Virus rejection and removal in pilot-scale air-gap membrane distillation.

Membrane distillation (MD) is a thermally-driven process that can treat high concentration streams and provide a dual barrier for rejection and reduction of pathogens. Thus, MD has potential applications in treating concentrated wastewater brines for enhancing water recovery and potable water reuse. In bench-scale studies, it was demonstrated that MD can provide high rejection of MS2 and PhiX174 bacteriophage viruses, and when operating at temperatures greater than 55 °C, can reduce virus levels in the concentrate. However, bench-scale MD results cannot directly be used to predict pilot-scale contaminant rejection and removal of viruses because of the lower water flux and higher transmembrane hydraulic pressure difference in pilot-scale systems. Thus far, virus rejection and removal have not been quantified in pilot-scale MD systems. In this work, the rejection of MS2 and PhiX174 at low (40 °C) and high (70 °C) inlet temperatures is quantified in a pilot-scale air-gap MD system using tertiary treated wastewater. Both viruses were detected in the distillate which suggests the presence of pore flow; the virus rejection at a hot inlet temperature of 40 °C for MS2 and PhiX174 were 1.6-log10 and 3.1-log10, respectively. At 70 °C, virus concentrations in the brine decreased and were below the detection limit (1 PFU per 100 mL) after 4.5 h, however, viruses were also detected in the distillate in that duration. Results demonstrate that virus rejection is lower in pilot-scale experiments because of increased pore flow that is not captured in bench-scale experiments.

Modeling the energy consumption of potable water reuse schemes.

Potable reuse of municipal wastewater is often the lowest-energy option for increasing the availability of fresh water. However, limited data are available on the energy consumption of potable reuse facilities and schemes, and the many variables affecting energy consumption obscure the process of estimating energy requirements. By synthesizing available data and developing a simple model for the energy consumption of centralized potable reuse schemes, this study provides a framework for understanding when potable reuse is the lowest-energy option for augmenting water supply. The model is evaluated to determine a representative range for the specific electrical energy consumption of direct and indirect potable reuse schemes and compare potable reuse to other water supply augmentation options, such as seawater desalination. Finally, the model is used to identify the most promising avenues for further reducing the energy consumption of potable reuse, including encouraging direct potable reuse without additional drinking water treatment, avoiding reverse osmosis in indirect potable reuse when effluent quality allows it, updating pipe networks, or using more permeable membranes. Potable reuse already requires far less energy than seawater desalination and, with a few investments in energy efficiency, entire potable reuse schemes could operate with a specific electrical energy consumption of less than 1 kWh/m3, showing the promise of potable reuse as a low-energy option for augmenting water supply.

Membrane Distillation Provides a Dual Barrier for Coronavirus and Bacteriophage Removal.

The persistence of pathogenic microorganisms in treated wastewater effluent makes disinfection crucial to achieve wastewater reuse. Membrane processes such as ultrafiltration and reverse osmosis (RO) have shown promising results for virus and other contaminant removal from treated wastewater effluents for reuse application. However, RO produces a concentrate stream which contains high concentrations of pathogens and contaminants that often requires treatment and volume reduction before disposal. Membrane distillation (MD) is a treatment process that can reduce RO concentrate volume while augmenting the potable water supply. MD is also a dual barrier approach for virus removal as it operates at a high temperature and permeates only the vapor phase through the membrane interface. The effects of temperature on viable virus concentration and membrane rejection of viruses in MD are investigated in this study using two nonenveloped phages frequently used as enteric virus surrogates (MS2 and PhiX174) and an enveloped pathogenic virus (HCoV-229E). At typical MD operating temperatures (greater than 65 °C), viable concentrations of all three viruses were reduced by thermal inactivation by more than 6-log10 for MS2 and PhiX174 and more than 3-log10 for HCoV-229E. Also, membrane rejection was greater than 6-log10 for MS2 and PhiX174 and greater than 2.5-log10 for HCoV-229E.

A modeling framework to evaluate blending of seawater and treated wastewater streams for synergistic desalination and potable reuse.

A modeling framework was developed to evaluate synergistic blending of the waste streams from seawater reverse osmosis (RO) desalination and wastewater treatment facilities that are co-located or in close proximity. Four scenarios were considered, two of which involved blending treated wastewater with the brine resulting from the seawater RO desalination process, effectively diluting RO brine prior to discharge. One of these scenarios considers the capture of salinity-gradient energy. The other two scenarios involved blending treated wastewater with the intake seawater to dilute the influent to the RO process. One of these scenarios incorporates a low-energy osmotic dilution process to provide high-quality pre-treatment for the wastewater. The model framework evaluates required seawater and treated wastewater flowrates, discharge flowrates and components, boron removal, and system energy requirements. Using data from an existing desalination facility in close proximity to a wastewater treatment facility, results showed that the influent blending scenarios (Scenarios 3 and 4) had several advantages over the brine blending scenarios (Scenarios 1 and 2), including: (1) reduced seawater intake and brine discharge flowrates, (2) no need for second-pass RO for boron control, and (3) reduced energy consumption. It should be noted that the framework was developed for use with co-located seawater desalination and coastal wastewater reclamation facilities but could be extended for use with desalination and wastewater reclamation facilities in in-land locations where disposal of RO concentrate is a serious concern.

A review of polymeric membranes and processes for potable water reuse.

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 in the treatment of wastewater to potable water quality and highlight recent advancements 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.

Experimental results from RO-PRO: a next generation system for low-energy desalination.

A pilot system was designed and constructed to evaluate reverse osmosis (RO) energy reduction that can be achieved using pressure-retarded osmosis (PRO). The RO-PRO experimental system is the first known system to utilize energy from a volume of water transferred from atmospheric pressure to elevated pressure across a semipermeable membrane to prepressurize RO feedwater. In other words, the system demonstrated that pressure could be exchanged between PRO and RO subsystems. Additionally, the first experimental power density data for a RO-PRO system is now available. Average experimental power densities for the RO-PRO system ranged from 1.1 to 2.3 W/m2. This is higher than previous river-to-sea PRO pilot systems (1.5 W/m2) and closer to the goal of 5 W/m2 that would make PRO an economically feasible technology. Furthermore, isolated PRO system testing was performed to evaluate PRO element performance with higher cross-flow velocities and power densities exceeding 8 W/m2 were achieved with a 28 g/L NaCl draw solution. From this empirical data, inferences for future system performance can be drawn that indicate future RO-PRO systems may reduce the specific energy requirements for desalination by ∼1 kWh/m3.

Organic ionic salt draw solutions for osmotic membrane bioreactors.

This investigation evaluates the use of organic ionic salt solutions as draw solutions for specific use in osmotic membrane bioreactors. Also, this investigation presents a simple method for determining the diffusion coefficient of ionic salt solutions using only a characterized membrane. A selection of organic ionic draw solutions underwent a desktop screening process before being tested in the laboratory and evaluated for performance using specific salt flux (reverse salt flux per unit water flux), biodegradation potential, and replenishment cost. Two of the salts were found to have specific salt fluxes three to six times lower than two commonly used inorganic draw solutions, NaCl and MgCl(2). All of the salts tested have organic anions with the potential to degrade in the bioreactor as a carbon source and aid in nutrient removal. Results demonstrate the potential benefits of organic ionic salt draw solutions over currently implemented inorganics in osmotic membrane bioreactor systems.