ALAN is able to recover the organic fraction of municipal solid waste, food waste that can no longer be used and assimilable fractions, which account for 30 to 40% of the weight of municipal solid waste. Initially composting was used, however today the process of biodigestion is used, as it has undoubted advantages from the reduction of odour emissions to the recovery of energy and matter.
Biodigestion is a process that uses various types of substrates, from agricultural crops, that take away land for food production, to livestock waste, to sewage sludge and finally to food by-products and the organic fraction of municipal solid waste. The latter is one of the most interesting sources because its treatment spurs separate collection and allows for a higher production of biogas and better quality compost. Its separate collection has also lead to a drastic reduction of the amount of municipal waste sent to landfills or incinerators.
Anaerobic digestion is defined as the degradation of the organic substance by micro-organisms under anaerobic conditions. This is a different process from composting, which is strictly aerobic.
Conventionally, depending on the type of bacteria used, there are two different temperature ranges in which anaerobic digestion is carried out: with mesophilic bacteria at temperatures between 20-45 °C, with an optimal range of 37-41 °C; with thermophilic bacteria, optimum operating conditions require a temperature range of 50-56 °C.