Treatment Of Wastewater Containing Sulfide (S～(2-)) By Electro-Coagulating And Biological Approaches

During anaerobic treatment of wastewater from differently industrial sections, such as pulp mill, food processing, chemical industry, antibiotic pharmacy and so on, Sulfate Reducing Bacteria (SRB) in reactor utilize sulfate as electron donors and deoxidize it into sulfide in the presence of high sulfate concentration (low COD/SO₄^2-). Due to the fact that a large amount of sulfide has adverse effect on anaerobic reaction, therefore, it is of essence that sulfide removal by using electro-coagulating and biological approaches be needed. In the present investigation, the treatment process and characteristics of wastewater containing sulfide by a tube electro-coagulator were examined. The results indicated that following factors including pH values, sulfide concentrations, electrolysis time, current density, electrolytes all were able to influence removal efficiency of sulfide, but an optimized conditions for pH=6-9,current density=0.42A/dm², electrolysis time=30min, sulfide concentration=500mg/L, the removal rate was up to over 90%. In development of the biological approach for the treatment of the wastewater containing sulfide, a strain of Thiobacillus thioparus was screened and identified ,its growth characteristic was studied, followed that the bacteria were enriched and formed by bio-membrane in up-flow packed tower by a rapid bio-membrane forming method resulting in milking-like sulfur formed in the wastewater during the biological treatment. Single-factor influencing analytical tests had revealed that the operation of up-flow packed tower by a strain of Thiobacillus thioparus was experimented, and discovered that efficient removal of sulfide from the wastewater was obtained while production of sulfur occurred. The key influencing factors of sulfide bio-oxidation reactors were found to be: dissolved oxygen, sulfide volume loading rate. The results showed, the removal percentage of sulfide was over 90% at pH of 6.2-9.0 and temperature of 30±2℃ when the sulfide influent concentration, dissolved oxygen , sulfide volume loading rate was 148.14mg/L, 1.5mg/L, from 6m³/(m³.d) to 50m³/(m³.d), respectively. The tests demonstrated that the relation formula between optimum dissolved oxygen and influent sulfide concentrations was y=0.0045x+0.3867(r²=0.9721), according to various influent sulfide concentrations , i.e. a given sulfide influent concentration corresponding to an optimal dissolved oxygen if the removal rate of sulfide in this reactor was set up to over 95%. Microbiologically original sulfur was produced steadily, when R-mt (the rate of dissolved oxygen vs sulfide consumption) varied in a rage of 0.53-1.46, and the produced sulfur rate was up to the maximum amount and 89% sulfide could be turned into sulfur when R-mt=0.83 at a given amount of supply oxygen, the pH of effluent going up gradually upon increasing sulfide concentrations. Multi-factor influencing analytical tests have indicated that at various influent concentrations of sulfide i.e. 85.76,177.83, 269.55, 394.26 mg/L, a series of orthogonally designed analysis tests were carried out when three levels of sulfide volume loading rates and dissolved oxygen were selected and the microbial reactor was kept at pH of 7.0±0.1 and temperature of 30±2℃. The results gained indicated that the removal percentage of sulfide and sulfate production rate were linearly related to sulfide volume loading rate and dissolved oxygen. Several regression functions were established and the parameters were strongly correlated with influent concentrations of sulfide. It has been found that the models of removal for sulfide, sulfate production and sulfur production could be expressed as following: Sr=0.0145CinVLR-0.0345Cin.DO-0.0343Cin-6.06VLR+17.074DO+110.48 Sp=-0.0511Cin.VLR+1.0082Cin.DO-0.002C2in+0.8778Cin-1.4348VLR-81.35DO-28.122 W=(Cin.Sr%-1/3×Sp)/Cin×100% Where, Sr: sulfide removal percentage (%),VLR: sulfide volume loading rate(kg/(m3.d)),DO: dissolved oxygen(mg/L),Cin: influent concentrations of sulfide(mg/L),Sp: sulfate production(%),W: sulfur production (%). The models above were valid as well in the independent tests with relative error less than 5%. In this investigation, furthermore, a new spectrophotometer method was also developed for determination of trace amount of sulfur, The minimum detection limit was discovered to be as low as 3.0×10-2 mg/L. The test revealed that the present innovative method was characterized by convenience, high sensitivity and well recurred. Sulfur estimation method in the paper was well testified by spectrophotometer determination method with a relative error of below 5%. It may be concluded that the present study dealing with electro-coagulating and biological approaches for treatment of wastewater containing high concentration of sulfate provided the evidence for the feasibility of forecasting the result of sulfide bio-oxidation and selecting optimal parameters of reactors. The approaches were also beneficial for technology design and run of wastewater treatment technology.