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A by-product is a secondary product derived from a manufacturing process or chemical reaction. It is not the primary product or service being produced. A by-product can be useful and marketable or it can be considered waste.

IEA offers the following definition for the purpose of life-cycle assessment:[1]

... main products, co-products (which involve similar revenues to the main product), by-products (which result in smaller revenues), and waste products (which provide little or no revenue).

Major by-products

Animal sources

Template:See also

  • blood meal – from slaughterhouse operations
  • poultry by-product meal – clean parts of the carcass of slaughtered poultry, 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
    • feather meal – from poultry processing
  • fetal pigs
  • lanolin – from the cleaning of wool
  • leather - hides and skins from slaughterhouse operations processed via the leathermaking process
  • manure – from animal husbandry
  • meat and bone meal – from the rendering of animal bones and offal
  • poultry litter – swept from the floors of chicken coops
  • whey – from cheese manufacturing


  • acidulated soap stock – from the refining of vegetable oil
  • bagasse – the fibrous residue remaining after sugarcane or sorghum stalks are crushed to extract their juice
  • black liquor from the production of cellulose pulp using the kraft process
  • bran and germ – from the milling of whole grains into refined grains
  • brewer's yeast – from ethanol fermentation
  • cereal food fines – from breakfast cereal processing
  • corn steep liquor – from corn wet-milling
  • 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
  • soybean meal – from soybean processing
  • stover – residual plant matter after harvesting of cereals
  • straw – from grain harvesting
  • tall oil from the production of cellulose pulp using the Kraft process
  • vinasse – from the fermentation of sugar to ethanol fuel

Minerals and petrochemicals

  • asphalt – from the refining of crude oil
  • fly ash – from the combustion of coal
  • slag – from ore refining
  • gypsum – from flue-gas desulfurization
  • He - from natural gas extraction
  • ash and smoke – from the combustion of fuel
  • mineral oil – from refining crude oil to produce gasoline
  • salt – from desalination
  • Mo – from Cu extraction


  • sludge – from wastewater treatment
  • waste heat - from electricity production and usage
  • CO2 - process of burning

See also

  • By-product synergy