Evaluation of industrial waste black cumin (Nigella Sativa) for biohydrogen production without pretreatment

The depletion of fossil fuels and the fact that fossil fuels pollute the environment accelerated the trend toward environmentally friendly energy alternatives such as biohydrogen. As one of the hydrogen production methods, biological hydrogen production processes are clean, sustainable, cost-effective and operation-easy processes that eliminate a series of disadvantages in the other hydrogen production processes. This study examined usability of black cumin obtained as waste from vegetable oil industry in the production of biohydrogen with dark fermentation without any pretreatment under different operating conditions (pH: 4.0, 5.0, 6.0 and hydraulic retention time (HRT): 36, 24 h) in a completely stirred-tank reactor and fluidized bed reactor. The best hydrogen production was established at pH 5.0 during the operating period. In completely stirred-tank reactor and fluidized bed reactor, the maximum hydrogen production measured at pH 5.0 was 25.3 and 11.1 mL/day, respectively. In the study that used mixed culture, the predominant microbial population was found to be Enterobacteria, Salmonella bongori, CFB group bacteria, Brenneria goodwinii, Erwinia amylovora, Thiofractor thiocaminus, Sulfurospirillum sp. and Hydrogenimonas thermophila at pH 5.0. Within the scope of the study, it was concluded that waste black cumin, which has not been tried before in any biohydrogen research, can be used successfully for biohydrogen production.