Organic industrial waste includes a wide range of organic materials obtained from industrial and commercial operation. These organic wastes, either liquid or solid, are a good substrate for biogas generation by making use of the anaerobic digestion process. Anaerobic digestion of organic industrial waste is fast gaining popularity worldwide.
Many industries produce liquid and solid wastes that are suitable for anaerobic digestion, such as food processing, pharmaceuticals, organic chemicals, paper manufacturing and tannery industries. Some of the wastes might be difficult to digest as a sole substrate, but they can be biochemically degraded in combination with manure or sewage sludge. The combined digestion of different wastes is called co-digestion.
The global food processing industry produces a large number of organic residues and by-products that can be used as biomass energy sources. In recent decades, the fast-growing food and beverage processing industry has remarkably increased in importance all over the world. The food processing industry consists of the following sub-sectors:
- Processing, preserving of meat and its product
- Canning and preserving of fruit and vegetables
- Manufacture of vegetable oil and fats
- Manufacture of dairy products
- Grain mill products
- Manufacture of prepared animal feeds
- Manufacture of bakery products
- Manufacture of cocoa, chocolate and sugar confectionery
- Manufacture of other food products
- Manufacture of soft drink
Solid wastes include peelings and scraps from fruit and vegetables, food that does not meet quality control standards, pulp and fibre from sugar and starch extraction, filter sludges and coffee grounds. Liquid wastes are generated by washing meat, fruit and vegetables, blanching fruit and vegetables, pre-cooking meats, poultry and fish, cleaning and processing operations.
Pulp and paper industry is considered to be one of the highly polluting industries and consumes large amount of energy and water in various unit operations. The wastewater discharged by this industry is highly heterogeneous as it contains compounds from wood or other raw materials, processed chemicals as well as compound formed during processing.
A tremendous potential exists for these industrial wastes to be anaerobically digested to produce biogas, or fermented to produce ethanol, and several commercial examples of waste-to-energy conversion already exist in different parts of the world. The use of biogas technology is increasing rapidly for industrial wastewater treatment. There are more than 2,500 vendor-supplied systems in operation or under construction throughout the world. Over 30 types of industry have been identified as having wastewaters amenable to anaerobic digestion treatment, including processors of beverages, chemicals, food, meat, milk, pulp and paper, and pharmaceutics.