Microwave assisted hydrothermal pretreatment of arecanut husk with anaerobic spent media for biohydrogen production using mono and coculture of microorganisms

Arecanut husk, an abundant and inexpensive lignocellulosic waste, can serve as a feedstock for biohydrogen (H2) production, providing advantages for both energy generation and agro waste reutilization. This study, therefore, evaluated and optimized the pretreatment parameters and microbial inocula for H2 production using arecanut husk. It was subjected to microwave followed by hydrothermal treatment at a low pH, using spent medium from dark fermentation to release soluble sugars. Taguchi method was applied to optimize the pretreatment parameters, resulting in a maximum soluble sugar concentration of 0.653 g/L at arecanut husk concentration, microwave power, microwave treatment time and autoclaving time of 1.5%, 80%, 1 min and 30 min, respectively. Subsequently, H2 production from pretreated arecanut husk was examined using different microbial inocula either individually or in coculture. H2 production was maximum with C. acetobutylicum in a stirred tank bioreactor (20.3 mL/g) followed by anaerobic sludge biomass, C. ljungdahlii, elephant dung and cow dung. The H2 yield in the bioreactor was 6.2% higher than serum bottle experiments. Also, sludge individually as well as in coculture with C. acetobutylicum (1:1) yielded 9.7 and 11.2 mL/g respectively. During the fermentation, acetic acid, propionic acid and butyric acid were produced as the intermediates.