|M.Sc Student||Cohen Barak|
|Subject||Desalination via a Novel Bio-electrochemical Approach -|
Microbial Desalination Cell (MDC)
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Carlos Dosoretz|
|Full Thesis text|
The central objective of this research was to characterize the operation of a microbial desalination cell (MDC) fed with synthetic wastewater for desalination of brackish water. The MDC is a microbial fuel cell (MFC), generating energy by direct decomposition of organic matter, modified by adding electrodialysis (ED) membranes that are used to desalinate brackish water. In principle, MDCs can harvest their energy requirements from a range of available organic matter and the entire process is completed in one combined reactor adding to energy conservation and reduced power loss.
The study focused on the leakage of organic compounds present in wastewater as well as biofilm formation on the membranes. The main hypothesis was that organic matter leakage may occur through the anion exchange membrane (AEM), and deteriorate the quality of the desalinated water while promoting biofilm formation on the membranes, especially AEM, thus decreasing system performance.
For the purpose of this research, four commercially available ion exchange membranes were screened for optimum performance: fast rate of salt removal and low rate of organic leakage. A dedicated lab-scale MDC reactor was designed and operated in several different operational modes: full batch, recirculation and multiple desalination cells with recirculation (mdc-MDC). The quality of the desalted water was checked for traces of organic matter and the rate of salt removal was assessed. During operation leakage of organic matter from the anode chamber into the desalination chamber was observed in all the configuration tested. This organic leakage also reached the cathode chamber, resulting in biofouling of the cation exchange membrane (CEM) as well as on both sides of the AEM. The mdc-MDC was found to be the fastest to remove salts from brackish water, with a salt removal rate of 0.504 mS/cm/day, and a generated voltage of 300-350 mV; however the full batch MDC displayed the lowest rate of organic leakage 0.45 mg/l/day and generated voltage of 220-230 mV. The MDC reactors were operated with external resistors of 500 Ω and 200 W. When a greater external resistor was applied, a higher voltage was measured, and the salt removal rate measured was 0.44 mS/cm/day compared to 0.29 mS/cm/day, respectively.
In conclusion while energy-efficient salt removal occurs, there is detectable organic leakage into the desalination chamber primarily due to the concentration gradient, resulting in the contamination of the treated water. Further research is required for a better understanding of this phenomenon and ways to control it.