The main parameters for consideration in the process integration are the feedstock, bioreactor configurations and methods for enhancing the process efficiency.

12.4.1 Feedstock

The range of organic matter types that can be subjected to anaerobic digestion is wide; from low organic load wastes such as municipal sewage to high organic load wastes (such as the organic fraction of the municipal solid wastes). Specifically, the industrial sector (e. g. breweries, sugar mills, distilleries, food­processing industries, tanneries, and paper, pulp industries) generate large amounts of organic wastes. Food products and agro-based industries contribute 65-70% of the total industrial wastewater in terms of organic load (Zafar, 2008). The term ‘residues’ is often preferred to ‘waste’ whenever possible, in order to assign a value of exploitable resource to the organic matter rather than being a problem to be solved. The term ‘feedstock’ is also often preferably used to describe the material fed to a digester.

Feedstocks with a high biomethane potential can be classified as follows:

• Agricultural (livestock manure, agricultural residues, animal mortalities, energy crops)

• Industrial (wastewater, sludges, by-products, slaughterhouse waste, spent beverages, biosolids)

• Municipal (sewage sludge, organic fraction of municipal solid waste)

A database including the biochemical methane potential of various feedstocks can be found at the website (http://www. emu-bioconversion. eu/). Data are collected (but not validated) from literature and, after standardisation of the units, the chemical composition and the methane potential of various feedstocks are included in the database.