| The increasing production of sludge and the serious shortage of sludge treatment capacity and the serious backwardness of treatment methods have formed sharp contradictions,sludge pollution has become an inevitable environmental problem in China.Anaerobic digestion was the most commonly used method for sludge stabilization.Under anaerobic conditions,microorganisms can use their biochemical functions to degrade organic,produce biogas and reduce the concentration of toxic and harmful substances in the sludge.Whereas traditional anaerobic digestion of sludge had some problems,such as difficult to hydrolyze,long anaerobic reaction time,low methane production.The use of pretreatments may help to disrupt cell structure and improve waste activated sludge biodegradability,thereby accelerating the rate of anaerobic reaction and increasing methane production.In the present study,the effects of mixed alkali treatment,thermal treatment and thermal combined mixed alkali treatment on the biodegradability and anaerobic digestion performance of waste activated sludge were comprehensively investigated,the kinetics of sludge anaerobic digestion for methane production was also explored.The main research contents are as follows:The sludge was pretreated by mixed alkali treatment,thermal treatment and thermal combined mixed alkali treatment.The dissolution effect of the sludge was determined by measuring parameters such as soluble chemical oxygen demand(SCOD),protein,polysaccharide,ammonia nitrogen,and volatile fatty acid(VFAs)in the sludge.The results showed that the content of organic in the sludge after pretreatment was significantly increased.The order of sludge dissolution by each pretreatment method was: mixed alkali-thermal treatment > simultaneous treatment of thermal and alkali treatment > thermal-mixed alkali treatment > mixed alkali treatment > mixed treatment > control group(untreated).The higher the content of sodium hydroxide in the mixed alkali used for pretreatment,the larger the SCOD dissolution rate of the sludge.The maximum dissolution rate was 4:1+80 °C treatment group,which was 112.8%.Furthermore,the dissolution of mixed alkali-thermal treatment group sludge was better than the superposition effect of the separate treatment.The pre-treated sludge was used for anaerobic reaction,study the gas production trend,the variation trend of the substrate,the organic removal rate and the sludge volume reduction effect.After 30 days of anaerobic reaction,the anaerobic digestion performance of the mixed alkali-thermal treatment sludge was better than the effect of the separate treatment.The order of cumulative methane,organic removal rate,sludge reduction(TS,VS removal rate)were: mixed alkali-thermal treatment > thermal treatment(80 °C)> mixed alkali treatment(3:2)> control.For mixed alkali-thermal treatment,the cumulative methane production of the sludge increased gradually with the increase of sodium hydroxide content in the mixed alkali.The maximum cumulative methane production was 4:1+80 °C treatment group,which was 430 mL/gVS,Increased by 308.7% compared with untreated sludge.Compared with the mixed alkali treatment group,the inhibition period in the anaerobic digestion process was greatly shortened,indicating that the low heat treatment combined with the mixed alkali treatment can reduce the inhibitory effect of mixed alkali on the anaerobic digestion,thereby shortening the inhibition period and increasing the methane production.Fitting the methanogenesis kinetics of each group of sludge was carried out by first-order kinetics and Modified Gomerptz model.The fitting results show that the Modified Gompertz model was more consilient with the methanogenesis kinetics.Whether the untreated group or the pretreatment group(mixed alkali treatment,heat treatment,mixed alkali-heat treatment)obviously has inhibition in the initial stage of anaerobic digestion,and the cumulative methane production of the whole methanogenic was an “S” curve. |
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