Evaluation of alternative methods of preparing hydrogen producing seeds from digested wastewater sludge

Abstract

Six digested sludges, pre-treated by different methods (heat-shock, aeration, acid and base treatments, 2-bromoethanesulfonic acid (BESA) inhibition and iodopropane inhibition) as well as an untreated sample were compared for their suitability in the preparation of hydrogen producing seeds by cultivations in a sucrose medium. The heat-shock and acid treatment methods completely repressed methanogenic activity; however, they also partially repressed hydrogen production. The base treatment option did not completely repress methanogenic activity and also significantly impacted hydrogen production. The aeration method was unsuccessful at completely repressing methanogenic activity; however, it did not significantly affect the hydrogen production activity. The BESA and iodopropane pre-treatment methods specifically inhibited the methanogens, and there were no significant effects found on hydrogen production. Similar to the aeration pre-treated digested sludge sample, the untreated sludge showed high hydrogen production activity and a small amount of methanogenic activity (lower than the activity detected in the base treatment sample). In the subsequent second-step batch cultivations with the same sucrose medium and the diluted media, methanogenic activity was not detected in any of the test bottles. The microbial seed prepared from base treatment exhibited the highest hydrogen production activity, whereas those prepared from acid treatment did not exhibit any activity. Again, the microbial seed prepared from untreated sludge also exhibited relatively high hydrogen producing activity. A lower pH was detected at the end of the cultivation in all the test bottles. Interestingly, the variations in pH in the different tests bottles indicate that pH is an important parameter in the control of methanogenic activity.