Biological polymers produced by microbial fermentation are naturally biodegradable and are potential environment-friendly substitutes for synthetic plastics. However, broader applications are restricted by high production costs. In this study, activated sludge bacteria in a conventional system treating a wastewater that contained xenobiotic organics were induced by nitrogen deficiency in the reactor liquor to accumulate intracellular storage polymers, which can be extracted as a low-cost source of biodegradable plastics. Chromatographic analysis of the extracted polymers revealed a composition of poly-hydroxyalkanoate and a number of related co-polymers. Alcaligene spp. in the activated sludge microbial consortium was identified as the main genus that accumulated these polymers. When the C:N ratio was increased from 20 to 140, specific polymer yield increased to a maximum of 0.39 g polymer/g dry cell while specific growth yield decreased to 0.26 g dry cell/g carbonaceous matter consumed. The highest overall polymer production yield of 0.11 g polymer/g carbonaceous matter consumed was achieved when the C:N ratio was maintained at a nitrogen- deficient level of 100. The specific polymer yield in the isolated Alcaligene spp. cells reached as high as 0.7 g polymer/g dry cell mass. While reducing the costs of biodegradable plastics, this technique also reduced the amount of excess sludge generated from the wastewater treatment process by 39%.

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