Effects of Potassium Ferrate and Low-Temperature Thermal Hydrolysis Co-Pretreatment on the Hydrolysis and Anaerobic Digestion Process of Waste Activated Sludge

This study evaluated the effect of potassium ferrate (PF) and low-temperature thermal hydrolysis co-pretreatment on the promotion of sludge hydrolysis process and the impact on acid production in the subsequent anaerobic digestion process. The analytical investigations showed that co-pretreatment significantly facilitated the hydrolysis process of the sludge and contributed to the accumulation of short-chain fatty acids (SCFAs). The pretreatment conditions under the optimal leaching of organic matter from sludge were hydrothermal temperature of 75°C, hydrothermal treatment time of 12 h, and PF dosage of 0.25 g g−1 TSS (total suspended solids), according to the results of orthogonal experiments. By pretreatment under proper conditions, the removal rate of soluble chemical oxygen demand (SCOD) achieved 71.8% at the end of fermentation and the removal rate of total phosphorus (TP) was 69.1%. The maximum yield of SCFAs was 750.3 mg L−1, 7.45 times greater than that of the blank group. Based on the analysis of the anaerobic digestion mechanism, it was indicated that the co-pretreatment could destroy the floc structure on the sludge surface and improve organic matter dissolving, resulting in more soluble organic substances for the acidification process. Furthermore, microbial community research revealed that the main cause of enhanced SCFAs generation was an increase in acidogenic bacteria and a reduction of methanogenic bacteria.