Simultaneous COD Removal and PHA Production in an Activated Sludge System under Different Temperatures
Keywords:Activated sludge, polyhydroxyalkanoate, nutrient limitation, biodegradable plastics, temperature effects.
The purpose of this study was to investigate PHA production by activated sludge biomass under different temperatures. The two-step approach, i.e. utilizing a growth phase followed by a nutrient(s) limitation phase, was applied to stimulate PHA accumulation. Each of three intended temperatures, 10oC, 20oC and 30oC, was investigated with combined N&P limitation. Four liter (L) fully aerobic SBRs were used for all experiments, and operated with a 6 h cycle time, a 10 h HRT and a 10 day SRT. The maximum PHA cellular contents and total concentrations achieved during the N&P limitation periods in the 10 and 20oC systems were very similar, i.e. 45 and 43% of the TSS and 2133 and 2239 mg/l, respectively, whereas the 30oC results were lower at 33% of TSS and 1476 mg/l. The biomass temperature clearly had a strong inverse effect upon PHA productivity. It decreased from 427 and 204 to 148 mg/l-day as reactor temperature increased from 10 to 20 and 30oC, respectively. As well, the PHA yields decreased from 0.38 to 0.16 and 0.11 mg PHA/mg CODu, respectively. The results strongly indicate that activated sludge PHA accumulation stimulated by combined N and P limitation is inversely correlated with temperature.
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