Biohydrogen production by anaerobic fermentation of food waste

Abstract

This study was conducted to improve hydrogen fermentation of food waste in a leaching-bed reactor by heat-shocked anaerobic sludge, and also to investigate the effect of dilution rate ( D) on the production of hydrogen and metabolites in hydrogen fermentation. Among various reaction constraints affecting the fermentation of food waste, a key factor is the adjustment of environmental conditions during the fermentation because various components of food waste have different characteristics of degradation. D was used as a tool to keep the optimum conditions of hydrogen fermentation. The fermentation efficiency (58%) at initial D of 4.5 d −1 was higher than those (51.4, 55.2, and 53.7%) at initial D of 2.1, 3.6, and 5.5 d −1 . The chemical oxygen demand (COD) removed was converted to hydrogen (10.1%), volatile fatty acids (VFA) (30.9%), and ethanol (17.0%). The butyrate/acetate ( B/ A) ratios were maintained over 3.2 in the first 2 days. In addition, the fermentation efficiency improved from 58.0% to 70.8% by adjusting D from 4.5 to 2.3 d −1 depending on the state of degradation. The COD removed was converted to hydrogen (19.3%), VFA (36.5%), and ethanol (15.0%). Compared to 0.7–2.2 with no D control, the B/ A ratios were kept high (2.0–2.7) on days 3–7, accompanied by the second hydrogen peak. The trend of B/ A ratios was similar to the hydrogen production. D control led environmental conditions to favor hydrogen production. This meant that the fermentation efficiency was improved by the enhanced degradation of slowly degradable matters. Moreover, D control could delay the shift of predominant metabolic flow from hydrogen- and acid-forming pathway to solvent-forming pathway.