Completely Autotrophic Nitrogen Removal In A Three-dimensional-Electrode-Biofilm Reactor

Compared with traditional biological denitrification technology, electrode biofilmdenitrification method is of high efficiency, user-friendly control and clean outcome,which is suitable to handle ammonia nitrogen wastewater with low C/N and nitratenitrogen wastewater. This paper studied the film-hanging and domestication of reactorand denitrification performance, and discussed electrochemistry function and theinfluence of filling third electrode in reactor on systematic denitrification performance.This paper first constructs a three-dimensional electrode biofilm reactor, the metaltitanium rod is used as anode, and active carbon fiber felt as the cathode and activecarbon particles as the third electrode, acetate fiber membrane is adopted to separateanode and cathode regions. Aerobic environment in anode region of reactor is suitablefor nitration reaction, while anaerobic environment is suitable for denitrificationreaction.In the process of turning on the electrode biological membrane reactor, the densityof inflow NH₄⁺_-N should be controlled for30mg/L, pH for7.8, temperature for30℃,and the operation cycle for24h. After100d cultivating and domestication, effluentammonia nitrogen conversion rate of reactor negative pole reached62%when thecurrent is30mA, in the meantime, TN dislodge rate is59%, the density of inflowNO₃^-_-N less than1.0mg/L，and without accumulation of NO₂^-_-N, which make thethree-dimensional electrode biological membrane reactor starting autotrophicdenitrification achieved successfully. The reactor runs stable in its operation when underthe condition of handling low load ammonia nitrogen waste water, with the effluentammonia nitrogen percent conversion up to more than85%, strain away rate of totalnitrogen is larger than70%. Moreover, the reactor not only can handle ammonianitrogen waste water with low C/N, but also can dispose nitrate nitrogen waste waterunder the completely autotrophic nutrition condition, when the inflow NO₃^-_-Nconcentration reaches30mg/L, the final strain away rate of NO₃^-_-N reaches75%,without accumulation of nitrite nitrogen, and is of better denitriding performance.Experimental results show that current is the main influence reason for theoperation of electrode biological membrane reactor, the change of current strength willdirectly change the DO environment and pH environment of the reaction system. In thisexperiment, the maximum effective current strength is30mA, under this condition, the reactor current efficiency reaches above200%.The experiment also indicates that when electrode-biofilm reactor disposingammonia nitrogen waste water, the influence of electrochemistry oxidation to theprevious2h become more remarkable, while to2h later is weakened, and the organismsaction plays the leading effect role.2h later is we say the first order reaction kinetics.Through analysis the electrochemical experimental results, under the operationcondition of the experiment, the ammonia nitrogen dislodged by electrochemistryoxidation takes up8%of which by electrode-biofilm reactor. However, when theelectrode-biofilm reactor disposing nitrate nitrogen waste water, the influence ofelectrochemistry restore effect is not so remarkable. But we can observe electric fieldtransfer effect obviously. The statistical analysis that the reduce volume of effluent nitricacid salt density caused by electric field transfer takes up6%of which by theelectrode-biofilm reactorThe third electrode filled in negative pole of three-dimensional-electrode-biofilmreactor is the major influence reason for the performance of reactor systemdenitrification, which can improve the systematic denitrification performance by around50%. The influence mainly represent in that the reactor electrode specific surface areais increased, the adhered microbe volume added which effectively separate the oxygentransferring from the anode zone to the cathode area, and adjust pH value of theenvironment, improve reactor’s current efficiency and unit space-time production. In thethird electrode of the reactor, each grain would form to a tiny electrolytic cell. Thennitration and denitrification reaction will occur in both ends of particle at the same time.Nitration also could take place in micro environment of negative pole denitrificationarea, which is helpful for the total nitrogen dislodging.