Effect Of Steam Explosion On Sewage Sludge Properties And Biogas Production By Anaerobic Digestion

Organic matter rich in sewage sludge from Wastewater Treatment Plant(WWTP)can be converted to renewable energy substance through anaerobic fermentation technology,which can promote the reduction and harmlessness of sludge,and then make less damage to the environment.In this study,waste activated sludge was pretreated with steam explosion and their change of physical and chemical property of the sludge was studied.The effect of different pretreatment conditions on anaerobic fermentation was emphatically studied,and a suitable range of pretreatment condition was put forward.Simultaneously,the feasibility of anaerobic fermentation coupling steam explosion pretreated sludge with kicchen waste at a medium temperature was investigated as well.The contents and main findings of this paper are as follows:1.Through changing pressure and holding time of steam explosion pretreatment,dissolution of organic matters such as SCOD,protein and polysaccharide in Waste activated sludge were compared.Physical structure of the pretreated sludge was explored,as well as the acid production ability by anaerobic fermentation.It was showed that after steam explosion pretreatment,SCOD in sludge liquid phase increased to 9544 mg/L,which was 37.7 times higher than the blank(253.8 mg/L).Polysaccharides,protein and nucleic acid concentrations were increased by 12.5,19.4 and 3.64 times that of the blank,respectively,and all concentrations increased with the increase of pretreatment pressure and holding time.Steam explosion pretreatment did change the sludge structure and size.The sludge structure was cracked,and the average particle size of sludge was 52.59% lower than that of the blank.It was showed that the maximum acid yield by anaerobic fermentation with steam explosion pretreated sludge was 234.76 mg COD/g VSS,which was 1.72 times higher than that of the blank.Compared with other pretreatment methods,steam explosion pretreatment has the advantages of shorter running time,better effect and higher acid production rate.2.In order to investigate effect of steam explosion intensity on biogas production ability of the pretreated sludge,low intensity and high intensity conditions were set for the sludge pretreatment,and the pretreated sludge was then used in anaerobic fermentation for biogas production.Appropriate steam explosion condition for sludge pretreatment used for anaerobic fermentation was discussed as well.The results show concentration of SCOD,protein and polysaccharide in the sludge liquid phase showed an rising trend with the increase of the pretreatment intensity,and the highest concentration can reach 9718 mg/L,866 mg/L and 1457mg/L,respectively(1.5MPa 12min).Biogas production was significantly improved by anaerobic fermentation with pretreated sludge.The highest yield reached 536 mL/d(1.5 MPa,8 min),and it was found that the daily biogas production kept a decline trend.The maximum biogas production rate with steam explosion pretreated sludge reached 122.1 m L/g VSadd(1.5 MPa,8 min),which was 5.45 times higher than that of the blank.The pH was in the range of 7.2-7.5 during the fermentation process,and the maximum concentration of ammonia nitrogen reached 1543 mg/L(1.5MPa,12min).making no inhibition to the anaerobic fermentation process.The biogas production rate showed a rising trend with the increase of pretreatment intensity when the intensity was relatively low,and it reached 107.6 mL/g VSadd under higher pretreatment intensity(1.5MPa,12min).For biogas production by municipal sludge with anaerobic digestion,a more suitable steam explosion pretreatment intensity coefficient should be less than 4.0.3.Study on anaerobic fermentation by steam explosion pretreatment sludge coupling food waste at medium temperature was carried out in a 30 L anaerobic fermentation tank.The co-fermentation was carried out by adding the kitchen waste to the steam explosion pretreated sludge and the feasibility of the process was discussed.After successful start of anaerobic fermentation system,the average methane and biogas yields in the second,third and fourth stages reached 58.6% and 257.1 mL/g VSadd,54.7% and 339.2 mL/g VSadd,55.6% and 374.6 m L/g VSadd,respectively.Co-fermentation efficiency by steam explosion pretreated sludge coupling kitchen waste was better than that by unpretreated sludge coupling kitchen waste or pretreated sludge without kitchen waste.The addition of kitchen waste not only stabilized the reactor operation,but also reduced the ammonia concentration from 1846.4 mg/L to 1606.8 mg/L,playing a certain role in dilution.In addition,TS and VS were reduced by 44.6% and 49.5%,respectively.It confirmed the feasibility of anaerobic fermentation by steam explosion pretreated sludge coupling food waste at a medium temperature.