Effects of stepwise thermal hydrolysis and solid-liquid separation on three different sludge organic matter solubilization and biodegradability

Separate digestion after pretreatment could be a promising process for sludge treatment. In this study, a novel process coupling two-step thermal hydrolysis pretreatment (THP) and separate digestion of liquid and solid fractions was applied on three different sludge to investigate the organic components solubilization and methane production potentials based on mass balance. Results showed that 61.94-69.08% of protein and 84.19-86.75% of polysaccharides were dissolved, while only 35.20-38.55% and 61.61-69.92% were detected in the liquid fraction, respectively. This indicated that not only disintegration and dissolution, but also hydrolysis occurred during THP. Organic matter was mainly dissolved in the first-step THP, and protein and VFAs were the main components. Although separate digestion did not improve the total methane production, the liquid fractions contributed 51.08-73.92% to the sum of liquid and solid fractions. The organic solubilization and biogas production are essentially related to the organic components, instead of the total organic content.