Biohydrogen gas production from wastewater treatment sludge by dark fermentation

The decrease in fossil fuel resources revealed an urgent need for new and clean energy sources. Hydrogen is a clean and high energy fuel and considered as potential substitute for fossil fuels. Chemical, physical and biological methods are used for the production but, biological methods have certain advantages over the others. Dark fermentation is one of the biological hydrogen gas production processes. It is simple and practical with high rate and yield of formation. Sustainable biohydrogen production requires available and low cost, carbon containing raw material. Wastewater treatment sludge, which is an important environmental problem, could be a suitable raw material for biohydrogen production due to its high organic substance content. Utilization of waste sludge for hydrogen generation may help sludge management and sustainable energy production.In the light of these facts, the study aimed to determine the significant factors that affect hydrogen production from waste sludge by dark fermentation. For this purpose, sludge hydrolysis method and conditions were determined in the first stage of the study. Three hydrolysis methods as single stage acid, single stage heat treatment and two stage sequential acid-heat treatment were applied to sludge. Two-stage hydrolysis provided 4 times and 0.5 times higher total sugar concentrations compared to acid and heat treatment,respectively, under optimized conditions as t=60 min, pH=2 and T=135 degrees celcius. In the second stage of the study, the effects of media composition and fermentation conditions on hydrogen gas production from filtrate and hydrolyzed sludge were investigated. The most important factors were initial biomass concentration and fermentation pH. The yield of production reached to 3.3 mol/glucose at 5g/L biomass concentration and at pH=5. External addition of nitrogen and protein did not affect the production substantially. The yields and rates of production form filtrate were slightly higher than the rates and yields from sludge.