Study On Process And Mechanism Of Sludge Cracking By Hydraulic Cavitation Technology

In recent years,nearly 80%of the world’s municipal sewage is treated by activated sludge process,its biggest disadvantage is to produce a large amount of surplus sludge,which is also a dilemma we are facing.Surplus sludge is a compound pollutant rich in microorganisms,organic pollutants,bacteria,colloidal particles,etc.,if not properly treated,it will cause indelible harm to the society.Hydraulic cavitation is a new sludge reduction technology,using water to generate high pressure,can reduce the sludge sludge reduction microbial cell wall and microbial body structure,so that the intracellular material can flow out,improve the utilization of organic matter in the cell.However,traditional methods usually involve high processing costs,long processing times,low processing capacity or chemical by-products.Compared with other methods,hydraulic cavitation has the advantages of convenient operation,flexibility and ability to adapt the operation parameters to the required conditions,and has the development and application potential of large-scale application.Taking hydraulic cavitation pretreatment technology as an example,this study studied the influence of cavitation technology on activated sludge reduction,dissolution of organic matter and sludge characteristics,and discussed the theoretical mechanism of hydraulic cavitation reduction of activated sludge.In this paper,bibliometrics and Citespace visualization tools were used to systematically describe the research in the field of sludge pretreatment in recent ten years,and to evaluate the status quo,academic impact and research hotspots of sludge pretreatment technology.At the same time,the performance of hydraulic cavitation cracking urban sludge and the synergistic effect on activated sludge and its mechanism are also studied.The main results of this paper are as follows:（1）In the past decade,sludge pretreatment has been widely concerned by scholars,and the number of articles published has increased exponentially,which can be divided into three stages:initial stage（2010-2012）,rapid development stage（2012-2018）,and steady development stage（2018-2020）.Sludge pretreatment technology can be divided into physical method,chemical method and biological method,among which biological method is the most widely used.The results have been published in Bioresource Technology,Water Research,And Journal of Chemical Engineering.（2）In this study,the effects of initial sludge concentration,sludge solution temperature,operating inlet pressure,initial PH of sludge,running time and cavitation elements on the reduction of activated sludge by hydraulic cavitation treatment were studied respectively,so as to obtain the optimal treatment conditions of activated sludge by hydraulic cavitation treatment.The results show that the best treatment effect is obtained by using the plate with three holes and several holes,and the best treatment effect is obtained when the treatment temperature=35℃,the inlet pressure=5 bar,the running time=120 min,and the PH=10.（3）Combined with the above optimal treatment conditions,this study used waste activated sludge MLSS,MLVSS and DD_SCODto indicate sludge reduction and organic matter dissolution,respectively.The degree of sludge dewatering increased with the increase of treatment time,but the sludge quality increased with the increase of cavitation time when the reaction time exceeded a certain limit,and the dewatering was more affected by cavitation than mechanical action.（4）It is concluded that hydraulic cavitation can destroy the floc structure of sludge,significantly reduce the particle size of activated sludge,increase the disintegration degree of activated sludge,and promote the release of soluble organic matter.In addition,the mechanical action of hydraulic cavitation has little effect on the active composition of activated sludge.The high intensity cavitation effect can lead to the rupture of microbial cell membrane and improve the digestion or incineration performance of activated sludge significantly.（5）The mechanical action of hydraulic cavitation destroys the floc structure of sludge,resulting in the dispersion of activated sludge.Cavitation further destroys EPS of activated sludge,resulting in destruction of microbial cell membranes.The pollutants on the surface of sludge particles and the membrane structure of microorganism are not affected by cavitation,and the dissolved organic matter in sludge increases with the increase of sludge concentration.From solid phase to liquid phase,the free radicals generated by cavitation decompose into small molecular organic matter and reduce the biomass of sludge.According to the research results of this experiment,it can provide effective theoretical and technical support for the subsequent more efficient and environmentally friendly treatment of large-scale organic sewage.