Biorefineries for sustainable waste valorization

Industrial production of biofuels such as ethanol, butanol, biodiesel, etc. utilizes plant-based feedstocks (corn, sugarcane, sugar beet, oil seeds, algae) with high concentration of carbohydrates or lipids. Most of these feedstocks, after extraction of sugar, starch, and lipid for the synthesis of biofuel, contain high concentrations of fiber, protein, and minerals which could be utilized and upcycled into potential animal feeding ingredients to support sustainable food supply. In addition, human beings generate large volumes of food wastes each year which include crop residues, organic processing wastes, fruit/vegetable discards, etc. These food wastes and discards contain readily available nutrients including carbohydrates, starch, lipids, proteins, and minerals but are prone to be spoiled quickly. Converting food wastes and discards into appropriate feeding ingredients would significantly reduce the cost, energy, and carbon footprint for animal feed production and achieve a sustainable food supply. On the other hand, biomass that is not feasible for feed, organic wasting materials such as sewage sludge, municipal solid wastes, and animal manure are major concerns for environmental pollution including air, soil, and water and contribute largely to "greenhouse" effect. Treatments of these organic wasting materials by thermochemical transforming, composting, and anerobic digestion can efficiently reduce their environmental impacts while producing materials of benefit such as bio-fertilizer, biochar, energy, and industrial-valued chemicals. Among these products, bio-fertilizer and biochar can be applied to agricultural land to improve soil fertility which could directly affect the productivity of crops that grow on the soil. Therefore, an integrated biorefinery of agricultural and food wastes including the production of biofuel, animal feed, bio-fertilizer, with appropriate treatment of wasting materials from agricultural processing and animal production should be a trend for a more sustainable agricultural economy. In this chapter, different types of biorefineries and their contribution to the supply of energy and food, with protection of soil, water, and air quality to facilitate the formation of a circular economy will be discussed.