Comprehensive Analysis of Raw and Ash Oil Refinery Sludge and Its Impact on Soil Characteristics

Abstract

Annually, substantial quantities of sludge are generated by oil refineries in Iraq. This sludge exists in raw or ash forms that are categorized as hazardous to ecological systems because of the presence of toxic components, notably hydrocarbons and heavy metals. This study characterizes oil refinery sludge (ORS) in its raw and ash forms and assesses their adverse effects on soil properties through extensive analysis. Mixed raw sludge–soil and ash sludge–soil samples were prepared at proportions of five percent, 10 percent, and 20 percent. The results revealed that raw sludge mainly comprised amorphous and solid phases. The amorphous phase contained 38 percent carbonaceous species ascribed to the aliphatic functional group, whereas the solid fraction was identified based on the presence of heavy metals and inorganic components. Meanwhile, the solid phase was predominant in ash sludge samples that had greater concentrations of inorganic components and heavy metals. Contaminated soil samples exhibited increasing heavy-metal levels. Pollution indices, including the single pollution index (SPI), contamination factor (Cf), environmental risk index (ERi), and potential environmental risk index (PERI), revealed that ash sludge poses a greater ecological threat to soil than raw sludge, and the contamination ranking was Cd > Ni > Cr > CO > Cu > Pb > Zn > Fe > Mn > V. Oil refinery sludge in its raw and ash forms has toxic characteristics; therefore, its disposal in soil should be reconsidered. Regular monitoring and strict enforcement of environmental regulations are essential. In addition, investment in alternative eco-friendly and sustainable treatment strategies is strongly recommended to preserve natural resources.