Performance Of Biological Removal Of Ammonium-Nitrogen And Sulfate In Wastewater

With the rapid development of the economy and the progress of the society, the discharge of living wastewater and industry wastewater including the organic wastewater which has high concentration of ammonium and sulfate all over the world is increasing day by day. The wastewater which has high concentration of ammonium and sulfate is included here. At present the main method to treat this kind of wastewater is to treat it step by step. The traditional main method to remove sulfate in wastewater is to use SRB to reduce sulfate sulfureted hydrogen under anaerobic conditions. However this method has lots of shortages, such as high operation cost, more solid waste, hard operation conditions, and unsatisfactory effects and so on. There are relatively many ways to treat wastewater with high concentration of ammonium. But these ways also have many disadvantages, such as high operation costs, smaller scale, hard controlling and secondary pollution. So it is very necessary to find a method to remove sulfate and ammonium simultaneously and to avoid all these problems mentioned above.In this study, two different processes of biological desulfurization and nitrogen removal were supposed and primary study was conducted on them. Manmade solutions were used as influents and were put into different reactors: Anoxic Suspended growth reactor, Anoxic SBR reactor, Anaerobic CSTR reactor and EGSB reactor. Depending on the experimental data and phenomana, the reacting conditions were studied.According to the performance of the Anoxic Suspended growth reactor, conditions suitable for the aimed react were as follows: low concentration of COD, high concentration of sulfate and ammonium and low pH value. Elemental sulfur and nitrogen were found in the reactor and the amount of them increased with reacting time, it meaned the aimed reacts were happened in the reactor, but theaimed reacts didn't go along smoothly in the reactor.Anoxic SBR reactor and Anaerobic CSTR reactor were applied to pretreat the wastewater with ammonium and sulfate in order to supply sulfide and nitrate foe the following simultaneous desulfurization and denitrification react. In the Anoxic SBR reactor, when DO was more than 2.0mg/L, aeration time was 6 hours, the maximum treatment load of the reactor was 900mgN/L, and its removal efficiency could arrive to about 99%, and the efficiency of ammonium transformation to nitrate was about 70%. Influent with high concentration of sulfate had a high osmosis pressure and it had a remarkable influence on nitration react. The critical value was between 18.8×10⁵Pa～ 19.2×10⁵P. With the decrease of osmosis pressure, the nitration function of the reactor resumed gradually. In the CSTR reactor, when the concentration of sulfate and COD was 1000mg/L and 3000mg/L respectively, in order to obtain a satisfactory sulfate removal and transformation efficiencies, the advisable system conditions were as follows: pH value was about 7.5, alkalinity was about 2000mg/L, COD/SO₄^2- ratio was above 2.0. In the static experiment, when the concentrations of sulfate and COD were 1000mg/L and 3000mg/L, respectively, in order to obtain a satisfactory sulfate removal and transformation efficiencies, the advisable concentrations of NO2- and NO3- were suggested less than 200 and 250mg/L, respectively.In the EGSB reactor, autotrophs and heterotrophs coexisted in the ecosystem, and cooperated to remove sulfide, nitrate and TOC simultaneously while elemental sulfur was obtained. The feasibility of simultaneous desulfurization and denitrification under mixotrophic condition was investigated via continuous-flow tests, and key factors of the process, such as pH value and S/N ratio, were discussed. The results suggest: the simultaneous removal of sulfide, nitrite and TOC as well as elemental sulfur accumulation could be achieved under mixotrophic condition. Low alkalescent pH condition was favorable to the process. S/N ratio had a remarkable influence on the process. The optimum S/N ratio to acquire the best efficiencies of both sulfide removal and elemental sulfur accumulation was supposed to be 5/6.