Treatment Of Oily Sludge By Chemical Hot Washing - Biodegradation

A large number of oily sludge can be produced from the process of crude oil mining, refining and transportation. It not only will induce the environmental pollution, but also be a waste of crude oil resource while the oily sludge is discharged directly without any disposal. The remediation of Petroleum-contaminated soil is drawing a greater attention, which involves physical-, chemical- and biological- control methods. Because the oily sludge, collected from an oilfield in Xinjiang, is high oil content, a single approach to treat the oily sludge cannot achieve the requirement of "National Clean Production Promotion Law" and "Environmental Solid Waste Pollution Law". For the purpose of oil recovery and detergency of oily sludge, chemical heat wash-biodegradation combined method was selected. The results of this work will provide technical data for the treatment of petroleum contamination.Gravimetic and column chromatography methods were adopted to analyze the ingredient of the oily sludge sample. Oil content is 26.07%, water content is 2.07%; the main ingredient of the oil in oily sludge is Saturates and aromatics of 86.25% and low asphaltenes of only 1.58%.In the study of chemical heat washing, washing effects of common surfactants were inspected. The washing effect of surfactant (LAS). alkyl phenol ethoxylates (APEO) and dispersant Na2SiO3 was better than others. To further strengthen the washing effect, orthogonal experiment was carried out to optimize the detergent compound formula. It can be found that there was a strong interaction between LAS and APEO, which enhanced washing effect and reduced the amount of the detergent. The best detergent formulation was:LAS 2 g/L, APEO 3 g/L, Na2SiO3 3 g/L. The optimal washing condition were determined: liquid-solid ratio 10:1, temperature70℃ and washing time 1 h. The oil content of sludge sample reduced from 26.07% to 1.21% by washing. The components removed by washing were analyzed by the infrared spectroscopy (IR). It turned out that the main four components (saturates, aromatics, resin, asphaltenes) of oil in oily sludge were removed in some extent. Especially, saturates were removed obviously.In the study of biological degradation, crude oil from the washed sludge was used as the target substrate degradation in the experiment. The soil near the Turpan-Hami Oilfield in Xinjiang Province was the source of bacteria. Seven strains were isolated by artificial screening, which could grow in the medium with oil as carbon source. Predominant strain was identified by measuring the degradation rate of crude oil. The degradation rate in seven days was 41.83% for the Predominant strain (bacteria4 #). To improve the degradation efficiency, orthogonal experiment was designed to study the effects of culture condition on the oil-degrading capacity of the bacteria in the slurry phase. Optimal levels of factors were: initial pH 7.0, carbon-nitrogen ratio 100:3, carbon-phosphorus ratio 100:1, respectively. Microbial oil-degradation rate was 43.68% by bacteria 4 # in such conditions.The oil content of sludge sample reduced from 26.07% to 0.68% by chemical heat washing-biodegradation combined method. The residual oil rate of sludge is less than 2%, reached the sludge landfill standards and close to discharge standard standards of agricultural sludge.