Abstract
Anaerobic digestion has been widely employed in waste treatment for its ability to capture methane gas released as a product during the digestion. Certain wastes, however, cannot be easily digested due to their low nutrient level insufficient for anaerobic digestion, thus co-digestion is a viable option. Numerous studies have shown that using co-substrates in anaerobic digestion systems improve methane yields as positive synergisms are established in the digestion medium, and the supply of missing nutrients are introduced by the co-substrates. Nevertheless, large-scale implementation of co-digestion technology is limited by inherent process limitations and operational concerns. This review summarizes the results from numerous laboratory, pilot, and full-scale anaerobic co-digestion (ACD) studies of wastewater sludge with the co-substrates of organic fraction of municipal solid waste, food waste, crude glycerol, agricultural waste, and fat, oil and grease. The critical factors that influence the ACD operation are also discussed. The ultimate aim of this review is to identify the best potential co-substrate for wastewater sludge anaerobic co-digestion and provide a recommendation for future reference. By adding co-substrates, a gain ranging from 13 to 176% in the methane yield was accomplished compared to the mono-digestions.
Highlights
Many industries face difficulties in treating their high-strength wastewaters
This review aims to serve as a guideline for other researchers to achieve optimum operating conditions for co-digestion leading to minimal operational problems and maximum biogas production
These two studies indicated that a higher portion of the food waste (FW)/FVW co-substrate brought about enhancement in methane yield compared to mono-digestion of wastewater sludge alone
Summary
Wei Ling Chow 1 , Siewhui Chong 1 , Jun Wei Lim 2 , Yi Jing Chan 1, * , Mei Fong Chong 3 , Timm Joyce Tiong 1 , Jit Kai Chin 4 and Guan-Ting Pan 5, *. Received: 20 August 2019; Accepted: 20 September 2019; Published: 1 January 2020
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