Initial pH Conditions Shape the Microbial Community Structure of Sewage Sludge in Batch Fermentations for the Improvement of Volatile Fatty Acid Production

Abstract

Conversion of wastewater treatment plants into biorefineries is a sustainable alternative for obtaining valuable compounds, thus reducing pollutants and costs and protecting the environment and human health. Under specific operating conditions, microbial fermentative products of sewage sludge are volatile fatty acids (VFA) that can be precursors of polyhydroxyalkanoate thermoplastic polyesters. The role of various operating parameters in VFA production has yet to be elucidated. This study aimed to correlate the levels of VFA yields with prokaryotic microbiota structures of sewage sludge in two sets of batch fermentations with an initial pH of 8 and 10. The sewage sludge used to inoculate the batch fermentations was collected from a Sicilian WWTP located in Marineo (Italy) as a case study. Gas chromatography analysis revealed that initial pH 10 stimulated chemical oxygen demands (sCOD) and VFA yields (2020 mg COD/L) in comparison with initial pH 8. Characterization of the sewage sludge prokaryotic community structures—analyzed by next-generation sequencing of 16S rRNA gene amplicons—demonstrated that the improved yield of VFA paralleled the increased abundance of fermenting bacteria belonging to Proteobacteria, Bacteroidetes, Chloroflexi, and Firmicutes phyla and, conversely, the reduced abundance of VFA-degrading strains, such as archaeal methanogens.

Study on the effect of alkali on the production of volatile fatty acids from rhamnolipid‐alkali‐thermal pretreated waste activated sludge

“…Consequently, it comprehensively impacts the fermentation acidification efficiency of the sludge. 22 Research has also confirmed that higher VFAs yields are obtained under alkaline conditions. Therefore, investigating the mechanism of alkali in the combined pretreatment process of rhamnolipids-alkali-thermal is crucial for a comprehensive understanding and application of this technology.…”

“…The addition of NaOH not only affects the changes in sludge disintegration, organic matter composition, and dissolution concentration during the pretreatment stage but also influences the characteristics of microbial community in the subsequent anaerobic fermentation stage. Consequently, it comprehensively impacts the fermentation acidification efficiency of the sludge 22 . Research has also confirmed that higher VFAs yields are obtained under alkaline conditions.…”