Experimental Study On Advanced Treatment Of Nitrogen Containing Wastewater By Three Dimensional Biofilm Electrode Reactor

A three dimensional biofilm electrode reactor(3D-BER)was developed for advanced treatment of nitrogen-containing wastewater.The new three-dimensional electrode biofilm reactor combines the anodic oxidation and cathodic reduction to achieve the nitrification-denitrification process in the same reactor.The configuration of the 3D-BER was flat plate,and the anode and cathode were arranged in parallel.Graphite plate was used as anode material,stainless steel plate as cathode material,granular activated carbon as particle electrode.The anode area was inoculated with nitrate bacteria and nitrite bacteria,and the cathodic zone was inoculated with autotrophic denitrifying bacteria,and buffer zone was set between the anode and cathode.The denitrification efficiency and influencing factors of the reactor under pure electrochemical conditions were studied.Then,the 3D-BER was started by inoculation of microorganisms to study the denitrification effect and the main influencing factors.The results of electrochemical experiments showed that under the optimal conditions(HRT=8h;current strength=80mA;influent ammonia nitrogen concentration = 50mg/L;pH=7),the removal rate of ammonia nitrogen was only 18.93%.Compared with the start-up reactor,the removal effect is quite different.so the effect of denitrification was dominated by biological effect.In the experiment of biofilm formation,the nitrifying bacteria in the anode zone were separated from the hydrogen autotrophic denitrifying bacteria in the cathode zone.The reproduction rate of nitrifying bacteria was faster,and the film hanging cycle was short.After 15 days of biofilm growth,the removal rate of ammonia nitrogen could reach 80%.And in the anode region,the brown film can be observed on the surface of the particle electrode.While the hydrogen autotrophic denitrifying bacteria in the cathode zone were cultured outside the reactor by using the external hydrogen source,and then transferred into the reactor after completion of culture.Although the removal rate of nitrate nitrogen reached 99% after 15 days of culture,film hanging cycle of the autotrophic denitrifying bacteria was long,and the white biofilm could be observed after 45 days of culture.After the completion of the reactor,the main influencing factors were subjected to single factor experiments.Experimental results showed that: When H=12h,ammonia nitrogen removal rate was 79.14%,the effluent nitrate nitrogen concentration and nitrite nitrogen concentration were 3.07mg/L and 0.14mg/L.Compared with the treatment effect of HRT=8h(ammonia nitrogen removal rate is 73.01%,effluent nitrate nitrogen concentration 6.70mg/L and nitrite nitrogen concentration 0.20mg/L)is better.Therefore,longer HRT can improve the nitrogen removal efficiency of the reactor and avoid the accumulation of nitrate nitrogen and nitrite nitrogen in the reactor.The current intensity will affect the amount and configuration of hydrogen produced by the cathode,and change the pH value near the electrode.When the current intensity is 40 mA,the ammonia nitrogen removal rate is the best,which can reach 79.14%.In theory,pH has a great effect on the activity of microbial enzymes,but the 3D-BER has a certain buffering capacity for pH,and the effluent pH is basically stable at about 7.When the concentration of ammonia nitrogen was 20mg/L,the removal rate of ammonia nitrogen was 91.13%,and the total nitrogen removal rate was 68.75%.The oxygen produced by anode can alleviate the shortage of oxygen in anode zone.When the influent DO was controlled at 2-4mg/L,the removal efficiency of total nitrogen was better,which was about 70%.The orthogonal experiment shows that the order of the five major factors affecting the nitrogen removal in the 3D-BER is as follows It is HRT > current intensity > DO > ammonia concentration > influent pH.The optimum reaction conditions are as follows: HRT=16h;ammonia concentration =20mg/L;current intensity I=50mA;DO=4mg/L;influent pH=7.The removal rate of ammonia nitrogen can reach 99.48%,and the total nitrogen removal rate is 95.31%.