Evaluation of Ca(OH)2 disintegration on high-solid sludge floc structures and subsequent anaerobic digestion

Abstract

Lime pretreatment was tested at different doses on high-solid sludge. Subsequently, the effects of this pretreatment were investigated in terms of the damage of extracellular polymeric substance and cell structures and the subsequent high-solid anaerobic digestion (HSAD). Moreover, the relationship between them was discussed. Results showed that higher lime dose was favorable to COD solubilization, wherein more proteins were released than carbohydrates under the same lime dose. When lime dose was below 0.04 g/g-TS, the COD solubilization was mainly caused by the disintegration of EPS, and when the lime dose was higher than 0.06 g/g-TS, the damages of cell walls and membranes were observed and led to the further COD solubilization. The HSAD process was accelerated by 7–16 days after lime pretreatment, and the biogas production increased by 22.9%–34.8% when lime dose was higher than 0.04 g/g-TS. Thermogravimetric analysis results suggested that Ca2+ could be removed from the liquid phase by precipitating with the CO2 produced during the HSAD process, thereby increasing the methane content.