In this work, the potential of using microbial community engineering for production of polyhydroxyalkanoates (PHA) from glycerol was explored. Crude glycerol is a by-product of the biofuel (biodiesel and bioethanol) industry and potentially a good substrate for bioplastic production. A PHA-producing microbial community was enriched based on cultivation in a feast-famine regime as successfully applied before for fatty acids-based biopolymer production. A glycerol-fed sequencing batch reactor operated at a 2-day liquid and biomass residence time and with feast-famine cycles of 24 h was used to enrich a mixed community of PHA producers. In a subsequent fedbatch PHA production step under growth-limiting conditions, the enriched mixed community produced PHA up to a dry weight content of 80 wt.%. The conversion efficiency of substrate to PHA on electron basis was 53%. Since glycerol is entering the metabolic pathways of the cell in the glycolytic pathway, it was anticipated that besides PHA, polyglucose could be formed as storage polymer as well. Indeed, polyglucose was produced in low amounts (∼10 wt.%). The results indicated that the feast-famine-based enrichment strategy was comparably successful to obtain a microbial community compared to fatty acids-based enrichment described before.

PHA, a naturally occurring biopolymer produced by a wide range of microorganisms, is known for its applications as bioplastic. In recent years the use of agro-industrial wastewater as substrate for PHA production by bacterial enrichments has attracted considerable research attention. Crude glycerol as generated during biodiesel production is a waste stream that due to its high organic matter content and low price could be an interesting substrate for PHA production. Previously we have demonstrated that when glycerol is used as substrate in a feast-famine regime, PHA and polyglucose are simultaneously produced as storage polymers. The work described in this paper aimed at understanding the effect of the cycle length on the bacterial enrichment process with emphasis on the distribution of glycerol towards PHA and polyglucose. Two sequencing batch reactors where operated with the same hydraulic and biomass retention time. A short cycle length (6 h) favored polyglucose production over PHA, whereas at long cycle length (24 h) PHA was more favored. In both communities the same microorganism appeared dominating, suggesting a metabolic rather than a microbial competition response. Moreover, the presence of ammonium during polymer accumulation did not influence the maximum amount of PHA that was attained.

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