Study On Treatment Of Low Concentration Organic Wastewater Containing Sulfate By EGSB Reactor

In the water treatment industry,anaerobic treatment of sulfate-containing industrial organic wastewater has always been one of the more difficult problems.First,sulfate-reducing bacteria and methanogenic bacteria have the same metabolic substrates,so there is a substrate competition relationship between the two.And,from the perspective of chemical thermodynamics and enzymatic reaction kinetics,sulfate-reducing bacteria are more competitive and affinity for common substrates than methanogens,resulting in primary inhibitory effect on the biological process of methanogens;secondly,when sulfate is reduced,sulfide that is toxic to anaerobic microorganisms will be produced,resulting in secondary inhibitory effect on the biological process of methanogens.There are also thorny problems in the anaerobic treatment of low-concentration organic wastewater.Due to the low concentration of organic matter in the inlet water,the driving force of mass transfer between organic matter and anaerobic microorganisms decreases in the reactor,resulting in a weakening of the metabolic activity of microorganisms and the low treatment efficiency of the reactor.The anaerobic treatment of low concentration organic wastewater containing sulfate under appropriate COD/SO₄^2-conditions was studied.Taking advantage of the more affinity of sulfate reducing bacteria for organic substrates to help decompose part of the organic substrates in the wastewater,it will be possible to avoid the primary and secondary inhibitory effect caused by sulfate reduction reaction,and let sulfate reducing bacteria cooperate with methanogens to achieve the purpose of simultaneously treating sulfate and organic pollutants and improving the treatment efficiency of anaerobic digestion reactor.At the same time,it can also provide a new technical route for anaerobic treatment of low concentration organic wastewater containing sulfate.Taking the fructose industrial wastewater（COD=1400～2000 mg/L）as the test water,the impacts of Hydraulic Retention Time（HRT）on the operation performance,gas production performance and anaerobic microbial growth of Expanded Granular Sludge Bed（EGSB）reactor for treating low concentration organic wastewater was studied.The data reference is provided for subsequent experiments.The results showed that the COD removal rate was about 70%after the reactor was started and stabilized at 37℃and HRT of 36 h.Then,with a gradual decrease in the HRT from 36 h to 9 h,the COD removal rate first increased and then decreased.When the HRT was 18 h,the COD removal rate was the highest,up to 80%.After further shortening the HRT to 12h,the effluent COD slightly increased and the removal rate decreased to less than 75%,but the daily removal of organic pollutants was relatively higher.When the HRT was shortened to 9 h,the COD removal rate decreased to about 65%.The biogas conversion rate increased with the shortening of HRT,and will not increase with the shortening of HRT after reaching the peak.When the HRT was 18 h,the biogas conversion rate reached the peak value of about 0.5 m3/kg COD.After the EGSB reactor was operated for 23 days under the HRT of 36 h and 24 h,the sludge concentration in the reactor did not increase but decreased,and the sludge volume decreased by about 1/5.Then,with the shortening of HRT,the sludge concentration stopped decreasing and had an increasing trend.Under the condition of HRT of 12h,the effect of adding sulfate on the treatment of low-concentration industrial organic wastewater in the EGSB reactor was explored,in which this paper focused on the change of removal capacity of the reactor on organic matter and sulfate under different inlet water COD/SO₄^2-conditions,and the reasons and mechanisms for the change of the treatment efficiency of the EGSB reactor were analyzed by the changes in effluent water quality,biogas composition and electron flow specific gravity.The research shows that the addition of sulfate can improve the treatment effect of EGSB reactor on low concentration industrial organic wastewater,and the COD of effluent water shows a trend of first decreasing and then increasing with the decrease of the inlet water carbon-sulfur ratio(COD/SO₄^2-:15,10,7 and 4).When the influent COD/SO₄^2-is 7,the EGSB reactor has the best treatment effect,and the COD removal rate is above 75%.Compared with the absence of sulfate components,the removal effect of EGSB reactor on organic pollutants has been improved,while the sulfate removal rate has been maintained at a relatively high level（close to 90%）.However,with the further reduction of influent COD/SO₄^2-to 4,the quality of the effluent water deteriorated significantly,and the COD removal rate dropped to less than65%,and the sulfate removal rate dropped to less than 75%.After that,the sulfate concentration in the influent water was stabilized at about 430 mg/L,the COD/SO₄^2-was restored to 7 by increasing the influent organic substrate concentration.The study found that the treatment effect of the reactor was restored to more than 75%.Due to the influence of substrate diversion,methanogenesis was affected at the beginning,and the biogas production and methane production continued to decline with the decrease of influent COD/SO₄^2-.When the influent COD/SO₄^2-was 15,the biogas production and methane production were about 0.43 m3/kg COD and 0.33 m3/kg COD respectively,and when the influent COD/SO₄^2-was reduced to 4,the biogas production and methane production decreased to about 0.37 m3/kg COD and 0.29 m3/kg COD respectively.