Sludge Incineration Bottom Ash Enhances Anaerobic Digestion of Primary Sludge toward Highly Efficient Sludge Anaerobic Codigestion
Wei Wei, Xiaoqing Liu, Lan Wu, Dongbo Wang, Teng Bao, Bing‐Jie Ni
Abstract
In wastewater treatment plants (WWTPs), two main sludge streams, i.e., primary sludge (PS) and waste activated sludge (WAS), are generally mixed for anaerobic codigestion. However, the methane production is usually restricted by the poor and slow biodegradability of PS, and an effective approach for its efficient codigestion with WAS is still lacking due to its highly different sludge properties from those of WAS. Herein, we reported a novel strategy through using the sludge incineration bottom ash to enhance the anaerobic digestion of PS and its codigestion with WAS. Biochemical methane potential (BMP) test results showed that ash additive at 0.6–1.2 g/g-dry matter (DM) significantly enhanced PS anaerobic digestion, identified by an up to 18.2% increase in specific methane production. This was accompanied by a significantly improved dewaterability in the digestate. The transformations of metabolic intermediates revealed that the ash additive accelerated the hydrolysis and acidogenesis processes, which were also supported by the increased hydrolysis rate (k) of PS determined through kinetic modeling. Ash additive was then experimentally demonstrated to be effective in enhancing the anaerobic codigestion of PS and WAS, with the increased volatile solids (VS) destruction being approximately 19.8%, representing a reduction of digestate volume by 12.6%. The novel strategy proposed in this study provides a new paradigm of an integrated sludge-control by sludge to bring significant economic benefits to wastewater treatment and sludge disposal.