Study On The Bio-electrochemical Denitrification Part Of CANNED Process

In this paper, the nitrogen removal efficiency of bio-electrochemical denitrification part of CANNED (Complete Autotrophic Nitrite-nitrification and Electrochemical Bio-denitrification Combined Process) was studied. NH4+-N and NO2--N were added separately and then together in order to determine that the concentration changes of NH4+-N and NO2--N in denitrification process were interaction or not. At the same time, two stages were taken to study the the proportion of electrochemical action and microbial biological denitrification for nitrogen removal process of electrochemical biological denitrification reactor of CANNED i.e. pure electrochemical stage and biological membrance hanging after the success of the electrochemical microbial synergy stage.The nitrogen removal efficiency of pure electrochemical stage before the biofilm inoculation stage of the CANNED process was studied in the first phase.The results showed that, there was a certain degree of removal of NH4+-N and NO2--N with the HRT24h, current of0.25A, current density of0.052mA/cm2and ORP about-200mv, when the concentrations increased from100mg/L to400mg/L. The removal rate of NO2--N changed gradually from40%down to20%with its concentration increasing; the bio-electrochemical part NH4+-N removal efficiency was kept at about35%with its concentration increasing.When NO2--N and NH4+-N were added at the same time, the nitrogen removal efficiency were almost the same as the two were added separately. It can concluded that there was little interaction on the removal rate of NO2--N and NH4+-N in the bio-electrochemical denitrification reactor.In the second phase, nitrogen removal efficiency of electrochemical microbial synergy stage were studied after the inoculation stage in CANNED process. The results showed that, when the influent nitrogen forms were NO2--N and NH4+-N, and the concentrations increasded from100mg/L to400mg/L, NO2--N and NH4+-N both had high removal rates, which were about above90%. It mainly composed of three aspects of the causes. One was related to the sulfur autotrophic denitrification bacteria and hydrogen autotrophic denitrification bacteria which were attached on sulfur granules and activated carbon granulars, and sulfur autotrophic denitrification reaction and hydrogen autotrophic denitrification reaction took place; The second aspects was because of the reactor’s anaerobic conditions, under which NO2-N and NH4+-N would take place anaerobic ammonia oxidation reaction under the effect anaerobic ammonia oxidation bacteria; the third aspect was the result of the energized condition, under which chloride ions turned into chlorine on the surface of the anode, then reacted with water to generate chlorine, and NO2-N and NH4+-N in water reacted with chlorine then to be removed. Of all the three aspects, the autotrophic denitrification was the main reason. When NO2-N and NH4+-N were added respectively, their removal rates were not as high as they were added together’s. This was because when NO2--N and NH4+-N were added separately, autotrophic denitrification and anaerobic ammonia oxidation reaction would not take place, and only the electrochemical played a major role.