Many agricultural crops are processed into consumer products, often resulting in the generation of processing wastes. The types of wastes produced are numerous and varied. Among those most frequently mentioned as potential bioenergy and bioproduct feedstocks are cotton gin trash, waste fats and greases, whey, and food industry wastes (e.g., cull fruits and vegetables, fruit and vegetable seed pits, citrus peels and pulp, nut shells, fruit and vegetable pumice, and seafood shells among other items).
Cotton gin trash includes materials such as leaves, burs, stems, and sticks that are contained in the harvested cotton and separated at the cotton gin as well as cotton seed hulls. Studies generally estimate that less than one million dry tons of cotton gin trash is available.
Waste fats and greases include the fat portion of livestock carcasses that are not processed into human food products as well as recycled restaurant cooking oils (i.e., yellow grease and trap grease). About 4.2 million metric tons (4.6 million tons) of fats and greases are processed by the rendering industry annually, with an estimated additional 381 billion pounds of trap grease produced and collected by the septic industry annually.
Whey is the liquid that remains after the milk is curdled to produce cheese. An estimated 935,000 metric tons (1.03 million tons) of whey and lactose are produced annually in the U.S.
Little data is available regarding quantities of food industry wastes and the few studies that have assessed these materials are generally limited to evaluating only one or a few types of materials and usually for a single city or state.