Monday, April 30, 2007

Pretreatment of methanogenic granules for immobilized hydrogen fermentation

Bo Hu, Zhanyou Chi, and Shulin Chen. Biological System Engineering, Washington State University, L.J. Smith 213, Pullman, WA 99163

Hydrogen can be produced through fermenting sugars in a mixed culture under anaerobic conditions. Anaerobic granular sludge was proposed as immobilized hydrogen producing bacteria to be used in the immobilized hydrogen culture after methanogenic activity of granule was eliminated in the pretreatment process. This paper reports first time chloroform treatment as an effective method to directly convert methanogenic granule to hydrogen producing granule. Chloroform treatment was tested along with acid and heat treatments of sewage sludge and methanogenic granule in this study for their effectiveness to eliminate methanogenic activity. The results showed that chloroform was the most effective among the three methods tested. Acid and heat treatments that were proved to be effective for sewage sludge treatment were observed not completely effective for application to granules because of the protection from the granular structure. Methane production was almost completely inhibited in both sewage sludge and granule with addition of only 0.05% chloroform into the culture medium. If the chloroform concentration was controlled at low levels, chloroform could selectively inhibit methanogenic activity while did not influence the hydrogen production. At certain high concentration range, chloroform also inhibited hydrogen production. Chloroform caused irreversible methannogenic activity elimination at the pretreatment and methane production stopped even without chloroform addition after the pretreatment; meanwhile, hydrogen production recovered to normal after chloroform addition stopped. The experimental data showed that chloroform treated granule could be repeatedly cultured for eight times without obvious damage. Chloroform treated granule provide a great potential for application in the immobilized hydrogen fermentation.