Abstract

Conventional membrane bioreactor (MBR) is unable to remove nutrients to an acceptable level without additional operation units. However, submerged membrane electro-bioreactor (SMEBR) featured by a compact hybrid vessel, where biological processes, membrane filtration and electrokinetic phenomena take place simultaneously, is able to increase efficiency of nutrient removal. In SMEBR, nitrification and denitrification process happen due to creating alternately aerobic and anoxic conditions by supplying adequate direct current density (CD) and dissolved oxygen (DO). In order to upgrade total nitrogen (TN) removal, the research objective was to develop a novel SMEBR-Anammox. This research was the first attempt to create simultaneously aerobic condition for nitrifiers and anoxic for denitrifiers and anammox in a sole reactor. The experiments consisted of four phases where performances of Anammox, MBR, SMEBR and SMEBR-Anammox were tested and compared. All the reactors were fed with the synthetic wastewater while mixed-liquor suspended solids (MLSS) concentrations, current densities (CD) and dissolved oxygen (DO) were the influencing factors and they underwent optimization process. The same UF membrane module, temperature, SRT and HRT were applied in all tests.
In SMEBR-Anammox system, nitrifiers transform ammonia to nitrite and then to nitrate in aerobic phase, then, denitrifying bacteria generate gas nitrogen from nitrate in an anoxic phase. Furthermore, anammox bacteria use remaining nitrite to transform ammonia directly to nitrogen gas. Anammox (anaerobic/anoxic ammonium oxidation bacteria) was proven to be an effective method to eliminate high quantities of ammonium from wastewater; however their growth requires preserving special anoxic conditions during the entire process. Subsequently, an additional operation unit was constructed. Variation in these parameters affected the concentration of ammonia nitrogen, nitrate nitrogen, phosphorous and chemical oxygen demand (COD) in the effluent. At steady state operation, the removal efficiencies of ammonia, nitrate improvement, phosphorus and COD in the SMEBR-Anammox were 97%, 99.95%, 99.91% and 99.87%, respectively. Accordingly, phosphorous removal was due to electrocoagulation process and phosphorous accumulative organism (PAO) growth while COD removal was the result of biological processes and flocculation.