Upscaled open-culture production of microbial flocculants from industrial wastewaters

Flocculants are widely used for solid-liquid separation despite environmental risks such as microplastics accumulation or release of toxic compounds. Microbially-secreted biopolymers are potential biodegradable, nontoxic alternatives. We demonstrate the feasibility of overproducing microbial exopolymers [extracellular polymeric substances (EPS)] from glycerol- and carbohydrate-rich industrial waste(water) in open-culture bioreactors. Two semi-pilot scale airlift bioreactors were operated with (airlift-MBR) and without membrane (airlift) to treat pure glycerol, biodiesel wastewater, and potato starch hydrolysate. Efficiency of EPS production with respect to supplied chemical oxygen demand reached values of 42% from pure glycerol, 30% from biodiesel wastewater, and 22% from potato starch hydrolysate. The airlift bioreactor showed stable continuous operation compared to airlift-MBR which was affected by membrane fouling. The produced EPS had net anionic charge and high molecular weight between 1 and 2.5 MDa. Both untreated EPS-rich mixed liquor produced in the bioreactors and extracted EPS therefrom showed promising flocculation potential comparable to anionic polyacrylamide.