Browsing by Author "Ghazi, Mubina"

Conventional fossil fuel-based plastics have become an indispensable part of our lives. However, their widespread usage has resulted in a substantial rise in plastic waste generation. Given these circumstances, there is an increasing urge to explore alternate options, particularly bio-based plastics, which are sourced from renewable natural resources. Polyhydroxyalkanoates (PHAs) are microbial-derived polymers that stand out for their sustainability and biodegradability. Microbial PHA production from industrial wastes, particularly using activated sludge, has gained interest recently. Wastewater treatment plants generate a substantial amount of sewage sludge that requires innovative disposal methods. Hence, recycling organic materials from sewage sludge into biodegradable plastics is a potential option. The study aimed to develop bacterial inoculum cultivation for a pilot-scale bioreactor (500-1000 L). The study investigated the effect of phosphorus limitation, potentially preventing the hydrolysis stage and enhancing PHA accumulation. The effects of 3-fold concentrated activated sludge on PHA-accumulating bacteria were evaluated. Three fermentations were conducted in a 5 L bioreactor utilizing activated sludge from the Ali-Juhakkala wastewater treatment plant in Lahti. Each bioreactor experiment was carried out under different operational conditions, including pH, and phosphorus concentration. The results showed that fermentation conducted at a high pH of 7.0-7.8 with phosphorus limitation did not show PHA accumulation. However, fermentation carried out at a slightly acidic pH of 5.6-6.4 with limiting phosphorus showed the best PHA accumulation after 5 days. The microbial community was dominated by Gram-negative and actinobacteria. A third fermentation conducted in the same pH range of 5.4-6.4 without phosphorus limitation showed no PHA accumulation. Overall, the results suggest that the PHA content was highest at 63.6 mg/g VS in fermentation under phosphorus limitation at slightly acidic pH, which provided optimal bacterial inoculum cultivation.