Centralized anaerobic digestion (CAD). In CAD, many farms
cooperate to feed a single large digestion plant with a single or
a variety of co-substrates [33]. The substrates used are mainly
agricultural manures and biogenic waste materials from
industry [34]. The advantages of CAD are similar to those given
above for co-digestion. Today, CAD has become a standard
technology which is used in most European countries as well as
in Asia and the USA [34]. There are benefits in using this
cooperative arrangement in terms of substrate supply,
economics and sustained gas supply. In addition, a single CAD
plant can serve a wider community whose members would
otherwise not sustain an anaerobic digestion plant on an
individual process.