PHA Production and Wastewater Treatment With Phototrophic Purple Bacteria: Effect of Transitioning OLR and HRT on Biopolymer Composition and Process Yield

This study investigated the effect of transitioning organic loading rates (OLR) and hydraulic retention times (HRT) on polyhydroxyalkanoates (PHA) production from wastewater using PHA‐accumulating phototrophic purple bacteria. These bacteria were cultivated under light‐feast anaerobic conditions in a photo‐assisted continuous stirred tank reactor (P‐CSTR) fed with acidogenic fermented cattle manure and sugarcane molasses. Transitioning OLRs of 0.7, 1.6, and 2.0 g COD/L.d were tested, followed by HRTs of 48, 72, and 112 h at the optimal OLR. The desired conditions to boost PHA production were an OLR of 0.7–1.2 g COD/L.d and HRT of 112 h, attaining a maximum PHA accumulation of 86.3% g PHA/g VSS, and production yield of 94.5% g COD PHA /g COD removed . The system also indicated efficient pollutant elimination of 96.6% NH 4 ‐N, and 82.5% COD. Shorter HRTs (48 h) were less effective in COD removal but promoted higher poly‐3‐hydroxyvalerate production in the copolymer content (48.8% of PHA). In contrast, poly‐3‐hydroxybutyrate content increased at high OLRs. The results highlight that transitioning OLR and varying HRT significantly influenced the process performance, PHA accumulation yield, and biopolymer quality. Thus, OLR and HRT are the critical control parameters for optimizing PHA production, tailoring polymer properties, and ensuring enhanced wastewater treatment.