Enhancement of PHA Production by a Mixed Microbial Culture Using VFA Obtained from the Fermentation of Wastewater from Yeast Industry

Abstract

Wastewater from the yeast production industry (WWY) is potentially harmful to surface water due to its high nitrogen and organic matter content; it can be used to produce compounds of higher commercial value, such as polyhydroxyalkanoates (PHA). PHA are polyester-type biopolymers synthesized by bacteria as energy reservoirs that can potentially substitute petrochemical-derived plastics. In this exploratory work, effluent from WWY was used to produce PHA, using a three-step setup of mixed microbial cultures involving one anaerobic and two aerobic reactors. First, volatile fatty acids (VFA; 2.5 g/L) were produced on an anaerobic batch reactor (reactor A) fed with WWY, using a heat pretreated sludge inoculum to eliminate methanogenic activity. Concurrently, PHA-producing bacteria were enriched using synthetic VFA in a sequencing batch reactor (SBR, reactor C) operated for 78 days. Finally, a polyhydroxybutyrate (PHB)-producing reactor (reactor B) was assembled using the inoculum enriched with PHA-producing bacteria and the raw and distilled effluent from the anaerobic reactor as a substrate. A maximum accumulation of 17% of PHB based on cell dry weight was achieved with a yield of 1.2 g PHB/L when feeding with the distilled effluent. Roche 454 16S rRNA gene amplicon pyrosequencing of the PHA-producing reactor showed that the microbial community was dominated by the PHA-producing bacterial species Paracoccus alcalophilus (32%) and Azoarcus sp. (44%). Our results show promising PHB accumulation rates that outperform previously reported results obtained with real substrates and mixed cultures, demonstrating a sustainable approach for the production of PHA less prone to contamination than a pure culture.

Microbial Recycling of Bioplastics via Mixed-Culture Fermentation of Hydrolyzed Polyhydroxyalkanoates into Carboxylates

“…Though in case PHA is part of the composite materials, it may be more complicated to chemically upcycle PHA since the other chemicals that could thermolyze also may interfere with such recovery processes. Still, once PHAs are not sorted out of the waste stream, a co-fermentation of PHA with the other biodegradable parts present in the waste streams may become attractive [ 24 ]. Starch-based plastics and PLA packaging, for example, are also promising materials for producing carboxylates since carboxylates are likely produced as an intermediate in the anaerobic digestion of bioplastics to methane [ 22 ].…”

“…If a mixed microbial bioprocess can be established using both the 3-HB and crotonate similar to the observations with the pure cultures, the carboxylates recovery from both key hydrolysates could be warranted in the envisioned PHA-based plastic recycling process. Subsequently, these carboxylates could be used as substrates for PHA production [ 24 ]. By combining all steps, a PHA cycle can be established.…”

A review on microbes mediated resource recovery and bioplastic (polyhydroxyalkanoates) production from wastewater

“…PHA, produced from organic fraction has a molecular weight of 8∙105 kDa and is comprised of hydroxybutyrate/hydroxyvalerate 53/47 (%). In another work, Ospina-Betancourth et al, [ 144 ] used yeast production industry wastewater (WWY) for the production of polyhydroxyalkanoates in sequential anaerobic reactors (reactor A) followed by two aerobic reactors (reactor B and C). VFAs produced in an anaerobic batch reactor (for 78 days), raw as well as distilled effluent from reactor A were used as feed PHA-production in reactors B and C (aerobic).…”

Valorization of Reground Pasta By-Product through PHA Production with Phototrophic Purple Bacteria

“…PHA production from by-products or wastes is being widely tested by exploiting aerobic organisms, including both pure cultures and MMCs [15][16][17][18][19]. In this study, the possibility of producing PHAs, and consequently valorizing a farinaceous by-product (reground pasta), has been investigated in a lab-scale semi-continuous system by using a phototrophic mixed culture (PMC) enriched in phototrophic purple bacteria (PBB).…”