Wastewater as renewable feedstock for bioplastics production: understanding the role of reactor microenvironment and system pH

Abstract

Considerable interest in the development of biobased polymers is being garnered due to their diverse applications and biodegradability. In this communication, bioplastics (as polyhydroxyalkanoates) production using wastewater as a substrate was studied by varying the reactor microenvironment (aerobic and microaerophilic) and operating pH (6, 7 and 8). Redox reactions occurring in the mixed culture during polyhydroxyalkanoates production were investigated. Maximum polyhydroxyalkanoates production in terms of dry cell weight (%) was observed in microaerophilic operation (56%), compared to aerobic (34%) operation. Neutral pH showed better polyhydroxyalkanoates synthesis (56%) than basic (44%) and acidic (28%) redox microenvironments. Neutral pH operation documented higher dehydrogenase enzyme activity, reduction currents, substrate degradation than acidic and alkaline pH at microaerophilic environment that correlated well with higher polyhydroxyalkanoates production. Biopolymer composition showed the presence of co-polymer, poly-(3-hydroxybutyrate-co-3-hydroxyvalerate). Fluorescence in situ hybridization analysis revealed the presence of phylum Proteobacteria, Acidobacteria and Firmicutes in mixed culture which are known for polyhydroxyalkanoate production. This study illustrated that efficient utilization of wastewater for bioplastics production at optimum conditions can be viewed as viable solution for tackling the problems of increasing waste advocating the concept of ‘waste to wealth’.