Heavy Metal Contamination in Biomass-Based Fuels: Risks and Mitigation Strategies

Abstract

Biomass is a potential renewable energy source to reduce dependence on fossil fuels. However, heavy metal contamination in biomass, especially from agricultural waste, poses environmental and health risks. This study analyzed the heavy metal content in various types of biomass, including oil palm empty fruit bunches (EFB), rice husk, wood pellets, and biocoke, and evaluated mitigation strategies that can be applied. The results showed that EFB had the highest heavy metal content, with concentrations of Pb (2.5 mg/kg), Cd (1.8 mg/kg), As (0.9 mg/kg), and Hg (0.5 mg/kg), compared to wood pellets which had lower levels (Pb: 0.8 mg/kg, Cd: 0.3 mg/kg, As: 0.2 mg/kg, Hg: 0.1 mg/kg). Several mitigation strategies have been shown to be effective in reducing heavy metal content. The washing method with a weak acid solution can reduce Cd content by up to 40% and As by up to 35%, while adsorption with biochar can reduce Pb levels by up to 50% and Hg by up to 60%. In addition, the volatility of heavy metals increases significantly at temperatures above 600°C, which increases the risk of hazardous air emissions. Overall, most biomass samples are still within safe limits according to EN 14961 and EPA standards, although some agricultural wastes are close to the threshold. Therefore, strict monitoring and broader mitigation strategies are needed to ensure that biomass remains safe for use as fuel. Implementation of appropriate technology will improve the sustainability of biomass energy and reduce negative impacts on the environment and human health.