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Fouling of polyamide membranes during reverse osmosis (RO) is a major challenge for adopting membrane technologies to treat highly contaminated waters, especially those containing organic foulants (e.g., natural organic matter (NOM), polysaccharides) and dominant cations (e.g., sodium, magnesium, calcium). This work combines bench-scale membrane fouling experiments with detailed characterization of feedwater chemistry and fouling layer composition/morphology to reveal fundamental mechanisms of (in)organic fouling during RO. Divalent cations are shown to promote fouling by hydrophobic NOM containing aromatic and carboxyl groups, while NOM fouling in the presence of a monovalent cation, sodium, occurs by smaller fulvic acids containing larger fractions of carboxyl groups and other oxygen-rich moieties. Calcium-carboxyl bridging occurs in solution and near the membrane surface to induce NOM aggregation on nanometer length scales. In complex waters containing foulant mixtures, co-fouling by calcium-carboxyl bridging and CaCO3 precipitation influence membrane performance at longer timeframes. However, the flux decline observed for the co-fouling mechanism was less significant than the sum of its parts, suggesting both synergistic and antagonistic fouling mechanisms should be considered in membrane design/operation. These results encourage the design of pretreatment processes to reduce concentrations of multivalent ions and hydrophobic NOM in RO feedwaters, and of membrane materials to limit attachment/deposition of aggregates to/on polyamide surfaces.

Treatment of nontraditional source waters (e.g., produced water, municipal and industrial wastewaters, agricultural runoff) offers exciting opportunities to expand water and energy resources via water reuse and resource recovery. While conventional polymer membranes perform water/ion separations well, they do not provide solute-specific separation, a key component for these treatment opportunities. Herein, we discuss the selectivity limitations plaguing all conventional membranes, which include poor removal of small, neutral solutes and insufficient discrimination between ions of the same valence. Moreover, we present synthetic approaches for solute-tailored selectivity including the incorporation of single-digit nanopores and solute-selective ligands into membranes. Recent progress in these areas highlights the need for fundamental studies to rationally design membranes with selective moieties achieving desired separations.

The colonias along the United States-Mexico border are generally self-built neighborhoods of low-income families that lack basic infrastructure. While some government assistance has provided roads and electricity, water and wastewater services are still lacking in many colonias. This research is the first to collect a comprehensive dataset on water, sanitation, health, and living conditions in these unincorporated neighborhoods through collection of water samples and surveys; 114 households in 23 colonias across three geographically diverse Texas counties are studied. Water quality is assessed via traditional microbial indicators, chlorine, and arsenic. This complex dataset requires an advanced statistical tool to disentangle relationships among diverse factors. Structural equation modeling is utilized to identify relationships among surveyed and measured variables. The model reveals that colonias residents with well/hauled water accurately predict their water quality, while those with treated+piped water tend to think that their water is worse than it actually is. Dwelling quality and connection to sanitary sewers influence perceived health risks and household health, respectively. Furthermore, these communities have an overwhelming need and desire for point-of-use water treatment. This model can inform decision making and may be adapted to probe other questions and social dynamics for water and sanitation in unincorporated communities elsewhere.

The Minamata Convention on Mercury, which entered into full force in August 2017, was signed by more than 100 countries, including several where artisanal and small-scale gold mining is practised, ...

Alongside the rising global water demand, continued stress on current water supplies has sparked interest in using nontraditional source waters for energy, agriculture, industry, and domestic needs. Membrane technologies have emerged as one of the most promising approaches to achieve water security, but implementation of membrane processes for increasingly complex waters remains a challenge. The technical feasibility of membrane processes replacing conventional treatment of alternative water supplies (e.g., wastewater, seawater, and produced water) is considered in the context of typical and emerging water quality goals. This review considers the effectiveness of current technologies (both conventional and membrane based), as well as the potential for recent advancements in membrane research to achieve these water quality goals. We envision the future of water treatment to integrate advanced membranes (e.g., mixed-matrix membranes, block copolymers) into smart treatment trains that achieve several goals, including fit-for-purpose water generation, resource recovery, and energy conservation.

Silver nanoparticles (Ag NPs) are an attractive addition to membranes used for drinking water treatment due to their antimicrobial properties. This research examined the role of stabilizing agents, used during the synthesis of Ag NPs, on their detachment/dissolution from ceramic membranes exposed to different types of drinking water sources typical in the United States. Ag NPs that had been stabilized by citrate, polyvinylpyrrolidone (PVP), or branched polyethylenimine (BPEI) were deposited on the surface of porous aluminum oxide membranes, which are commonly used for municipal water treatment. Results demonstrated that Ag NP stabilizer influenced release from the membranes. For Ag NPs electrostatically stabilized (citrate), hard water was found to remove the Ag NPs for longer periods of time and in higher quantities than in water without hardness. The reverse was found for sterically stabilized Ag NPs (BPEI and PVP). Additions of natural organic matter (NOM) to waters filtered by membranes coated in citrate Ag NPs were found to prolong the release of the citrate Ag NPs in the hard water test conditions. Variations in total Ag released from ceramic membranes were explained by differential impacts on the NP and membrane electrical double layers when switching from Ag NP deposition to filtration water chemistry conditions (zeta potential measurements are provided in this paper). Despite these differences, our findings show that, in waters that do not contain NOM, Ag release quickly falls below silver drinking water standards (0.1 mg L−1) and greater than 50% remained on the membranes. This study demonstrates that the type of Ag NP stabilizing agent and water chemistry should be considered when these membranes are utilized for municipal water treatment.

Laccases were studied for their ability to remove two compounds, 2-chlorophenol and sulfamethoxazole, in batch studies, both in buffered solutions and in wastewater samples from different points in a municipal water resource recovery facility. Two enzymes with and without a mediator (acetosyringone) were investigated: a commercial product derived from Myceliphthora thermophile and a laboratory-generated enzyme mix derived from Tramates versicolor. The chlorophenol was removed rapidly by the commercial enzyme in the presence of acetosyringone, but the primary products were coupling complexes of the reactants. Excellent removal was achieved without acetosyringone by the natural enzyme mix. Sulfamethoxazole was poorly removed in all laboratory-generated chemically buffered solutions, but was very well removed, without the addition of mediators, in secondary effluent suspensions from a municipal water resource recovery facility. Mechanistic studies are still required, but the results suggest that treatment via direct addition of enzymes is feasible to remove recalcitrant compounds in municipal wastewater.

The detection of pharmaceuticals in water and wastewater has triggered human and ecological health concerns. As highly toxic compounds, chemotherapy agents (CAs), such as the cyclophosphamide (CYP) and ifosfamide (IFO) structural isomers, represent a unique threat. This research elucidated the fate of CYP and IFO during ozonation and advanced oxidation by hydroxyl radicals (HO•). Novel semi-batch reactors were used to determine the second-order rate constants for CYP and IFO with O3 and HO•. These reactors provided independent control of the oxidant exposure through continuous and constant aqueous ozone and peroxone (O3-H2O2) addition. The rate constants for transformation of CYP and IFO by ozone were 2.58 ± 0.40 M−1s−1 and 6.95 ± 0.21 M−1s−1, respectively, indicating that ozone alone is not suitable for treating CAs. Transformation of CYP and IFO by hydroxyl radicals was fast, with rate constants of 2.69(±0.17)×109 M−1s−1 and 2.73(±0.16)×109 M−1s−1, respectively. The major transformation products formed by O3 and HO attack consisted of the 4-hydroxy-, 4-keto-, dechloroethyl-, and imino- derivatives of CYP and IFO. Low yields of the active metabolites of the CAs, namely phosphoramide mustard and isophosphoramide mustard, were detected. These findings suggest that treated water may retain the ability to alkylate DNA and confer toxicity.

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Many of the six million residents of unincorporated communities in the United States depend on well-water to meet their needs. One group of unincorporated communities is the colonias, located primarily in several southwestern U.S. states. Texas is home to the largest number of these self-built communities, of mostly low-income families, lacking basic infrastructure. While some states have regulations that mandate minimum infrastructure for these communities, water and sewage systems are still lacking for many of their residents. Unprotected wells and self-built septic/cesspool systems serve as the primary infrastructure for many such colonias. This research was designed to probe how wells and septic/cesspool systems are influenced by heavy rainfall events. Such events are hypothesized to impact water quality with regard to human health. Inorganic and microbiological water quality of the wells in nine colonias located in Nueces County, Texas, were evaluated during dry and wet periods. Nueces County was selected as an example based on its flooding history and the fact that many colonias there depend entirely on well-water and septic/cesspool systems. The results demonstrate that well-water quality in these communities varies seasonally with respect to arsenic (up to 35 μg/L) and bacterial contamination (Escherichia coli), dependent on the amount of rainfall, which leaves this population vulnerable to health risks during both wet and dry periods. Microbial community analyses were also conducted on selected samples. To explore similar seasonal contamination of well-water, an analysis of unincorporated communities, flooding frequency, and arsenic contamination in wells was conducted by county throughout the United States. This nationwide analysis indicates that unincorporated communities elsewhere in the United States are likely experiencing comparable challenges for potable water access because of a confluence of socioeconomic, infrastructural, and policy realities.

In aquatic environments, Hg(II) is strongly reactive with the dissolved organic matter (DOM) and form complexes with acidic functional groups like carboxylic acids, phenols, ammonia, alcohol, and reduced sulfur ligands (Sred). It has been suggested, however, that both the concentration of Hg(II) and the composition of the DOM influence the potential for the removal of Hg(II) in water treatment.Jar test experiments were performed at optimum coagulation conditions of pH and alum dose, using unfractionated DOM, humic substances (humic acids and fulvic acids) and different Hg(II) concentrations. Samples used in this work were obtained from the International Humic Substances Society (IHSS) and were selected based on the differences in aromatic carbon, reduced sulfur content, acidic functional groups concentration, geographical location, and commercial availability.Results showed that good removal of Hg(II) can be achieved by alum coagulation under two circumstances: (1) when the DOM is low in Sred ligands but rich in aromatic content and (2) when the DOM is rich in Sred ligands and low in aromaticity. At low Hg/DOM ratio (0.05 μg Hg/mg DOM), Hg(II) removal can be as high as 95%, while at high Hg/DOM ratio (1.0 μg Hg/mg DOM) Hg removal can be as high as 73%. The aromaticity of the DOM and the presence of Hg(II)-binding ligands in the fraction of carbon that adsorbs to aluminum hydroxide flocs were the key variables that control the removal of mercury. All the same, the character of DOM determines the extent of the removal of carbon and the minimum amount of Hg(II) that can be removed from solution.

Poor selectivity of conventional desalination membranes for boron often necessitates multi-stage treatment trains to achieve desired boron removal for end uses such as irrigation. One approach to membrane design for improved single-pass boric acid removal is via incorporation of chelating ligands that selectively sorb boron. In this study, membranes based on epoxy-amine cross-linked poly(glycidyl glycidyl ether) (PGGE) were synthesized and functionalized with N-methyl- d -glucamine (NMDG), a polyol known to interact selectively with boron. PGGE and PGGE-NMDG membranes exhibited boron sorption isotherms that were well-described by dual mode isotherms. PGGE-NMDG sorbed 2.5 mmol B/g dry polymer from a neutral aqueous solution containing 100 mmol B/L, which was almost three times the adsorption density of a commercial boron selective resin, Amberlite IRA743. The membranes were regenerated in acid without a significant loss of boron sorption capacity over four cycles. Interactions between boron and NMDG and PGGE sites (e.g., epoxides) impacted boron diffusion in both membranes. The use of ligand functionalized membranes to capture target solutes such as boron requires high loading of interacting sites to maximize uptake capacity. Establishing fundamental structure/property rules for boron selectivity could lead to new material designs with improved boron separation properties for water purification.

This research examined how variations in synthesis methods of silver nanoparticles affect both the release of silver from ceramic water filters (CWFs) and disinfection efficacy. The silver nanoparticles used were stabilized by four different molecules: citrate, polyvinylpyrrolidone, branched polyethylenimine, and casein. A multilevel statistical model was built to quantify if there was a significant difference in: a) extent of silver lost, b) initial amount of silver lost, c) silver lost for water of different quality, and d) total coliform removal. Experiments were performed on location at Pure Home Water, a CWF factory in Tamale, Ghana using stored rainwater and dugout water (a local surface water). The results indicated that using dugout vs. rainwater significantly affects the initial (p-value 0.0015) and sustained (p-value 0.0124) loss of silver, but that silver type does not have a significant effect. On average, dugout water removed 37.5μg/L more initial silver and had 1.1μg/L more silver in the filtrate than rainwater. Initially, filters achieved 1.9 log reduction values (LRVs) on average, but among different silver and water types this varied by as much as 2.5 LRV units. Overall, bacterial removal effectiveness was more challenging to evaluate, but some data suggest that the branched polyethylenimine silver nanoparticles provided improved initial bacterial removal over filters which were not painted with silver nanoparticles (p-value 0.038).

In adoption decisions for decentralized sanitation technologies, two decision makers are involved: the public utility and the individual homeowner. Standard life cycle cost is calculated from the perspective of the utility, which uses a market-based discount rate in these calculations. However, both decision-makers must be considered, including their differing perceptions of the time trade-offs inherent in a stream of costs and benefits. This study uses the discount rate as a proxy for these perceptions and decision-maker preferences. The results in two case studies emphasize the dependence on location of such analyses. Falmouth, Massachusetts, appears to be a good candidate for incentivizing decentralized sanitation while the Allegheny County Sanitary Authority service area in Pennsylvania appears to have no need for similar incentives. This method can be applied to any two-party decision in which the parties are expected to have different discount rates.

Surface properties of engineered silver nanoparticles (AgNPs) are strongly affected by environmental transformation. The fate and transport of these transformed AgNPs is largely unknown and cannot be fully explained by the traditional Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. The objective of this study was to investigate the changes in the composition and surface properties of polyvinylpyrrolidone (PVP) capped AgNPs after environmental transformation and their subsequent effects on the flocculation and filtration of these transformed AgNPs during water treatment processes. To study the aggregation and deposition behavior of the transformed particles, PVP-AgNPs exposed to humic acid (HA) and/or sulfidation were characterized, followed by separate flocculation, granular media filtration, and quartz crystal microgravimetry (QCM) experiments. X-ray photoelectron spectroscopy revealed that HA exposure modified the original PVP capping via adsorption and/or ligand exchange and that sulfidation stripped the PVP from the particle surface as a result of the formation of silver sulfide. Sulfidation thereby reduced the stability of PVP-AgNPs in self-aggregation but enhanced the mobility of AgNPs in granular media filtration and quartz collector deposition. Without unbound macromolecules in the background solution, polymers on the particle surface largely prevent self-aggregation but allow favorable clean bed deposition. This difference between the effects on self-aggregation and granular media filtration is in contrast to traditional DLVO theory. QCM yielded two types of results, the initial rate of deposition and the ultimate deposition, and both gave insights into expected filtration behavior.

Natural organic matter (NOM) in water can cause the formation of disinfection byproducts (DBPs) when NOM reacts with a disinfectant such as chlorine. Nanofiltration (NF) and reverse osmosis (RO) are effective treatment methods to remove NOM. However, the simultaneous presence of both NOM and divalent cations such as Ca2+ can enhance fouling in NF and RO. Therefore, an appropriate pretreatment to remove such cations before NF or RO would delay fouling and perhaps improve water recovery and NOM removal efficiency. Electrodialysis (ED) is potentially an excellent pretreatment method because it separates inorganic ions well using ion exchange membranes (IEMs) but does not separate NOM well because of its size and consequent low diffusivity. This research focused on ion and NOM separation with ED using three different types of commercially available IEM pairs, two different commercially available NOM sources, and six different influents at 500 mg/L total dissolved solids in the presence or absence of both hardness (Ca2+ and Mg2+) and NOM. The target waters of interest in this research were drinking water supplies that require little or no desalination but substantial removal of NOM; after NOM separation in NF or RO, some or all of the ED concentrate can be added to the NF/RO permeate to create the finished water prior to disinfection. The results indicate that ED can effectively separate alkaline earth metal ions without separation of NOM. Cation exchange membranes with high exchange capacity, high selectivity for divalent cations are desirable, and both anion and cation exchange membranes should have low affinity for organic adsorption. The process would work particularly well for NOM with relatively low hydrophobicity, since NOM adsorption to most surfaces increases with hydrophobicity.

Compromised water quality risks public health, which becomes particularly acute in economically marginalized communities. Although the majority of the clean-water-deprived population resides in Sub-Saharan Africa and Asia, a significant portion (32 million) lives in Meso- and Latin-America. Oaxaca is one of the marginalized southern states of Mexico, which has experienced high morbidity from infectious diseases and also has suffered from a high rate of infant mortality. However, there has been a paucity of reports on the status of water quality of culturally diverse rural Oaxaca. This study follows community-based participatory research methods to address the data gap by reporting on water quality (chemical and microbiological) and by exploring social realities and water use practices within and among communities. Surveys and water quality analyses were conducted on 73 households in three rural communities, which were selected based on the choice of water sources (i.e., river water, groundwater, and spring water). Statistically significant variations among communities were observed including the sanitation infrastructure (p-value 0.001), public perception on water quality (p-value 0.007), and actual microbiological quality of water (p-value 0.001). Results indicate a high prevalence of diarrheal diseases, a desire to improve water quality and reduce the cost of water, and a need for education on water quality and health in all the surveyed communities. The complexities among the three studied communities highlight the need for undertaking appropriate policies and water treatment solutions.

The single-collector removal efficiency based on the colloidal filtration model is widely used to quantify deposition of nanoparticles in porous media filtration. The validity of this theor...

On Cape Cod, eco-toilets could help mitigate an existing pollution problem, but observed adoption rates have been extremely low. A household survey was used to examine primarily nonmonetary...

The objective of this research was to investigate the sensitivity of electrodialysis performance to variations in voltage application and membrane type when treating brackish water reverse osmosis (BWRO) concentrate waste, which typically exceeds multiple salt solubility limits. Synthetic BWRO concentrates from Arizona, Texas, and Florida of 7890–18,600 mg/L total dissolved solids were prepared with 6–10 mg/L of poly-phosphonate antiscalants. Experimentation was performed using a laboratory-scale electrodialyzer a nominal transfer area of 64 cm 2 per membrane. Flow, pressure, conductivity, temperature, and pH were measured continuously, and periodic process samples were analyzed for anion and cation concentrations. The three BWRO concentrates were successfully treated with stack voltage applications of 1.0–1.5 V/cell-pair with initial current densities of 200–600 A/m 2 and final salinity removal ratios up to 98%. This paper shows consistent specific energy consumption (approximately 0.03 kWh/m 3 per Volt/cell-pair applied per meq/L separated) for electrodialysis treatment for several concentrates across a range of salinity and composition. Successive electrodialysis treatment recovered more than 78% of BWRO concentrate without precipitation, corresponding to calcite and dolomite saturation ratios of 15. These results demonstrate that electrodialysis processes can effectively minimize concentrate waste from BWRO processes, with simulated system recoveries up to 95%.

The objective of this research was to investigate the sensitivity of electrodialysis performance to variations in voltage application and membranes when treating brackish water reverse osmosis concentrate waste. Synthetic BWRO concentrates from Arizona and Texas of 7890–14,800 mg/L total dissolved solids were prepared with poly-phosphonate antiscalants. Experimentation was performed using a laboratory-scale electrodialyzer with two sets of membranes (AMV-CMV and PCSA-PCSK) with a nominal transfer area of 64 cm 2 per membrane. Flow, pressure, conductivity, temperature, and pH were measured continuously, and periodic samples were analyzed for specific anion and cation concentrations. The BWRO concentrates were successfully treated with stack voltage applications of 0.5–1.5 V/cell-pair for salinity removal ratios up to 99% with current density less than 500 A/m 2 . This paper highlights that (1) the specific energy consumption was proportional to the applied voltage and equivalent concentration separated ( i.e. , approximately 0.03 kW h/m 3 per Volt/cell-pair applied per meq/L separated); (2) lower voltage applications decreased the relative separation rate of sulfate compared to chloride; and (3) water transport by electro-osmosis was independent of voltage application or resulting current densities, while it is affected by the ion exchange membranes.

The objective of this research was to investigate the sensitivity of electrodialysis performance to variations in hydraulic flow when treating brackish water reverse osmosis (BWRO) concentrate waste. A synthetic BWRO concentrate from Arizona of 7890 mg/L total dissolved solids was prepared with poly-phosphonate antiscalants, and desalinated with a laboratory-scale electrodialyzer with 10 cell-pairs and a transfer area of 64 cm 2 per membrane. Flow, pressure, conductivity, temperature, and pH were measured continuously, and periodic process samples were analyzed by ion chromatography and inductively coupled plasma-optical emission spectrometry for anion and cation concentrations, respectively. The BWRO concentrate was successfully treated with a stack voltage application of 1.0 V/cell-pair and current densities less than 280 A/m 2 for salinity removal ratios up to 99% (without precipitation). The superficial velocities were controlled in a range of 1.2 to 4.8 cm/s, which corresponded to Reynolds numbers of 10 to 40. This paper shows the polarization parameter (ranging from 2.0 to 3.6 A/m 2 per meq/L) as a function of Reynolds number and removal ratio, and, at maximum sensitivity, the polarization parameter was proportional to Reynolds number raised to the 0.132 power.

This research investigated the extent of fluoride contamination in the Bongo District of northeast Ghana and the relationships of this fluoride contamination to the underlying geology and precipitation patterns, social and cultural attitudes towards water, and age divisions inherent in water usage patterns and the consequent demands placed on a borehole. The fluoride concentrations measured in the area are higher than reported in earlier literature. High fluoride levels are geographically confined to one geologic formation and appear to be inversely correlated to regional precipitation. Fluoride variation studies, tracking concentrations over 8 months, also reflect this link to local precipitation patterns. This localized analysis of water contamination issues addresses broader gender and policy issues inherent in supplying potable water.

The recovery of usable product water in brackish water reverse osmosis (RO) desalination is limited by the potential for membrane scaling. This limited recovery results in high costs of disposal of the concentrate (waste) stream. Concentrate treatment to improve recovery is vital, and treatment that includes antiscalant oxidation prior to precipitation and solid/liquid separation might allow increased precipitation through antiscalant deactivation. Ozone and hydrogen peroxide were used to oxidize phosphonate-type antiscalants under varying conditions of water composition, pH, ozone dose, and antiscalant type; orthophosphate (P) is an oxidation product and was used to measure the extent of oxidation. Antiscalant oxidation increases with ozone dose (1–10 mg/L O 3 ) and in the presence of calcium, from 1 mg/L P to 7 mg/L P for an antiscalant concentration of 27 mg/L as P. The addition of hydrogen peroxide causes only minor increases in antiscalant oxidation. The extent of oxidation varies with pH as a function of metal–ligand speciation, with the doubly-protonated metal–ligand species dominating the reactivity of the antiscalant. In the presence of calcium, the primary oxidation pathway for phosphonate antiscalants is through direct reaction with ozone (70–80% of measured P). In the absence of calcium, ozone and hydroxyl radicals appear to contribute relatively equally to oxidation. These results suggest phosphonate antiscalants can be oxidized with relatively low ozone doses, thereby deactivating the chelating behavior of the antiscalant and allowing increased precipitation of scaling salts such as calcium and magnesium.

Hurricane Harvey devastated large parts of the US Gulf Coast in 2017, and its floodwaters posed a number of threats to the environment and human health. In particular, an estimated 375 000 Texas residents experienced issues related to the provision of safe drinking water at the peak of the hurricane. In this study, physical, chemical, and biological water quality was monitored in two drinking water systems in Texas following Hurricane Harvey to understand the relationship between water quality parameters and changes in the drinking water microbiota. Results show initial surges in total organic carbon, trihalomethanes, and bacterial concentrations in finished water immediately following Hurricane Harvey. Microbial community analyses highlight the dependence of the distribution system microbiota on distribution system characteristics (i.e. water age), raw water quality, and disinfectant residual, among other factors. While both systems had problems maintaining disinfectant residual in the weeks following the hurricane, stabilization of water quality occurred over time. Overall, this study provides an understanding of the challenges associated with maintaining drinking water quality in the wake of a natural disaster and can be used to better prepare drinking water managers and engineers to combat changing weather patterns in the future.

Silver nanoparticles are used in a wide variety of consumer products and are therefore rapidly becoming ubiquitous in the natural environment; they can be expected to be found in the natural waters used as drinking water supplies. This research investigated whether such particles could be expected to be removed in conventional water treatment plants such as flocculation and filtration. Both flocculation and granular media filtration experiments with citrate-capped silver nanoparticles were performed at different ionic strengths and in the presence and absence of natural organic matter. The results were generally consistent with theories of particle destabilization that have been developed for larger particles (greater than 1 μm), suggesting that silver nanoparticles are likely to be removed in conventional treatment processes.

The goal of this research was to compare the pollutant removal effectiveness of biofiltration systems containing different media and plant species. A laboratory column study was conducted by using three media and two plant species, each with and without a submerged zone intended to promote denitrification. Twenty experiments were run by using synthetic storm water over the course of nine months, and ten of them were analyzed. The three media used were concrete sand, masonry sand, and a medium that meets the City of Austin’s biofiltration specifications. The plant species were Buffalograss 609 and Big Muhly, both commonly found in Texas. The results of this study showed a significant improvement in nutrient removal with the presence of these plants in the filter. The columns without plants were found to export substantial amounts of nitrate/nitrite, whereas the columns with the plants demonstrated a substantial removal of nutrients (59–79% of the total nitrogen and 77–94% of the total phosphorus). ...

This article examines the influence of three common stabilizing agents (citrate, poly(vinylpyrrolidone) (PVP), and branched poly(ethylenimine) (BPEI)) on the attachment affinity of silver nanoparticles to ceramic water filters. Citrate-stabilized silver nanoparticles were found to have the highest attachment affinity (under conditions in which the surface potential was of opposite sign to the filter). This work demonstrates that the interaction between the electrical double layers plays a critical role in the attachment of nanoparticles to flat surfaces and, in particular, that predictions of double-layer interactions are sensitive to boundary condition assumptions (constant charge vs constant potential). The experimental deposition results can be explained when using different boundary condition assumptions for different stabilizing molecules but not when the same assumption was assumed for all three types of particles. The integration of steric interactions can also explain the experimental deposition results. Particle size was demonstrated to have an effect on the predicted deposition for BPEI-stabilized particles but not for PVP.

The U.S. Environmental Protection Agency is developing a nationwide standard for turbidity in construction site runoff. It is widely expected that conventional measures for erosion and sediment control cannot meet this standard; consequently, innovative practices for managing sediment on construction sites must be developed. One emerging practice is the use of polyacrylamide (PAM) to improve sediment control by promoting flocculation of particles in runoff. Effective use of this practice requires an understanding of how the properties of soil and PAM affect flocculation. The objective of this study was to develop such an understanding. A protocol for creating modified synthetic stormwater runoff from soil samples was developed, and synthetic runoff suspensions were created with soil from six Texas construction sites. Particle size distribution was used to compare the synthetic runoff suspensions with grab samples of stormwater from one site. Flocculation tests were performed on the synthetic runoff suspensions with PAM doses ranging from 0.03 to 10 mg/L. The polymers used included anionic PAMs of 0% to 50% charge density and 0.2 to 14 Mg/mol molecular weight and one copolymer. A neutral PAM and the copolymer were the most effective in reducing the turbidity of all the synthetic runoff suspensions below 200 nephelometric turbidity units at doses of 10 mg/L. Hardness tests indicated interparticle bridging to be the bonding mechanism. The high-molecular-weight (HMW) anionic PAMs were effective on only two of the six synthetic runoff suspensions. As the charge density of these HMW PAMs increased, their effectiveness decreased.

In electrodialysis, a theoretical understanding of overlimiting current (greater ionic transport beyond the electroneutrality limit) has not been clearly demonstrated, despite two hypothetical explanations: the water splitting reaction and electro-convection. To suggest another possible mechanism for this phenomenon, the Nernst-Planck-Poisson equations were solved via the Painleve equation of the second kind. Numerical simulations found that the initiation of overlimiting current involves a substantial redistribution of the ionic charge near the membrane surface. To maintain a constant ionic charge in the aqueous phase near the membrane while the non-electroneutral space charge region grows, the shrinking electric double layer in the aqueous-phase releases ionic charges toward the membrane. Frequent repetition of this charge redistribution can contribute additional current above the limiting current without a large investment of electrical potential. A sensitivity study found that the relationship between the growth of the space charge region and applied potential is independent of the membrane's ion exchange capacity and the ionic diffusivity; however, the amount of the ionic charge created in the space charge region was greater with a greater bulk concentration or with an electrolyte solvent of a greater permittivity. These findings are consistent with previous experimental studies in the overlimiting current regime.

Experimental estimation of the selectivity coefficient of ion-exchange membranes involves significant error amplification, but no previous studies quantified the error propagation. Errors in measuring the concentration of the mono-valent cation can be magnified up to 500 times in estimating the selectivity coefficient of mono- to di-valent cations. Further, arithmetic averaging of individual estimations led to systematic overestimation of the selectivity coefficient. To avoid this overestimation, we suggested a least-square method to determine the selectivity coefficient over a range of conditions. In addition, a cohesive explanation for the consistency of the selectivity coefficient with changes in ionic content and equivalent fraction has been lacking in previous literature. We found that the selectivity coefficient of mono-valent potassium to di-valent calcium was consistent with the aqueous-phase ionic content from 5 to 100 mN and the aqueous-phase equivalent fraction from 0.2 to 0.8. The valence effect (membranes favoring di-valents over mono-valents) plays an important role in maintaining this consistency. The consistency is also governed by the aqueous-phase activity coefficients and thus depends on the aqueous-phase activity (i.e., unit of the aqueous-phase concentration). The consistency is maintained with the molarity but lost with fractional units, such as mole or equivalent fraction, for the aqueous-phase concentration.

The performance of electrodialysis is strongly dependent on the boundary layer thickness near an ion-exchange membrane. While a thinner boundary layer is known to enhance the ionic separation, the effects of statistical properties of the boundary layer thickness, such as the variation of the thickness and the correlation between the two boundary layers facing across the spacer, have not been elucidated. These effects were estimated by the Monte Carlo method incorporated into an analytical model. The analytical model simulates the binary ionic transport in four distinct regions of an electrodialysis cell pair: the bulk solution, boundary layer, ion-exchange membrane, and interface between the aqueous solution and ion-exchange membrane. The model current and potential relationships found that a greater variation or more positive correlation improves the ionic separation in the non-Ohmic regime. A bench-scale electrodialyzer was operated in a batch recycle system to develop steady-state current and potential relationships. Comparison between the model and experimental results found that the mean boundary layer thickness was tens of micrometers and the standard deviation of the thickness was similar to or greater than the mean thickness with the sheet-flow type mesh spacer.

In ion-exchange membrane systems such as electrodialysis, the overlimiting current phenomenon still remains a difficult topic to study due to the complicated solution method for the Nernst–Planck–Poisson model. In this study, the Nernst–Planck–Poisson equations were prepared to simulate the steady-state binary ionic transport in the diffusion boundary layer near an ion-exchange membrane. The system of differential equations was converted into the Painleve equation of the second kind in such a way that the converted model domain explicitly shows the transition point from the space-charge region to the electroneutral region in the diffusion boundary layer even before the differential equation is solved. Based on this property, mathematical expressions were proposed to estimate the limiting current density and the width of the space-charge region in the diffusion boundary layer near an ideally perm-selective ion-exchange membrane. The so-called Airy solution of the Painleve equation of the second kind was used to describe the ionic transport in the space-charge region. It was also found that the Airy function of the second kind with its derivative describes the behavior of the electric double layer developed from the ion-exchange membrane surface. In addition, a relatively simple numerical method, including a stability criterion, was used to solve the Painleve equation of the second kind to simulate the ionic transport in the diffusion boundary layer near an ion-exchange membrane.

A population balance model was developed to simulate simultaneous precipitation and flocculation during precipitative softening. Rate coefficients for nucleation, crystal growth, and flocculation were extracted from experimental particle-size distribution (PSD) data based on changes in the total number and total volume of particles. Three models of flocculation were evaluated: rectilinear, curvilinear, and an empirical size-independent model. Model simulations were compared with experimental PSD data to test which model was most appropriate. The curvilinear precipitative flocculation model was superior when seeded precipitation occurred at moderate mixing intensities ( G=50–100 s−1 ) . However, the curvilinear model overpredicts the formation of very large particles and requires values of the collision efficiency greater than 1.0, suggesting a more complicated dependence of the PSD dynamics on mixing intensity and saturation ratio than presently included in the model. At higher mixing intensities ( G=300...

Natural organic matter (NOM) removal during water softening is thought to occur through adsorption onto or coprecipitation with calcium and magnesium solids. However, details of precipitate composition and surface chemistry and subsequent interactions with NOM are relatively unknown. In this study, zeta potentiometry analyses of precipitates formed from inorganic solutions under varying conditions (e.g., Ca-only, Mg-only, Ca + Mg, increasing lime or NaOH dose) indicated that both CaCO3 and Mg(OH)2 were positively charged at higher lime (Ca(OH)2) and NaOH doses (associated with pH values above 11.5), potentially yielding a greater affinity for adsorbing negatively charged organic molecules. Environmental scanning electron microscopy (ESEM) images of CaCO3 solids illustrated the rhombohedral shape characteristic of calcite. In the presence of increasing concentrations of magnesium, the CaCO3 rhombs shifted to more elongated crystals. The CaCO3 solids also exhibited increasingly positive surface charge from Mg incorporation into the crystal lattice, potentially creating more favorable conditions for adsorption of organic matter. NOM adsorption experiments using humic substances extracted from Lake Austin and Missouri River water elucidated the role of surface charge and surface area on adsorption.

Reverse osmosis membrane technology has developed over the past 40 years to a 44% share in world desalting production capacity, and an 80% share in the total number of desalination plants installed worldwide. The use of membrane desalination has increased as materials have improved and costs have decreased. Today, reverse osmosis membranes are the leading technology for new desalination installations, and they are applied to a variety of salt water resources using tailored pretreatment and membrane system design. Two distinct branches of reverse osmosis desalination have emerged: seawater reverse osmosis and brackish water reverse osmosis. Differences between the two water sources, including foulants, salinity, waste brine (concentrate) disposal options, and plant location, have created significant differences in process development, implementation, and key technical problems. Pretreatment options are similar for both types of reverse osmosis and depend on the specific components of the water source. Both brackish water and seawater reverse osmosis (RO) will continue to be used worldwide; new technology in energy recovery and renewable energy, as well as innovative plant design, will allow greater use of desalination for inland and rural communities, while providing more affordable water for large coastal cities. A wide variety of research and general information on RO desalination is available; however, a direct comparison of seawater and brackish water RO systems is necessary to highlight similarities and differences in process development. This article brings to light key parameters of an RO process and process modifications due to feed water characteristics.

To investigate the dependence of filter ripening on particle size and surface charge, multiple experiments were conducted under different particle destabilization conditions including pH control, alum, and polymer destabilization. Laboratory‐scale filtration experiments were performed at a filtration velocity of 5 m/h using spherical glass beads with mean diameter of 0.55 mm as collectors. Particle suspensions with a broad size distribution and a 1.7 µm mean particle size were filtered through a 10 cm depth filter column. Better initial solids removal was confirmed under favorable particle and collector conditions (i.e., under smaller surface charge), but better initial particle removal does not necessarily mean better overall particle removal efficiency. It was shown that changes of the particle size distribution (PSD) in the effluent can significantly influence overall particle removal efficiency. Chemical parameters such as zeta potential can be important during the initial stage of filtration...

Filtration experiments were performed with a laboratory-scale filter using spherical glass beads with 0.55 mm diameter as collectors. Suspensions were made with Min-U-Sil 5 particles, and two different methods (pH control and polymer dosing) were used for destabilization. In the pH control experiments, all particles had negative surface charge, and those with lower (absolute value) charge were selectively attached to the collectors, especially during the early stage of filtration. This selective attachment of the lower charged particles caused the zeta potential distribution (ZPD) of the effluent to move to a more negative range. However, the ZPD of the effluent did not continue moving to more negative values during the later stages of filtration, and this result was attributed to two reasons: ripening effects and detachment of flocs. In the polymer experiments, substantial differences were found between experiments performed with negatively charged particles (underdosing) and those with positively charged particles (overdosing). With under-dosing, the results were similar to the pH control experiments (which also had negatively charged particles), but with overdosing, the effluent's ZPDs in the early stages did not overlap with those of the influent and more highly charged particles were removed more efficiently than lesser-charged particles. It is hypothesized that, despite a substantial period of pre-equilibration of media and coagulant, this equilibrium shifted when particles were also added. It was assumed that coagulant molecules previously adsorbed to the particles desorbed and subsequently attached to the filter media because of surface area differences in the particle and filter media.

The objective of this paper is to demonstrate that membrane performance (flux, rejection, and permeate particle size distribution as a function of time) can be influenced by modifying the membrane pore size characteristics. Poly(ethylene teraphthalate) (PET) track-etched (T-E) membranes with nominal pores sizes ranging from 0.2 to 10 μm were uniaxially stretched to increase the major axis, aspect ratio, pore area, and porosity while decreasing the minor axis. Permeation results for pure water feed as well as separate feed suspensions of spherical particles and irregular-shaped particles showed that flux can be increased and flux decline decreased by stretching membranes. Additionally, rejection of both irregular-shaped and spherical particles was increased by stretching membranes.