A by-product is a secondary or incidental product deriving from a manufacturing process, a chemical reaction or a biochemical pathway, and is not the primary product or service being produced. A by-product can be useful and marketable, or it can have severe ecological consequences.

Major by-products

Animal sources

• dried blood and blood meal - from slaughterhouse operations
• chicken by-product meal - clean parts of the carcass of slaughtered chicken, such as necks, feet, undeveloped eggs, and intestines.
• chrome shavings - from a stage of leather manufacture
• collagen and gelatin - from the boiled skin and other parts of slaughtered livestock
• feathers - from poultry processing
• lanolin - from the cleaning of wool
• manure - from animal husbandry
• meat and bone meal - from the rendering of animal bones and offal
• poultry byproduct and poultry meal - made from unmarketable poultry bones and offal
• poultry litter - swept from the floors of chicken coops]
• whey - from cheese manufacturing
• fetal pigs

Vegetation

• acidulated soap stock - from the refining of vegetable oil
• bran and germ - from the milling of whole grains into refined grains
• brewer's yeast - from ethanol fermentation
• corn stover - residual plant matter after harvesting of cereals
• distillers grains - from ethanol fermentation
• glycerol - from the production of biodiesel
• grape seed oil - recovered from leftovers of the winemaking process
• molasses - from sugar refining
• orange oil and other citrus oils - recovered from the peels of processed fruit
• pectin - recovered from the remains of processed fruit
• sawdust and bark- from the processing of logs into lumber
• straw- from grain harvesting

Minerals and petro chemicals

• asphalt - from the refining of crude oil
• fly ash - from the combustion of coal
• slag - from ore refining
• gypsum - from Flue gas desulfurization
• ash and smoke - from the combustion of fuel
• mineral oil - from refining crude oil to produce gasoline
• salt - from desalination

Other

• sludge - from wastewater treatment

See also

• By-product synergy