Biochar production to support circular bioeconomy: from waste biomass to a valuable product

Circular bioeconomy activities, which turn waste streams into new products, can play an important role in improving soil quality and carbon storage. There are significant opportunities for developing the use of agricultural residues, by-products, and organic waste. In this context, biochar, a carbon-rich material produced by the pyrolysis of biomass, is receiving much attention in recent times for its distinctive properties. Among them, the biochar amendment to soil have known to improve soil fertility, providing a trophic and spatial niche for microorganisms, soil remediation from toxic metals and organic contaminants, catalyst for industrial applications, and feed supplement to improve nutrient intake efficiency. Moreover, the loss of soil fertility due to erosion and the loss of organic matter, coupled with the ever-increasing production of waste biomass, makes the biochar production and its use as soil amendment a model of circular bioeconomy. Despite the promising outlook, the overall benefit of using biochar remains highly debated. In this context, the main criticism is due to the heterogeneity of biochar itself, in terms of physical, chemical, and biological properties highly influenced by production variables such as feedstock types and treating conditions. The aim of this chapter is to describe the state of the art on biochar production for circular bioeconomy in agricultural farming systems to achieve a dual benefit: (1) increasing soil carbon storage using agricultural waste biomass and (2) maintaining and/or improving soil quality regulating nutrients biogeochemical cycle and water retention.