Simultaneous hydrogen production and consumption in Anaerobic mixed culture fermentation

Abstract

The aim of the present study is to investigate the relevance of homoacetogenic H2 consumption on the bio-hydrogen yield and products distribution in mixed culture fermentation. A hybrid anaerobic reactor was operated for 93 days with variable pH and organic loads between 8-16 g glucose/L.d for this purpose. High initial H2 yield decreased gradually to an equivalent of 0.02-0.4 mol H2/mol glucose consumed. The distribution of the dissolved organic products was influenced strongly by reactor pH, while the overall H2 yield was not. Low H2 yield is attributed mainly to homoacetogenesis at pH > 4.6 and to reduced products formation at pH < 4.6. Simultaneous hydrogen production and consumption occurred and at least 22 % of the produced molecular hydrogen, mainly from butyrate fermentation, was used for the reduction of CO2 to acetate.