Polyhydroxyalkanoates production from industrial wastewaters using a mixed culture enriched with Thauera sp.: Inhibitory effect of the wastewater matrix

Abstract

Industries all over the world generate huge amounts of wastewater, which needs to be treated. The integration of polyhydroxyalkanoates (PHA) production into wastewater treatment is a promising strategy for resource recovery that improves the sustainability of industrial wastewater treatment plants. This study aims to investigate PHA production from several industrial wastewaters using a microbial mixed culture enriched in bacteria of the genus Thauera. The wastewaters were classified based on the volatile fatty acid (VFA) concentration and the presence of ethanol: (W1) wastewater with VFA <12 mM (anaerobically treated dairy, yeast and paper mill wastewaters), (W2) wastewater with VFA >12 mM (acidified sugar, paper mill and brewery wastewaters), and (W3) wastewater with VFA >12 mM and ethanol (acidified starch, distillery and dairy wastewaters). No PHA accumulation was obtained with wastewaters in the category W1 because the VFA concentration was low and was used for biomass growth and maintenance. The maximum PHA accumulation of 46.5% cdw was achieved from acidified paper mill wastewater. For other wastewaters in the categories W2 and W3, PHA accumulation was in the range of 37–45.6% cdw. In the W2 category, PHA accumulation inhibition due to VFA concentration was observed in the case of acidified sugar wastewater, while for wastewaters in the W3 category inhibition was provoked by the wastewater matrix itself. Nevertheless, PHA accumulation inhibition was overcome by wastewater dilution. The presence of ethanol in wastewaters within the category W3 (>27 mM) decreased PHA accumulation circa 20%. The thermal characteristics of the copolymer PHB:PHV obtained in the present study are similar to those of commercial PHAs. Additionally, the produced copolymer was used successfully as a carbon source for nitrate removal (0.72 mg NO3−/mg PHA). This study shows that resource recovery in the form of biopolymers is an option for several industrial wastewaters and that the copolymers obtained are biodegradable.