The link of feast-phase dissolved oxygen (DO) with substrate competition and microbial selection in PHA production

Improving PHA production in a SBR of coupling PHA-storing microorganism enrichment and PHA accumulation by feed-on-demand control

With volatile fatty acids as substrates, the typical polyhydroxyalkanoates (PHAs) production by mixed culture always includes two steps: PHA-storing culture enrichment via aerobic dynamic feeding strategy and PHA accumulation under nutrient-limited condition. To simplify the PHA-production steps, the enrichment and accumulation step were coupled in a SBR. At start-up period, to investigate the effect of settling selection, one acetate-fed SBR was operated by settling selection-double growth limitation (SS-DGL) strategy, while the other was operated by DGL strategy. The results showed that the stable operation in SBR1 was obtained at about 21, 12 days faster than SBR2, implying the settling selection accelerated the start-up process. After omitting the settling selection under the stable operation, the SBR1 was run above 15 days. The results showed that the performance was not substantial altered. Therefore, the settling selection affected the start-up process but not the stable operation. At operational period, based on the sharp decreasing of oxygen uptake rate (OUR), the poly-β-hydroxybutyrate (PHB) content was improved 13%, from 70 to 83% by feed-on-demand control-double growth limitation (FD-DGL). And the harvested volumetric productivity was 5.0 gPHB/L/day, almost 1-folder improvement. That was to say, the PHB production in a SBR of coupling the enrichment and accumulation step was improved by feed-on-demand control. Meanwhile, the FD experiment can keep steady running for 10 SRTs. Therefore, the SS-DGL/FD-DGL strategy was a promising method for PHA production.

Effect of famine-phase reduced aeration on polyhydroxyalkanoate accumulation in aerobic granules

The effects of variable aeration in the famine period on polyhydroxyalkanoate (PHA) accumulation in aerobic granules were investigated. Results showed that regardless of the aeration rates used during famine period, all aerobic granules achieved a similar chemical oxygen demand removal and PHA content. The decrease in famine-period aeration rates accelerated the maximum PHA accumulation together with increase in granular size and settling ability. The PHA-accumulating microorganisms were found to have shifted closer to the surface of the granules when the aeration rate was reduced. Moreover, PHA compositional changes occurred, where the hydroxyvalerate content had increased with the reduction in aeration rate. Ultimately, the results indicate that the requirement of aeration for PHA accumulation in aerobic granules is highly insignificant in the famine phase. PHA production in aerobic granules under zero aeration in the famine period may result in an energy input reduction of up to 74%.

Recent Advances and Challenges towards Sustainable Polyhydroxyalkanoate (PHA) Production

Sustainable biofuels, biomaterials, and fine chemicals production is a critical matter that research teams around the globe are focusing on nowadays. Polyhydroxyalkanoates represent one of the biomaterials of the future due to their physicochemical properties, biodegradability, and biocompatibility. Designing efficient and economic bioprocesses, combined with the respective social and environmental benefits, has brought together scientists from different backgrounds highlighting the multidisciplinary character of such a venture. In the current review, challenges and opportunities regarding polyhydroxyalkanoate production are presented and discussed, covering key steps of their overall production process by applying pure and mixed culture biotechnology, from raw bioprocess development to downstream processing.