Characteristics Of Coupled Ultrasonic And Alkaline Pretreatment On Enhancing Anaerobic Digestion Of High-solid Sludge

Disintegrating sludge with pretreatment technology is an effective way to enhance the anaerobic digestion performance.In this paper,ultrasonic and alkaline method were applied to pretreat the high-solid sludge.The disintegration effects and improvements of anaerobic digestion performance by individual ultrasonic pretreatment,individual alkaline pretreatment and coupled ultrasonic and alkaline pretreatment were studied.A full scale coupled ultrasonic and alkaline pretreatment test was carried out.The microbial community structure in the high-solid anaerobic digeste was studied.The main research results were as follows:A novel,efficient and energy saving multi-transducer ultrasonic path reactor was developed with a total volume of 250 L and a total power of 10 kW.The sludge could be pretreated with a capacity of 5 m~3/h and an energy consumption of 2 kWh/m~3.Compared with the full-scale ultrasonic reactors in the international studies,the capacity of this full-scale ultrasonic reactor was 2-5 times higher,and the energy consumption reduced by 50%.Test of high-solid sludge pretreated by alkaline pretreatment showed that the extracellular polymeric substances(EPS)was easy to be damaged and could be disintegrated firstly,the microbial cell wall began to be damaged when CaO dose was0.06 g/g-TS,and the disintegration of cell membrane was observed when CaO dose was higher than 0.08 g/g-TS.And it was found that EPS disintegration contributed more to biogas production than cell disintegration.There was a synergistic effect when coupled ultrasonic and alkaline pretreatment technology was used to disintegrate high-solid sludge.The pretreatment could improve the microbial EPS disintegration degree,and disintegrate the cell wall and cell membrane under low alkaline dose,thus more organic matters were released and methane yield was improved.A full-scale coupled ultrasonic and alkaline pretreatment test was established.It was found that the chemical oxygen demand(COD)solubilization of high-solid sludge reached 19.5%~23.0%.The energy balance results showed that the coupled ultrasonic and alkaline pretreatment-anaerobic digestion system is technically economically feasible.High-throughput sequencing molecular biology method was used to study the microbial community structure in anaerobic digester of high-solid sludge.The results illustrated that with the increase of solid concentration,the concentrations of volatile fatty acid(VFA)and ammonia nitrogen increased,and the abundances of Firmicutes and Methanosaeta decreased gradually,while the abundance of Bacteroidetes increased gradually.