A Technical Review of the Effects of Bone Char, Spent-palm Bunch, and Inorganic Fertilizer in the Biodegradation of Hydrocarbon-Polluted Soil

This paper critically reviews the comparative mechanisms of bone char, Spent-Palm-Bunch (SPB), and NPK (Inorganic) fertilizers in driving the biodegradation of saturated, aromatic, resin, and asphaltene fractions in polluted tropical soils. Following a transparent search of relevant literatures, we identify the primary studies that report bone char, SPB, or NPK amendment of hydrocarbon-contaminated soil, extract their soil type, contaminant loading, amendment dose, trial duration, microbial response, hydrocarbon-fraction removal, pH shift, and stated limitations. Only one identified study places bone char and NPK head-to-head on the same soil under the same protocol; no identified study places all three amendments together. Kinetic modelling (first- and second-order decay) and Response Surface Methodology (RSM) have been applied within single-amendment studies to optimize dose and predict half-life, but never across amendments to test whether bone char, SPB, and NPK differ significantly in mechanism or outcome. We identify critical knowledge gaps in comparative field validation, bio-char/waste matrix optimization, and long-term ecosystem recovery. Finally, an integrated conceptual framework is proposed to guide scalable, bioremediation strategies, critical field-validation, dose-standardization, and joint-modelling work for hydrocarbon degraded tropical soils.