Acidogenic fermentation of organic residual solids from municipal solid waste

Abstract

Solid waste represents a threat to the environment and human health. Organic residues can be converted to valuable products through biological processes, reducing the volume and risks associated to the degradability of the waste. Acidogenic fermentation (AF) is the mixed-culture microbial conversion of organics to volatile fatty acids (VFA), such as acetic, propionic, and butyric acids. VFA are chemical platforms used for the synthesis of high value-added products. There is currently a lack of understanding on mechanisms to control pathways to avoid unwanted by products; and maximise VFA yields. In this thesis, organic residual solids (ORS) have been used as substrate to study the effect of different fermentation conditions such as pH, hydraulic retention time, carbon to nitrogen ratio, CaCO3 addition, urea addition, feeding mode, inoculum pre-treatment, and enzymatic pre-treatment. It was found that fermentation conditions highly influence the type of VFA generated and the VFA yield. Fed-batch feeding mode resulted in increased VFA concentrations and yields; and longer chain fatty acids were produced. A large-scale process was also proposed followed by an economic assessment of the AF process using ORS as substrate, further demonstrating the economic potential of biological waste conversion to high-value products. The assessment concluded that most of the variable operational cost is due to feedstock pre-treatment and product recovery, due to the high cost of enzymes and the energy required for VFA recovery.

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ORCID for Yue Zhang: orcid.org/0000-0002-5068-2260

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