Integrated Simulation of Wastewater Treatment, Sludge Pre- Treatment and Anaerobic Digestion

Combined lab testing and model application was conducted to develop an approach to model TH pretreatment of sludges prior to anaerobic digestion. Anaerobic degradability of a variety of raw and thermal hydrolysis pretreated sludges were evaluated in batch digestion tests. The batch test provides an effective approach to evaluate the stoichiometric conversion of constituents thus providing a good understanding of the extent of digestion, especially if the influent and effluent constituents are properly measured. The raw sludge characteristics were estimated by simulation of the full scale wastewater treatment plant and then employed as input parameters for simulation of the batch digestion tests. In this batch digestion simulation study, TH-treatment did not appear to enhance the ultimate digestibility of the sludges tested. The existing model was capable of simulating the observed overall COD removal and CH4 generation responses of both the raw and TH-treated sludges. Hence, TH treatment did not appear to convert any non-biodegradable COD fractions to biodegradable fractions. However, examination of the simulated fractions suggested that the particular characteristics of the sludges tested in this study were the reason for the negligible increase in biodegradability for the TH-treated samples. This result reinforces the need to consider the characteristics of the sludge source when assessing biosolids treatment. The use of modeling is essential in this regard. Soluble COD concentrations for raw sludge digestions were adequately simulated with the existing model. Simulated residual soluble COD concentrations for TH-treated sludges were consistently less than the observed values, thus suggesting that TH-treatment of sludges formed non-biodegradable soluble COD.