Abstract
The production of biochar from waste materials by pyrolysis can play a significant role in materialising the circular economy. The application of biochar with positive impacts are attributed by the unique properties of biochar, including its surface area, porous structure, functionality and adsorption capacity. The application of biochar with higher stability and resistance due to higher fixed C content contributes to a better C sequestration in the soil. The application of biochar with higher surface area and electrical conductivity is better for adsorption whereas biochar rich with nutrient element is suitable for plant uptake and agricultural purposes. The properties enabling such applications are found to have a varying degree of dependence on the feedstock composition and pyrolysis temperature. The biochar has been conventionally produced from lignocellulosic-rich biomass. There is increasing interest in the use of manure and food waste to produce biochar via pyrolysis. These wastes differ significantly on their lignocellulosic content and mineral content, ash content and elemental content. This difference could give rise to different biochar yield and providing varying properties. Different structural and degradability of the organic pools could lead to different optimum processing condition and the properties of biochar. In this review, the feedstock of interest is lignocellulosic biomass, food waste and manure where the variation in their compositions may contribute to specific properties of the biochar, such as stability, polarity, pH, cation exchange capacity, heating value, surface area and minerals content. The desired applications of biochars include C sequestration, fuel, soil amendment, enhanced crop nutrient and adsorption for pollutant remediation. This paper provides an overview for an optimal selection of the feedstock composition and the properties of the biochar produced via pyrolysis, and their subsequent applications. Overall, it was found that the applications as a soil amendment and adsorption material are the most commonly suited applications for biochar derived from the three reviewed feedstock. Lignocellulosic biomass-derived biochar showed a more significant advantage for C sequestration and as fuel, while manure- and food waste-derived biochar showed a greater functionality in retaining soil nutrients and absorbing pollutants.
