Acidogenesis of waste activated sludge—Biohydrogen production with simultaneous short chain carboxylic acids

Abstract

The potential of waste activated sludge (WAS) as acidogenic fermentation feedstock for biohydrogen (H2) and short chain carboxylic acids (SCA) production was studied. Primarily, WAS was subjected to pretreatment using physical, chemical and physicochemical methods to accelerate the SCOD solubilization. Alkaline-catalyzed physiochemical pretreatment of WAS resulted in higher degree of solubilization (DOS) (1% NaOH (v/v): DOS: 40.9%, SCOD: 14.6 g/l) followed by acid (1% H2SO4 (v/v): DOS: 36.4%, SCOD: 8.84 g/l). The organic-rich hydrolysate (alkaline-catalyzed) was acidogenically fermented for the production of H2 and SCA at varying initial pH conditions (6, 7 and 10) against the untreated WAS as a control. Acidogenic fermentation of pretreated WAS at pH-10 resulted in higher H2 (29%) and SCA production (4.9 g/l) followed by pH-6 (23%; 3.6 g/l), pH-7 (10%; 1.2 g/l) and control (5%; 0.3 g/l), respectively. SCA distribution profiles were also varied as a function of pH and retention time. Maximum SCA concentration in pH-10 system owed the highest acidification (37.9%) followed by pH-6 (25.5%), pH-7 (8.0%) and control (1.91%). The outcome of the study infers the potential of WAS as a resource for various biobased products synthesis in the framework of biorefinery. Hydrogen is a green fuel and SCA are considered as building blocks for various high-value products synthesis, production of which using WAS addresses the sustainability to current wastewater treatment units.