Experiment Research Of Simultaneous Removal Of Carbon, Nitrogen And Sulfur From Waste Water With The Anoxic/Oxic Process

The predominant feature of wastewater discharged from the Biology Pharmacy and foodprocessing industry is the high concentration of COD, ammonia and sulfide, which make itdifficult to treat. The study is based on the principle that the ammonia can be oxidized tonitrate by nitrifying bacteria under aerobic conditions, and the sulfur-oxidizing bacteria canuse the sulfide as electron donor and nitrate as electron acceptor to remove nitrate and sulfidesimultaneously. The A/O （hypoxia/aerobic） reactor was built, in which the aerobic tank wasused to achieve the conversion of ammonia to nitrate, and the anoxic tank was used to removeCOD, nitrate and transform sulfide to elemental sulfur. In such process, organic matter,ammonia and sulfide could be removed synchronously and the accumulation of sulfur couldbe achieved.The process was run under the conditions of continuous flow with different ratio ofcarbon, nitrogen and sulfur, the feasibility of the removal of carbon, nitrogen sulfur by theA/O process was studied. The operating efficiency with different carbon source wasinvestigated; the main factors of the process were analyzed and their respective optimizedvalues were obtained. The results showed that:（1） Comparing with the process of nitrificationand denitrification, the A/O process could work steadily under lower C/N condition when theinflow water containing S^2-.（2） Under mixotrophic conditions, the anoxic process of the A/Osystem could achieve the removal of carbon and nitrogen with the accumulation of sulfur, theconversion rate of sulfur achieved73.53%when the C/N was2.5and the S/N was3in theinfluent. Moreover, the removal rate of TN and COD were96.54%and91.37%, individually.（3） When sodium acetate was used as carbon source, the operating efficiency of the processwas higher than that using glucose as carbon source, sulfur conversion rate reached themaximum value of74.84%when the C/N was2.5, sulfur conversion rate obtained themaximum value of61.77%when the C/N was3using.（4） Compared to the process ofnitrification and denitrification, more alkali was accumulated when the water contained S^2-, soacid addition was necessary to maintain the solution in the process.（5） When the solution pHof anoxic tank increased from7.5to9.5, the S^2-removal rate and S⁰conversion rate decreased,acid condition was beneficial for this process.（6） When the reflux ratio increased from2to5,the S⁰conversion rate increased at first and then decreased, the maximum value was achievedwhen the reflux ratio was3, the removal efficiency of carbon and nitrogen kept at a highvalue.（7） Increasing load will lead to the decline of the removal efficiency of carbon, nitrogenand sulfur in the system, the maximum load of the influent was0.20g S^2-/g MLSS, when the load is greater than this value, the operation efficiency of the system will decline quickly.