Optimized process for the odd‑carbon volatile fatty acids (OCFA) directional production: Anaerobic co-digestion of disused grease with sludge by anaerobic sequencing batch reactor

Abstract

Odd‑carbon volatile fatty acids (OCFA) are a kind of desired carbon source for biological nitrogen and phosphorus removal (BNR) and the synthesis of polyhydroxyalkanoates (PHAs). This study explored and realized the directional production of OCFA continuously and steadily in the process of anaerobic co-digestion with disused grease and aerobic sludge. For that purpose, the anaerobic sequencing batch reactor (ASBR) was performed under 9.64 ± 0.5 g/L of mixed liquid suspended solids (MLSS) and 7.14-d hydraulic residence time (HRT) conditions. On focus, the initial NH4+ concentration of each cycle was adjusted to enrich propionic acid and maintain the stable operation of ASBR for the directional production of OCFA. Experimental results demonstrated that this process facilitated the enrichment of associated propionic acid-generating bacteria with the maximal OCFA yields of 3889.24 mg/L. Volatile fatty acids (VFAs) yield (2240.06–2941.12 mg/L), OCFA/VFAs (86.48–90.95%) and various ecological conditions gradually stabilized during the operation of ASBR. Moreover, the concentration of inorganic ion: PO43− (22.65–28.15 mg/L) and NH4+ (63.01–108.94 mg/L) were within the regulatory range available for downstream processes. Therefore, the ASBR process can be used for the continuous and stable production of OCFA.