Studies On Promotion Of Anaerobic Digestion By Sulfate Reducing Bacteria

Anaerobic biological treatment has many advantages as following: high organic loading, low energy consumption, and little excess sludge, etc, while the biogas producted in anaerobic digestion process is a very good energy. Therefore anaerobic biological treatment is a very promising treatment process of the organic pollutants. However, the problem of propionic acid accumulation is a key issues, which has been restricted practical application of anaerobic biological treatment. In this study, we founde that sulfate reducing bacteria can regulate the ecological balance of microorganisms in the anaerobic digestion system. Propionic acid can be rapid degraded by anaerobe, which can prevent propionic acid accumulation in anaerobic system. Our results can guide the engineering design of anaerobic reactor, reduce or even avoid propionic acid accumulation of anaerobic treatment process, and improve the stability of anaerobic treatment systems.We researched on the impact of sulfate reducing bacteria on propionic acid transformation in anaerobic reactor; the impact of appropriate sulfate adding on anaerobic reactor stability; the optimum temperature, pH conditions of cooperative anaerobic system of acid-producing bacteria, methanogenic bacteria and sulfate reducing bacteria; the impact of sulfate addition on anaerobic system. Also, we use PCR-DGGE technology to dynamic monitor microbial communities of anaerobic sludge. The main results was shew as follows:(1) Effects of sulfate reduction on propionic acid transformation in anaerobic process by adding sulfate was studied. Our results show that sulfate adding can promote conversion rate of Propionic acid in anaerobic reactor and decrease the inhibition of methanogenic bacteria by Propionic acid, consequently enhance the COD removal rate; the DGGE pattern shows that there are some changes of methanogenic bacteria communities in the adding sulfate system, and simultaneously the dominant community changed. It may suggest that sulfate reducing bacteria has a positive action on the transformation of propionic acid in anaerobic reactor. Therefore, we can adjust the cooperation among sulfate reducing bacteria, acidproducing bacteria and methanogenic bacteria to maintain stability of the anaerobic reactor.(2) Resistance of anaerobic system adding sulfate and anaerobic system not adding sulfate was studied. Under 6kg/m³Â·d volume load conditions, average COD removal of anaerobic system adding sulfate is 76.2%, average methane production is 270mL/g; average COD removal of anaerobic system not adding sulfate is 72.9%, average methane production is 259mL/g. Under 8kg/m³Â·d volume load conditions, average COD removal of anaerobic system adding sulfate is 60%, average methane production is 216mL/g; average COD removal of anaerobic system not adding sulfate is 50%, average methane production is 178mL/g. Our results show that the resistance of anaerobic system adding sulfate is gooder than anaerobic system not adding sulfate.Resilience of anaerobic system adding sulfate and anaerobic system not adding sulfate was studied. Our results show that the resilience of anaerobic system adding sulfate is gooder than anaerobic system not adding sulfate in case of load shock. Under 6kg/m³Â·d volume load conditions, the convalescence of anaerobic system adding sulfate is 4 days; the convalescence of anaerobic system not adding sulfate is 6 days. Under 8kg/m³Â·d volume load conditions, the convalescence of anaerobic system adding sulfate is 7 days; the convalescence of anaerobic system not adding sulfate is 11 days. The DGGE map shows there is a change of methanogenic bacteria communities in two anaerobic systems load shock, but in the adding sulfate system methanogenic bacteria community maintain a good diversity. We believe that the rich diversity of methanogenic bacteria before and after the load shock may make sulfate system less affected by the load shock, and quickly resumed to normal operation state,and we also believe the rich diversity of methanogenic bacteria in adding sulfate system should be related to metabolism of sulfate reducing bacteria.(3) The best temperature and best pH condition of cooperative anaerobic system with acidproducing bacteria, methanogenic bacteria and sulfate reducing bacteria was studied. Our results show that 35℃is the best temperature condition and 7.2 is the best pH condition.(4) Effect of anaerobic system with quantity of adding sulfate was studied. Our results show that the promotion of anaerobic reactor by sulfate reducing bacteria is best, when COD/SO₄^2- is 27:1. When COD/SO₄^2- is below 40:1, the sulfate concentration is too low to create condition of subsistence for methanogenic bacteria, therefore it can not enhance operation of anaerobic reactor. When COD/SO₄^2- is more than 27:1, competition between acidproducing bacteria and methanogenic bacteria or the toxic action of sulfate would affect the operation of anaerobic, and also affect the promotion of anaerobic reactor by sulfate reducing bacteria.