Large quantities of biodegradable food waste in the form of fruit and vegetables are still being deposited in landfill sites in Ireland. The development of an anaerobic digestion process using fermentative species which degrade the carbohydrate-rich waste could divert the food waste from landfills. We identified fermentative species grown on glucose and sucrose at mesophilic and thermophilic temperatures using molecular biology techniques. The dominating fermentative bacteria of the mesophilic sludge were of the Bacteroidetes and Spirochaetes classes. Although both groups of bacteria are typically fermentative their substrate range appears to be limited. The dominating fermentative bacteria in the thermophilic sludge was Thermoanaerobacterium aotearoense of the Clostridia class. The indications are that Thermoanaerobacterium aotearoense may be highly suitable to biodegrade a carbohydrate-rich influent feed due to its possibly very rapid growth rate and also an extensive substrate range.