(3cz) Process Optimization and Economic Analysis of the Production of Biocrude and Other Lipidic Materials by Sewage Sludge Microorganisms In Wastewater Treatment Plant Biorefineries

Municipal wastewater treatment plant activated and anaerobic digester sludges present an abundant source of lipidic materials in its raw form or after enhancement via manipulation of cultivation conditions. Initial studies found that the enhancement process, which involves the batch cultivation of activated sludge in a high carbon-to-nitrogen (70:1) ratio wastewater medium with a high sugar load (60 g/L), increased its lipid content by 70 % compared with raw activated sludge. Biodiesel yield from the enhanced activated sludge also reached 10 % CDW compared to 2 – 3 % in raw sludge. However, the conversion of substrate to lipids was relatively lower than those observed in most pure cultures of oleaginous microorganisms. Optimization of specific environmental parameters of the batch fermentation process was conducted, particularly the culture pH, since changes in culture pH levels are known to significantly affect the composition of the microbial community in activated sludge. The effect of the culture pH was investigated by testing different fermentation runs with controlled pH levels of 4, 7, and 10 and compared with previous results wherein pH levels were uncontrolled. Subsequently, different feeding regimes and fermentation modes (discontinuous fed-batch, semi-continuous feeding, continuous) were also tested to improve lipid yields and conversion. The enhancement process was also applied to anaerobic digester sludges in order to asses the potential of extracting lipids and other high value products from all sludge streams and reduce the output of waste sludges from wastewater treatment facilities. The lipid extracts obtained from raw and enhanced sludges were then fractionated using polar and nonpolar solvents and characterized using gas chromatographic methods to determine the identities and profiles of the lipidic materials and determine their potential applications. Process and economic analysis of the process was conducted with the aid of the SuperPro^® simulation software in order to design and evaluate the proposed wastewater treatment plant biorefinery concept in an industrial scale.