Utilization of waste materials generated in different industries is important from the points of ecology, economics and conservation of non-renewable resources. One of the main waste materials in petroleum industry is oil sludge, which is produced by the treatment of wastewater, from various refining and tank cleaning processes. Biotreatment or otherwise biodegradation by natural populations of microorganisms is one of the primary mechanisms by which petroleum and other hydrocarbon pollutants can be eliminated from the environment. The biotreatment technology by biopiles, which is applied in Thessaloniki Refinery area of Hellenic Petroleum S.A., for the case of the solid residual material (SRM) (dewatered oil sludge) derived from oil refinery sludge, is presented in this study. Experimental results presented herein demonstrate the fact that the biotreatment method of biopiles in the case of solid residual material stemming from oil refinery sludge can achieve high biodegradation efficiencies for organic s...