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Waste Oil Pit Cleaning
What is a waste oil pit?
What can be done?
What will work in the rain forest?
Inverse Emulsification
What is a waste oil pit?
A so-called pit is a leftover from oil exploration and oil production on land. Typically the oil companies in earlier years left drilling mud and crude oil, discharged in connection with drilling and testing of the new well, in ponds or pits next to the drilling hole. Over the years the lighter fractions of the oil have evaporated and in many cases additional contamination has taken place due to the dumping of chemicals, refinery waste, and debris. Consequently the pits may contain extremely viscous and debris laden asphalt-like oil, which is very difficult to recover. The soil in the bottoms and sides, as well as the surrounding land may suffer from serious oil pollution. Contaminated water from the pits may in connection with rain overflow into rivers and lakes.
In some cases attempts have been made to cover the problem by soil, or by burning the content of these pits. But such behaviour only adds to the problem, as the costs of proper cleaning afterwards increases substantially.
Thousands and thousands of waste oil pits are still distributed throughout the world, threatening the surrounding environment, ground water, people and especially children, as well as animals. (Back)
What can be done?
There are only a few ways to do proper pit cleaning, and even fewer of them will be able to cope with the very old, extremely viscous and debris laden pits. You have to consider whether the cleaning must be done in-situ or ex-situ. It gives a lot of meaning to do in-situ cleaning, as this minimizes further environmental damage caused by transportation and double handling of the oil, soil, water, debris, etc.. If, however, the pit is located close to a refinery or a municipal waste incineration plant with electric power generation, it may in some special cases be feasible to bring the whole problem to such a facility for treatment.The less difficult pits, with relatively fresh and light oil waste, may be cleaned according to methods as described in the "Response Tactics – Land Spills" section of this handbook.
Dependent on climate, geography/geology, and lifestyle of local inhabitants, the cleaning must be more or less complete.
In the Amazon Rain Forest, where the locals drink the water from the rivers and have their children and animals close to the contaminated sites, the cleaning requirement will be high, and pit closures using concrete or quicklime stabilization should be ruled out, due to the rain and groundwater’s ability to continue washing out oil and heavy metals.
But in the deserts, with sparse population, and if there is no groundwater, it may be safe to recover whatever you can pump and dig out, and then stabilize the remaining oil. Bio-degradation may be an option to stabilization if the required amount of humidity can be obtained. (Back)
So, what will work in the rain forest, where the pits contain extremely viscous oil, water, and debris?
Well, there are a couple of complete and environmentally friendly processes for the in-situ cleaning of difficult waste oil pits. The most affordable is based on an inverse emulsification of the asphalt-like crude in the old pits, which makes the oil liquid for easy recovery. The most expensive an most foreign currency costly in-situ process is extracting the oil from the pits by an evaporation/condensation process, using heat, generated from the recovered oil. This containerized process is very efficient cleaning oil, sediments and water, provided a technique for bringing the asphalt-like oil to the processor is available. This technology will not be described in further detail here, but you may want to check Soil Recovery.
Inverse Emulsification:
A biodegradable dispersant is mixed with water and thereafter sprayed on the pit. By using compressed air (large bubbles) and pressure water from fire pumps, the dispersant is mixed with the oil, which gradually becomes more and more liquid. Sand and stones sink to the bottom and debris is relatively easy recovered for final cleaning. As the compressed air nozzles are pointing downwards, this process treats the bottom and the water in the pit at the same time as treating the oil. Heavy oil products in the bottom sediments will be washed out, and (dependent on the dispersant) air bubbles from the agitation process enable the oil to float to the surface. Even if the gravity is higher than 1!(Most dispersants or surfactants will not have this important capability of re-floatation, but some may compensate for this by being extremely fast making the asphalt pumpable and fast separating the oil from the sediments. They may, however, cause difficulties separating water and dispersed oil)
The oil water mixture is easily recovered, using overflow weir skimmers. The agitation and cleaning of the water and the bottom sediments by means of compressed air continues. Once the water meets the country’s EPA requirements, it will, upon approval by the authorities, be discharged to the surroundings (in some cases it will in addition be necessary to use simple filtration). With a little remaining water left in the pit, the bottom and sides are now pressure washed with water and dispersant to a depth of 0.5 m, by high pressure cleaners. In this way the remaining oil from bottom and sides will be washed out. The oil is skimmed off the surface and the last bit of water discharged, when clean enough. The sides and bottom sediments are tested to meet the allowed total hydrocarbon content. It may be too costly to clean the sediments completely, using the washing process. Climate permitting, natural or supported biodegradation may take over once the level has reached for instance 2000 PPM of hydrocarbons in the soil and sediments. Biodegradation works extremely fast on oil which has been dispersed.
The debris, which mainly is wood, should be cleaned to a reasonable level and used as fire wood for cooking by the local inhabitants. It is important to underline that only small debris, such as oil wetted leaves and small branches, which cannot be cleaned without excessive efforts, should be incinerated.
The recovered oil may after filtration be re-injected into production, or it may be used for the production of asphalt and/or fuel for thermoelectrically power plants. In any case: The result of using this process should not cause a new waste problem.
The described process requires mainly low-technology machinery, and - apart from skimmers and special pumps – all equipment, such as tank trucks, back hoes, water pumps, and compressors, are readily available in most countries. Contracts may be performed by local contractors based on local labour under supervision of an external response management. (Back)
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