Anaerobic caproate production on carbon chain elongation: Effect of lactate/butyrate ratio, concentration and operation mode

The objective of this study was to understand how lactate-to-butyrate ratio and substrates concentrations affect the caproate production and product structure. The results showed that a higher butyrate-to-lactate ratio is beneficial to caproate production at low initial lactate concentration. Low pH (5.0) and low substrate concentration (20 mM and 40 mM) effectively decreased propionate production via restrained acrylate pathway, resulting in higher electron efficiency of caproate. With the optimum mole ratio of lactate to butyrate (1:4) and 80 mM initial butyrate concentration, the electron efficiency of caproate reached the maximum (43.10%). Moreover, high butyrate concentration suppressed the production of odd-carbon-number carboxylates while promoting the production of caproate. Compared with the batch operation, the caproate production in semicontinuous operation was enhanced by 3.45 times to 30.91 ? 1.07 mM as the acrylate pathway was successfully inhibited in semi-continuous experiments due to low pH and low lactate concentration.

Automated summary

By adjusting the ratio of butyrate to lactate and substrate concentrations, caproate production and electron efficiency can be enhanced. Inhibiting propionate production under low pH and low substrate concentration conditions is crucial. Semi-continuous operation could significantly increase caproate production compared to batch operation.