FEASIBILITY OF HYDROGEN PRODUCTION FROM ANAEROBIC MIXED FERMENTATION

This study reports the effects for selectively enriching hydrogen-producing microbial species present in biological sludge produced during animal wastewater treatment. The purpose for the enrichment methodology was to enhance production of hydrogen gas under mixed anaerobic fermentative conditions of organic substrates. Methodology to enrich hydrogen-producing bacteria included pH adjustment of natural inocula to 3 and 5 with and without heat treatment (by wet heatshock of natural inocula). Enriched mixed bacteria were cultivated at initial pH values of 5, 6, and 7 with synthetic organic wastewater (carbon source was mainly glucose) containing different levels of nitrogen (2.0 and 0.8 g/L as total nitrogen) at mesophilic temperature (at 35°C) under static batch conditions. The culture pH significantly affected hydrogen production. Maximum specific hydrogen production achieved over the entire culture time was 223 mL H2/g cell and 379 mL H2/g cell in culture at pH 7 using inocula that had been enriched at pH 3 with and without heat treatment (HT and NHT), respectively, before adding culture. HT of inocula enriched at pH 3 contributed positively to hydrogen production. Enrichment at pH 5 had weak potential to enhance hydrogen evolution irrespective of NHT and HT. At maximum production of hydrogen (at culture pH 7 after enrichment at pH 3 with HT), the major intermediate metabolites were acetate and n-butyrate (as volatile fatty acids), and ethanol (as organic solvents). Propionate was not detected. No significant effects were found on hydrogen production using supplements with different nitrogen levels.