with microfiltration (MF), reverse osmosis (RO), and an ultraviolet-hydrogen peroxide advanced oxidation process (UV-AOP). Six nitrosamines were surveyed: NDMA,
N-nitrosomethylethylamine (NMEA),
N-nitrosodiethylamine (NDEA),
N-nitrosodi-
n-propylamine (NDPA),
N-nitrosopiperidine (NPip), and
N-nitrosopyrrolidine (NPyr). Only NDMA was detected and at all treatment steps in the IWPF, with influent concentrations ranging from 20 to 59
ng/l. Removals for RO and UV ranged from 24% to 56% and 43% to 66%, respectively. Overall, 69±7% of the original NDMA concentration was removed from the product water across the advanced treatment process and, in combination with blending, the final concentration did not exceed the California drinking water notification level of 10
ng/l. NDMA removal data are consistent with findings reviewed for other advanced treatment facilities and laboratory studies.
The aqueous photolysis of seven alkyl nitrosamines was studied by irradiation in a solar simulator. Nitrosamines included N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine (NMEA), ...N-nitrosodiethylamine (NDEA), N-nitrosodi-n-propylamine (NDPA), N-nitrosodi-n-butylamine (NDBA), N-nitrosopiperidine (NPip), and N-nitrosopyrrolidine (NPyr). Direct photolysis at irradiations of 765 W/m2, representing Southern California midsummer, midday sun, resulted in half-lives of 16 min for NDMA and 12−15 min for the other nitrosamines. The quantum yield for NDMA was determined to be Φ = 0.41 and Φ = 0.43−0.61 for the other nitrosamines. Quantified products of NDMA photolysis included methylamine, dimethylamine, nitrite, nitrate, and formate, with nitrogen and carbon balances exceeding 98 and 79%, respectively. Indirect photolysis of nitrosamines in surface water was not observed; increasing dissolved organic carbon (DOC) slowed the NDMA photolysis rate because of light screening. Removal of NDMA measured in tertiary treated effluent flowing in a shallow, sunlit engineered channel agreed with photolysis rates predicted based on the measured quantum yield and system parameters. Because biodegradation is relatively slow, aquatic photolysis of NDMA is generally expected to be more significant even at relatively low levels of solar irradiation (t 1/2 = 8−38 h at 244−855 W/m2, 51° N latitude, 1 m depth).
One alternative adsorbent (AA) and five ion exchange (IX) resins were tested for the removal of per‐ and polyfluoroalkyl substances (PFAS) from groundwater in pilot‐scale columns for up to 19 months ...using empty bed contact times (EBCTs) representative of full‐scale treatment. For the six detected PFAS in the pilot feed water, the long‐chain PFAS (perfluorooctanoic acid PFOA, perfluorooctanesulfonic acid PFOS, and perfluorohexanesulfonic acid PFHxS) were well removed with only PFOA, which is a perfluoroalkyl carboxylic acid (PFCA) eventually breaking through as the media became exhausted. Perfluorobutanesulfonic acid (PFBS), a short‐chain perfluorosulfonic acid (PFSA), was also well removed, whereas short‐chain PFCAs (perfluoropentanoic acid PFPeA and perfluorobutanoic acid PFBA) were not removed (i.e., immediate breakthrough). Overall, IX and AA demonstrated superior removal of PFSAs compared to PFCAs (i.e., later breakthrough of PFSAs translating to longer media life). Media life varied, ranging from 6 to 15 months before adsorbents reached a significant PFOA breakthrough. The performance of the two adsorbents piloted at shorter EBCT reasonably predicted the longer (representative) pilot EBCT results (within ±20–30%) for the same adsorbents following data scaling. This suggests that pilot‐scale testing may be conducted at a faster pace and therefore more economically.
Practitioner Points
Long‐chain PFAS (PFOA, PFOS, and PFHxS) were well removed by five ion exchange and one alternative adsorbent tested herein.
One short‐chain PFAS (PFBS) was well removed with no removal of two other short‐chain PFAS (PFBA and PFPeA).
Performance of the two adsorbents piloted at shorter EBCT reasonably predicted the longer (representative) pilot EBCT results for the same adsorbents following data scaling.
Performance of the two PFAS removal adsorbents piloted at shorter empty bed contact time reasonably predicted the longer (representative) contact time results following data scaling. This suggests that pilot‐scale testing to find PFAS treatment adsorbents may be conducted at a faster pace and therefore more economically.
Water withdrawals and discharges from municipal wastewater-treatment plants in semiarid regions result in more urban streams becoming dependent on wastewater effluent for base flows. Such ...wastewater-effluent-dominated streams support perennial-stream ecosystems that would not otherwise exist. At the same time, ecosystems downstream of effluent discharges can improve water quality, support water re-use, create habitat, and provide urban amenities. By identifying measures of success for biota, habitat, hydrology, geomorphology, and water quality, water managers can better design, operate, and monitor effluent-dominated water courses under future climate conditions. This requires the development of clearly defined ecological and social objectives, as well as a better understanding of the consequences of increasing reliance on wastewater effluent to sustain the biota of effluent-dominated streams. Successful quantification of the costs and benefits of these projects is likely to attract the attention of agencies and communities that have the power to turn the environmental perturbations associated with effluent discharges into new forms of environmental enhancement.
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