Thermal hydrolytic pre-treatment increased process efficiency and changed the microbial community structure in full- and laboratory-scale anaerobic co-digestion of sewage sludge and household waste. THP pretreatment study

Future estimated population increases and intensification of renewable energy production poses challenges on waste treatment plants to improve their effectiveness. This study examines the effects on full-scale anaerobic digestion of wastewater sludge and food waste by implementation of thermal hydrolysis process (THP) pretreatment. Whether the THP was vital to reach the higher process capacity required to meet the estimated population increase within the municipality was evaluated through batch trials and continuously-fed laboratory-scale digester operations. Performance data from full- and laboratory-scale digesters were collected and microbial community structure was evaluated via Illumina 16S rRNA gene sequencing. Implementation of THP at the full-scale plant increased the methane yield with 20% and enhanced the degradability. The results indicated that THP was not essential to increased capacity with maintained stability at the full-scale processes. However, extended sludge retention time, improved methane yields and hygenisation of the digestate were factors still highlighted by the plant to promote its installation. Comparing digester communities revealed clear differences in taxonomy after the THP installation, involving increased contribution of the Clostridia class in the full-scale digesters. Differentiated profiles in laboratory-scale digesters indicated that a slight temperature increase from 37 to 42°C in association with the THP installation and altered ratio of wastewater sludge versus food waste were strong deterministic factors for shaping of microbial communities. In overall, present study can aid full-scale plants in choosing management strategies with the attempt to improve anaerobic digestion processes