However, in case of wet biomass with a high moisture content, it results in a negative impact on the
energy efficiency of the gasification process due to the fact that drying costs more energy than the energy
content of the product for some biomass types. An alternative method applied for the conversion of wet
biomass such as sewage sludge, cattle manure and food industry waste is anaerobic digestion. This
process is however characterized by a slow reaction and typical residence times are almost 2–4 weeks.
Besides, the fermentation sludge and wastewater from the reactors should further be treated.