Year

2017

Degree Name

Master of Philosophy (Environmental Engineering)

Department

School of Civil, Mining and Environmental Engineering

Abstract

Anaerobic digestion (AD) is a biological process in the absence of oxygen to stabilize organic waste while producing biogas, a mixture formed mainly of methane and carbon dioxide. Mono AD using a single substrate has some inherent drawbacks associated with the risk of imbalance carbon over nutrient (C/N) ratio and low biogas yield. Thus, anaerobic co-digestion (AcoD) has recently emerged as a promising option to overcome these disadvantages of mono-digestion and to improve the economic feasibility of biogas production at wastewater treatment plants (WWTPs). In the context of a WWTP, AcoD can be defined as the AD process involving sewage sludge and one or several other organic waste materials (such as food waste and fat oil and grease). While the potential of AcoD to enhance biogas production is attractive, there remain several challenges to be addressed in the large-scale AcoD operation. For example, both synergistic and antagonistic effects during AcoD have been reported in the literature. Thus, it is imperative to determine a suitable range of organic loading at which the synergistic effect of AcoD can be realised. In addition, most AcoD investigations reported to date were at small lab scale level, and thus, findings from these previous studies may not be directly applicable to full scale operation.

This thesis work consists of two components. In the first component, the relationship between organic loading and the synergistic effects during AcoD of sewage sludge and food waste was explored through systematic biomethane potential (BMP) evaluation. The specific objectives include (i) evaluating the process performance and stability from total solids (TS), VS, and soluble chemical oxygen demand (COD) removal, (ii) determining the hydrolysis rate constant (Kh) based on the reaction kinetics, (iii) appraising the biomethane yield and the synergistic effect at various organic loadings. The second component involves pilot-scale evaluation of AcoD of sewage sludge and several different waste beverages (hereon referred to as beverage rejects). These beverage rejects are alcoholic and non-alcoholic drinks that were discarded during production or distribution due to various reasons (e.g. contamination, damage during transportation and storage, and expired products).

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.