The role of biochar in a circular economy: from agriculture to water and wastewater treatment applications

Biochar is a sustainable carbonaceous solid material derived from biomass pyrolysis, which abides to circular economy principles in several ways that concern both its production and its several application fields. Biochar is produced by valorizing different organic waste biomass, such as agricultural waste, municipal solid waste, sewage sludge and industrial biowaste, to create a beneficial and valuable product that can then be used in many fields. Thus, biochar production serves perfectly the circularity paradigm as it renders a previously considered waste material to a valuable input material for a new production process. The grounds for the increasing use of and interest in biochars is their favourable physicochemical characteristics, such as the high carbon, macro- and micro- nutrient content, the high porosity and specific surface area, and the abundance of surface functional groups. Biochar can be effectively used as soil amendment providing fertilizing properties to the applied soil that leads to higher crop production and increased crop nutrient content and quality. At the same time, it provides a stable source of carbon to the soil for several years after its application, contributing this way to CO2 mitigation. Biochar can also be used as an adsorbent due to its carbonaceous porous structure to remediate polluted soil, water and wastewater from either organic or/and inorganic pollutants, even in low pollutant concentrations. his abstract will present a comprehensive range of studies on biochar production from different sources and its use in different sectors. One of the latest applications is its use as a substrate in Constructed Wetlands for sustainable wastewater treatment, in order to enhance the various pollutant removal/transformation processes. Three different research studies will be presented where biochar was produced from green waste (e.g., olive tree branches) and used as substrate in various Constructed Wetland pilot units that treat domestic wastewater, landfill leachate and olive mill wastewater as an ecological treatment technology. Furthermore, an agronomic application of biochar as soil amendment in a pot experiment for the cultivation of lettuce will be shown. Finally, the environmental application of biochar produced from sewage sludge as adsorbent will be presented towards the decontamination of water and wastewater from organic emerging micro-contaminants.