Study on the effects of carbon dioxide atmosphere on the production of biochar derived from slow pyrolysis of organic agro-urban waste.

[Display omitted] • The effect of CO 2 atmosphere on biochar production and properties was studied. • Compared to inert N 2 , CO 2 significantly affects the pyrolysis products. • CO 2 promotes biochar yields (400–600 °C) for all feedstocks. • Surface area and porosity of biochar can be improved using CO 2 in pyrolysis. • CO 2 biochar contained higher C, lower O/C and O/H ratios. Slow pyrolysis, a widely recognized thermochemical technique, is employed to produce biochar usually under inert atmospheres. Recently, there is a growing interest in utilizing CO 2 as a carrier gas during pyrolysis as an alternative to inert atmospheres, aiming to modify the resulting pyrolytic products and make them suitable for different applications. This study investigated and compared the impact of CO 2 atmosphere with N 2 on pyrolysis of food waste, rice husk, and grape tree branches waste via slow pyrolysis at temperatures of 400, 500, and 600 °C at 5 and 15 °C/min for 1 h, to evaluate biochar production and its properties. The results demonstrate that CO 2 atmosphere increased the biochar yield for all feedstocks and significantly influenced the physicochemical properties of biochar. Compared to N 2 , CO 2 -derived biochar exhibited less volatile matter, higher carbon content, lower O/H and O/C molar ratios and enhanced textural properties. This study highlighted the potential of utilizing CO 2 for biochar production and tailoring biochar properties for specific applications and the findings contribute to the establishment of sustainable and efficient waste management systems and the production of value-added biochar products. [ABSTRACT FROM AUTHOR]