Pilot-scale investigation of polyhydroxyalkanoates synthesis using mixed microbial cultures from fermented thermally hydrolyzed sludge.

A pilot-scale method for the sludge-based biosynthesis of polyhydroxyalkanoates (PHA) was constructed to address excess sludge disposal and reduce PHA production costs. Thermally hydrolyzed sludge (THS) was fermented and subjected to liquid separation to obtain a filtrate containing > 13,000 mg/L volatile fatty acids (accounting for 50 % of the soluble chemical oxygen demand). Using this filtrate as the substrate, a PHA-accumulating mixed microbial culture (Brachymonas 76 %) was successfully enriched. When the filtrate was used as the sole carbon source, the maximum PHA content reached 43 % of the dry cell weight (DCW) with DCW being 1.902 g/L. After adjusting the C/N ratio of the filtrate from 7.7 to 15 by adding carbon sources, the PHA production was further improved, achieving a PHA content of 45 % of DCW and DCW was 3.749 g/L. This pilot-scale study establishes a closed-loop system for efficient sludge resource utilization by converting sludge into high-value PHA.