Biological hydrogen production from paper mill effluent via dark fermentation in a packed bed biofilm reactor

This study assessed the feasibility of continuous hydrogen production in an anaerobic packed bed biofilm reactor (APBR) using paper mill effluent (PME) without any pretreatment or modification. To form a microbial biofilm on supports, the reactor was seeded with a thermal pretreated anaerobic sludge. After the start-up stage, under mesophilic conditions and pH control, the system performance in the case of hydrogen production as biofuel and VFAs as valuable by-products as well as COD removal was investigated at different hydraulic retention times (HRTs) (24, 16, 12, 8, 4, 2 and 1.2 h). The highest hydrogen concentration in the produced gas was 41.5 % obtained at HRT 4 h. The highest hydrogen production rate and yield were 6.21 L H2 d- 1 L-1 at HRT 2 h and 0.96 mmol H2 g-1 COD at HRT 8 h, respectively. With decreasing the HRT from 24 to 1.2 h, the OLR was increased from 27.35 to 547 g COD L-1 d-1 that positively affect the hydrogen production rate for all HRTs except for the shortest HRT. Furthermore, COD removal efficiency was reduced from 25.2 to 6 %. Low value of COD removal efficiency is because of conversion of organic inlet to valuable metabolites such as VFAs in the effluent.