Mixed culture resource recovery from industrial waste glycerin pitch: Microbial analysis and production of bio-flocculants extracellular polymeric substances

Conventional glycerin pitch (GP) waste management strategies exacerbate environmental pollution. Resource recovery from GP has been demonstrated using chemical methods and fermentation using pure cultures, but the use of mixed cultures remains undetermined. Thus, our previous study investigated the potential of mixed cultures resource recovery from GP where we have successfully cultivated microorganisms from activated sludge to produce extracellular polymeric substances (EPS) and polyhydroxyalkanoates (PHA) from GP. In this study, microbial community of the enriched microorganisms was characterized and the potential of EPS as bioflocculants was investigated. Cultivation reactor performance and bioinformatic analyses revealed that the aerobic dynamic feeding strategy cultivated EPS producers such as Rhodocyclaceae Thauera (18.62 %), Rhodanobacteraceae Dokdonella (9.26 %) and Phacelicystidaceae Phaselicystis (2.39 %). Batch tests with 1.5 g C/L GP revealed that the enriched microorganisms could remove the organic compounds in GP by 83 % to produce 128 mg EPS/g volatile solids. The EPS extracted displayed optimal kaolin flocculation activities of 100 % at 2.5 mL dosage and pH 7 using 1 % (w/v) calcium chloride. The EPS were also reported to have optimal flocculation activities of 71 % and 100 % with real oleochemical wastewater, WW1 and WW2, respectively at 7.0 mL dosages and pH 7 using 8 % (w/v) calcium chloride. The study proposes using mixed cultures to convert GP into EPS for use as bio-flocculants, which would introduce a circular economy concept in the oleochemical industry.