Effect of Citrus sinensis peel-derived biochar on the concentrations of heavy metals in soil irrigated with municipal wastewater

Abstract

Wastewater is widely used for irrigation and can accumulate heavy metals in the soil, potentially causing harm to human health and the environment. In this study, a pot experiment was used to assess the impact of biochar in soil properties enhancement as well as mitigation of the concentration of Cd, Cu, Zn and Pb to lettuce (Lactuca Sativa) in a soil irrigated with wastewater. Citrus peel biochar pyrolised at 400°C was applied on soil in three levels (0%, 5%, and 10%). The lettuce plant was harvested after 28 days of planting, and the concentrations of heavy metals were determined in roots and leaves using atomic absorption spectroscopy (AAS). The result obtained shows the increase in soil properties with an increase in biochar concentration, the result also shows the p-value of leaves and roots as 0.744 which is not statistically significant at 95% confidence interval. The result obtained shows a decrease in the uptake of heavy metals by the lettuce plant in both parts of the plants (leaves and roots) as follows: the concentration of cadmium was not detected at all levels in both roots and leaves, in un-amended samples (Leaves) the concentration of Cu, Pb, and Zn were 0.141, 0.252, and 1.116 respectively while in roots the concentration of Cu, Pb, and Zn were 0.205, 0.266, and 1.248 respectively. At 5% amendment (leaves) Cu decreased by 48.2% (0.073), Pb by 42.86% (0.144), and Zn by 66.13% (0.378). At 10% amendment (leaves) Cu decreased by 71.63% (0.040), Pb by 53.57% (0.117), and Zn by 48.03% (0.580). While in roots almost similar reductions were observed. These findings show the potential of biochar as an effective strategy for soil properties improvement as well as reducing heavy metals uptake by the plants, with implications for sustainable agriculture in an environment contaminated with heavy metals.