To What Extent Can Thermal Hydrolysis Improve the Biodegradability of Municipal Sludge

Thermal hydrolysis Pretreatment (THP) has been full-scale implemented as a pretreatment means to expedite the rate of municipal sludge anaerobic digestion (AD). However, it is generally unknown how much methane potential remains after the primary TH-AD, and whether a secondary TH can further enhance the recovery of the residual methane potential. In this study, a biological methane potential (BMP) test was first performed on the digestate collected from a pilot-scale TH-AD process to exhaust its digestibility. After that, the sludge was processed in a secondary TH again and then run through another round of BMP test to check whether the TH has conferred new biodegradability on the sludge. Results showed that another 15% more methane can be further recovered. It was interesting to observe that this extra methane was recovered from the soluble COD produced during the secondary TH. Hence, it can be concluded that TH is capable of turning recalcitrant particulate biomass into biodegradable soluble organics. Several mechanisms responsible for the secondary TH enhancement was discussed