Influence of Substrate Load on Polyhydroxyalkanoates (Pha) Accumulation by Unenriched Mixed Cultures from Excess Sludge Fermentation Liquid

To reduce the production cost of polyhydroxyalkanoates (PHA) and disposal amount of excess sludge simultaneously, volatile fatty acids (VFAs) from alkaline excess sludge fermentation was used as carbon sources to synthesize PHA by unenriched mixed cultures. Released phosphorus and residual ammonium in the fermentative VFAs was controlled by adding magnesium to form struvite precipitation. Four VFAs liquids obtained was used to test the influence of initial carbon load and carbon to nitrogen ratio (C:N ratio) on the VFAs uptake rate, PHA storage rate and biomass growth rate. Results show that higher initial carbon substrate load results in relatively higher VFAs uptake rate and higher PHA storage rate, while higher initial C:N ratio results in relatively lower biomass growth rate from VFAs. VFAs generated from thermophilic alkaline sludge fermentation were a suitable carbon source for PHA production by mixed cultures.