Single-stage biopolymer production with yeast industry wastewater: effect of SRT and OLR on biopolymer production yield

Abstract

Polyhydroxyalkanoates (PHAs) are the most investigated biopolymers, which are released as intracellular granules by microorganisms and are gaining interest as a waste valorization product. Waste streams and activated sludge are attractive sources for reducing biopolymer production costs. High PHA production efficiency is achieved in pure culture and synthetic medium processes, whereas poor production yields are obtained with mixed microbial culture (MMC) and waste streams. In this study, different sludge retention times (SRT) (2, 4, and 6 days) were successfully operated with the activated sludge bacterial community under three different organic loading rates (OLRs) (0.5, 1, and 2 g COD/L.d.) by feeding the anaerobically treated yeast industry wastewater (YWW). The poly(3-hydroxybutyrate) (PHB) as the most common type of PHA was produced in the reactor where the enrichment and accumulation were achieved while YWW was used for both enrichment and accumulation phases. Under SRT-4 day and 2 g COD/L.d. OLR conditions, PHB content was found 30.18% (g PHB/g TSS). Fourier transform infrared spectroscopy (FTIR), thermo-gravimetric analysis (TGA), and molecular weight (M-v) analyses were performed to characterize the biopolymers generated from the MMC under various working conditions, and their properties were compared with commercial PHB. The PHB isolated from biomass has a crystalline structure, as demonstrated by the FTIR study. The biopolymer's M-v and degradation temperature were determined as 2.51 center dot 10(5) Da and 218 degrees C, respectively.