Effects of temperature on mixed culture PHA production using wastewaters

Abstract

This study was divided into two parts; the first one was to investigate the effects of temperature and nutrients limitation on PHA production using synthetic wastewater. The preselected temperatures of 10, 20 and 30 ํC were investigated under three conditions, i.e., only either N or P limitation and combined N&P limitation. The two-stage operation approach, i.e.a growth phase followed by a nutrients limitation phase was employed. The second was to investigate the potential of using high-strength candy industrial wastewater (carbohydrate; 10000-20000 mg/l COD) as a substrate for PHA production. Two tropical temperatures of 20 ํC and Thai room temperature (28-31ํC) were investigated with combined N&P limitation condition. Also, the effect of increasing of COD loading on PHA production was studied. In the first part, temperature clearly affected PHA productivities and yields, i.e., high productivities and yields could be obtained at low temperatures.Considering effect of nutrients limitation, combined N&P limitation provided the best results regarding PHA production, whereas P limitation was not recommended for the production of a large amount of PHA due to its low productivity and yield. For example, the highest PHA contents and concentrations obtained during N limitation were 40 %TSS and 2830 mg/l at 20 ํC with the yield of 0.2 mg/mg COD[subscript u]. During P limitation, the 10 ํC system showed higher PHAproduction; the PHA content of 52 %TSS and concentration of 1491 mg/l with low yield of PHA of 0.05 mg/mg COD[subscript u]. For the N&P limitation experiments, PHA productions in both of 10 ํC and 20 ํC systems were not much different. The highest was 45 %TSS PHA content and 2133 mg/l PHA concentration. In the second part, the highest PHA contents reached 23.4 %TSS obtained from experiment at 20 ํC temperature. The increase of COD loading in the feeding could help promote the PHA production. The highest PHA content of 17.8 % of TSS was obtainedwith the fed COD loading of 5 g/l-d. However, the PHA productivities in this part were higher than those obtained in the first part due to much higher cell concentrations. In conclusion, activated sludge biomass is capable of accumulating substantial amount of PHA. Temperature has a significant effect on PHA production. Also, combined N&P or only N limitations stimulate better PHA production than mere P limitation. Though industrialwastewater has a potential to be a substrate for PHA production, the optimum operation needs more investigation.