Study On Mesophilic Anaerobic Digestion Of Primary Sludge And Excess Activated Sludge

With the increase of sewage treatment rate, sludge treatment and disposal problems urgently need to be solved. Anaerobic digestion is remarkable in sludge reuse and stabilization. However, the efficiency of sludge digestion is low so that the energy output reduces, which limits the application of the anaerobic digestion in sludge treatment. Based on the characteristics of the excess activated sludge and the primary sludge with enhanced coagulation, the organic degradation and biogas production of the sewage sludge in a semi-continuous mesophilic anaerobic digestion were studied. The impact of high pressure homogenization pretreatment on the anaerobic digestion of the excess sludge was analyzed. Moreover, the influence of metal iron and aluminum on the anaerobic digestion of the primary sludge with enhanced coagulation was studied.The homogenization pressure of20,30,40and50MPa was applied on the excess sludge for sludge disintergration. The experiment results showed that the soluable COD (SCOD) and the sludge disintegration degree (DDCOD) of the excess sludge increased with increasingthe homogenization pressure, and their increasing rate significantly decreased when the homogenization pressure was higher than40Mpa. The influence of the number of homogenization cycle on the sludge disintergartion effect was studied. Results showed that the increase of the number of homogenization cycle promoted the sludge disintergration effectiveness. While the excess sludge was pretreated twice at a homogenization pressure of40MPa, the SCOD of the sludge supernatant increased from352.3mg/L to2037.2mg/L, DDCOD reached7.33%. Meanwhile, the sludge temperature increased from21℃to38℃, and the sludge volatile suspended solids (VSS) dropped from15.63g/L to14.07g/L. The high pressure homogenization technology effectively disintegrated the sewage sludge.After mesophilic anaerobic digestion, the digestion effect of the pretreated sludge was much better than that of the raw sludge, and there was a positive correlation between the digestion effectiveness and the homogenization pressure as well as the namber of homogenization cycle. While the sludge was pretreated twice an a homogenization pressure of40MPa, the VS and total COD (TCOD) removal were40.18%and61.30%, respectively, the biogas volume was3192ml, and the methane yield (methane production per gram VS removed) was356.78ml/gVS, which were1.3,2.7,1.1and0.3times higher than that for the raw sludge. The high pressure homogenization effectively promoted the sludge anaerobic digestion.The enhanced coagulation of the sewage with ferric and aluminium salts was carried out, and the impact of metal contents on the mesophilic anaerobic digestion of the primirary sludge with enhanced coagulation was investigated. Results showed that both iron ans aluminium had an inhabitation effect on the sludge anaerobic digestion. A slight inhabitation effect on anaerobic digestion was displayed for the primirary sludge which only contained iron, while the biogas yield (biogas production per gram VS removed) and the methane content (methane content per gram VS removed) showed a little improvement. The ferric salt was more favorable for the anaerobic digestion of the primirary sludge with coagulated with enhanced coagulation than the aluminum salts.