Study On The Key Factors Optimization And Energy Consumption Analysis Of Heating Disinfection Of Digested Slurry From Swine Manure

Recycling and safe discharge are one of the main ways to treat and utilize digested slurry from swine farms.However,the potential risk of pathogenic microorganisms exists in treating digested slurry discharged from psychrophilic and mesophilic biogas digesters.Referring to the pasteurization technology after anaerobic fermentation in the European Union(EU),the heating disinfection method was used to disinfect digested slurry and manure from a swine farm.Changes in the number of coliform bacteria and fecal coliform were used as indicators to evaluate the optimal disinfection effect under three key conditions:heating temperature(50～80℃),heating time(holding 15～60 min after heating up to the set temperature)and total solids(TS)content(2%～6%).To ensure the disinfection effect,the most energy-saving condition of heating disinfection was selected.Meanwhile,the energy consumption analysis of two processes,“anaerobic fermentation+heating disinfection”and“heating disinfection+anaerobic fermentation”,was performed to provide a reference for the development of large-scale swine farm digested slurry advanced treatment technology and safe reuse or discharge after disinfection treatment.The main conclusions are shown as follows:(1)In this study,heating disinfection conditions maintained at 60℃for 15 minutes were most suitable for killing specific pathogenic microorganisms in digested slurry from swine manure.After the treatment,the number of coliforms in digested slurry decreased from 1.02×10~5±3.99×10~4 CFU/mL to less than 1 CFU/mL,and the number of fecal coliforms decreased from 9.90×10~4±6.11×10~4 MPN/mL to less than 0.03 MPN/mL,which meet the requirements of reclaimed water quality standard(SL368-2006)for pathogenic microorganisms disinfection in the reuse of reclaimed water for agriculture.Compared with the EU heating disinfection standard using 70℃for 60 minutes,the energy consumption is reduced while ensuring the disinfection effect.The heating temperature and time had a significant influence on the disinfection effect of swine manure digested slurry(P<0.01).The TS of digested slurry had no significant impact on the disinfection effect(P>0.05),but had significant impact on the temperature increase rate of digested slurry(P<0.01).In this study,heating 300 mL digested slurry with different TS(2%,4%,and 6%)in the anaerobic fermentation from 35℃to 60℃needed 17.7,22.3 and 28.0 minutes,respectively.(2)In this study,heating disinfection conditions maintained at 70℃for 60 minutes were most suitable for killing specific pathogenic microorganisms in swine manure wastewater.The number of coliforms in swine manure wastewater decreased from 1.35×10~6±4.27×10~5 CFU/mL to less than 1CFU/mL,and the number of fecal coliforms decreased from 1.06×10~6±1.78×10~5 MPN/mL to less than0.03 MPN/mL,which meet the requirements of reclaimed water quality standard(SL368-2006)for pathogenic microorganisms disinfection in the reuse of reclaimed water for agriculture.The heating temperature and time had a significant influence on the disinfection effect of swine manure wastewater(P<0.01).The TS of swine manure wastewater had a significant influence on the number of coliforms in swine manure wastewater(P<0.01),and had no significant impact on the number of fecal coliforms in swine manure wastewater(P>0.05).In addition,the TS of swine manure wastewater had significant impact on the temperature increase rate of swine manure wastewater(P<0.01).In this study,heating 300mL swine manure wastewater with different TS(2%,4%,and 6%)in the ambient condition from 20℃to 70℃were 38.7,44.0 and 47.7 minutes,respectively.(3)The net energy production of“anaerobic fermentation+heating disinfection process”(process A)is higher than“heating disinfection+anaerobic fermentation process”(process B).One metric ton of swine manure wastewater is considered in the energy production and consumption calculation of the two processes.In process A,the energy consumption of anaerobic fermentation is 19.95 kWh,the energy consumption of heat treatment is 29.69 kWh,and the biogas production capacity is 118.56 kWh,leading to the net process energy of 68.92 kWh.In process B,the energy consumption of heat treatment is 60.40 kWh,the energy consumption of anaerobic fermentation is 2.15 kWh,and the biogas production capacity is 123.42 kWh,leading to the net process energy of 60.87 kWh.According to the calculation results of energy consumption,the energy consumption and production capacity of process A are lower than that of process B,but process A has higher net energy production in the comprehensive analysis,so that“anaerobic fermentation+heating disinfection process”is recommended.