Effect of pH control and uncoupled carbon and nitrogen feeding strategy on enrichment of mixed microbial culture for polyhydroxyalkanoates production

Abstract

Abstract Polyhydroxyalkanoates (PHA) production via a combination of mixed microbial culture (MMC) and waste carbon substrate has shown to be a more economical solution compared to pure culture process. Although crude glycerol has been proven as a promising feedstock, there are still limited study on the effect of operating conditions such as pH and nutrient feeding strategy on PHA production using crude glycerol. This study aims to investigate the feasibility of enrichment of PHA accumulators in mixed culture without pH control when uncoupled carbon and nitrogen feeding strategy was implemented. Enrichment was conducted in a sequencing batch reactor (SBR) with cycle duration of 24 hr and organic loading rate (OLR) of 1000 mg C/(L.d). Feast and famine strategy was successfully implemented, with feast/famine (F/F) ratio of 0.43 indicating good PHA storage response. The cyclic profile of substrate and PHA concentration has also proven the successful implementation of F/F regime. Biomass concentration of 779 mg/L was obtained by the end of week 5 with PHA content of 16.2% g PHA/g VSS. During the cycle, pH between 6 to 8 was recorded which suggests that extreme acidic or alkaline condition detrimental to PHA accumulators cultivation was not observed in this study. This study demonstrates that enrichment of PHA accumulators is feasible when pH is not controlled under uncoupled C and N feeding strategy.