465789 Role of Membrane in Iemb Treatment of Groundwater Highly Contaminated with Oxyanions

Tuesday, November 15, 2016: 4:55 PM
Plaza A (Hilton San Francisco Union Square)
Pini Littman, Water Quality, Mekorot Water Companuy, Ramle, Israel, Lior Farkas, Zuckerberg Inst. fro Water Research, Ben Gurion Univ., Midreshet Sde Boker, Israel, Alon Zelichower, Zuckerberg Inst. for Water Research, Ben Gurion Univ. of the Negev, Midreshet Sde Boker, Israel, Shalom Fox, Civil and Environmental Engineering, Colorado School of Mines, Golden, CO, Yoram Oren, The Jacob Blaustein Institutes for Desert Research, Ben Gurion University of the Negev, Midreshet Ben Gurion, Israel, Zeev Ronen, Hydrology & Environmental Microbiology, Zuckerberg Institute for Water Research, Ben-Gurion University of the Negev, Sde Boker, Israel and Jack Gilron, Zuckerberg Inst. for Water Research, Ben Gurion University of the Negev, Midreshet Sde Boker, Israel

Role of Membrane in IEMB treatment of groundwater highly contaminated with oxyanions  

Perchlorate contamination of ground water is a worldwide concern. Several sites in Israel's coastal aquifer are contaminated with perchlorate, with hundreds of ppm found in one area accompanied with significant concentrations of nitrate and chlorate  as well.  This has prevented water production from wells in the area. 

The ion-exchange membrane bioreactor (IEMB)  [1] is a hybrid process for safe treatment of groundwater highly contaminated with oxyanions (perchlorate, nitrate, and chlorate).  By Donnan dialysis anionic contaminants migrate across an anion exchange membrane (AEM) from a feed-water compartment to a bio-compartment. Once in the bio-compartment, the anions undergo microbial reduction to safer species such as chloride ions and nitrogen. 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 secondary contamination of the treated water.  This contrasts with standard anaerobic bioreactors for treating such contaminations, for which the Ministry of Health requires additional barriers including MF, UV and GAC.

The present study examined the role of membrane type in performance of the IEMB in removing perchlorate and other anions (nitrate and chlorate) at levels of hundreds mg L-1 from ground water with a mixture of high levels of oxyanions.   This was based on Donnan dialysis studies and 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. To understand the results, conductivity and selectivity measurements were carried out on the different membranes.  The anion exchange membranes examined included ACS (Tokuyama Soda),  PCA-100 (PC-Cell GmBH), and AMI-7001 (Membrane International).

For ACS membrane and all experiment conditions studied here, perchlorate dominates the flux across the AEM and fluxes deviated from linear dependence on the driving force at less than 0.5 mM. 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 perchlorate driving force (EDF) value above 0.7 [mM] perchlorate had a negative effect on the other anions resulting in a decrease in the flux for both nitrate and chlorate while its own flux only increased.  

Figure 1 – Results of Donnan dialysis on ACS membrane.  Oxyanions specific flux vs. the Effective Driving Force (EDF) of (A) perchlorate, (B) chlorate, (C) nitrate and (D) anions total flux vs. the total EDF, for IEMB Donnan dialysis experiments fed with () RHGW and bio media, () synthetic anions solution and NaCl 0.1N and RHGW and NaCl 0.1N () into the water compartment and bio-compartment, respectively.  

Figure 2: Specific flux in Donnan dialysis on synthetic mixture of oxyanions using PCA-100 anions exchange membrane.  Bio-side contained 0.1 N  NaCl.

On the other hand, experiments with PCA-100 membranes showed a linear dependence of flux on driving force to much higher levels and much less intereference of the perchlorate on the transport of nitrate and chlorate (Figure 2).   Tests  of membrane conductivity  and regenerability supported the improved results with the PCA-100 membranes.  Another type (AMI-7001) also showed promise based on conducitivity but may be problematic in terms of polymer structure.  The membrane selectivity for perchlorate and the other oxyanions over chloride was clearly lower for the PCA-100 membranes than ACS.  A qualitative model will be proposed to explain these findings and relate it to the differences in ion exchange membrane structure. 

If time allows, the implications of these findings for operating the IEMB as a plug flow reactor will be outlined.  

[1]      A.D. Fonseca, J.G. Crespo, J.S. Almeida, M.A. Reis, Drinking water denitrification using a novel ion-exchange membrane bioreactor, Environ. Sci. Technol. 34 (2000) 1557–1562.

 

[2]      S. Fox, Y. Oren, Z. Ronen, J. Gilron, Ion exchange membrane bioreactor for treating groundwater contaminated with high perchlorate concentrations., J. Hazard. Mater. 264 (2014) 552–9.

 

 


Extended Abstract: File Not Uploaded
See more of this Session: Membranes for High Tds Waters and Difficult Separations (Invited Talks)
See more of this Group/Topical: Separations Division