| Free nitrous acid(FNA)has positive effect on the biodegradation of waste activated sludge(WAS),but the mechanism is uncertain.In this study,we selected 2min and 2 W/mL as a effective way to elute extracellular polymeric substance.And free nitrous acid treatment experiment verified its high efficiency on sludge disintegration.The organic matters released and sludge dewaterability deteriorated.FNA treatment had subtle influence on extracellular polymeric substance.After that,five different pretreatments of sludge were compared to elucidate the enhanced mechanism through the variation of sludge physicochemical properties,including capillary suction time(CST),extracellular polymeric substances(EPS)and bound water.Group 1 was as the control using raw sludge without any treatment.Group 2(US)was used to assess the ultrasonic effect,Group 3(FNA)was designed to evaluate the FNA effect Group 4(US/FNA)was to explore the combined effect of ultrasonic/FNA treatment Different from Group 4,the ultrasound was used to wash EPS from WAS in Group 5(US(W)/FNA).In this experiment,the sludge firstly pretreated by ultrasound,then washed three times with deionized water and centrifuged at 4000 g for 10 min to separate the supernate and pellet.The pellet was dissolved to 300 mL.The soluble extracellular polymeric substances(S-EPS)and loosely bound EPS(LB-EPS)increased for all pretreatment comparing with raw sludge,but the tightly bound EPS(TB-EPS)decreased.The result was similar to the ultrasonic reinforcement sludge.The sludge filterability was in connection with the existence of humic acid in LB-EPS.Experimental results demonstrated that FNA had a weaker influence on disruption of S-EPS and LB-EPS matrix except TB-EPS.This study showed that FNA was very effective in disintegrating cell membrane,indicated by increasing percentage of DNA and live/dead cells in solution.The percentage of DNA in the supernatant increased rapidly and the viability of cells decreased after involved FNA treatment.The release of organic matters as well as humic acid in LB-EPS caused the deterioration of sludge dewaterability. |
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