Oil and Chemical Recovery and Treatment

Due to the varieties of organisms in aquatic populations, each with its own unique chemistry and composition, it is difficult to write a precise chemical formula for the composition of a bacterial population. Rather, the range of the principal compounds is approximately 100-125:20:1 for carbon, nitrogen, and phosphorous, respectively. For complete degradation oxygen is also required: Two molecules of oxygen are required per molecule of carbon in order to form CO2, the end product of aerobic decomposition.

Oil is a carbon-rich source, deficient in N and P. Dispersants help break down the oil but for complete bacterial action, oxygen, some phosphorous, and nitrogen are required; and the use of dispersants often leads to oxygen depletion in the water. Dispersants can also be quite toxic to several forms of aquatic life. For example, 973 000 gallons of Corexit© was used in dispersing part of the Deepwater Horizon spill, and according to health reports, the dispersant compound has the potential for creating asthma-like symptoms in exposed humans and can damage gills of marine creatures. The aquatic effects of dispersants are often not fully described in the Material Safety Sheets.

The oil will contain a variety of fine particles, and it is often viscous, sticky and it adheres to solid surfaces such as booms, and it is generally acknowledged to be difficult to remove easily. There are a number of floating devices, which will enhance recovery of the floating oils. Some are wheels, brushes, or belts, which have an affinity for the oils and attract the oils to their surface. The belts, brushes, and wheels processed through a series of rollers or scrapers which either squeeze out the oil or scrape the belt surface to remove the oil.

The oil is collected in a separate container. The concentration of oil in the collected material seldom exceeds 15%. Vacuum trucks and suction devices are often employed for collection of the oil, at a slightly lower oil to water (1-2%) ratio. The temperature of the water and oil is always a factor, and thicker oil will not only be more difficult to recover, but the ratio of oil to water will be even lower.

Once recovered, if the viscosity is low enough, the oil can be processed through a coalescer to concentrate the oil. Otherwise, for heavier oils, an API separator is often used. An API separator is a long rectangular tank with baffles to prevent short-circuiting. Typical retention times are 30-60 min, and the oil/water mix feeding the separator should not be fed by a centrifugal pump because of the emulsification factor associated with the pump impeller. Some coalescers do not have this problem because they use a fiber mat as the separation medium.

In one instance, an oil collector employing a buoyant polyethylene rope was used for an oil collection device from a tank. Vegetable oils clung to the rope on one cool evening and increased the diameter of the rope from 1 cm to around 5 cm. At the 5 cm diameter, the rope plus oils were too heavy for automated equipment to lift and run through compression rollers which would remove the oils. The oils congealed and behaved more like grease, clinging to everything and ultimately burning out the motor on the oil recovery device. This may not be an uncommon occurrence, and choice of the oil recovery system has to be made with respect to the properties of the oil to be recovered.

 






Date added: 2025-01-04; views: 21;


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