Why You Should Be Using an Oil Skimmer for Water Treatment

April 9, 2021
Oil Skimmers and oil waters separators that remove oil, and even “knock out” high initial concentrations of oil from wash water at tank wash facilities simplify water treatment and ensure compliance with wastewater discharge regulations.

In the transportation industry, tank trucks that haul food-grade oils are required to be thoroughly washed out between loads before any new product is introduced.  Facilities that clean these tank trucks produce oily water from a combination of the wash water infused with the oil residue clinging to the inside of the tank.

This oily wash water must be disposed of properly. So, to comply with the various local, state, and federal EPA requirements in this regard, facilities that clean tank trucks must find cost-effective water treatment solutions involving oil and water separation equipment 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.

There are other economic benefits to recovering and handling waste oil properly. Once separated from the wash water, the residual vegetable waste oils can be sold at a profit to companies making biofuels.

The process of separating residual vegetable oils from tank truck wash water poses a number of challenges and the oil-water separation process must accommodate a long list of variables. Every tank truck wash facility is unique in many respects: The number of trucks that need to be washed, the cycle time of the wash, the type of washing equipment used, truck sizes, types of oils hauled, oil/water ratios, peak periods of use, changing flow rates, environmental conditions, and facility size and layout can all vary greatly from site to site.

In addition, these facilities operate in different locations with different local and state regulatory requirements.

To make matters more challenging, certain types of vegetable oils will solidify at room temperature. These include oils that are naturally more highly saturated, such as coconut oil, and other types of vegetable oils that are “hydrogenated” by man-made processes (e.g., palm, soy, canola oil). These types of hydrogenated oils can be particularly difficult to remove from wash water because they require relatively high temperatures during the wash cycle to become and remain liquid.

In the tank wash process, the proportion of wash water to oil can also vary during the washing cycles, thus putting a sometimes high and variable demand on the oil-water separation equipment that follows.

To accommodate all these variables and efficiently remove oil from the wash water, the application should be analyzed by professionals so that the oil separation and removal equipment can be properly matched to the requirements of the application.

Ideally, oil removal systems should cost-effectively, continuously, and actively remove food-grade oil no matter the levels of oil concentration, flow rate or temperature of the wash water with minimal maintenance and direct supervision. Fortunately, such systems exist today and are growing in popularity.

“Typically, a number of factors influence the ultimate design of an efficient oil removal system, including flow rate, the concentration of oil in the mix, the specific gravity of the oil to be removed, and the temperature, among others,” according to Jim Petrucci, vice president at Oil Skimmers, Inc., a Cleveland, Ohio based manufacturer specializing in separating and recovering all types of waste oils, greases, and fats from water.

Oil Skimmers Used in The Separation Process

At some facilities, there are pits or sumps where oily wash water collects and oil separates naturally and floats to the surface. In this scenario, an oil skimmer should be used to remove the floating oil from the surface of the water.

There are a variety of oil skimmers that can be applied to this task. Some use passive oil removal methods such as slotted pipes or overflow weirs. The problem with these passive methods is that they can be labor-intensive and require regular monitoring, maintenance, and manual adjustment to perform sufficiently.

If they are not maintained and adjusted to meet the flow, they can either take too much fluid—which takes too much water along with the waste oil—or they can take too little oil relative to the flow—becoming easily overwhelmed with oil and grease, permitting an oil layer to form on the surface of the water.

Oil build-up can lead to bacteria growth, creating odors, health risks, and bogging down the effectiveness of the separation process. These passive skimming devices are one of the primary causes of excessive maintenance requirements and poor performance issues in oil-water separation situations.

The most efficient and effective way to remove the oil after oil and water separation is with an oil skimmer that uses a Free-Floating Collector Tube.

Tube-type oil skimmers actively and continuously remove oil 24/7 as it rises to the surface of the water. As the tube moves across the surface, oil adheres to the outside, then the tube travels through a series of ceramic scrapers that remove the oil. The recovered oil drains by gravity into a collection vessel.

Tube skimmers are not affected by water level fluctuation or floating debris and solids, remove very little water in the process, and operate continuously with minimal attention or maintenance.

One successful example of an oil skimmer in use at a tank truck wash facility involves a mid-west-based trucking company with a fleet of over 200 tanker trucks—many of which are used to haul soybean oil. The trucking company cleans its trucks after each transportation job. Each tanker hauls approximately 48,000 lb. of oil, so a material amount of residual oil clings to the inside of the tank and mixes with water during the wash cycle.

Local regulations require the trucking company to remove all residual oil from the wash water before discharging it into the sewer system; however, when the trucking company reassessed their existing oil removal process, they found glaring inefficiencies.

To clean out the tankers, the maintenance crew was spraying water into the trailers and emptying the oil-infused wash water into holding tanks where the crew had to manually skim the oil from the surface of the wastewater. This practice met local wastewater regulations but was inefficient and labor-intensive.

As a result, the company’s operations manager sought a more efficient and cost-effective method to remove oil from the wastewater before it was treated further in the company’s existing dissolved air flotation (DAF) unit.

The company decided to install a Model 5H Brill tube-type oil skimmer, mounting it directly on the edge of their existing main wastewater holding tank. Subsequent to the installation of the tube-type oil skimmer from Oil Skimmers, Inc., the trucking company no longer needed to manually collect sludge from the wastewater, delivering substantial labor savings.

The company notes that the oil skimmer, which runs continuously, is so effective it enhances the performance of their DAF unit and reduces the amount of flocking agent required, further reducing costs.

According to the company’s operations manager, the oil skimmer saved enough time and money to more than pay for its cost within a few weeks, while helping the company easily meet the city’s wastewater requirements.

Oil Water Separators

In more difficult applications when the waste oil does not have the time or the space to rise naturally to the surface of the water, there is a need for equipment that will facilitate the separation of oil and water so that the oil can be removed. These conditions typically warrant the installation of an oil and water separator with “coalescing media.”

Coalescing media inside a separator accelerates the separation of oil from the wash water by providing additional surface area required for non-emulsified oil droplets to combine or coalesce, forming larger, more buoyant droplets which can then rise to the surface more quickly and easily.

Conceptually, the physics of an oil-water separator is straightforward. Typical separators are designed to achieve separation of oil and water successfully under relatively stable and ideal conditions, such as a consistent flow rate, proper temperature, and relatively low oil concentration. But as a practical matter, the many variables in play in tank wash applications can destabilize the separation process in a typical oil-water separator, causing it to perform poorly.

Should operating parameters fluctuate from the design parameters of a traditionally designed oil-water separator, it can become overwhelmed, resulting in excessive maintenance and, most critically, too much waste oil escaping into the effluent.

Separate And Skim – SAS Tank Oil Water Separators with Active Oil Removal

A more efficient and cost-effective option today is to install an oil-water separator tank with an integrated oil skimmer that provides continuous, active oil removal. Integrating an oil skimmer into the oil-water separator design will do more to prevent oil build-up after separation and allow the coalescing media to remain clean.  This increases efficiency and minimizes the need for labor, supervision, and maintenance.

An example of such a system involves a Midwest-based, food-grade transportation company, specializing in the bulk transport of edible oils, syrups, milks, and other food products. After a merger with another trucking company expanded its customer base, the tank washing operation quickly became a constraint on growth.

“In our business, tank washing is just as important as the oil transport itself,” explains the company’s Plant Manager. “The challenges with our tank washing operations were becoming a growing impediment to our growth plans. We needed to clean and turn around our oil-carrying trucks faster and more cost-effectively.”

The company’s tank truck washing facilities served up to a hundred vehicles daily and involved a process in which a custom hot water spray system was lowered into the tanks through the top hatch. 

To treat the oily water that emerged from the truck cleaning process, the company had relied for many years on an oily water separator and the effluent was discharged to a municipal water treatment plant; however, the volume and mix of the truck wash changed over time the separator became overburdened with oil. The effluent contained so much residual oil that the treatment plant stopped accepting it. Facing the prospect of incurring costly third-party disposal fees, the firm turned to Oil Skimmers, Inc., for options.

The team at Oil Skimmers, Inc. determined that the tank wash operation had several challenges, among them: the wash process generated periodic spikes in the concentration of oil during the wash cycle. High and fluctuating concentrations of oil are major challenges for typical oil-water separators. In addition, the food-grade vegetable oil was often the hydrogenated type that can easily become thick and viscous without adequate heat to flow properly. Because the wash water-cooled as it drained, the oil could start to solidify by the time it reached the oil separator tank, clogging the system, slowing treatment, and increasing maintenance requirements.

In response, the Oil Skimmers, Inc. team custom-designed a flexible oil-water separation “Separate and Skim” SAS Tank to meet the plant’s tough operating conditions.

Oil Skimmers, Inc’s SAS Tank oil-water separator was equipped with additional features, multiple process stages, and controls to separate and then actively remove oil from the wash water with minimal supervision or maintenance. The system was designed to be capable of efficiently handling peak oily wash water flows in the process, maintaining temperature control, and removing the oil from the water actively and continuously, all in a compact size and form factor that fit the space allotted in the shop. The economics more than met shop management’s expectations.

This SAS Tank oil water separator design had three levels of oil removal and separation, including advanced capabilities to “knock out” the oil that would have been excessive and overwhelming to more typical oil-water separators. An integrated Brill type oil skimmer with a free-floating collector tube providing continuous, Active Oil Removal, completed the final “knock out” of oil. SAS Tanks with these features, delivering at least three levels of oil removal, have come to be known as the TAKO or “Triple Action Knock-Out (TAKO)” tanks and have become the standard for tough oil-water separator applications. 

According to Petrucci, both standard SAS Tank oil-water separators and TAKO Tanks for tougher applications are capable of featuring a wide range of options and controls. “We can handle the most straightforward or the toughest oil and water separation challenges with as much or little customization as is needed to meet the requirements of the customer’s application.”

While customizing the configuration and options to efficiently remove oil from tank truck wash water today is important, so is working with a partner that can easily make adjustments when circumstances change. As volumes, oil-water ratios, and other factors continue to evolve, adapting and tailoring the oil-water separator design to both current and future needs will reliably minimize the cost of compliance as well as labor, operation, and maintenance.

“Whether the application involves just oil skimming, or separation of oil and water prior to skimming, it is important to consider all the factors that can be essential to productivity and profitability,” concludes Petrucci.

For more information about oil skimmers, oil removal systems, or how to design an oil-water separator for your application, call 440-237-4600; email: [email protected]; visit www.oilskim.com; or write to Oil Skimmers, Inc., 12800 York Road, Cleveland, OH 44133.