Production of medium-chain carboxylic acids using sewage sludge pretreated by combined Fenton and persulfate oxidation

Abstract

Medium chain carboxylates (MCCs) production from sewage sludge (SS) is an economically and environmentally feasible technology for recovering value-added chemicals from SS. To improve MCCs production from SS, Fe (II)-mediated advanced oxidation processes (AOPs) including Fenton oxidation (FO), persulfate oxidation (PO), and combined Fenton-persulfate oxidation (CFP) were adopted to examine their effect on fermentation. Highest total MCCs concentration of 3445.85 mg COD/L was achieved in CFP treated group, followed by PO treated group (2678.78 mg COD/L), control group (2367.72 mg COD/L) and FO treated group (2294.14 mg COD/L). MCCs produced in all groups were dominated by caproate, and all three AOPs treatment promoted longer-chain MCCs (i.e. heptylate and caprylate) production. Microbial analysis showed that genus Romboutsia, Paraclostridium, Clostridium_sensu_stricto_1, norank_f_Anaerolineaceae and Acetobacterium that were positively correlated with MCCs production were significantly enriched in CFP treated group, which contributed to the highest MCCs production in CFP treated group. The functional enzymes analysis showed that both PO and CFO treatment promoted MCCs production by strengthening the fatty acid biosynthesis pathway during the chain elongation (CE) process.