(604e) Discrete-Continuous Simulations for Performance Evaluation of Sequential Batch Reactor System for Lipid Accumulation from Volatile Fatty Acids By Activated Sludge Microorganisms Following Seasonal Stochastic Variations

An active research area on the sustainable production of fuels and chemicals is the use of wastewater sludge microorganisms to produce value-added substances. This use of undefined mixed cultures of microorganisms in wastewaters to produce bioenergy materials and other chemicals has been viewed as a new promising technology owing its advantages to lesser operating costs and more stability of the microbial systems involved as compared to using pure microbial cultures. One of the target products is biocrude oil (or biodiesel from microbes), which can be produced from the transesterification of microorganisms with high lipid content. It has been shown that return activated sludge (RAS) from wastewater plants can accumulate high lipid content by feeding on media with high carbon to nitrogen ratio using glucose and xylose as the carbon sources under aerobic incubation. The commercialization of the aerobic lipid accumulation by sludge, however, is challenged by the relatively high cost of the typical monosaccharide substrates glucose and xylose. An on-going study aiming to make this biocrude oil technology economical is the utilization as substrates the volatile fatty acids (VFAs) such as acetic acid, propionic acid and butyric acid produced from the anaerobic digestion of lignocellulosic biomass wastes. The VFAs, however, have inhibitory effects to some extent. A proposed technology that minimizes the inhibitory effect and promotes lipid accumulation from VFAs is a fed-batch reactor or sequential batch reactor (SBR). It is of interest to evaluate the performance of sequential batch reactor (SBR) system configurations that accept input sludge of microorganisms content that vary with the seasons year round.

The performance of a sequential batch reactor (SBR) system in processing the lipid accumulation from volatile fatty acids (VFAs) of activated sludge subject to the seasonal variation has been investigated. To capture annual variations of activated sludge concentration, data was collected from a wastewater treatment plant and the data fitting resulted to a distribution of GAMM (0.645, 12.4).  A continuous-discrete model of the SBR is then constructed in Arena® utilizing low to high level programming modules including the Visual Basic Application  (VBA) platform for the script of evaluating the differential equations describing the biological process of sludge on VFAs. Simulation results show that the economics of the process is dictated not only by the kinetics of the biological process but also by the logistics of the operation.