Acidogenic valorization of vegetable waste for short chain carboxylic acids and biohydrogen production: Influence of pretreatment and pH

Abstract

The present study aimed to valorize the vegetable waste fraction of organic municipal solid waste (VW) for the production of biobased products viz., reducing sugars (RS), short chain carboxylic acids (SCA)/volatile fatty acids (VFA) and biohydrogen (H2). Firstly, VW was subjected to pretreatment using physical (PS), chemical (CHE) and physicochemical (PSC) methods for RS production. Among the studied pretreatment methods, PSC resulted in higher RS solubilization with acid catalyzed conditions (1% H2SO4/HCl: 42.4/40.8 g/l). Subsequently, resulting organic-rich PSC hydrolysate (RS) was acidogenically fermented for the production of SCA and biohydrogen at varying initial pH conditions (4, 6 7 and 10). Acidogenic fermentation at pH-6 resulted in higher SCA (0.62 g SCA/g RS) and biohydrogen production (1.22 l) followed by pH-10 (0.53 g SCA/g; RS, 0.94 l), pH-7 (0.37 g SCA/g; RS, 0.58 l) and pH-4 (0.32 g SCA/g; RS, 0.27 l). SCA composition at pH 6, 7 and 10 was majorly composed of acetic acid, while butyric acid was found to be dominant at pH 4. SCA's are known to be platform chemicals and hydrogen is a green fuel, production of which using VW accounts the sustainability to current solid waste management practices with the scalable co-product synthesis.