Effect of process variables on the production of Polyhydroxyalkanoates by activated sludge

Polyhydroxyalkanoates are known to be temporarily stored by microorganisms in activated sludge, especially inanaerobic-aerobic processes. due to the problems resulted from the disposals of plastic wastes and excess sludgeof wastewater treatment plants, the production of polyhydroxyalkanoates by treating activated sludge anddetermining the effect of process variables were the main issues of this paper. in this research, an anaerobic-aerobicsequencing batch reactor was used to make microorganism adapted and a batch aerobic reactor was used forenriching them. the variables affecting polyhydroxyalkanoates production including aeration time, sludge retentiontime, and volatile fatty acids concentration of the influent in sequencing batch reactor, and also carbon to nitrogenratio and cultivation time in polymer production reactor, were investigated using taguchi statistical approach todetermine optimum conditions. the maximum polymer production of 29% was achieved at sludge retention timeof 5–10 days, aeration time of 2 hours, supplementation of 40% of volatile fatty acids in the influent and increasingof carbon to nitrogen ratio of polymer production reactor to above 25 g/g. based on the results, in optimumconditions, the volatile fatty acids concentration which increased the production of polyhydroxyalkanoates up to49% was the most effective variable. carbon to nitrogen ratio, sludge retention time and aeration time were rankedas the next affecting parameters. although the polyhydroxyalkanoates content achieved in present study is muchlower than that by pure culture, but the proposed method may still serve well as an environmental friendly meansto convert waste into valuable product.