Research On The Variation Regulation Of Rheological Properties Of Sludge And Its Influencing Factors

In recent years, the problem of sludge treatment and disposal has become increasinglyprominent with the rapid construction of sewage treatment facilities. And the anaerobicdigestion has become an important sludge biological treatment technology because of itsunique advantages, such as low consumption and high efficiency, small environmental impact,generating new energy and so on, but the operation effect of anaerobic digestion of sludge inChina is not ideal. The rheological characteristics of anaerobic digestion of raw materials is animportant parameter for the design and operation of anaerobic digestion process, which hasgreat influence on the stirring, mass transfer, heat transfer of anaerobic digestion and thetransportation of sludge. Thus, it is necessary to study the variation regulation of rheologicalproperties of sludge and its influencing factors, in order to play a guiding role for thedevelopment of anaerobic digestion.In this article, firstly, the physicochemical properties and rheological characteristics ofsludge of a municipal wastewater treatment plant in Beijing was analyzed, and the modelfitting of its rheological properties was conducted, and then the impact of water content ofsludge and temperature on the rheological properties was analyzed. As concentrated sludgeand digested sludge were the feeding and discharging of the anaerobic digestion tank,respectively, it could be known that how the rheological properties of sludge changed afteranaerobic digestion through the comparison of their rheological characteristics, therefore, acontrastive analysis of rheological characteristics of concentrated sludge and digested sludgewas made. Taking into account that the hydrolysis and fermentation stage was the limit step ofanaerobic digestion, the pretreatment of sludge can improve this situation, and it also hadimpact on the rheological properties, so the rheological properties of the pretreated sludge andraw sludge was also compared. The specific results were as follows:(1) The water content of concentrated sludge and digested sludge after dewatering wasabout80%. The degradation of organic matter in the sludge was35.04%through mesophilicanaerobic digestion. The pH value of the sludge was6.94~7.92, which belonged to the rangeof neutral to slightly alkaline. In addition to cadmium, mercury, the content of heavy metals inthe sludge did not exceed the standard, and they were significantly lower than the nationalstandard values.(2) With the increase of the shear rate, the shear stress of sludge increased, and itsviscosity decreased. A shear thinning phenomenon was exhibited, and it instructed that thesludge is a pseudoplastic fluid. The Ostwald de Vaele model, i.e. the power law model, is themost suitable for fitting the rheological characteristics of the sludge. The rheologicalparameters of the sludge varied with the change of the water content and temperature, and thesludge with high water content tended to display the characteristics of Newton fluid.(3) The differences of rheological parameters of concentrated sludge and digested sludgevaried with the variation of the water content, and it depended on the degree of fixing EPStransferred into soluble EPS and the level of the organic matter degradation in the process of anaerobic digestion. At the same shear rate, both the viscosity and shear stress of the twokinds of sludge decreased with the increase of temperature, but the range of the viscosity ofthe digested sludge was smaller than the concentrated sludge.(4) Overall, the first2hours of the alkali pretreatment was the efficient time of alkali,while for heat pretreatment and thermo alkaline pretreatment, the efficient time was the first0.5hour. No matter which kind of pretreatment methods was used to deal with the sludge, itsshear stress and viscosity would increase at the same shear rate. The sludge with watercontent of90%showed special variation regulation, and its reason needed further study.