Effect of Oily Sludge Land Treatment on Soil Conditions

Land treatment is a method of handling wastes produced by the petroleum refining industry and others. This method allows the simultaneous treatment and final disposal of the waste. This study represent a fundamental filed investigation to follow the land treatment method for disposing of an oily sludge produce by Daura Refinery Wastewater Treatment Plant. The sludge typically consists of (84.5-86.2)% water, (4.7-5.3)% oils, and (8.4-9.25)% sediments. It is characterized by law contents of phenol, nitrogen, and heavy metals of environmental concern. Loamy sand soil land located inside Daura Refinery was selected and divided into a1-sq. meter plots. A range of sludge application rates was applied to add the sludge to (mix with) the upper 15 cm soil layer of 18 plots, whereas 6 plots left as control plots. The applications range included three applications ratios of (fresh sludge wt, : dry soil wt.) as (1:3), (1:6), and (1:10), each of them was applied in three application intervals: weekly, monthly, and seasonally. Selection of the best application rate was made with regard to sludge degradation and land area requirements. Soil samples were tested for oil residue, heavy metals, total nitrogen, electrical conductivity, pH, and aggregate stability. The results show that, monthly (1:10) application rate caused neither considerable downward oil migration in the soil nor significant accumulation of oil, heavy metals, or salts in the soil. However, it maintained neutral soil pH and improved soil aggregate stability. Oil biodegradation in the soil was encouraged by soil weakly tillage.