Are We Caught in The FOG?

Fats, oils, and greases, (FOG) are generated continuously in our country every day. These materials may eventually cause clogging and related problems in public sewer systems, municipal waste treatment facilities and building piping systems. Other issues that can arise are health and waste concerns. More treatment processes may be needed to keep the water supply acceptable for daily use. If these oils and greases are not efficiently intercepted, costs for building piping, sewer maintenance and additional treatment processes will increase both for building owners and for the local municipality. Collecting FOGs can be positive and can provide opportunities to recycle some of these materials for various applications, such as potential use as fuel for vehicles or for heating.

Interceptors, referred to by various names - grease traps, grease interceptors, hydro-mechanical type interceptors, grease recovery devices or grease recovery appliances -are paramount in saving our current and future water systems. Many interceptors are designed to efficiently separate and retain the fats, oils and greases used in a variety of food service applications. This protects a building's plumbing system and the public piping system and alleviates work and expense for the local water treatment facility. Installing an interceptor close to the source of the grease output can protect the entire downstream pipeline within a building and beyond from potential FOG accumulation. If allowed to pass from commercial kitchen fixtures, these materials could eventually change from a greasy liquid form into a solidified state, which would cause downstream pipe clogging within a building and in the public water system.

A typical grease interceptor works on a principle based on the difference in weight or specific gravity between water and the oils or greases mixed within the influent. As the influent flows into the interceptor, it is directed along a designed flow path through a baffle or a set of baffles. This lengthens the flow path of the greasy fluid and alleviates the turbulence in the separating chamber. Since the weight of the grease is slightly less than that of the water, the grease flows upward, thereby floating in the tank or separating chamber. The non-greasy water then exits the interceptor through a flow path along the bottom of the unit. Eventually, as more grease enters the unit and separates, an accumulation of the FOG collects at the top of the fluid level and can be removed at a scheduled time.

It is important to note that solids particles may be mixed with the fats, oils and greases, hindering the separation process somewhat. When solid particles from foods are allowed to enter the grease interceptor and remain in contact with the oils and greases, the potential for odors can increase. To relieve this situation, using a solids interceptor in conjunction with the grease interceptor is recommended. A solids interceptor installed upstream will keep solids from entering the grease interceptor.

As more municipalities become aware of FOG problems, new steps will undoubtedly be taken to correct them. Various states have begun instituting their own codes or are following some basic industry standards involving the selection and installation of grease intercepting units. Two similar and widely used industry standards are the American Society of Mechanical Engineers (ASME) A112.4.3, and the Plumbing and Drainage Institute (PDI) G101. These standards relate to the use of grease interceptors, how they are sized and their performance criteria.

For many years these two standards involved unit sizes up to 50-gallon-per-minute (gpm) flow rates. Recently however, sizes up to 100 gpm have been included. Each interceptor size has a rated flow that is designed and tested to requirements in the standards. The flow control device for each of these sizes ensures that the maximum flow for the unit will not be exceeded and that efficient performance will be ensured. A unit whose design follows the test criteria must have a resulting average minimum efficiency of 90%. Many units in the industry meet these criteria, and some are highly efficient, reaching 99% efficiency.

There are many options for interceptors available, allowing local code officials to determine what is acceptable and reasonable for use in their areas. Other important information regarding grease interceptor installation, sizing methods, testing procedures and certification is also contained in the standards. Furthermore, since the standards have been in place for decades and are widely accepted in the industry, they can serve not only as an invaluable tool for manufacturers pertaining to their design but also for municipalities that recognize the FOG problem and want to take action.

Different factors affect the separation of grease and water in a grease interceptor. Proper venting and installation of an accompanying flow control device are important. Every unit that follows the sizing method in the standards has a maximum flow rating. If the designed maximum flow rate is exceeded, the performance or efficiency of that unit can be compromised. Installing a flow control device in the upstream line will ensure that the flow rate is not exceeded. The flow control device usually has a vent that allows for the proper air intake to occur while the unit is operating.

How well a unit is maintained and periodically cleaned is another factor that affects its operation and performance. From a user's perspective, as well as that of a local authority, good maintenance is a necessity in operating a grease interceptor properly. Since the specific frequency and extent of use of every unit is different for each installation, the maintenance interval will also vary but should be continuous on a regular basis.

The size of the grease intercepting unit, as well as its particular design, are factors in determining the maintenance interval. Each unit should be sized on criteria as set forth in the standards, and FOG accumulation should not be allowed to exceed the design capacity. If capacity is exceeded, oils and greases may be passed on to the downstream piping, thus defeating the purpose of the installation. To keep this from happening, a unit should be checked by removing the cover to determine how much grease has been separated and contained, and then, if necessary, removing grease from the unit.

Different users and units may approach collection and removal in different manners. Some are willing to check a unit and remove the grease manually as it accumulates, while others may hire a local service to periodically collect the accumulated grease and dispose of it properly. These are usually the options relating to most of the typical passive units. It is always advisable to research how the collected FOG should be disposed of in a particular state or locality. There are various codes that govern disposal.

Through the establishment of standards such as PDI G101, typical passive grease interceptors, which follow the design and testing criteria and are certified, ensure a specific level of performance as long as they are maintained. Some manufacturers offer active units with varying features that automate some aspects of operation. Some grease recovery devices will sense and draw off grease from the separating chamber so that it is easily collected by the user. Other semi-automatic grease interceptors may offer sensing and alarm packages to make the user aware that grease capacity has been reached and removal is needed. Regardless of the method or unit design in operation, neglect is not an option if stopping potential FOG related issues and cloggings is desired.

Joseph Tripodi of Zurn Industries has been a mechanical engineer in the design of valves and plumbing products for approximately 10 years. He has EIT certification from the State Board of Pennsylvania and has developed patents related to grease removal and recovery. Contact him at joseph.tripodi@zurn.com.  For product information, visit www.zurn.com.