Production of biological polymers from organic wastes

Biologically‐produced polymers, from microbial fermentation are naturally biodegradable and are potential environment‐friendly substitutes for some synthetic plastics. However, broader applications are restricted by the high production costs and limitations in physical and mechanical properties. In this study, activated sludge bacteria in a conventional wastewater treatment system treating a wastewater that contained organic pollutants, were induced by nitrogen deficiency 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 accumulated these polymers. When the C:N ratio was increased from 20 to 140, the 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 were as high as 0.7 g polymer/g dry cell mass. The composition of the co‐polymers, and hence the physical and mechanical properties, could be controlled by manipulating the influent organic compositions.