Operation Characteristics Of Light Anaerobic Reactor For The Treatment Of High-concentration Sulfate Organic Wastewater

Sulfate organic wastewater has complex composition and a wide range of source,which is harmful to the environment.Besides,sulfur recovery and utilization of high-concentration sulfur-containing wastewater is also promising and attractive in the research of sulfur resource recycling.As sulfate reducing bacteria compete with methanogens,it will lead to low sulfate removal efficiency and high stability when the traditional biological method employed in the treatment of low COD/SO₄^2-ratio wastewater.Although a number of studies have been carried out to improve the sulfate removal efficiency,there are still problems such as system acidification,and excessively high H₂S content in biogas.Photosynthetic bacteria can use reducing sulfur compounds to alleviate the toxic effect of sulfides in water on microorganisms,and can promote the reduction of sulfate.The application of photosynthetic bacteria in traditional anaerobic reactors can solve the above problems,but there is still a lack of systematic research.The influence of light and carbon source on the anaerobic reactor were discussed.The characteristics of sludge and the change of microbial community structure were also studied.The main research results are as follows:（1）The performance of light and non-light systems under different COD/SO₄^2-ratios was investigated.Besides,the influence of light wavelength on the anaerobic system at low COD/SO₄^2-ratio was discussed.The results showed that the removal efficiency of COD and SO₄^2-and methane production performance of the reactor at the COD/SO₄^2-ratio of 2:1.What’s more,the light system performed better than the non-light system,reaching 70%,80%,1.39 L/L/d respectively.The study of optical wavelength found that the removal effect of SO₄^2-was improved to more than 85%at the COD/SO₄^2-ratio of 2:1 in the range of400～600nm and 500～700nm.Mass conservation accounting found that about 50%of COD in the light system was used by methanogens to produce methane,and MPA always occupied the majority of electron flow.According to the analysis results of sludge properties,light illumination was beneficial to the sludge particle size and promoted microorganisms to produce more extracellular polymeric substance to cope with environmental pressure,and thus maintaining the stability of the system,promoting the growth of microorganisms and maintaining a high VSS.Light can promote the removal of sulfate and organic matter,increase the content of methane in the gas,and improve the competitive inhibition and cooperative treatment of each bacterial community,which is beneficial to the stable operation of the system.（2）The effects of ethanol on sulfate reduction process and microbial structure were studied by replacing starch hydrolysates with ethanol at low COD/SO₄^2-ratio.The results showed that the removal efficiency of SO₄^2-and methane production performance of the reactor with 25%ethanol addition were 80%,1.64 L/L/d respectively,higher than that of the control group at the COD/SO₄^2-ratio of 2:1.The methane content in the biogas was more than 40%,the proportion of CH₄-COD was about 50%,MPA occupied more electron flow,and the proportion of sulphate converted into liquid phase increased.When the influent carbon source was changed,the methane content in biogas increased to 55%under the condition of 50%ethanol.When all the carbon source were ethanol,the COD removal rate of the reactor reduced to less than 20%,and the SRB utilized all the electron flow.According to the analysis results of sludge properties,the carbon source had no significant effect on the change of sludge particle size at low COD/SO₄^2-ratio,and adding 25%and 50%ethanol as a mixed carbon source could alleviate the pressure on microorganisms from changes in water intake,while the abundance of acid-producing bacteria and methanogens would be inhibited and VSS reduced when all carbon source was ethanol.When ethanol is added to a complex carbon source,which can promote the reduction of sulfate,and at the same time increase the methane content in the biogas,and which is conducive to the recovery of resources.（3）16S rRNA sequencing showed that at the end of operation of the light reactor,the dominant bacteria in it were Prevotella,Ethanoligenens,Desulfovibrio and Methanosaeta,and the reactor had a higher population richness under the light condition.When adding 25%ethanol as a mixed carbon source,the dominant bacteria in it were Clostridium,Lactococcus,Desulfovibrio and Methanosaeta.Moreover,the addition of ethanol to the intake carbon source could greatly improve the relative richness of Desulfovibrio.Ethanol as a single carbon source would reduce the microbial community richness of the anaerobic system and reduce the treatment performance of the system.