The Effect Of Acetate Production From Anaerobic Fermentation Of Sewage Sludge By Sulfate Reducing Bacteria

The impact of sulfate-reducing bacteria(SRB)on the fermentation product such as VFA and H2, during the anaerobic fermentation of sewage sludge, was investigated by adding different concentrations of inhibitors of molybdate and sulfate. Furthermore, a real-time PCR method targeting Dsr A gene was established to investigate the relationship between quantity of SRB and fermentation product in the sludge. Results were shown as follows:(1)The concentration gradient experiments showed that, to inhibit SRB completely, the threshold concentration of molybdate was 15 mmol/L during the anaerobic fermentation of sewage sludge. The concentration of acetate would increase with molybdate reduced, acetate percent can reach as high as 83% of the total volatile fatty acids (VFAs) in the anaerobic system without molybdate. Such as propionate and butyrate could be detected only when the concentration of molybdate was higher than 5mmol/L. In the low concentration of molybdate system, only acetate and isovalerat was detected.(2) Sulfate and molybdate were used to adjust the activity of SRB and a real-time PCR method targeting Dsr A gene was established to quantify the SRB in the sludge. he results showed that SRB increased significantly with the addition of sulfate and the system became to typical"acetate-type"fermentation. SRB also maintained a certain number in the system without sulfate. Results also showed that molybdate could inhabit SRB, but could not kill SRB in short period of time.(3) Propionate and butyrate were used to study the different fermentation products between sulfate-reducing system and SRB inhibited by molybdate. Result showed that, propionate and butyrate were utilized to produce acetate by SRB in a short period of time. But the difference of other VFA was not obvious. HSRB would consume H2, so there was no H2 in the sulfate-reducing system.(4) As an inhibitor, CHCl3 did not inhibit SRB on incomplete oxidation of propionate, butyrate and valerate. So that acetate would account for more than 80% of the total VFA. But the difference of acetate under different concentrations of CHCl3 was not obviously. SRB utilized H2 only when sulfate was existence, and CHCl3 did not inhibit the process.(5) Used molybdate as a supplementary inhibitor showed that, SRB played an important role in the fermentation even without electron donor in the CHCl3 system. Comparing with the molybdate system, the VFAs increased 14%-35% respectively, and the total VFA increased 22%.