Effects of sulfite and freezing co-pretreatment on the volatile fatty acids production of waste activated sludge in anaerobic fermentation

Volatile fatty acids (VFAs) produced during the anaerobic fermentation of waste activated sludge (WAS) are renewable energy sources. However, the biodegradability of untreated WAS is significantly low, thereby imposing a substantial constraint on the generation of VFAs during anaerobic fermentation of WAS. In this study, the experimental results showed that freezing and sulfite co-pretreatment had a synergism on the disintegration of WAS and the production of VFAs. The optimal freezing temperature for VFAs production were-20 C-degrees, 8 h and sulfite dosage of 1400 mg/L resulted in the VFAs reaching a highest concentration of 627.58 mg/L, which was 17.41 times higher than that of the blank group. In addition, the disintegration effect of WAS has been improved, the concentration of soluble chemical oxygen demand (SCOD), proteins and polysaccharides were 7.21, 5.56 and 2.58 times than the blank group, respectively. The microbial community analysis revealed an increase of the OUT of co-pretreatment. Also showed that co-pretreatment could increase the abundance of Levilinea, Unclassified_Anaerolineaceae and Blvii28_wastewater_sludge_group, which might increase VFAs production. Furthermore, compared to sulfite pretreatment or freezing pretreatment, the co-pretreatment significantly enhanced the disintegration efficiency of WAS; shortened the hydrolysis required time for WAS; provided the higher concentration of substrates for VFAs production; and improved the overall efficiency of sludge anaerobic fermentation.