EVALUATION OF CARBON AND NITROGEN RATIO ON THE PRODUCTION OF POLYHYDROXYBUTYRATE FROM ACTIVATED SLUDGE THROUGH PARACOCCUS PANTOTROPHUS

Abstract

Various microorganisms synthesize and accumulate polyhydroxyalkanoates (PHAs) as energy reserves to survive under nutrient deficient conditions. Since these PHAs are biodegradable, biocompatible and non-toxic so they can serve as potential alternatives to petroleum based plastics, helping to reduce plastic pollution. This research aimed to investigate the impact of C/N ratio on polyhydroxybutyrate (PHB) yield capacity of gram-negative bacterium Paracoccus pantotrophus in activated sludge samples collected from municipal wastewater treatment plants. Activated sludge was cultivated in sequencing batch reactor (SBR) using aerobic dynamic feeding. The PHA content produced was extracted through pretreatment by sodium hypochlorite and then the extracted polymers were purified by using NH₄OH solution and ethanol. The highest PHB yield (2.85 g/L) was obtained when hydroxyphenylacetic acid was used as the primary carbon source at a C/N ratio of 6.1 while acetic acid resulted in a relatively low PHB yield (0.45 g/L) at a C/N ratio of 40. On the other hand, valeric acid at a C/N ratio of 12.1 resulted in the highest biomass concentration (6.1 g/L) while hydroxyphenylacetic acid resulted in the lowest dry cell mass (0.28 g/L) suggesting that carbon type significantly influences metabolic pathways leading to polymer storage. Such an inverse relationship between biomass growth and PHB accumulation highlights the metabolic adaptability of P. pantotrophus in response to nutrient limitations. These findings will help enhance industrial strategies for treatment of wastewater and for maximizing microbial PHB bioplastic production capacity.