The Efficiency Of Sulfur Oxidizing Bacteria To Control H₂S By Using NO₃^-in Sludge Aerobic Composting Process

The overall sludge production of sewage treatment plants in China is increasing year by year.Aerobic composting,as a disposal technology with low cost and convenient operation,has been widely studied.However,the odor generated in composting process is easy to cause serious air pollution,which greatly limits the application value of this technology.The results showed that the main odor components of aerobic composting were NH₃ and H₂S.At present,the prevention and control technology of NH₃ and H₂S odor in aerobic composting has some defects,such as the value of composting products reduced in ectopic control,high treatment cost and so on.If sulfur oxidizing bacteria can oxidize S^2-by using NO₃^-produced by nitrifying bacteria in the process of sludge aerobic composting,in that way,the effect of controlling NH₃ and H₂S release in situ by biological agents can be achieved.It would have a good application prospect.At present,the research of sulfur oxidizing bacteria using NO ₃^-to oxidize S^2-is mostly carried out in the water phase system,but less in the solid pha se sludge system,and the solid phase may be unable to participate in the reaction due to the different positions of ions.In this study,a certain amount of sulfur oxidizing bacteria was added in the initial stage of composting,and nitrate was added to simulate the process of producing NO₃^-by nitrifying bacteria.The aim was to explore the feasibility and the better removal rate of H₂S of sulfur oxidizing bacteria using NO₃^-to control the release of H₂S by setting up sulfur oxidizing bacteria and NO₃^-coexistence system with different dosage.The experimental results showed that:sulfur oxidizing bacteria could control H₂S by using NO₃^-,and adding 5%logarithmic sulfur oxidizing bacteria and 300mg/kg nitrate could achieve obvious removal effect of H₂S,with the removal rate of27.18%-42.83%.When the oxygen concentration of reactor was low,the removal efficiency of H₂S was high,but the release amount was large;When the oxygen concentration of the reactor was high,the situation was just the opposite.There were two possible ways to control H₂S:one was that sulfur oxidizing bacteria consumed NO₃^-and other electron acceptors to oxidize S^2-to SO₄^2-,the other was that sulfur oxidizing bacteria increased the p H value during composting which inhibited the transformation of S^2-to H₂S.The first way may played a major role.In addition,through the study on the efficiency of sulfur oxidizing bacteria in different spatial positions,it was found that sulfur oxidizing bacteria had stronger sulfur oxidation effect in the middle and lower layers of the pile.On this basis,the study of sulfur oxidation in the inner and outer layers of spherical reactor with different particle sizes showed that sulfur oxidation bacteria mainly occurred in the area with higher radial oxygen concentration in aerobic condition.Under anoxic conditions,sulfur oxidizing bacteria mainl consume NO₃^-to oxidize S^2-in sludge particles,and the smaller the sludge particle size is,the better the oxidation effect is.