Achieving high volatile fatty acid production from raw henna (Lawsonia inermis) biomass at mild alkaline conditions

Strong alkaline hydrolysis is usually employed to enhance fermentative production of volatile fatty acid (VFA) from plant biomass. However, this method is not ecofriendly due to the large consumption of energy/chemicals. In this study, a special henna plant biomass (Lawsonia inermis) containing the chemical compound lawsone, served as a fermentation substrate (without any pretreatment) for high VFA production under mild alkaline conditions (pH 9). The results indicated that the fermentative VFA production was 0.31 g per gram of henna biomass, which was comparable to other plant biomass pretreated with hydrothermal, strong acidic, and/or alkaline methods. Acetate was the main VFA component, and accounted for 69% to 82% of the COD fraction. The soluble lawsone concentration in the fermentation system ranged from 8.5 mg/L to 31.2 mg/L, which mediated the potential fermentation process. Thus, in this study henna was established as a feasible plant biomass for high fermentative VFA production in mild alkaline conditions.