Tank Truck Wash Facilities: Efficient, Cost-Effective Oil Removal from Wastewater
By Jim Petrucci In the transportation industry, regulations require tank trucks that haul food-grade oils to be thoroughly washed out before any new product is introduced. So, to comply with the various local, state and federal EPA requirements in this regard, facilities that clean tank trucks must find costeffective water treatment solutions to remove the residual oil in wash water before it is discharged into the sewer and sent to a municipal facility. Failing such regulatory compliance can be costly. After treatment, if the water contains too much residual oil, municipal water treatment centers can refuse to accept it and levy hefty surcharges and fines. In addition, when recovered efficiently, hydrogenated vegetable oils can be sold at a profit to companies making biofuels. However, every tank truck wash facility is unique and must accommodate a wide range of variables. These can include differing local or state regulatory requirements, the number of trucks washed, truck sizes, types of oils hauled, oil/water ratios, peak periods of use, changing 18 | SUMMER 2021
flow rates, en vironmental conditions, and facility size and layout. Exacerbating matters, hydrogenated vegetable oils (i.e., palm, soy, canola, etc.) can be particularly difficult to remove from wash water. Not only does it begin to solidify at relatively high temperatures, but the percentage of oil in the water can be quite high in the initial stages of the wash – a condition that can strain and even overwhelm oil removal equipment not designed to accommodate such high concentrations of oil. In such applications, several key factors virtually dictate the ultimate design of an efficient oil removal system: temperature, flow rate, specific gravity of the oil to be removed, and percent of oil solids in the total flow So, to accommodate all these variables and sufficiently remove oil from wash water to comply with regulation, the application should be analyzed by professionals and the oil removal solution essentially engineered to meet the specific requirements of the application. Ideally, these oil removal systems would cost-effectively, continuously, and actively remove food-grade oil no matter the levels of concentration,
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without costly maintenance or direct supervision. Fortunately, such systems exist today and are growing in popularity. Oil Skimmers When a tank truck wash facility has a pit or sump to collect oily wash water, and the oil in wash water naturally separates into a top layer, an oil skimmer can be utilized to remove the oil from the surface. The most efficient type of oil skimmer uses a free-floating collector tube that actively and continuously removes the oil and grease as it rises to the surface of the water. As the tube moves across the surface, oil adheres to the outside, then goes through a series of ceramic scrapers that constantly remove the oil, which then drains by gravity into a collection vessel. The skimmer is not affected by water level fluctuation or floating debris and solids, removes very little water in the process, and operates continuously with minimal attention or maintenance. The efficiency of an oil skimmer is not just about removing the oil continuously, but doing so without collecting a lot of water.
