Study On Rheological Properties And Gas Production Law Of Cattle Manure During Fermentation Process At Thermophilic Temperature

The rheological properties of fermentation raw materials during anaerobic fermentation process have an important influence on the design and selection of anaerobic digestion equipment,power consumption and heat and mass transfer during anaerobic digestion process.There has no study on the rheological properties of high concentration fermentation raw materials by using online viscometer at home and abroad.Therefore,in this paper,the HYND-50 vibration online viscometers were used to experimentally study the process of anaerobic fermentation biogas production at thermophilic temperature（52±1）℃by cattle manure with different initial TS,and measured the temperature,apparent viscosity,density,TS,daily gas production,cumulative gas production,CH₄ volume fraction,CO₂ volume fraction,daily methane production,cumulative methane production and pH value of cattle manure during the whole anaerobic fermentation process,and analyzed the effects of temperature and anaerobic digestion time on its rheological properties and gas production law.The main results of this paper are as follows:（1）With the increase of temperature,the apparent viscosity of the cattle manure with initial TS of 15%and 8%both showed a decreasing trend.Moreover,the decreasing trend of the apparent viscosity of cattle manure with TS of 15%was more obvious than that with TS of 8%.In addition,in the same temperature raising range,the larger the initial TS was,the biger the apparent viscosity was.（2）Under the condition of constant shear rate(1000 s^-1),through the linear regression line of lnη-1/T transformed by Arrhenius model,the flow activation energy of cattle manure with initial TS of 15%and 8%were 19.783 kJ/mol and 19.303 kJ/mol respectively.This result verified from the other hand that the larger the initial TS was,the thicker the cattle manure was,and the worse the fluidity was.Because the flow activation energy could be used as a measurement of the sensitivity of the apparent viscosity to temperature,the greater the flow activation energy,the more sensitive the apparent viscosity was to the change of temperature,and the worse the fluidity of the fluid was.（3）When the initial TS of 15%,the apparent viscosity of the cattle manure during the anaerobic fermentation process increased first,then decreased,and gradually became stable.It reached the maximum value of 4.39 mPa·s on the 2^th day of the reaction,and became stable after 48 days.At this time,the apparent viscosity was 1.00 mPa·s.When the initial TS of 8%,the apparent viscosity of the cattle manure decreased first and then increased,and then fluctuated with this change but the ultimate trend was decreasing.It reached the maximum value of 1.88 mPa·s on the 1^th day of the reaction.With the reaction going on,the final apparent viscosity was 0.79 mPa·s.At the same fermentation condition of thermophilic temperature（52±1）℃,the higher the initial TS was,the biger the apparent viscosity was.（4）The density of the cattle manure with initial TS of 15%and 8%both increased first and then decreased during the anaerobic fermentation process.When the initial TS of 15%,the initial density of cattle manure(the 2^th day)was 0.9916 g/cm³,and reached the maximum value of 1.1575 g/cm³ on the 6^th day of the reaction.With the reaction going on,the final density was 0.9480 g/cm³.In the whole process of anaerobic fermentation,the range was0.9480 g/cm³ to 1.1575 g/cm³.When the initial TS=8%,the initial density of cattle manure(the 2^th day)was 0.9619 g/cm³,and reached the maximum value of 0.9942 g/cm³ on the 4^thh day of the reaction.With the reaction going on,the final density was 0.8945 g/cm³.In the whole process of anaerobic fermentation,the range was 0.8945 g/cm³ to 0.9942 g/cm³.（5）Due to the influence of material deposition,most of the solid substances in the cattle manure were distributed in the lower layer of the reactor.With the reaction going on,the cattle manure in the reactor was gradually degraded and transformed,and the solid substances was gradually reduced,so the TS of the cattle manure was always reduced.When the initial TS of 15%,the range was 20.93%⁴.85%,when the initial TS of 8%,the range was10.37%¹.87%.（6）The anaerobic fermentation system could achieve constant temperature（52±1）℃fermentation for the cattle manure.When the initial TS of 15%,the peak daily gas production was 20.59 L,the cumulative production of biogas was 210.23 L,the volume gas production rate was 0.42 L/（L·d）,the periodic dry matter gas production rate was 0.17 m³/kg TS,the average CH₄ volume fraction was 51.7%,and the average CO₂ volume fraction was 41.6%,the cumulative methane production was 116.865 L,and the average methane production was2.34 L/d.When the initial TS of 8%,the peak daily gas production was 15.94 L,the cumulative production of biogas was 169.08 L,the volume gas production rate was 0.34L/（L·d）,the periodic dry matter gas production rate was 0.27 m³/kg TS,the average CH₄volume fraction was 49.6%,and the average CO₂ volume fraction was 42.6%,the cumulative methane production was 93.553 L,and the average methane production was 1.87 L/d.（7）The pH value of the cattle manure with initial TS=8%and TS=15%decreased rapidly in the initial stage of fermentation.With the reaction going on,the pH value increased and gradually became stable.