Shift in methanogenic community in protein degradation using different inocula

Abstract

Anaerobic digestion (AD) of protein-rich wastes is problematic due to production of ammonia and hydrogen sulfide. In this work, eight inocula were used in batch AD of solutions of gelatin and gluten at 3 g COD substrate/ 1g VSS inoculum. AD plants from which inocula originated were treating food waste or food wastewater, wastewater sludge, or a combination of them. Inocula were evaluated by fitting methane production data using the modified Gompertz model. Sequencing of 16 s rRNA of microorganisms showed that Methanoculleus was dominant in inocula from plants that were treating food waste, and Methanosaeta was dominant in the others. The maximum methane production rate varied by a factor of three for each substrate: 2.734-7.438 mLCH4 gCOD1 d-1 for gelatin, and 1.950 to 5.532 mLCH4 gCOD-1 d-1 for gluten. This study demonstrates that inoculum must be chosen appropriately when treating proteinaceous waste by AD.