Research On The Removal Efficiency Of Nitrate In Water By Using Biofilm-Eletrode Reactor

The biofilm-electrode denitrification is a method that it combines hydrogen autotrophic denitrifying bacteria and electrolytic hydrogen production to denitrifying. It has features of no organic carbon demanding and little secondary contamination. It is still able to effectively degrade nitrate nitrogen when there is no organic carbon. By adhering biofilm on the surface of the cathode and culturing hydrogen autotrophic denitrifying microorganisms, the paper preliminarily takes researches on three internal factors, namely the current density, temperature and inorganic carbon dosing and external factors, namely the concentration and C/N of nitrate in influent, that affect nitrate removal efficiency of the biofilm-electrode reactor.The conclusions of the research are as follows:1. The biofilm-electrode denitrification can effectively remove nitrate nitrogen in water, and does not cause problem of the nitrite nitrogen accumulation. The experiment shows that, in the condition of the temperature of 25℃, the current of 75mA, the nitrate nitrogen concentration of 40mg/L in influent and no organic carbon, the biofilm-electrode reactor can reach a maximum denitrification removal of 93% and denitration rate of 25.34mgN/(h·m2) and the nitrite concentration in effluent is 0.25mg/L.2. Current density has a significant impact on the effectiveness of the denitration in the biofilm-electrode denitrification. The test showed that when the current is less than 75mA, the efficiency of denitration increased with the increasing current. And the efficiency can reach 80% by the current increasing to 75mA. While the current is more than 75mA, the efficiency will decreased if the current continues increasing. And by the current increasing to 110mA, the efficiency of denitration is down to only 50%.3. Sodium bicarbonate can be used as inorganic carbon souse by microorganisms in biofilm-electrode denitrification, maintaining the solution in a slightly alkaline state and it improves the efficiency of denitrification. By adding 1.4g/L sodium bicarbonate, the pH is maintained at approximately 8 and the the removal of denitration is increased from 35% to 45% compared to the condition that it is without sodium bicarbonate dosing.4. When there is organic matter contained in influent, the efficiency of nitrogen removal can be further improved due to the effect of heterotrophic-autotrophic cooperation. The test showed that when C/N is less than 3, in the same time of reacting, the react time that the efficiency of nitrate removal reaches to 90% in biofilm-electrode reactor can be shortened more than 10h compared to the condition that only hydrogen autotrophic denitrification functions.5. The biofilm-electrode denitrification can effectively deal with the problem of surplus of nitrate nitrogen from the effluent in sedimentation tank secondary in the traditional craft of A2O. The experiment used the effluent in the secondary sedimentation tank in A2O and when the TN of the influent in the reactor is 22.95mg/L, the TN of the effluent is decreased to 1.17mg/L. The removal can reach more than 90% and the concentration of nitrate nitrogen is 0.05mg/L. The average denitrifying rate is 15.33mgN/(h·m2).