Study On Anaerobic Sludge Digestion In An EGSB Reactor After Combined Pretreatment Of Alkaline And High Pressure Homogenization

With the continuous strengthening of water pollution control,the amount of sewage treatment plants becomes larger,which produce more sewage sludge.The environmental pollution caused by sewage sludge is increasingly becoming noticeable.More than 80%of sewage sludge has not been effectively treated in China,and advanced sludge treatment technologies and equipment are still lacked.Anaerobic sludge digestion is common technology in sludge treatment and utilization.To improve the efficiency of anaerobic sludge digestion,exploiting suitable sludge pretreatment technologies has an important practical significance.This research use batch method of anaerobic digestion,studying the effects of three kind of pretreatment methods on anaerobic digestion of pretreated sludge,supernatant liquid and solid residue of pretreated sludge,respectively.Three kind of pretreatnent methods are high pressure homogenization,alkaline pretreatment and alkaline combined with high pressure homogenization pretreatment.This research used 30 MPa and 1 cycle to discuss the influence of high pressurehomogenization pretreatment on anaerobic digestion of supernatant liquid and solid residue of pretreated sludge.Biogas production,methane production,particle size of sludge et.were analyzed.Through adding alkaline to sewage sludge,the effect of alkaline dosage on anaerobic digestion ofsupernatant liquid and solid residue of pretreated sludge was discussed.Under the combined alkalineand high pressure homogenization pretreatment,the features of anaerobic digestion of supernatantliquid and solid residue of pretreated sludge were evaluated.After high pressure homogenization pretreatment of 30 MPa,the sludge floes and microbial cellswere destroyed.The organic matters were released from the solid phase to the liquid phase with aDDCOD of 18%.After anaerobic digestion of pretreated sludge,supernatant liquid and solid residue thebiogas production increased to 1.24 times,2.05 times and 1.08 times,respectively,compared to that of raw sludge.The average particle size of sewage sludge reduced from 7.177 ?m to 1.823 ?m after high pressure homogenization pretreatment.After alkaline pretreatment,sludge cells were cracked,and the SCOD increased.When alkaline dosage was 0.04 mol/L,the DDCOD was 21%.After anaerobic digestion,the pretreated sludge and supernatant liquid produced 1.26 times and 23.28 times biogas,respectively,compared to that of raw sludge,however,solid residue of pretreated sludge produced only 74.6%biogas of that of raw sludge.With the increase of alkaline dosage,the VS removal of sludge increased.When alkaline dosage was 0.04 mol/L,the VS removal of pretreated sludge,supernatant liquid and solid residuereached 30.86%,68.64%and 15.78%,respectively.Alkaline combined with high pressure homogenization pretreatment further promoted sludge cells cracking,particle size decreasing.The combined pretreatment also improved anaerobic digestion performances with a DDCOD of 43.32%.With the increase of alkaline dosage,the VS removal of pretreated sludge,supernatant liquid of pretreated sludge increased.After anaerobic digestion,the pretreated sludge,supernatant liquid of pretreated sludge produced 1.28 times and 54.72 times biogas respectively,compared to that of raw sludge,however,the solid residue of pretreated sludge produced only 58.14%biogas of that of raw sludge.With the increase of alkaline dosage,the VS removal of pretreated sludge and liquid and solid phases of pretreated sludge also increased.When the alkaline dosage was 0.04 mol/L,the VS removal of pretreated sludge and its liquid and solid phases reached 33.2%,70.74%and 30.56%,respectively.Alkaline combined with high pressure homogenization pretreatment promoted anaerobic digestion more effectively.There was a synergistic effect between the anaerobic digestion of liquid and solid phase pretreated.Under optimized conditions,an expanded granular sludge blanket(EGSB)reactor was used to treat the pretreated sludge.When the EGSB reactor operated stably,the COD removal of pretreated sludge reached 45%.The maximum yield of biogas and methane reached to 0.41 L/gCOD and 0.82 L/gCOD.Based on the anaerobic digestion effect in the EGSB reactor after combined sludge pretreatment,a pilot sludge treatment process was designed.