Study Of Biological Sulfur Recovery By Coagulation-sedimentation Method And Optimization Of Parameters

Sulfide wastewater can be well treated by desulfurization and denitrificationprocess, producing elemental sulfur (Hereinafter referred to as "bio-sulfur"). If thebiological sulfur won’t be separated, it will continue to be oxidized to sulfate, causingsecondary pollution of water bodies. Study on nature and separation method ofbiological sulfur is very small at home and abroad, mostly at the theoretical stage. Thisstudy aimed to explore properties of biological sulfur quantitatively, and further toexplore suitable separation method according to its characteristics. Finally, we designeda continuous operation and process to separate biological sulfur. In this study, featuresof four aspects were explored, such as particle size distribution, Zeta potential, spectrumanalysis and scanning electron microscopy. As for physical and chemical properties ofbiological sulfur, we initially selected the appropriate separation method-coagulatingsedimentation method. And best optimum parameters were determined by parameteroptimization tests. On this basis, we designed biological sulfur separation unit forcontinuous operation, desulfurization process coupled.The results showed that, about60%conversion of biological sulfur can beachieved by desulfurization and denitrification process. Overall, biological sulfurparticle size was of normal distribution,most particle size between2um-30um, thevolume average particle diameter being27.156um; Zeta potential value isapproximately-20mV, between±30mV; Biological sulfur particles are spherical withrough surfaces, with many small projections on the surface, the macromolecularpolymer; sulfur content of biological sulfur particles is about50%. The above biologicalproperties indicated that it can be separated by coagulating method.The results of parameter optimization tests showed that the flocculation effect ofbiological sulfur by PAC is obviously better than microbial coagulant and PAM, and themost suitable dosage was2.5mg PAC/mg S, when the biological sulfur flocculation ratewas87%-92%,0.6and0.8times higher respectively than microbial coagulant and PAM,at the same time, the removal rate of turbidity92%-98%,1.1and2.4times higherrespectively than microbial coagulant and PAM. In condition of best dosage, the best pHis5.5, at which time, the biological sulfur flocculation rate was up to88%-96%,0.7and1.1times higher respectively than microbial coagulant and PAM, at the same time, theturbidity removal rate up to93%-99%,0.7and1.6times higher respectively thanmicrobial coagulant and PAM. With the best the dosage and pH, the best flocculation ofstirring intensity is120r/min, in which time, biological sulfur rate was further increasedto90%-98%,0.5and1.2times higher respectively than microbial coagulant and PAM,at the same time, the turbidity removal rate up to94%-100%,0.7and1.3times higherrespectively than microbial coagulant and PAM. The continuous operation results of desulfurization-sulfur separation/recoveryprocess showed that, the efficiency separation of biological sulfur is up to90-92%, andturbidity is also about93%.And some certain economic benefits can be achieved.