Remediation of Crude Oil-Contaminated Nigerian Soils by Microwave Heating

Abstract Oil spillage in Nigeria poses a significant threat to the environment, particularly in the Niger Delta region, which covers over 112,000 km2 and includes extensive areas that have become unsuitable for agriculture due to petroleum contamination. Microwave (MW) heating was investigated as a remediation technique for loamy, clay, and sand soils contaminated with 1.3–5.1% w/w crude oil by varying the treatment time and microwave power input. Using a microwave power of 0.8 kW and a treatment time of 420 s, more than 99% removal of solvent-extractable oil was achieved for the clay soil, while approximately 90% and less than 50% were obtained for the loamy and sand soils, respectively. The results demonstrate that remediation efficiency is strongly influenced by soil type, with clay soils exhibiting the highest oil removal under the investigated conditions. The findings suggest that soil water may play a critical role in microwave heating performance. Higher water content could increase the dielectric constant and dielectric loss factor of the soil, thereby promoting microwave energy absorption and potentially enhancing oil removal. In addition to water content, soil mineralogy and dielectric properties may significantly influence the oil removal process. Experimental results showed that increasing the water content of sand soil from 1.6% to 14% increased oil removal by 6%. Similarly, increasing the water content of loamy soil from 3.3% to 14% increased oil removal by 40%. These findings indicate that controlled water addition is an effective strategy for enhancing the microwave remediation of contaminated soils.