Alkaline-thermal pretreatment was examined for waste activated sludge (WAS) disintegration and subsequent anaerobic digestion (AD). Pretreatment at 60 °C was estimated to provide better economic benefits than higher temperature conditions. The maximum methane yield of 215.6 mL/g COD was achieved when WAS was pretreated at 60 °C and pH 10 for 24 h, which was 46.6% higher than untreated WAS. The pretreatment condition also provided the maximum net savings. The degree of sludge disintegration, considering both loosely bound-extracellular polymeric substance and soluble COD, would be a better indicator to predict anaerobic digestibility than the solubilization rate that considers soluble COD alone. Microbial analysis implied that pretreatment facilitated the growth of hydrolytic bacteria, phyla Bacteroidetes and Firmicutes. In addition, sludge pretreatment enhanced the growth of both acetoclastic and hydrogenotrophic methanogens, genera Methanosaeta and Methanobacterium. The mild AT-PT would be useful to enhance the digestion performance and economic benefit of WAS digestion.
Keywords: Anaerobic digestion; Biogas; Economic assessment; Pretreatment; Waste activated sludge.
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