Efficient removal of Cd(II) and Pb(II) from aqueous solution using biochars derived from food waste

Massive amount of food waste has been generated annually, posing a threat to ecological sustainability and the social economy due to current disposal methods. Urgent action is needed worldwide to convert the traditional pathway for treating food waste into a sustainable bioeconomy, as this will significantly benefit food chain management. This study explores the use of pyrolysis to produce different types of food waste biochars and investigates their adsorption capabilities for removing Cd²⁺ and Pb²⁺ in aqueous solution. The results indicated that co-pyrolysis biochar from fresh food waste and rice husk (FWRB) exhibited superior adsorption performance for Cd²⁺ (61.84 mg·g^-1) and Pb²⁺ (245.52 mg·g^-1), respectively. Pseudo-second-order kinetics (0.74 ≤ R² ≤ 0.98) and Langmuir isotherms (0.87 ≤ R² ≤ 0.98) indicated that the immobilized Cd²⁺ and Pb²⁺ on biochars were mainly attributed to the chemisorption, including precipitation with minerals (e.g., carbonates, silicates, and phosphate), complexation with functional groups (-OH), cation exchange (-COO^-), and coordination with π-electrons. Furthermore, FWRB demonstrated reduced EC and Na content in comparison to food waste digestate biochar (FWDB) and food waste digestate co-pyrolysis with sawdust biochar (FWSB), with levels of Cd and Pb falling below China's current guideline thresholds. These findings suggested that co-pyrolysis of fresh food waste with rice husk could be applicable to the recycling of food waste into biochar products for heavy metal stabilization in contaminated water and soils.