Research On The Rheological Behavior Of Biochemical Sludge And Its Influencing Factors

Since sludge is a non-Newtonian fluid, the rheological behavior of sludge can therefore have a significant impact on various processes in a wastewater treatment plants (WWTPs), such as fluid transportation, mixing, oxygen diffusion, mass transfer, anaerobic digestion, chemical conditioning and mechanical dewatering. These are key factors affecting the operation efficiency and the energy consumption of the entire process. Considering the importance of the rheological behavior of sludge, especially in the sludge management, treatment and disposal, this study focused on the rheological behavior of biochemical sludge and its influencing factors. We hope the presented analyses will be useful for optimizing the operation and management of WWTPs.Two main aspects were contained in this study:on one hand, this work investigated the rheological behavior of sludge in a long-running digester and tried to establish a timely approach for monitoring the torque information of an anaerobic process. For these purposes, multi-methods were taken into consideration. Firstly, the treatment effect of AD reactor to artificial wastewater and its operational state were studied, mainly through the related aspects, such as COD removal efficiency, biomass proliferation, Volatile Fatty Acid (VFA) and Extracellular Polymeric Substances (EPS) variations; Secondly, general rheological behaviors of the sludge were obtained using related models, so as to the variation of related rheological parameters (yield stress, consistency coefficient and flow index). Besides, thixotropic behavior of sludge during the operational period was mainly analyzed. Thirdly, focusing on the relationship between macro rheological behavior and microcosmic structure of sludge, the influences of sludge concentration and EPS on sludge limit viscosity were elaborated. The last but not least, correlate the relationship between the timely torque signals and the rheological behavior and try to provide a useful reference to simplify the complex rheology study. On the other hand, in the present investigation, the effects of MV irradiation on the rheological characteristics of sewage sludge were studied. Two key aspects were investigated:(1) investigating the variation of the rheological characteristics of sewage sludge in terms of apparent viscosity, yield stress, thixotropy after MV irradiation; and (2) the effects of MV irradiation on the microcosmic physico-chemical characteristics of sewage sludge in terms of particle size and distribution, zeta-potential, total solids (TS), and the polysaccharide and protein content in the sludge solids. In addition, we attempted to quantitatively describe various rheological behaviors using mathematical models.The specific results were as follows:(1) The on-line torque sensing approach was an efficient method to obtain timely torque signals, which could give a reliable prediction to the variation in the rheological behavior of sludge, and further provide useful information to monitor the operation of AD digester;(2) The thixotropic index of sludge in the digester decreased continuously along with the operational time, which showed a weakening tendency in the interaction among sludge particles;(3) Both the content of total solids (TS) and EPS had close relationships with the limit viscosity of sludge, but TS showed a positive impact, while, the impact of EPS was negative;(4) During the process of MV irradiation, two effects (evaporation and physical destruction of macromolecules) actually occur simultaneously. Significant changes of rheological behavior of the sludge samples before and after being treated with MV irradiation have been found. The changes in the microcosmic composition of sludge are direct reasons leading to the variation of apparent of rheological behavior.