|M.Sc Student||Lehmann David|
|Subject||An electrochemically-Regenerated Ion Exchange Process for|
Separation of NH4+ from Wastewater and
its Oxidation to N2(g)
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Ori Lahav|
|Full Thesis text - in Hebrew|
In 2010, the Israeli government published a new set of quality standards for wastewater effluents. Among many other guidelines, the standards require that the maximal concentration of TAN (total ammonia nitrogen) should not surpass 1.5 mgN/L for effluents released to natural streams. The quality standards were set for wastewater treatment plants (WWTP) effluents in order to protect lakes and other natural water bodies from: (1) eutrophication (2) oxidation of ammonia to nitrite and nitrate and the consequential decrease in dissolved oxygen and pH values that can harm aquatic life in receiving water bodies; and (3) uncontrolled concentrations of ammonia and nitrite can be toxic to the aquatic life.
For complying with the new standards, most of the existing WWTPs in Israel required renovation that normally includes expansion (e.g. Netanya, Raa’nana and Ashdod WWTPs).
The present research evaluated a complementing novel approach to increase the capacity of treatment plants to remove ammonia via a physicochemical based process. The process that was tested is comprised of an ion exchange step for ammonium separation from the wastewater and an electrochemical stage for converting ammonium to N2(g). The motivation for implementing this new physicochemical process arises from the following advantages:
• A physicochemical treatment for removing ammonium can be accomplished by an easy-to-use system comprising only a few operational variables.
• Operation is completely automatic and the end product is stable.
• Ammonium is converted to nitrogen gas in a single step (as compared with 2 stages in the prevailing nitrification/denitrification biological processes) which requires transfer of only 3 electrons.
• An ion exchange based process can meet the new standards mentioned above and decrease the negative environmental impact of high TAN concentrations in the effluents.
• Unlike processes that are based on conventional biological nitrification, which tend to fail from time to time (due to toxic shock, high organic load, low temperature, etc.), the new process is almost oblivious to environmental conditions.
Description of the examined process: wastewater is pumped through a chabatize-zeolite filled ion exchanger for a predetermined number of bed volumes. The effluents from the ion exchange column, now with a low TAN concentration, are discharged. (ii) Next, a highly concentrated NaCl solution is passed through the zeolite column and the ammonium is released into the regeneration solution. The regeneration solution is circulated through an electrolyzer which converts the TAN into innocuous N2(g). The regenerant solution, after the electrolysis, is ready to extract new ammonium from the resin. (iii) Finally, the ion exchange column is set up to treat a new influent by extracting the remaining reagent solution from the column using backflow air stream from a compressor. This process (steps i-iii) is repeated for multiple cycles.
The process was operated successfully under various conditions: 1) polishing treatment, 2) main treatment (replacement of the biological nitrogen removal) and, 3) inorganic industrial wastewater treatment. Results showed OPEX of about 16 NIS/kg ammonia removed and Capex of approximately 5 million NIS for a plant capacity of 1,000 m3/h at influent ammonia concentration of between 4.5 and 9 mg/L.