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The use of agro-industrial wastes as substrates for polyhydroxyalkanoate (PHA) production by mixed microbial cultures is an alternative to lower the price of these biopolymers. However, when submitting these wastes to pre-fermentation, lactate and ethanol can be produced in addition to volatile fatty acids (VFAs). In this study, the impact of ethanol on PHA storage and in the carbon flux of the process were assessed. The co-production of extracellular polymeric substances (EPS) and its impact on PHA production was investigated. PHA production yield showed a decrease from 0.92 ± 0.004 to 0.63 ± 0.002 Cmol-PHA.Cmol-S-1 with the increase of ethanol content from 5 to 20 Cmmol.L-1. EPS production was directly proportional to the ethanol's fed, reaching a maximum EPS total content of 6.70 Cmmol for the maximum ethanol supplied. EPS acted as a protection strategy, which benefited PHA specific storage rate for the highest ethanol content tested. These results indicate that ethanol-rich feedstocks can be valorised through the simultaneous production of two value-added biopolymers.
Rangel et al. (Thu,) studied this question.