Effects of Rice and Sorghum-straw Derived Biochars on Selected Plants Grown on Spent Oil-Contaminated Soil

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The increased presence of Heavy Metals (HMs) in soil has been a great public health and environmental concerns in developing countries. Spent oils that are discharged indiscrimately into the environment or used as herbicides have been found to contribute to the release of HMs into the soil. The use of biochar as an amendment agent in Spent Oil-contaminated Soil (SOS) has been found to be a simple, cheap, and sustainable HMs remediation technology. This study aimed at investigating the potential of Rice and Sorghum Straw-derived Biochars (RSSB) on HMs mobility in Tridax procumbens, Zea mays, Tithonia diversifolia and Pennisetum glaucum grown in SOS. The objectives of the study were to determine the: (i) physicochemical properties of RSSB; (ii) functional properties of RSSB; (iii) physicochemical properties and HMs contents of SOS; (iv) growth potential of the selected plants in SOS; (v) mobility of HMs in the selected plants; and (vi) phytoextraction potentials of the selected plants. Biochars derived from rice and sorghum straws by slow pyrolysis were characterized for physicochemical and functional properties using standard methods. Composite soil was spiked with spent oil (5% v/w), potted and amended with different concentrations (0, 1, 2 and 3% w/w) of biochar. The soil was incubated for 30 days and physicochemical properties were determined using standard methods. Seeds of the selected plants were sown in the treated soil and their growth attributes were measured with standard methods. Harvested plant parts and soil samples were digested and analyzed for copper, zinc, lead, cadmium and chromium contents using Atomic Absorption Spectrophotometer. The transfer factor and bioconcentration factor of the test plants were determined with standard models. Data were subjected to Analysis of Variance while Duncan’s Multiple Range Test at p≤0.05 was used to separate the means. The findings of the study were that: (i) rice biochar had pH (8.54), ash (52.37%), Mg (0.70%), K (11.88%) and Si (14.36%) contents while sorghum biochar had pH (8.41), ash (35.07%), Mg (0.69%), K (7.89%) and Si (14.72%) contents; (ii) the biochars possessed micropores and macropores and functional groups such as OH (3400 cm-1) and aromatic compounds, C-H (900 to 885 cm-1); (iii) biochars significantly (p≤0.05) increased soil properties such as pH (20.66%), water holding capacity (36.67%) and porosity (37.29%) but significantly (p≤0.05) reduced heavy metals below the permissible limits recommended by WHO; (iv) rice biochar at 3% increased the height of the plants: Pennisetum glaucum (76.03%), Zea mays (81.50%), Tithonia diversifolia (39.27%) and Tridax procumbens (66.42%) while sorghum biochar at 3% increased the height of the plants: Pennisetum glaucum (157.61%), Zea mays (23.01%), Tithonia diversifolia (83.33%) and Tridax procumbens (66.66%); (v) the biochars significantly reduced (p≤0.05) the availability of Cu, Zn, Pb, Cd and Cr; and (vi) only Zea mays extracted Cu and Cr while others stabilised the HMs. The study concluded that RSSB amended spent oil-contaminated soil by reducing the availability of the HMs and improving the properties and nutrients required to support plant growth. The study therefore recommended the two biochars for the remediation of SOS.



Rice, Sorghum-straw, Sorghum-straw Derived Biochars, Spent Oil-Contaminated, Soil