Study On Simultaneous Nitrogen And Carbon Removal Of Low C/N Wastewater Based On Membrane Aerated Biofilm Reactor And Anaerobic Ammonia Oxidation Coupling Process

Conventional nitrogen removal via nitrification and denitrification consumes lots of oxygen and carbon.Low C/N wastewater(e.g.,municipal wastewater in southern China,supernatant of anaerobic digestion)treatment is facing high cost from extra carbon source for denitrification.Membrane aerated biofilm reactor(MABR)has advantages of high oxygen transfer efficiency from bubble-free aeration and good nitrification.There is no need for carbon source during nitrogen removal via anaerobic ammonia oxidation(ANAMMOX)process.Thus,the hybrid MABR and ANAMMOX has significant potential for low C/N wastewater treatment.This study tried firstly to realize nitritation by MABR,then explored the combination of short denitrification and ANAMMOX,finally established hybrid MABR nitrification-short denitrification-ANAMMOX to acheive good simultaneous carbon and nitrogen removal from synthetic low C/N wastewater treatment.One-month cultivation showed that routine activated sludge from municipal wastewater treatment plant could be assimilated into shortcut nitrification activated sludge(ammonia removal over 90% and nitrite accumulation up to 85%)and shortcut denitrification activated sludge(nitrate removal over 90% and nitrite accumulation up to 85%).Multiple batch tests indicated that the optimum C/N of substrates was 3.5:1 for shortcut denitrification,which followed zero-order reaction kinetics with nitrate decreasing and nitrite increasing rate of 1.35 and 1.24 mg/L/min(i.e.,its ratio very close to the theoretical value of 0.95).ANAMMOX followed also zero-order reaction kinetics with ammonia and nitrite decreasing rate of 0.116 and 0.130 mg/L/min(i.e.,its ratio of1.12 close to the theoretical value of 1.32).Based on the reaction rate,the optimum ratio of shortcut denitrification and ANAMMOX sludge was around 1:10 and further verified via the batch tests with mixing these two kinds of sludge,where the conversion and removal of nitrate,nitrite,ammonia and COD were best at this ratio.The assimilated shortcut nitrification sludge was seed into the MABR for biofilm cultivation.However,the nitrite accumulation was only 15-20%,resulting in the apparent full nitrification in MABR.The comparative studies with SBR clarified that high oxygen transfer efficiency from membrane bubble-free aeration resulted in oxygen-rich environment in biofilm on membrane surface,thus enriched nitrite oxidation bacteria in biofilm and eventually converted most ammonia into nitrate.Further optimization on aeration pressure showed that the ammonia and nitrate in MABR effluent could meet the substrate requirements of the proposed post hybrid shortcut denitrification and ANAMMOX under aeration pressure of 6 k Pa.Therefore,a lab-scale MABR nitrification-shortcut denitrification-ANAMMOX was successfully started for a synthetic low C/N wastewater(COD of 175 mg/L,ammonia nitrogen of 100 mg/L)treatment under the optimum conditions(aeration pressure of 6 k Pa,reaction time of 9 h,mixing ratio of shortcut denitrification and ANAMMOX sludge of 1:10).After 15 cycles operation,effluent ammonia nitrogen decreased to 12 mg/L and its removal was up to 90%,effluent nitrate and nitrite nitrogen was below 3 mg/L,and effluent COD was well below 50 mg/L.The hybird process achieved excellent simultaneous carbon and nitrogen removal from low C/N wastewater with the removed nitrogen loading rate up to 180 mg/L/d.