The effectiveness of various biochar types in enhancing the phytoremediation of soils polluted with petroleum hydrocarbon

Abstract Background Biochar can enhance phytoremediation in petroleum hydrocarbon polluted soils, making it an intriguing soil amendment option for remediating polluted soil. Biochar can improve the fertility of depleted soils through a range of mechanisms. This study can contribute valuable insights into the origin of biochar and enhance our understanding of the efficacy of different biochar types in remediating petroleum hydrocarbon polluted soils. Aims To assess the efficacy of different biochar types and plant growth in remediating petroleum hydrocarbon polluted soils. Methods A field experiment was conducted at the automobile workshop (commonly called mechanic village) from July to October 2021, using a randomized complete block design. The land was sectioned into designated plots with three replicates. Maize stalk biochar (MSB) and nipa palm biochar (NPB) were treated differently in each plot at a rate of 20 t ha −1 . Plots containing no biochar were used as controls. Initial and final soil analyses were conducted. Results Preliminary soil assessments revealed higher values of soil bulk density (1.51 g cm −3 ), moisture content (35.02%), organic carbon (41.01 g kg −1 ), cation exchange capacity (13.27 cmol kg −1 ), total petroleum hydrocarbon content (PHC t ) (775.83 mg kg −1 ), cadmium (Cd) (5.41 mg kg −1 ), chromium (Cr) (25 mg kg −1 ), lead (Pb) (33.51 mg kg −1 ), and zinc (Zn) (0.91 mg kg −1 ) in the polluted soil than in the unpolluted counterpart. The polluted soil displayed lower hydraulic conductivity ( K s ) (1.17 cm h −1 ), available phosphorus (69.46 mg kg −1 ), manganese (Mn) (6.38 mg kg −1 ) and iron (Fe) (4.18 mg kg −1 ) contents than the unpolluted soil. The PHC t , Cd, and Cr were significantly decreased following the application of biochar. NPB recorded the lowest petroleum hydrocarbon (19%), lead (37%), manganese (57%), and zinc (69%) contents, whereas MSB had the lowest cadmium (50%) and chromium (27%) contents when compared with the control. Between heavy metal accumulations in the leaves and fruits, a greater accumulation of Cd, Cr, and Pb was found in the leaves, whereas Ni accumulation was found in the fruits. The highest Cd (47.0 mg kg −1 ) and Ni (8.3 mg kg −1 ) accumulations in the leaves were recorded in NPB treated plots. Similarly, Cd (5.3 mg kg −1 ), Cr (3.7 mg kg −1 ), Pb (21.6 mg kg −1 ), and Ni (23.4 mg kg −1 ) accumulation in the fruits recorded the highest values in the NPB treated plots. The NPB plants were the tallest compared with the other treatments. In addition, NPB plants had the widest leaf area compared with other treatments. Conclusion The results indicated that the amendment of NPB may be suitable for the phytoremediation of soils polluted with petroleum hydrocarbons.