| Managing food waste by dry mesophilic anaerobic digestion technology, has theadvantage of high utilization of the reactor volume and low output of digestive. Studieshad shown that the composition, temperature, TS, stirring intensity and particle size andother factors of the food waste would effect anaerobic digestion reactor gas productionefficiency and operational stability, these factors could also influence the rheologicalproperties of anaerobic digestion sludge, which would change the heat and mass transferof materials, thereby affecting other factors that relevant the stable operation of thereactor.This paper takes anaerobic digestion sludge of food waste as research object,investigating the rheological property of anaerobic digestion sludge by usingsequencing batch reactor first, on which basis, operates semi-continuous anaerobicdigestion reactor, combining reactor operating characteristics under high total solidcontent and high organic load, in order to evaluate the feasibility of taking dynamicviscosity as indicators to assess the reactor run stability to provide basic data foroptimization the operation of dry anaerobic digestive system.①Rheological characteristic study for mesophilic anaerobic digestion sludge offood waste in sequencing batch reactorIn sequencing batch reactor,taking anaerobic digestion sludge of food waste as theresearch project to study the relationship sludge between rheology with total solid (TS)content and shear rate (γ), then investigate the time-related property and thixotropic ofdigested sludge. Dynamic viscosity determined by a rotary viscometer, TS was22.48%~12.09%, the shear rate (γ) was2.09s-1~41.8s-1during test.②Operating characteristics of semi-continuous reactor under high total solid andrheological properties of anaerobic sludge in reactor.Conducting mesophilic anaerobic digestion of food waste in semi-continuousreactor, combining the operating characteristic of reactor under high total solid content(TS21.41%~29.54%) and high organic load rate (4.5~5kgVS·m-3·d-1), to assess thefeasibility for taking dynamic viscosity as a indicators of reactor running stability.Taking sludge rheology test as the research project by using anaerobic digestedsludge of food waste in semi-continuous reactor to study the effect of temperature (T),total solid content (TS) and shear rate (γ) to the rheology of anaerobic digested sludge. the temperature range was20℃~70℃, TS21.41%~29.54%, shear rate (γ) of2.09s-1~41.8s-1during test.The results showed that the reactor is easily suppressed when TS exceeds27%andthe organic load rate exceeds5kgVS·m-3·d-1, Organic loading capacity of systemdecreased, when the TS increased; dynamic viscosity can be used as index to evaluateoperating stability of reactor. Compared to the normal operating phase, the dynamicviscosity of sludge get lower during suppression state. The inhibition to anaerobicdigestion sludge would cause irreversible effects to sludge activity and the capacity ofthe system would be significantly reduced for the secondary organic load.The results showed that the fluidity of the sludge enhanced when the temperatureincreased and temperature decreasing led to the fluidity reducing. The variation intemperature caused irreversible effects for sludge rheology. The dynamic viscosity gothigher when TS of sludge increased. Viscosity curves illustrated that the anaerobicdigestion sludge, known as a non-Newtonian fluid, possesses the shear-thinningcharacteristic. The curves of shear stress-shear rate demonstrated that the anaerobicsludge was time-related fluid. Viscosity-time curves further implied that anaerobicdigestion sludge was thixotropic fluid. The stirring system is essential when theTS>12%, and controlling the shear rate between10.4s-1to20.9s-1is properly. Theeffects of temperature, TS and shear rate on rheology get more obviously when TScontent increase. Experiment results can provide basic data for the design of stirredsystem and heat exchange system of anaerobic digestion. |
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