Research On The Anaerobic Digestion Of High-solid Sludge By Phosphate Buffer Solution Addition

Anaerobic digestion of high-solid sludge（HS-AD）provides an effective option for sludge treatment,which has such advantages as higher organic loading rate（OLR）,smaller operating volume of reactors and less consumption of energy for heating.However,the stabilization rate and methane production efficiency in HS-AD remains to be improved.The aim of this study was to investigate the effect of TS contents on anaerobic digestion,and then to further improve the HS-AD performance（including stabilization of sludge and methane production）by the addition of phosphate buffer solution（PBS）,which might cause the removal of inhibitory products.The study determined the optimal initial pH and dosage of PBS.The conclusions are as follows:VS removal rate reached 36.99%and cumulative methane production reached 127 mL·g^-1_VSS when the digestion was operated at TS of 20%,23.7%and 45.5%lower than those in liquid AD at TS of 5%,respectively.When operating at TS content of 15%or 20%,a 40-days prolonged lag phase was observed.At the TS content of 15%or 20%,the acidogenesis activities decreased rapidly with time,36.7%⁶9.0%lower than that at the beginning.Hydrogenotrophic methanogens Methanoculleus was found in dominant status at higher TS content,accounting for 43.2%.The relative abundance of acetoclastic methanogens Methanosarcina in liquid AD was at about 34.5%while in HS-AD it was at a low level of3.6%.When the initial pH of PBS was at 7.0 and at the concentration of 20mmol·L^-1,the highest VS removal rate of 42.3%was observed.The cumulative methane production obviously improved with the addition of PBS at the pH of 7.0,30.6%higher than the control group.However,PBS at pH of 7.5 or 8.0 inhibited the methanogenesis process,causing the methane production was 10.6%and 21.9%lower than that in the control group,respectively.The activities of acetate kinase and co-enzyme F₄₂₀increased when dosing PBS at the initial pH of 7.0,14.1%and 69.5%higher than that in the control group,respectively.Based on the optimal initial pH,the study investigated the performance of HS-AD at different concentrations of PBS dosing.36.33%of VS removal rate and 179.1 mL·g^-1_VSS of methane production were found after dosing PBS at the concentration of 40 mmol·L^-1,9.9%and 34.4%higher than the control group,respectively.After discussing the effect of TS contents on HS-AD and investigating the performance of HS-AD with the dosage of PBS at different initial pH as well as different dosing concentration,this thesis proposed the conclusion that it would achieve better performance of HS-AD,including better stabilization and better cumulative methane production,when adding PBS at initial pH of 7.0 and at the concentration of 40 mmol·L^-1.