“Hydrogen energy” could be a possible sustainable energy source to reduce global emissions of green house gases if it is produced from renewable sources such as biomass and wastewater. Biological hydrogen production in anaerobic bioreactors can be increased by either producing more H₂ by fermentative bacteria and/or by eliminating H₂ consuming methanogens. Removal of the dissolved gases (H₂, CO₂, CH₄ etc.) from the liquid phase was accomplished by the use of hydrophobic microporous membranes. Reduction in liquid phase H₂ partial pressure decreases the free energy and more H₂ was produced by fermentative bacteria. H₂ consumption also decreased, as less substrate H₂ was available for H₂ consuming methanogens. Objective of present study was to test the gas transfer membranes that would stop H₂ consuming methanogenesis in anaerobic bioreactor.

A membrane contactor with polypropylene microporous hollow fibers was used for dissolved gas removal from liquid phase. Two bioreactors, 1^st with membrane contactor and 2^nd without contactor (control), with 2-L liquid volume and 1-L headspace were operated at 35 °C with hydraulic retention time of 5 d. Liquid from 1^st bioreactor was circulated through membrane contactor to facilitate dissolved gas removal from liquid phase. The pH was controlled at 5.5. Glucose and nutrient solution were fed at the rate of 1:1 with organic loading rate of 3.0 gGlucose/L/d.

Volatile fatty acid analysis using gas chromatography (GC) showed clear shift in metabolic pathway. Acetate and butyrate were more than 10 times higher in the 2^nd bioreactor (control) while propionate was more than double in 1^st bioreactor (with membrane contactor). Chemical oxygen demand (COD) removals as a result of gas production were increased 3-4 times with using membrane contactors. These results indicated that more renewable energy in terms of gas production such as CH₄ and H₂ can be recovered by using gas transfer membranes. Results also showed that lower hydraulic retention time is required to stop H₂ consuming methanogenesis completely.

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