Optimising Processes for the Stable Operation of Food Waste Digestion

Anaerobic digestion (AD) is normally considered to be a stable process for the treatment of organic wastes and the production of biomethane. It is based on specialised bacteria that break down the organic materials by means of enzymes which in some cases are highly specific and contain trace quantities of rare metals. There are situations where the process stability is upset as a result of conditions within the digester, however, which in turn may be strongly influenced by the feedstock characteristics. One of the most common occurrences in this respect is due to a low carbon: nitrogen (C:N) ratio which for a digester fed at a normal loading leads to excess nitrogen in the form of ammonia. Ammonia has been recognised for at least 45 years as being toxic to the AD process, although it is now recognised that under some conditions the anaerobic bacteria can adjust themselves to tolerate higher concentrations.