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Enhanced economic feasibility of excess sludge treatment: acid fermentation with biogas production

Mo-Kwon Lee, Yeo-Myeong Yun, Dong-Hoon Kim
Published: 16 May 2019
BMC Energy , Volume 1; doi:10.1186/s42500-019-0001-x

Abstract: The excess sludge (ES) generated from wastewater treatment plants entails high expenditure for its treatment and disposal. In this study, firstly, the influence of mild-thermal (70 and 90 °C) and alkali-(pH 10 and 11) pretreatment methods on solubilization and acid generation from ES was investigated. The experimental results showed that the solubilization (SCOD/TCOD) increased as pretreatment intensity increased (70 °C < 90 °C < pH 10 < pH 11). However, organic acids generation was not consistent with the increased solubilization (pH 11 < 70 °C < 90 °C < pH 10). As a result of microbial analysis through next generation sequencing (NGS), it was observed that microbial community structure was greatly varied depending on the pretreatment methods. Bacteroidetes (70.8%), and Firmicutes (58.1%) were found to be dominant at thermal conditions of 90 °C and pH 10. Furthermore, the solid residue after acids generation was subjected to anaerobic digestion (AD) for CH4 production. The economic assessment showed that the thermal pretreatment at 90 °C followed by acid recovery and AD process enhanced the net profit of the treatment process with a positive gain of 2.53 USD/ton of sludge. Meanwhile, the alkali-pretreatment at pH 11 showed a negative value of − 2.0 USD/ton of sludge.
Keywords: organic acids / anaerobic digestion / excess sludge / Solubilization / economic assessment

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