Dark Fermentation

Dark fermentation is the fermentative conversion of an organic substrate into biohydrogen by bacteria breaking down organic material without light, distinguishing it from photofermentation. Several bacterial groups work through a process similar to anaerobic digestion, first breaking complex organic polymers into simpler compounds, which acidogenic bacteria then convert into organic acids, alcohols and hydrogen gas. Because industrial, agricultural and food-processing wastewater can serve as feedstock, dark fermentation can treat wastewater and produce hydrogen at the same time, addressing both feedstock availability and cost, though its energy conversion efficiency is low: typical yields run only one to two moles of hydrogen per mole of glucose, leaving 60 to 90 percent of the original organic material unconverted as volatile fatty acids and other compounds in the wastewater.