Sustainable Remediation Technique for Heavy Metals-Contaminated Soil Using Agro-Waste

Abstract

Investigating the potential of Vernonia amygdalina (bitter leaf) leaf extract to stimulate the removal of selected heavy metals (chromium, zinc and iron) in spent engine oil-contaminated soil, which would help in managing the agro-waste. To achieve this, 4kg of sandy loam soil was artificially polluted with a fixed used engine oil of 0.5L to simulate conditions of a spill. The leaf extract was derived from the bitter leaf plant which were harvested, washed with distilled water, blended and filtered to get the juice. The experiment used a randomized complete block design (RCBD), the set-up consisted of three treatments (T1, T2 and T3) and one control (T4), each replicated twice. The stated treatments contain 250, 500 and 750 g of the leaf extract except for the control with no treatment. The set-up was tilled and irrigated twice weekly for a period of 40 days. The nutritional (nitrogen, phosphorus and potassium) value of the bitter leaf extract and selected heavy metals were determined following standard procedures. The heavy metals content were determined before and after application of treatment, till the end of the experiment. After 40 days of treatment, chromium content dropped to 0.023, 0.015, 0.0065 and 0.121 mg/kg (T1, T2 T3 and T4), accounting for 61.76, 42.31, 25.81 and 19.01% reduction, respectively. Zinc and iron followed same trend. However, C reclaimed the selected heavy metals in the spent engine oil-contaminated soil, better than other levels of treatments.