Characterization and Remediation Potential of Sorghum and Rice Straw-Derived Biochars on Incubated Spent-Oil Contaminated Soil

Abstract

The volume and spread of spent lubricants that are indiscriminately let into the environment in developing countries are prohibitive for soil health and productivity, adversely altering soil structure, permeability and microbiota. These result to loss of arable lands and low vegetation cover, thereby contributing significantly to food insecurity and global warming. Biochars possess sustainable soil amendment potentials that depend on the choice of feedstocks. This study used suitable analytical techniques to characterize biochars derived from sorghum and rice straw after slow pyrolysis at 550°C for three hours and investigated their effects on the physicochemical properties of spent oil-contaminated soil in an incubation experiment. Both sorghum biochar (SB) and rice biochar (RB) have pH in the alkaline range (˃ 8.0), similar O/C ratio (0.24), and significant proportions of carbon (53.87–57.57%). Scanning electron microscopy of SB and RB surfaces revealed presence of porous structures. Fourier Transform Infrared Spectroscopy revealed presence of carboxyl, hydroxyl, halogens, and sulphur on the surfaces of SB and RB which are responsible for heavy metal adsorption. Compared with control, increasing biochar amendment at 1, 2 and 3% significantly increased the porosity, water holding capacity and pH of the soil. Besides, soil Fe increased while the extractable content of heavy metals decreased. From this study, the properties of SB and RB and corresponding application in spent oil-contaminated soil indicate their suitability for soil enrichment and amendment.