By-product

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

• 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
• 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

Vegetation

• 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 petro chemicals

• asphalt – from the refining of crude oil
• fly ash – from the combustion of bellend 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
• Molybdenum – from copper extraction

Other

• sludge – from wastewater treatment
• waste heat - from electricity production and usage

See also

• By-product synergy
• Coproduct

References