effect of volatile fatty acids in production of polyhydroxyalkanoates by activated sludge

polyhydroxyalkanoates (phas) is known to be temporarily stored by microorganisms in activated sludge, especially in the anaerobic-aerobic processes. the main objective of this study was to investigate the effects of fatty acids (vfas) compounds coexistence in substrate of sbr on phas productivity of activated sludge. it has been found that addition of different concentrations of vfas results in an increase of phas content of activated sludge in the range of 90-130% as compared to the one acclimatized with only sucrose as a carbon source. in this study the optimum concentrationof acetate and propionate as the sole carbon sources in the phas production reactor was also found to be 30-35 and 15-20 mgc/l.h.gss, respectively. finally, the work was conducted in order to try and control phas composition by applying carbon sources with different acetate to propionate ratios. it has been observed that inclusion of propionate in the carbon sources lowered phas productivity. the produced phas is composed mainly of 3-hydroxy-butyrate and 3-hydroxy-valerate, and when the propionate in the substrate was increased from 0 to 100% the mass ratio of 3hv produced is increased from 6 to 85%.