Effect of HRT on continuous $H_2$ production

Abstract

Most previous studies on continuous hydrogen fermentation were performed using simple hydrolysates (glucose and sucrose). However there are few reports on continuous operation using biopolymers like starch. In the research, effect of HRT on continuous hydrogen production in CSTR was investigated using corn starch as a substrate. The operation lasted for 128 days. Organic acid concentrations were observed on daily basis. VFA profile supported the fact that B/A ratio was the most important parameter to justify hydrogen yield at various HRTs. Highest hydrogen yield of 0.92 $mol.H_2/mol.hexose_{added}$ was observed at 12 hr HRT. Estimation modeling of homoacetogenism was also performed and quantification of hydrogen consuming acetate, at various HRTs, was evaluated. In addition, microbial characteristics at various HRTs were explored using PCR-DGGE analysis. Sequencing batch reactor processes offer distinct advantages when compared with continuous processes, including a high degree of process flexibility and no requirement for a separate clarifier. The characteristics of the reactor should therefore be compared with CSTR in continuous hydrogen production. Besides, little is known about effect of process intensification to maintain higher biomass on hydrogen production using ASBR. Feasibility of continuous hydrogen fermentation with varying HRTs in ASBR was observed using starch as a substrate. It was concluded that continuous hydrogen production in ASBR was impossible with varying HRTs unless it was converted in to CSTR in between while varying HRTs. Therefore, unbiased effect of various HRTs on $H_2$ producing ASBR in continuous mode was evaluated. Maximum $H_2$ yield of 0.58 $mol.H_2/mol.glucose_{added}$ was witnessed at 12 hr HRT. Homoacetogenism was found to be the major factor for inefficient performance of ABSR producing $H_2$. ASBR was found very efficient in glucose removal. PCR-DGGE analysis was also performed to identify the competent species of microorga...