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Biological hydrogen production from olive mill wastewater and its applications to bioremediation

Eroğlu, Ela
Hydrogen production by photosynthetic bacteria occurs under illumination in the presence of anaerobic atmosphere from the breakdown of organic substrates, which is known as photofermentation. In this study, single-stage and two-stage process development were investigated for photofermentative hydrogen production from olive mill wastewater by Rhodobacter sphaeroides O.U.001 within indoor and outdoor photobioreactors. It was proven that diluted olive mill wastewater (OMW) could be utilized for photobiological hydrogen production as a sole substrate source. However, pretreatment of the system is needed to reduce the dark color and bacteriostatic effects of OMW. In this study, several two stage processes including pretreatment of OMW followed by photofermentation were investigated to increase the hydrogen production yields in addition to the significant remediation of OMW. Explored pretreatment methods contain chemical oxidation with ozone or Fenton’s reagent, photodegradation by UV radiation, adsorption with clay or zeolite and dark fermentation with acclimated or non-acclimated sewage sludge. Among these different two-stage processes; clay treatment method resulted the highest hydrogen production capacity. As a result of clay pretreatment, 65% of the initial color and 81% of the phenolic content were decreased. Hydrogen production capacity was 16 LH2/LOMW without pretreatment, while it was enhanced up to 29 LH2/LOMW by two-stage processes. Moreover, clay pretreatment process made it possible to utilize highly concentrated OMW (50% and 100%) media for hydrogen production and for remediation. On the aspects of environment, treatment of OMW was achieved in the present work. The final composition of the organic pollutants in the effluent of two-stage processes was below the wastewater discharge limits. The overall results obtained throughout this study may open a new opportunity for the olive oil industry and for the biohydrogen area as a result of the effective biotransformation of OMW into hydrogen gas and valuable by-products.