Section 19. LAND DISPOSAL
LAND TREATMENT OF OILY WASTES-REDUCTION OF
CRUDE OIL IN SOILS
Wan-Fa Yang, Professor and Director
Graduate Institute of Environmental Engineering
National Taiwan University
Taipei, Taiwan
Republic of China
Allen Chao, Assistant Professor
Charles Smallwood, Jr., Professor
Department of Civil Engineering
North Carolina State University
Raleigh, North Carolina 27650
The extensive use of petroleum oil as an energy source and as raw material has made it
one of the most ubiquitous pollutants of the environment. The development of a suitable
treatment for oily waste has been a major topic for research. Unlike the carbohydrates
found in municipal and industrial wastewaters, the hydrocarbon compounds in the oily
waste are difficult to decompose by microorganisms in the classical biological treatment
systems. Many research efforts have been directed towards developing and utilizing a land
treatment system for the disposal of oily wastes. The soil system has been considered an
ideal medium for disposing of concentrated oily wastes because it provides a wide spectrum
of bacteria and a large surface area upon which bacterial reactions might take place. However, the mechanism of oily waste treatment using the soil system is not clearly understood.
Other mechanisms are possible.
The successful isolation of hydrocarbon decomposing bacteria from oil polluted sediments [ 1 ] has led to the generally accepted belief that microbial decomposition is the
primary cause of reduction of the oil that has been applied to the soil. Although it has
been concluded that microorganisms such as Pseudomonas and Candida are capable of
decomposing chain and cyclic hydrocarbons [2,31, the environmental factors affecting
the microbial reduction of oil in soils are inconclusive or controversial. For example,
Loynachan [41 observed that mixing the soil may improve the transfer rate of oxygen which
is needed by the microorganisms, and thus it may also enhance the oil reduction rate. In
contrast, Odu [51 reported that there is no apparent difference of reduction of oil whether
the soil is disturbed or not. It is a well known fact that balanced nutrients, such as nitrogen
and phosphorus, are needed for the microbial degradation of organic carbon matter. In
this regard, some researchers [6,7) found that addition of fertilizer enhances the oil
decomposition rate but the results by others [8,9) refuted this conclusion.
Many of the constituent substances of petroleum oil are volatile and unstable under
normal conditions. If left in an open container, the petroleum oil is known to evaporate
and to undergo physical and chemical reactions that change its composition. Thus, it is
probable that when disposed of in a soil system, the oily wastes may be subject to a variety
of reduction mechanisms. These may include evaporation, photodecomposition, adsorption, percolation and plant interception among the many others. Microbial degradation is
thus not the only possible mechanism that contributes to the oil reduction in soils.
Therefore, ignoring the nonbiological reduction mechanisms may contribute to inconclusive or controversial explanations of the reduction of oil in soils systems.
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