Anaerobic Co-Digestion of Wastewater Sludge: A Review of Potential Co-Substrates and Operating Factors for Improved Methane Yield

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.

Bioelectrochemical Methane Production from Food Waste in Anaerobic Digestion Using a Carbon-Modified Copper Foam Electrode

“…It is in agreement with the higher methane production obtained in the ABD reactor, which is attributed to the DIET pathway activated by electroactive bacteria. It is well known that excessive acidification usually occurs in the anaerobic digestion of food waste, which could destroy the balance of acidogenesis and methanogenesis [7,35]. However, in the ABD reactor, both pH and alkalinity showed stronger process stability compared to the control reactor.…”

The effect of brewery spent grain application on biogas yields and kinetics in co-digestion with sewage sludge

“…Interestingly, a major decline was noted when HRT were shortened to 18 d. The observed tendency might indicate the process inhibition caused by significant VFA concentration in the BSG (Table 2). Its high concentration in AD may lead to a decrease in pH value resulting in acidification and the creation of conditions which are especially toxic for methanogens (Murto, Bjórnsson & Mattiasson, 2004), thus contributing to a decrease in methane production and finally to the process failure (Angelidaki, Ellegaard & Ahring, 1999;Chen, Cheng & Creamer, 2008;Franke-Whittle et al, 2014). Moreover, the possible occurrence of phenolic compounds, formed through BSG drying and milling may affect the process performance (Sežun et al, 2011;Retfalvi, Tukacs-Hajos & Szabo, 2013;Sawatdeenarunat et al, 2015).…”

Optimisation and Modelling of Anaerobic Digestion of Whiskey Distillery/Brewery Wastes after Combined Chemical and Mechanical Pre-Treatment

“…The strength of the model terms on CO 2 content of generated biogas by AD pot ale and spent grain pot ale mixture was defined as C 2 > BC > B >C and C 2 > C > BC > B based on the coefficient of the final equation in terms of coded factor (Equations (10) and (11)). The final mathematical models on CO 2 content of produced biogas are given in Equations (12) and (13).…”

“…Due to the high organic content, large disposal volume, and the acidic nature, pot ale is the major concern of the waste management of whiskey distilleries. As such, AD with advantages over other waste management methods like low energy requirement, odour limitation, less by-product generation, and higher ability to cope with recalcitrant nature of whiskey distillery/brewery waste streams is a suitable alternative waste treatment method [9][10][11][12]. There are four main stages in the AD process-namely hydrolysis, acidogenesis, acetogenesis, and methanogenesis-and the reactions in each stage are carried out by different bacteria.…”