Low cost semi-continuous bioprocess and online monitoring of hydrogen production from crude glycerol

Abstract

High process costs arising from expensive media components, hydrogen partial pressure buildup in the head-space of the reactor, sharp decrease in medium pH due to accumulation of organic acids, substrate inhibition, as well as loss of biomass due to short hydraulic retention times are the major bottlenecks of fermentative hydrogen production. Therefore, the purpose of the present investigation was to develop a process to deal with all these problems at a time. The proposed approach demonstrates enhanced hydrogen production by a low cost process involving crude glycerol (CG), the waste from the biodiesel production process, as the only feedstock. This semi-continuous type of fermentation carried out in a 7.5 L bioreactor helped to eliminate substrate inhibition with no compromise in cumulative hydrogen production. By controlling product inhibition and the negative effect of by-product accumulation, as well as by preventing the loss of active biomass, a production of 5.18 L-H₂ per L-medium has been achieved. This amount is higher than the 2.02 to 2.68 L-H₂ per L-medium previously reported for CG bioconversion. Reduction of feed CG concentration from 120 g L⁻¹ to 60 g L⁻¹ was found to improve the glycerol utilization from 65% to 91%.