Biohydrogen production from chemical wastewater as substrate by selectively enriched anaerobic mixed consortia: Influence of fermentation pH and substrate composition

Influence of fermentation pH and substrate composition (composite chemical wastewater as primary carbon source) on molecular H 2 production was studied in batch experiments using sequentially pretreated [heat-shock ( 100 ∘ C ; 2 h) and acid (pH 3; 24 h)] anaerobic mixed consortia as inoculum. Sequentially coupled repeated pretreatments showed positive influence on the overall H 2 generation. Effective H 2 production was evidenced at fermentation pH 6 ( 1.25 mmol H 2 / g COD ) compared to 5 ( 0.71 mmol H 2 / g COD ) and 7 ( 0.27 mmol H 2 / g COD ). Fermentation pH of 6.0 was found to be optimum for effective H 2 generation with the pretreated inoculum. The feed consisting of only glucose as primary substrate showed low H 2 yield, while feed with chemical wastewater admixed either with glucose or sewage wastewater as co-substrates demonstrated high H 2 yield. Addition of co-substrate (glucose or sewage wastewater) along with chemical wastewater showed enhanced H 2 yield. Glucose concentration exceeding 2 g/l resulted in reduced H 2 yield. Higher VFA concentrations were recorded in experiments carried out at fermentation pH 5 than 7. At fermentation pH 6 VFA composition showed the presence of acetate, butyrate, and propionate with relatively lower concentration of ethanol. Acid-forming pathway with acetic acid as a major metabolite dominated the metabolic flow during the H 2 production.