New insight into Fe(VI)-driven carbon migration and recovery in short-term anaerobic fermentation of waste activated sludge

Abstract

The short-chain fatty acids produced from waste activated sludge were deemed as the preferred carbon sources, however the specific carbon migration and recovery patterns have been rarely reported. This study demonstrated that Fe(VI) was capable of driving interphase carbon release and biotransformation towards carbon recovery in short-term anaerobic fermentation (48 h). Interestingly, the Fe(VI)-derived alkaline condition played the foremost and continuous driving force in interphase carbon migration with the proportions of 50.53–70.52 %, while the advanced oxidization provided the second most contributions of 25.46–45.82 % in short-acting role. Correspondingly, numerous extracellular and intracellular carbon sources of 136.66 mg C/g VSS were released in 4-h Fe(VI) treatment by structural protein molecule loosening, which were mainly composed of proteins (tryptophan and tyrosine), polysaccharides and humic acids. Meanwhile, 48.73 % of the dissolved carbon sources were bio-transformed for improving sludge acidification, contributing to the overall carbon recovery of 63.68 mg C/g VSS. The effective carbon source extraction was implemented by solid–liquid separation. The high C/N in fermentative liquid was achievable, suggesting considerable bio-availability of the recovered carbon sources. This indeed created economic benefits and carbon-emission reduction depending on alternative carbon source utilization and residual sludge solid reduction.