Investigation of impact of slow-release fertilizer and struvite on biodegradation rate of diesel-contaminated soils

Fossil fuel remains the most used form of energy in the world and while it is only available in some countries, there is always the need to transport it to disadvantaged countries, which often results in oil spillages. Distribution of petroleum and petroleum products upstream and downstream also results in oil spillages. In cases where there is ineffective or no containment during and after oil spillages, the problem of oil pollution could be worsened by migration and seepage into receiving systems. In such a case, there is a need to identify and apply appropriate remediation techniques to reduce the impact and extent of the spillage. Some microbes have been identified as having the ability to degrade hydrocarbons and could potentially be harnessed for oil spillage clean-up but, would require sustainable nutrients supply to enhance biodegradation rate and efficiency. This study investigated the impact of slow-release fertilizer and struvite on the biodegradation rate and efficiency of diesel-contaminated soils with a view to determining whether struvite could be applied in the biodegradation of oil-contaminated soils as an alternative, low-cost, and sustainable approach. The test models were dosed with a cumulative oil loading of 178 mg m ⁻² week ⁻¹ based on the derived oil loading of 9.27 g m ⁻² year ⁻¹ with a view to comparing the efficiency of the nutrient sources. The nutrient sources, Osmocote Plus controlled-release fertilizer granules and struvite were applied at a one-off rate of 17 g m ⁻² to provide nutrient requirements and enhance biostimulation. The effect of the nutrients was studied by monitoring microbial growth in different growth media, the evolution of Carbon dioxide, elemental content by Inductively Coupled Plasma Atomic Emission Spectrometry, Electrical conductivity of effluent, Total Petroleum Hydrocarbons by infra-red spectroscopy, and pH of effluent. The results showed that Osmocote® plus controlled-release fertilizer is more effective in enhancing microbial growth than Struvite slow-release fertilizer hence, a relatively faster bioremediation rate. It should be noted that struvite accumulation in public water pipe works is an issue of environmental concern hence, any meaningful utilization and application of this “waste” in the bioremediation of contaminated soils would offer a sustainable and low-cost means of disposal of what is hitherto an environmental problem. However, it may require augmenting of the deficient nutrients to enhance effectiveness. This could be accomplished by incorporating naturally occurring nutrient sources such as rock phosphate, kelp, and bedrock nitrogen for sustainability.