Potable Reuse Applications Research Articles

Optimizing ozone treatment for pathogen removal and disinfection by-product control for potable reuse at pilot-scale

Reclaimed water poses environmental and human health risks due to residual organic micropollutants and pathogens. Ozonation of reclaimed water to control pathogens and trace organics is an important step in advanced water treatment systems for potable reuse of reclaimed water. Ensuring efficient pathogen reduction while controlling disinfection byproducts remains a significant challenge to implementing ozonation in reclaimed water reuse applications. This study aimed to investigate ozonation conditions using a plug flow reactor (PFR) to achieve effective pathogen removal/inactivation while minimizing bromate and N-Nitrosodimethylamine (NDMA) formation. The pilot scale study was conducted using three doses of ozone (0.7, 1.0 and 1.4 ozone/total organic carbon (O3/TOC) ratio) to determine the disinfection performance using actual reclaimed water. The disinfection efficiency was assessed by measuring total coliforms, Escherichia coli (E. coli), Pepper Mild Mottle Virus (PMMoV), Tomato Brown Rugose Fruit Virus (ToBRFV) and Norovirus (HNoV). The ozone CT values ranged from 1.60 to 13.62 mg min L−1, resulting in significant reductions in pathogens and indicators. Specifically, ozone treatment led to concentration reductions of 2.46–2.89, 2.03–2.18, 0.46–1.63, 2.23–2.64 and > 4 log for total coliforms, E. coli, PMMoV, ToBRFV, and HNoV, respectively. After ozonation, concentrations of bromate and NDMA increased, reaching levels between 2.8 and 12.0 μg L−1, and 28–40.0 ng L−1, respectively, for average feed water bromide levels of 86.7 ± 1.8 μg L−1 and TOC levels of 7.2 ± 0.1 mg L−1. The increases in DBP formation were pronounced with higher ozone dosages, possibly requiring removal/control in subsequent treatment steps in some potable reuse applications.

Dichloramine Hydrolysis in Membrane Desalination Permeate: Mechanistic Insights and Implications for Oxidative Capacity in Potable Reuse Applications.

Dichloramine (NHCl2) naturally exists in reverse osmosis (RO) permeate due to its application as an antifouling chemical in membrane-based potable reuse treatment. This study investigated mechanisms of background NHCl2 hydrolysis associated with the generation of oxidative radical species in RO permeate, established a kinetic model to predict the oxidative capacity, and examined its removal efficiency on trace organic contaminants in potable reuse. Results showed that NHCl2 hydrolysis generated transient peroxynitrite (ONOO-) and subsequently dissociated into hydroxyl radical (HO•). The maximal HO• exposure was observed at an RO permeate pH of 8.4, higher than that from typical ultraviolet (UV)-based advanced oxidation processes. The HO• exposure during NHCl2 hydrolysis also peaked at a NH2Cl-to-NHCl2 molar ratio of 1:1. The oxidative capacity rapidly degraded 1,4-dioxane, carbamazepine, atenolol, and sulfamethoxazole in RO permeate. Furthermore, background elevated carbonate in fresh RO permeate can convert HO• to carbonate radical (CO3•-). Aeration of the RO permeate removed total carbonate, significantly increased HO• exposure, and enhanced the degradation kinetics of trace organic contaminants. The kinetic model of NHCl2 hydrolysis predicted well the degradation of contaminants in RO permeate. This study provides new mechanistic insights into NHCl2 hydrolysis that contributes to the oxidative degradation of trace organic contaminants in potable reuse systems.

Comparative analysis of reverse osmosis and nanofiltration for the removal of dissolved contaminants in water reuse applications

The increasing demand for drinking water has led to the adoption of unconventional water sources, such as water reuse. Reverse osmosis (RO) and nanofiltration (NF) membranes are effective barriers against trace organic contaminants in potable water reuse applications. However, the use of RO is being challenged by NF, primarily due to NF's potential to achieve similar contaminant removal as RO but with higher productivity and lower energy requirements. This study compares NF and RO membranes in terms of contaminant removal and energy consumption for potable water reuse applications. RO (BW30XFR) and dense and loose NF (NF90 and NF270) membranes were tested in bench-scale systems, and RO (TW30) and NF (NF9) membrane elements were tested in an engineering scale system utilizing UF-filtered reclaimed wastewater. The highest solute passage was observed using NF270 membrane. There was no difference between NF90 and BW30XFR in terms of divalent ion passage, but NF90's total organic carbon and monovalent ion passages were higher. Both NF90 and BW30XFR highly rejected negatively charged trace organic contaminants (TOrCs), though rejections were lower for neutral and positively charged compounds. Furthermore, all compounds were highly rejected in the engineering-scale system by NF9 and TW30. These results highlight the potential of dense NF membranes as an energy-efficient barrier for contaminant removal.

DNA origami: thinking ‘outside the fold’ for direct integrity testing of membranes for virus removal in potable reuse applications

Increasing water scarcity and water quality impairment are drivers for broader implementation of potable reuse. To maximize the sustainability of these systems, it is important to address pathogen log reduction value (LRV) ‘gaps’.

The Role of Ozonation as an Advanced Oxidation Process for Attenuation of 1,4-Dioxane in Potable Reuse Applications

ABSTRACT The combination of ozone and hydrogen peroxide (O3/H2O2), or the peroxone process, has often been used as an advanced oxidation process (AOP) in groundwater remediation and drinking water applications. This historical precedent sometimes leads to the misconception that H2O2 addition is required to achieve AOP conditions during ozonation. This is not the case for secondary or tertiary wastewater effluent applications, in which ozone reacts with abundant dissolved organic carbon (DOC) to generate hydroxyl radicals (∙OH). This study demonstrates the use of ozone with and without H2O2 addition to yield ∙OH exposures (up to 10−9 M-s) capable of achieving > 0.5-log10 attenuation of the industrial contaminant and probable human carcinogen 1,4-dioxane. This low molecular weight compound is commonly used as a surrogate when establishing AOP design criteria for potable reuse applications. DOC-normalized ozone doses (i.e., O3/DOC ratios) of ~ 1.0 and ~ 1.3 achieved 0.5-log10 attenuation of 1,4-dioxane with O3/H2O2 and O3, respectively. Also, a predictive model based on ∙OH exposure was accurate within approximately ± 10%. These results suggest that ozonation’s role as an AOP, even in the absence of H2O2, should be acknowledged in regulatory frameworks to reduce unnecessary treatment redundancy and facilitate broader implementation of potable reuse.

Pilot evaluation of the potential log removal credit using chemical markers for reverse osmosis and nanofiltration

Reverse osmosis (RO) and nanofiltration (NF) are widely applied membrane treatment technologies due to their ability to effectively remove particulates, dissolved compounds, bacteria, and viruses. However, in potable reuse applications, RO is given minimal log removal value (LRV) credit of 1–2 for pathogens due to the inability to demonstrate higher LRV performance daily. Therefore, systematic single-element membrane pilot tests (3 different RO and 1 NF membranes) were performed to assess the potential LRVs (> 4) for three chemical markers (i.e., sulfate, sucralose, and uranine) that could potentially enable membrane-based potable reuse systems to achieve higher credit. Lead- and tail-element tests, as well as new and chlorine-oxidized membranes, were tested to assess the effect of membrane location and damage on the marker LRVs. Undamaged and damaged membranes demonstrated LRVs of >5 for MS2 bacteriophage with no statistically significant differences observed for any of the 4 membranes tested regardless of membrane placement (i.e., lead vs. tail) or condition (i.e., new vs. oxidized). Statistical analysis by optimal cluster assignments for each membrane indicated there were little differences in effective LRVs between the three chemical markers. Though the LRVs could not achieve >4, likely due to diffusion limitations, they were > 2 for the three chemical markers that ranged from 2.7 to 3.6 across non-damaged lead- and tail-element tests for all three RO membranes. Uranine, while achieving LRVs of 2.9–3.6 for RO and 2.2–2.3 for NF for non-damaged lead- and tail-element tests, was deemed less preferable due to its high dose requirement and difficult chemical handling. Sulfate and sucralose proved to be effective as well but preferable with non-damaged, lead- and tail-element test LRVs of 2.7–3.5 for RO and 1.4–2.3 for NF. Damaged-membrane testing demonstrated the three conservative chemical markers were sensitive to the chlorine-oxidized membrane compromise, more so for RO than NF, before any virus breakthrough occurred.

Pilot-scale demonstration of dissolved organic nitrogen removal from an advanced water reclamation facility using enhanced coagulation

Most wastewater treatment facilities that satisfy stricter discharge restrictions for nutrients, remove dissolved inorganic nitrogen (DIN) species efficiently, leaving dissolved organic nitrogen (DON) to be present at a higher proportion (up to 85 %) of total nitrogen (TN) in the effluent. Discharged DON promotes algae growth in receiving water bodies and is a growing concern in effluent potable reuse applications considering its potential to form hazardous nitrogenous disinfection byproducts (N-DBPs). Enhanced coagulation is an established process in the advanced water treatment train for most potable reuse applications. However, so far, no information has been collected at the pilot scale to address DON removal efficiency and process implications by enhanced coagulation under real conditions. This study performed a comprehensive evaluation of DON removal from the effluent of the Truckee Meadows Water Reclamation Facility (TMWRF) by enhanced coagulation over the course of 11 months at the pilot scale. Three different coagulants (aluminum sulfate (alum), poly‑aluminum chloride (PACl), ferric chloride (FC)) and a cationic polymer coagulant aid (Clarifloc) were used. Optimum doses for each coagulant and polymer and ideal pH were determined by jar tests and applied at the pilot. Alum (24 mg/L) resulted in highly variable DON removal (6 % – 40 %, 21 % on average), which was enhanced by the addition of polymer, leading to 32 % DON removal on average. PACl (40 mg/L) and FC (100 mg/L) resulted in more consistent DON removal (on average 45 % and 57 %, respectively); however, polymer addition exerted minimal enhancement for these coagulants. Overall, enhanced coagulation effectively reduced DON in the tertiary effluent at the pilot scale. The treatment showed auxiliary benefits, including dissolved organic carbon (DOC) and orthophosphate removal.

Efficacy of simultaneous advanced oxidation and adsorption for treating municipal wastewater for indirect potable reuse

The main scope of this study was to compare the efficacy of different advanced oxidation processes (AOPs) combined with adsorption for treating secondary treated effluent of municipal wastewater in a continuous-lab-scale reactor. The results revealed enhanced removal of biological oxygen demand (BOD: C0: 14.1 and Ct: 0 mg L−1 (100%)), chemical oxygen demand (COD: C0: 40.5 and Ct: 4 mg L−1 (≤90%)), and total organic carbon (TOC: C0: 15.2 and Ct: 3.02–3.63 mg L−1 (∼80%)) by UV/PMS, O3/PMS, UV/O3/H2O2, and UV/O3/MnO2 processes followed by glass packed bed reactor (GPBR). Complete inactivation of the bacterial count was observed for all the studied processes. The GPBR showed the additional advantage of termination in the regrowth of bacterial count on the filtering medium. The gas-chromatography and mass spectrometry (GC-MS) analysis showed that AOP followed by adsorption reduced the concentrations of the by-products in the treated effluent. Overall, the synergy between AOP and adsorption improved the effluent quality to meet various indirect potable reuse (IPR) applications.

A comparative evaluation of reverse osmosis membrane performance when combined with anaerobic or aerobic membrane bioreactors for indirect potable reuse applications

The filtration performance and fouling behaviour of reverse osmosis (RO) membranes was investigated for the post-treatment of aerobic (Ae) and anaerobic (An) MBR effluents treating municipal wastewater for potable reuse. Both MBR effluents followed by RO can produce a water quality sufficient for indirect potable water reuse, while fluorescence excitation-emission scan suggests RO can effectively remove disinfection by-products precursors, ensuring the safety for chlorine based reuse water distribution by rejecting the dissolved organic matters in MBR effluents. AnMBR effluent leads to more fouling when compared to the AeMBR effluent with an average membrane fouling resistance of 12.35 × 1013 m−1 and 8.97 × 1013 m−1. Elemental analysis and membrane surface imaging results demonstrate that the foulant deposition sequence is organic and colloidal at first, followed by inorganic substances, while TOC and Ca are the most deposited foulants from both effluents. The unremoved ammonia in the AnMBR effluent may partially go through in the RO permeate and exceed the threshold in Singapore's PUB NEWater standard, while experiencing a significantly higher deposition rate of 13.8 % than the nitrate (0.02 %) from the AeMBR effluent. The findings suggest that the combination of AnMBR with RO offers a more sustainable approach than with the AeMBR but nutrients removal, with the potential of recovery, is recommended before the RO membranes to limit the fouling propensity and achieve a permeate of sufficient quality.

Impact of ozone-biologically active filtration on the breakthrough of Perfluoroalkyl acids during granular activated carbon treatment of municipal wastewater effluent

The presence of perfluoroalkyl acids (PFAAs) in municipal wastewater has highlighted the need to develop PFAA treatment approaches for wastewater effluent and potable reuse applications. Ozone (O3) and biologically active filtration (BAF) were investigated as standalone and combined pretreatment processes to improve the performance of granular activated carbon (GAC) for PFAA removal from wastewater effluent. As individual processes, ozonation at all three investigated doses (0.35, 0.75, 1.0 mg O3/mg DOC) and BAF at both tested empty bed contact times (EBCT; 15 and 20 min) led to significant improvement in PFAA removal by subsequent GAC treatment. With respect to standalone ozonation, the specific O3 dose of 0.75 mg O3/mg DOC was proven to be the optimum operating condition as further increase of the specific ozone dose to 1.0 mg O3/mg DOC did not provide considerable additional improvement. Extending the EBCT during standalone BAF from 15 to 20 minutes significantly improved the efficacy of GAC for the removal of tested PFAAs. Pretreatment with O3-BAF (0.75 mg O3/mg DOC; 20 min EBCT) in tandem outperformed both standalone ozonation and BAF for the removal of PFAA by GAC. Characterization of effluent organic matter (EfOM) by size exclusion chromatography (SEC) and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR-MS) before and after pretreatments suggest that among multiple co-occurring phenomena, the shift towards smaller and more polar EfOM may have predominantly alleviated pore constriction/blockage without having adverse impact on direct site competition. This observation is supported by SEC and FT-ICR-MS results indicating reduced EfOM molecular size through O3 and BAF pretreatment as well as transition to more hydrophilic byproducts.

Review: Reuse of Treated Wastewater

Abstract: Water reuse generally refers to the process of using treated wastewater (reclaimed water) for beneficial purposes such as agricultural and landscape irrigation, industrial processes, nonpotable urban applications (such as toilet flushing, street washing, and fire protection), groundwater recharge, recreation, and direct or undirected water supply. Its increased application has been facilitated by modern wastewater treatment processes that have advanced substantially during the twentieth century. Water Reuse is a reality at international. Several practices have emerged around the world as results of different needs, perspectives and policies. Accelerating development occurred in the past 15 years, especially in the application field of potable reuse. Technologies and treatment flowsheets have been studied and validated, demonstrating advanced water quality, safety and suitability for potable reuse applications. Reuse of wastewater after its treatment may be a good alternative for regions, which suffer from lack of pure water or have limited access to water resources. Effective water reuse applications require a combination of advanced treatment technologies. Increasingly these include a combination of low-pressure technologies MF/UF followed by NF/RO (high pressure) to provide a high-quality grade of water. Submerged membrane bioreactor systems (MBR) have also become a viable alternative for wastewater reuse technologies. Reuse technologies may be applied for municipal and industrial wastewater. Reuse of wastewater is only possible if sanitary and environmental safety is provided with no hazard for current ecosystem. That fact requires strict fulfilment of laws and regulation. Wastewater to be reused has to follow a certain sequence of treatment procedures to reduce concentration of pollutants in it. Water reuse (also commonly known as water recycling or water reclamation) reclaims water from a variety of sources then treats and reuses it for beneficial purposes such as agriculture and irrigation, potable water supplies, groundwater replenishment, industrial processes, and environmental restoration. Water reuse can provide alternatives to existing water supplies and be used to enhance water security, sustainability, and resilience that might be traditional methods (waste separation, sedimentation), methods of removal of certain components (nitrogen and phosphorus), disinfection

Pathogen reduction by ozone-biological activated carbon-based advanced water reclamation for reuse.

Ozone-biological activated carbon (ozone-BAC)-based technologies are emerging as an appealing option for potable reuse systems; however, uncertainty remains regarding the reduction of waterborne pathogens. Common log reduction requirements have been modeled after California Department of Drinking Water's 12-10-10 log reduction value (LRV) for enteric virus, Cryptosporidium, and Giardia, respectively. The objective of this research was to investigate appropriate LRVs of pathogens that can be achieved in ozone-BAC-based treatment systems and to assess the applicability of employing drinking water pathogen guidelines for potable reuse applications. A pilot scale ozone-BAC-based treatment train was operated at two water reclamation facilities in Reno, Nevada, USA. Virus, Cryptosporidium, Giardia, and bacterial indicators were monitored across individual and combined treatment processes. Pathogen barriers investigated include conventional filtration, ozonation, and ultraviolet disinfection. Based on sampling and treatment validation strategies, the three pathogen barriers can provide minimum LRVs of 13-9-9.5 for virus, Giardia, and Cryptosporidium. Secondary biological treatment can provide additional pathogen LRVs with site-specific sampling. The present study addresses regulatory uncertainties associated with ozone-BAC pathogen reduction. PRACTITIONER POINTS: Ozone-biological activated carbon-based advanced treatment can meet pathogen LRV requirements with a minimum of three pathogen barriers. Successfully applied drinking water pathogen reduction guidelines for potable reuse applications verified by operational criteria. Low presence of pathogens requires surrogates and indicator analyses and variety of monitoring techniques to verify pathogen log reduction.

Microbial community characterization in advanced water reclamation for potable reuse.

This study investigated the microbial community structure and composition across two treatment steps used in advanced water reclamation for potable reuse applications, namely Coagulation/Flocculation/Clarification/Granular Media Filtration (CFCGMF) and Ozone-Biological Activated Carbon filtration (O3/BAC). The study examined the richness, variations, and similarities of the microorganisms involved at each treatment step to better understand the role of ecology and the dynamics on unit process performance and the microbial community developed within it. The bacterial microbiomes at each treatment step were independently characterized using 16S metagenomic sequencing. Combining both treatment steps, a total of 3801 species were detected. From the total species detected, 38% and 98% were identified at CFCGMF and O3/BAC, respectively. The most abundant phyla were Proteobacteria, Bacteroidetes, Actinobacteria, and Firmicutes in both treatment steps. The identified species were classified based on their preferences to free-living style (59%) vs attached-living style (22%) showing a relatively low richness in the BAC media, but higher diversities. At the taxonomic class level, Betaproteobacteria was the predominant in both system processes. Additionally, a list of eight genera were identified as potential bacterial pathogens present in both process effluents. They are Aeromonas, Clostridium, Enterobacter, Escherichia, Flavobacterium, Legionella, Mycobacterium, and Pseudomonas. CFCGMF effluent yielded less pathogenic bacteria than both the ozone and BAC filter effluent from the O3/BAC process unit; their relative abundance accounted for about 2% and 8% for CFCGMF and O3/BAC, respectively. Detailed studies to characterize the microbial communities are crucial in interpreting the mechanisms and synergies between processes performance and microorganisms by identifying the needs and best practices to ensure public health protection. Key points • Microbial communities of two treatment processes are characterized using 16S rRNA sequencing. • Organisms that can tolerate ozone and form biofilms define microbial community in subsequent biofilters. • In relatively low abundances, potential pathogenic bacteria are detected in the treated water.

Pretreatment strategies for ion exchange to control brominated disinfection byproducts in potable reuse

The application of ion exchange (IX) resins to remove disinfection byproduct (DBP) precursors in wastewater effluents is challenging due to relatively high concentrations of competing anions. This study examined various pretreatment strategies to target competing ions to improve IX removal of DBP precursors, bromide and dissolved organic matter (DOM), measured as trihalomethane and haloacetic acid formation potentials (THMFP and HAAFP). IX batch experiments were performed with four commercial anion exchange (AIX) resins selective for bromide (BrP), DOM (A860), sulfate (MTA) and PFOA/PFOS (PFA), and one cation exchange (CIX) resin selective for iodide (CT). For single AIX treatments the bromide removal ranking was the following: PFA (58%) > MTA (51%) > BrP (43%) > A860 (16%), which corresponded with decreasing brominated THMFP removals and increasing bromine incorporation factors. For dual AIX combinations (PFA and BrP, MTA and BrP), either simultaneous or sequential treatments had the highest bromide (PFA + BrP [69%], MTA + BrP [67%], (PFA→BrP [77%], MTA→BrP [74%]) and Br-THMFP (THMFP [∼80%]) and Br-HAAFP (HAAFP [∼77%]) removals, and therefore the lowest fractions of brominated DBPs (Br-DBPs). Despite ozone (O3), biological active carbon (BAC), and granular activated carbon (GAC) pretreatments reducing the overall DOM concentration (33%), these pretreatment steps did not improve the bromide removals of the resins, although it did increase the Br-THMFP and Br-HAAFP removals by 2–38% and 13–20%, respectively. Nanofiltration (NF) pretreatment significantly removed sulfate (97%) resulting in an increased bromide removal of 19% by the AIX resins, which led to increased removal of Br-THMFP and Br-HAAFP by 93% and 96%, respectively. Among all the IX resins the CT resin had the highest bromide removal (83%) and lowest fraction of Br-DBPs. The results reveal pretreatment with existing technologies including AIX, O3/BAC/GAC, or NF can potentially enhance the removal of brominated DBP precursors by IX resins during potable reuse applications.

A Comparative Evaluation of Reverse Osmosis Membrane Performance When Combined with Anaerobic or Aerobic Membrane Bioreactors for Indirect Potable Reuse Applications

A Comparative Evaluation of Reverse Osmosis Membrane Performance When Combined with Anaerobic or Aerobic Membrane Bioreactors for Indirect Potable Reuse Applications

Per‐ and polyfluoroalkyl substance removal in carbon‐based advanced treatment for potable reuse

AbstractThe persistence of perfluoroalkyl acids (PFAAs) in wastewater effluent highlights the need for active monitoring and targeted removal of these compounds in potable reuse applications. The City of Altamonte Springs' permanent potable reuse demonstration facility, pureALTA, employs a carbon‐based advanced treatment process using multiple treatment barriers to provide potable water that meets state and federal regulatory requirements and health guidelines for unregulated contaminants. The combination of ozonation, biological activated carbon filtration (BAC), ultrafiltration (UF), granular activated carbon adsorption (GAC), and UV advanced oxidation process (UV AOP) showed complete removal of long‐chain PFAAs (perfluoroalkyl sulfonic acids with ≥6 carbons and perfluoroalkyl carboxylic acids with ≥7 carbons) with federal health guidelines, such as perfluorooctanoic acid and perfluorooctane sulfonate in the advanced treated water while maintaining total organic carbon (TOC) levels below 3 mg/L, the regulatory limit in Florida for indirect potable reuse. Ozone, BAC, and UF showed increases in PFAAs to varying levels based on the transformation of precursors. GAC was the critical process for both TOC and PFAA removal; as anticipated GAC media's age defined the extent of removal of short‐chain PFAAs such as perfluoropentanoic acid and perfluorohexanoic acid. Because of regulatory limits on TOC in Florida potable reuse projects and the absence of regulations on short‐chain PFAAs, TOC continues to dictate GAC media change‐out frequency and operating cost. However, the performance control strategy for GAC at pureALTA may change if stringent limits are set for short‐chain PFAAs in the future. As of May 2021, pureALTA has been in operation for more than 4 years and continues to operate, providing an opportunity for continued research and community engagement.Article Impact StatementThe study represents the first pilot‐scale evaluation of perfluoroalkyl acid removal and correlation to total organic carbon in a carbon‐based advanced treatment process for potable reuse in Florida.

Beware of Superbugs in a Post-COVID World.

Beware of Superbugs in a Post-COVID World.

Fate and Transport of Viruses within a High-Rate Plug-Flow Biofilter Designed for Non-Membrane-Based Indirect Potable Reuse Applications

Numerous chronic health effects might be caused by the presence of chemical constituents in reclaimed water; however, an acute risk for water-borne diseases is mostly associated with pathogens. For...

Rationale for constant flow to optimize wastewater treatment and advanced water treatment performance for potable reuse applications.

Population growth, the impacts of climate change, and the need for greater water security have made the reuse of wastewater, including potable use, increasingly desirable. As interest in potable reuse of wastewater increases, a variety of processes have been proposed for advanced water treatment following conventional wastewater treatment. In all cases, the operation and performance of advanced water treatment facilities (AWTFs) is improved when the treated wastewater feed is of the highest quality that can be achieved and the advanced water treatment (AWT) processes are operated at a constant flow. One proven method of optimizing the performance of wastewater treatment facilities (WWTFs) is constant flow operation with no extraneous return flows other than internal process recycle flows, such as return settled solids. A number of approaches can be used to achieve constant flow including flow equalization, divided treatment trains, and satellite treatment. The ways in which constant flow wastewater treatment benefits both WWTFs as well as the AWTFs are considered with special emphasis on the ability to achieve predictable log removal credits (LRCs) for specific microorganisms. Actual performance data from constant flow WWTFs are used to illustrate how LRCs are determined.Practitioner points Constant flow WWTFs should be considered to produce the highest quality secondary effluent for AWT.Flow equalization, divided treatment trains, and satellite treatment can be used to achieve constant flow to optimize wastewater treatment in small and medium size WWTFs.Flow equalization can be used to maximize the amount of wastewater that can be recovered for potable reuse.Important benefits of constant flow for wastewater treatment facilities include economic and operational savings, stable and predictable treatment performance, energy savings, ability to optimize performance for the removal of specific constituents, and the ability to assign pathogen log removal credits (LRCs).Important benefits of constant flow and optimized WWT for AWTFs include economic and operational savings; less pretreatment needed, including energy and chemical usage; elimination of the need to cycle treatment processes; and added factor of safety with respect to the required pathogen LRCs.In large WWTFs, constant flow for AWTFs will typically be achieved by effluent diversion; depending on the effluent quality additional pretreatment may be needed.The design and implementation of WWTFs and AWTFs for potable reuse should be integrated for optimal performance and protection of public health.

How permeable could a reverse osmosis membrane be if it was specifically developed for uncharged organic solute rejection?

AbstractHere, we present both experimental data and modeling results of the removal of four different polar organic solutes by six different commercial nanofiltration (NF) and reverse osmosis (RO) membranes in a natural groundwater matrix. These results are significant for two reasons. First, three of the polar organic solutes are contaminants commonly found in both drinking water aquifers and municipal wastewaters and, hence, are particularly relevant to the protection of public health in drinking water production and potable reuse applications. Second, our membrane transport model can be used (1) to understand the fundamental mechanism governing uncharged, polar organic solute rejection and (2) to make forward predictions about how one might alter NF/RO membrane chemistry and structure to achieve a desired level of rejection. Perhaps a disappointing conclusion is that, for uncharged, polar organic solutes, the only obvious means of improving rejection is to reduce pore size, increase barrier layer thickness, and/or decrease barrier layer porosity, all of which reduce water permeability and energy efficiency. However disappointing this conclusion may be, we believe the fundamental insights that can be derived from this work are significant and important for the drinking water and water reuse scientific communities.