Effect of water composition on perchlorate removal from polluted ground- water using Ion Exchange Membrane Bioreactor

Perchlorate contamination of ground water is a worldwide concern. At several sites in Israel\u27s coastal aquifer, hundreds of ppm of perchlorate was found accompanied with significant concentrations of nitrate and chlorate, consequently preventing water production from wells in the area. The IEMB hybrid process [1] allows safe treatment of high perchlorate (and nitrate and chlorate) contaminated groundwater. The Donnan dialysis process removes the perchlorate from the water compartment using an anion exchange membrane (AEM) to the bio-compartment where it undergoes microbial degradation to much safer components such as chloride. The AEM acts as a barrier and keeps both compartments completely separate. Glycerol is used as an exogenous carbon and electron source for the biodegradation process [2]. This arrangement keeps the carbon source, reaction byproducts and bacteria confined in the bio-reactor thus preventing the contamination of the treated water. The present study examines the performance of the IEMB in removing perchlorate and other anions (nitrate and chlorate) at levels of hundreds mg L-1 from polluted ground water from the Ramat HaSharon (RHGW) contaminated site. The IEMB removal of the polluting anions was studied initially for synthetic and actual ground water fed to the water side while feeding 0.1 N of NaCl to the bio-compartment. We further studied the effect of adding bacteria and bio-media to the bio-compartment. In all experiment setups it is obvious that perchlorate dominates the flux across the AEM. Even though perchlorate concentration is considerably lower than nitrate and chlorate, its flux is greater than the sum of the other anion fluxes. At an effective driving force (EDF) value above 0.7 [mM] perchlorate had a negative effect on the other anions transport across the membrane. Adding bacteria to bio-compartment side fed with RHGW and bio-media increased anions total flux by 15%-23% at the first two runs. A thick biofilm has developed on the membrane bio-side during the following two runs, resulting in a total flux decline of 18%-22% when compared to the pure Donnan dialysis experiment. Throughout all the bio-degradation experiment regardless of the anion load to the bio-compartment the bio-degradation efficiency of the trace anions was above 99%. This study is the first to treat highly polluted complex ground water in an IEMB. It further established the perchlorate strong interaction with the AEM, consequently affecting the flux of other anions in the treatment process. This research is the basis for upscaling the IEMB technology into the field Please click Additional Files below to see the full abstract

Seawater desalination for agriculture by integrated forward and reverse osmosis: Improved product water quality for potentially less energy

Seawater desalination for agricultural irrigation will be an important contributor to satisfying growing water demands in water scarce regions. Irrigated agriculture for food production drives global water demands, which are expected to increase while available supplies are further diminished. Implementation of reverse osmosis, the current leading technology for seawater desalination, has been limited in part because of high costs and energy consumption. Because of stringent boron and chloride standards for agricultural irrigation water, desalination for agriculture is more energy intensive than desalination for potable use, and additional post-treatment, such as a second pass reverse osmosis process, is required. In this perspective, we introduce the concept of an integrated forward osmosis and reverse osmosis process for seawater desalination. Process modeling results indicate that the integrated process can achieve boron and chloride water quality requirements for agricultural irrigation while consuming less energy than a conventional two-pass reverse osmosis process. The challenges to further development of an integrated forward and reverse osmosis desalination process and its potential benefits beyond energy savings are discussed

Water, Energy, and Cost: A Nexus Approach to Zero/Minimal Liquid Discharge Desalination Technologies

Desalination is increasingly essential to ensure water access as climate change and population growth stress fresh water supplies. Already in use in water-stressed regions around the world, desalination generates fresh water from salty sources, but forms a concentrated brine that requires disposal. There is a growing push for the adoption of zero/minimal liquid discharge (ZLD/MLD) technologies that recover additional water from this brine while reducing the liquid volumes requiring disposal. This analysis evaluates the cost, energy, and sustainability impacts of 7 overarching treatment trains with 75 different configurations. ZLD/MLD water recoveries are found to range from 32.6-98.6%, but with steep energy and cost tradeoffs that underscore the crucial role of ion-specific separations, heat integration, and clean energy sources. Ultimately, this analysis explores key tradeoffs between costs, energy, and water recovery, highlighting the increasingly tight connections at the central to the energy-water nexus and desalination

Oxyanion Removal from Impaired Water by Donnan Dialysis Plug Flow Contactors

In the last twenty-five years, extensive work has been done on ion exchange membrane bioreactors (IEMB) combining Donnan dialysis and anaerobic reduction to remove trace oxyanions (e.g., perchlorate, nitrate, chlorate, arsenate) from contaminated water sources. Most studies used Donnan dialysis contactors with high recirculation rates on the feed side, so under continuous operation, the effective concentration on the feed side of the membrane is the same as the exit concentration (CSTR mode). We have built, characterized, and modelled a plug flow Donnan dialysis contactor (PFR) that maximizes concentration on the feed side and operated it on feed solutions spiked with perchlorate and nitrate ion using ACS and PCA-100 anion exchange membranes. At identical feed inlet concentrations with the ACS membrane, membrane area loading rates are three-fold greater, and fluxes are more than double in the PFR contactor than in the CSTR contactor. A model based on the nonlinear adsorption of perchlorate in ACS membrane correctly predicted the trace ion concentration as a function of space-time in experiments with ACS. For PCA membrane, a linear flux dependence on feed concentration correctly described trace ion feed concentration as a function of space-time. Anion permeability for PCA-100 was high enough that the overall mass transfer was affected by the film boundary layer resistance. These results provide a basis for efficiently scaling up Donnan dialysis contactors and incorporating them in full-scale IEMB setups

Comprehensive experimental studies of early-stage membrane scaling during nanofiltration

Nanofiltration (NF) membranes have found more frequent use in recent years for the desalination of seawater and other sources of brackish water because they can be used at lower pressures than more traditional reverseosmosis (RO) technologies, and thus provide overall energy savings. However,membrane fouling still presents a common and significant challenge in practical applications. Currently, the performance of membrane-based liquid separation processes ismost often monitored by external, volumetric flow-based techniques that provide delayed information on fouling layer development. The delay between initial growth and the observation of fully established fouling reduces the efficacy of cleaning and remediationmeasures. The focus of this study is the use of ultrasonic time–domain reflectometry (UTDR) as a non-destructive method for real-time, in-situ monitoring of early-stage inorganic scaling layer formation on NF membranes. This work utilizes miniature-scale ultrasonic transducers that are internally integrated into a flat-sheet cross-flow filtration module and in contact with the membrane. Comparisons are made with results obtained from externally mounted UTDR transducers, a more commonly used arrangement. Results showthatwhile the internal sensors can be somewhatmore sensitive, the significance of this improvement can be negated by scaling deposition that is hindered by the presence of the sensor