An insight into enrichment strategies for mixed culture in polyhydroxyalkanoate production: feedstocks, operating conditions and inherent challenges

PHA production using a combination of mixed culture and carbon wastes has been demonstrated as a costreducing solution compared to the use of expensive pure culture process. Continuous research has been conducted with the aim to further reduce the production cost by simplifying the production scheme, as well as enhancing the performance of mixed culture in PHA production. Selection of the carbon feedstock and enrichment strategies needs to be essentially considered to obtain a culture enriched with PHA accumulators for a stable PHA production. Most of the studies implementing mixed culture process applied the feast-famine regime with periodical supply of carbon for culture enrichment. Results have revealed that the enriched culture showed a comparable performance with pure culture, in terms of PHA content (30-80%) and yield (0.4-0.8 g PHA/g S). However, a low productivity is the hindering factor to produce PHA at industrial scale by using mixed culture, which could be overcome by improvising the enrichment strategies. This review zooms into the evaluation of two step and three step processes in PHA production by utilising different feedstocks. Critical parameters to be considered for PHA production such as the suitable feedstocks, enrichment conditions, stability of the enriched culture and nutrient supplementation are being highlighted. The possible enrichment strategies that include uncoupled C and N supply and extended cultivation in overcoming the issue of low productivity are presented. The impact of different enrichment strategies on microbial community, characteristics of PHA produced as well as PHA production performance is worth investigating in future.

Automated summary

Research has shown that utilizing a combination of mixed culture and carbon wastes for PHA production can reduce costs, with the selection of carbon feedstock and enrichment strategies being crucial. Current studies mainly apply the feast-famine regime for culture enrichment, showing comparable performance in terms of PHA content and yield with enriched culture, yet low productivity remains a hindering factor.