Effect Of Biological Sulfur Reducing On The Treatment Of Cr(Ⅵ)-Containing Wastewater

Chromium-containing wastewater is a highly polluting wastewater and is a pollution problems worldwide.Sulfate biological reduction treatment of chromiumcontaining wastewater has the advantages of high efficiency,low energy consumption and convenient management,many scholars have studied the use of sulfate-reducing bacteria to treat chromium-containing wastewater.There are many Cr(Ⅵ)-containing wastewaters with pH<5 produced by industrial production,but there are few studies on the treatment of acidic chromium-containing wastewater.Based on this,this paper discusses the treatment of acidic chromium-containing wastewater with stronger acid resistance and less organic carbon source consumption.This paper investigated the factors(initial pH,initial Cr(Ⅵ)concentration and temperature)affecting the treatment of Cr(Ⅵ)-containing wastewater by biological sulfur reducing in acidic enⅥronment,and the reduction mechanism of Cr(Ⅵ)reduction by biological sulfur reducing.We constructed a continuous bioreactor to explore the continuous treatment effect of biological sulfur reducing on chromium-containing wastewater.The main results obtained are as follows:(1)Condition optimization test was taken in anaerobic flasks,result showed that the best conditions for the treatment of chromium-containing wastewater by biological sulfur reducing was:initial pH 4,initial Cr(Ⅵ)concentration of 50 mg/L,growth temperature of 35℃.Under the best condition,the removal rate of Cr(Ⅵ)could reach to 99%.Among all the influencing factors,the initial pH and initial Cr(Ⅵ)concentration have the greatest influence on the reduction of Cr(Ⅵ).The too high or too low pH will inhibit sulfur reduction.High initial concentration of Cr(Ⅵ)will have a toxic effect on the microorganisms,making the microorganisms difficult to surⅥve,and affecting the treatment of the biological sulfur reducing on the chromium wastewater.(2)Four possible Cr(Ⅵ)reduction pathways in the process of removal of Cr(Ⅵ)by sulfur elemental reduction were studied.:chemical adsorption on to organic substrates,biosorption on to microorganisms,direct biological reduction of Cr(VI)to Cr(III)mediated by bacterial metabolism,and indirect reduction by sulfur reduction(sulfur to sulfide)coupled with reduction of Cr(VI)by sulfide.The results show that under acidic conditions(pH4),the main removal route of Cr(VI)is the indirect removal by sulfur reduction,86%of Cr(VI)reduced in this way.Cr(VI)removed by direct reduction accounts for 9%,and only 5%of Cr(VI)is removed by organic matter adsorption and microbial adsorption.In the process of Cr(VI)indirect reduction by biological sulfur reducing,Cr(VI)is reduced to Cr(III),and the sulfide is oxidized to sulfate,the Cr(III)produced in the wastewater is removed from the wastewater mainly in the form of Chromium hydroxide precipitation.(3)The chromium-containing wastewater is treated by a Centrifugal impeller bioreactor.During the operation of the reactor,the influent Cr(VI)concentration was 50 mg/L,and the Cr(VI)concentration in the effluent was below 0.5 mg/L,the reduction rate of Cr(VI)was over 99%,and the pH of the effluent is 4.95-5.12.According to the economic cost analysis,the cost of treating chromium-containing wastewater by sulfur-reducing bacteria is (?)0.55/t.