Oil skimmers are very effective in removing oil from wastewater before discharge but are also perhaps the most efficient and economical approach.
Despite these advantages, oil skimmers are not found in every power plant. Some plants rely on less-efficient oil removal procedures, failing to recognize that even a single release could cost more money than upgrading a facility to modern oil-skimming equipment.
An oil skimmer (Figure 8) efficiently removes oil from water continuously and puts it into a collection tank, so it can then be recycled. Continuous removal also eliminates oil build-up, greatly reducing evaporation loss and the likelihood of oil escaping.
8. Skimming oil. Oil in plant sumps and other wastewater containment areas can be economically removed using an oil skimmer. In this design, a polymer hose passes through the sump to collect oil that is continuously skimmed from the surface of the hose and collected as illustrated. Courtesy: Oil Skimmers Inc.
Let’s review your options other than real-time oil skimming for removing oil from wastewater, and you can decide which approach is more attractive to you.
Absorbent Pads, Booms, or Pillows
Absorbent pads are one method a facility can use to remove waste oil. Pads are available in different shapes and sizes and are made from a variety of synthetic materials.
These are useful in an emergency, for removing small amounts of oil or soaking up oil on plant floors. If only a few pads or pillows are used per month, then they are most likely sufficient.
However, the results of using absorbents are not always environmentally sound. Only a small amount of oil can be squeezed out of the pad for recycling. The remaining oil must be disposed of in a landfill or burned. At some point, the cost associated with the purchase, disposal, and deployment of these absorbents will add up and may justify installing oil removal equipment.
Some facilities choose to hire a company to vacuum the oily layer from its wastewater, but this can often be expensive.
Having the oil removed once a quarter may not be cost prohibitive, but frequent use of this service can drive up costs. The company is not only charged for the operator’s time but also by the number of gallons hauled away. Due to the nature of the process, large amounts of water are taken with the oil, making for a very expensive removal method.
Another drawback to the vacuuming process is randomness. Soon after the removal service drives away, the oil begins to build up on the surface again. This build-up leads to other problems, not the least of which is the potential for bacteria growth, which can give an unpleasant odor to the water. The chance of oil escaping is also increased.
Water Treatment Plant
A facility’s wastewater must be treated before it can be reused or disposed of. This can be done internally with an onsite treatment plant, or the water can be sent to the local municipal wastewater treatment plant. Although the process at the treatment plant will in most cases handle the "oils," doing so will incur additional costs. These will range from additional surcharges imposed by local authorities for excess oil, to added costs of equipment, to filters and chemicals at an onsite treatment plant.
— Contributed by Jim Petrucci (firstname.lastname@example.org) vice president, Oil Skimmers Inc.