The Residua Of Oil Pollutants And Its Effects On Water-physical Properties Of Aquiferous Medium

The properties of aquiferous medium like soil and sand will be affected when the medium is contaminated by oil pollutants. The change in water-physical properties such as limit water content, water-holding capacity and capillarity will change the mechanical characteristic of medium as mechanical materials and water retaining capacity and the transport of water or pollutants in the aquiferous medium, which will affect the supply and polltuion of groundwater. The influence degree on the properties of medium varies with the remaining degree which depends on the characteristics of oil products and aquiferous medium. Therefore, diesel oil and crude oil with different characteristic are taken as testing oils, loam soil and sand are taken as aquiferous mediums in the studies. The experiments study the transplant and residual behavoir in which the remaining extent of different oil pollutants in the aquiferous is determined. Moreover, the water-physical properties of oil-polluted mediums with different pollution extent are tested. The conclusions are as follows:(1) The volatilization experiment of diesel oil and crude oil in the aquiferous medium is carried out to determine the effect of oil content, wind speed and temperature on volatilization velocity and residues. The result shows that the volatilization velocity increases with the increasing oil content, wind speed and temperature, and that under the same conditions, the residual ratio increases as oil content increases in the same period. For the aquiferous medium with the same oil content, the volatilization mass is higher and the residual ratio is lower with higher temperature and wind speed. Volatilization is an important factor for the decreases of diesel oil in aquiferous medium.(2) The study on infiltration and residua of diesel oil in the sand column with different water content demonstrates that the retained oil content decreases with the increasing initial water content of sand column. The residual ratio is between 3.31% and 11.32% when the intial water content of sand column ranges from 0.36% to 18%. In the oil-contaminated sand column filtered by water, the final residual mass of oil decreases with the increasing intial water content of sand column, and the final residual ratio of oil in the sand is in the range of 0.64%-2.68%.(3) The infiltration and residua of diesel oil in loam soil with different water content is studied, the result indicates that the infiltration velocity is the greatest in the air-dry soil, the infiltration is more difficult in soil with higher water content and diesel oil can't move downwards at saturate soil. The residual ratio of diesel oil in the air-dry loam soil is between 7.11% and 9.71%, and the residual ratio in the loam soil column with water content of 17.33% is less than 2.58%. The leaching test shows that most of diesel oil is kept below the oil-contaminated soil of about 5cm, so loam soil has better retention capacity to diesel oil.(4) The adsorption of diesel oil on the soil surface is further less than that of water, diesel oil only plays the role of liquid in loam soil, so diesel oil content affects the plastic index hardly. The loam soil particles are wrapped by crude oil in the high oil content soil, which results in a kind of"false viscosity", and the liquid limit to reach the flow state increases, but the plastic limit reduces lightly with the increasing oil content, thus the plastic index increases accordingly.(5) For diesel oli-contaminated sand, when the oil content is lower than 6%, water retaining capacity decreases with the increasing oil content. The oil that has lesser retaining force in sand will be washed out by water when the oil content goes on increasing, and water retaining capcacity won't go on reducing. For crude oil-contaiminated sand, the porosity and water retaining capacity will decrease when the oil content increases becasuse of the adhering of crude oil with high viscosity to sand surface. The influence of crude oil on water retaining capacity of aquiferous medium is greater than that of diesel oil.(6) The existence of crude oil in aquiferous medium weakens the capillary force, no capillary water rising is obeserved in the experiment. When the diesel oil content is less than 2% in sand, the height of capillary rise decreases with the increasing oil content, but the sand loses the water retaining capacity when the oil content is higher than 2%. For loam soil, the capillary water rising can be still obeserved when the diesel oil content is 12%, and the capillary water rising speed becomes slower and the maximum rising height becomes smaller with the increasing oil content.(7) Oil pollution worsens the permeability of aquiferous medium. When the sand is polluted by diesel oil, the permeability coefficient of sand can be reduced by 60%. The permeability coefficient of loam soil contaminated by diesel oil at 8% of oil content decreases by about 97%. When there is more crude oil in soil, it will cohere to the soil surface and block the pores of soil, the permeability coefficient will decrease with the increasing oil content. When the oil content is more than 8%, water cannot be penetrated in loam soil.