PLUMBING e Continued from p 130
backups to the fixtures. Allow clearances for cover and baffle removal, access for cleaning tools such as a vacuum hose and line of sight into the unit to be sure the job was done right. Some units may include other components such as supplemental strainer baskets or GRD components, which need to be considered for future removal.
Maintenance Every interceptor needs regular
maintenance to perform as advertised. If the grease is never removed, the unit will eventually fail and pass grease downstream. As the grease separates to the top, it is actually building a layer downwards from the static water level inside the unit. As this layer thickness increases, it is decreasing the effective separation volume, which means it takes less time for incoming, grease-laden water to get to the outlet. A lack of maintenance by facility
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personnel is commonly caused by, what we like to call “magic-box-in- the-corner” syndrome. Some people do not know that they have an interceptor in their restaurant; many others know it’s there, but are more than happy to leave it alone until it is too late. When sinks are backing up and the odor is unbearable, it is much too late. Some restaurants have even had to close for a day, losing business, which could have been avoided with a regular maintenance schedule. Unfortunately, some of this
misunderstanding or lack of knowledge is due to the typically high turnover rate in employees for these types of businesses. This only supports the need for an established regular maintenance schedule that, like so many other tasks in a food service establishment, becomes habit.
Sizing and solids Sizing of an interceptor can be, and
has been, done more than one way. There are even some antiquated codes still using a formula that considers hours of operation in a day, number of seats in the restaurant and proximity to a major highway to size a unit. Sizing by fixture units may also be somewhat risky as this method includes a factor of probability that a fixture is being used. So what happens in periods of peak flow? Is the interceptor large enough to effectively separate grease during these periods? Sizing by maximum anticipated
flow rate seems to be the soundest method, which fits well with hydro- mechanical units that are performance tested and rated by flow rate. This may
be easier than expected at first thought. Sources are available that provide tables showing maximum flow rate in “horizontal” gravity flow pipes for different slopes and pipe diameters. The plumbing system engineer has sized a pipe capable of taking wastewater away from fixtures, which also happens to be the pipe leading to the interceptor. The size of a hydro-mechanical
interceptor can be determined simply by knowing the pipe size and slope and then referencing a flow table for
sealed box that no one really wants to open unless needed, it would be beneficial for the box to tell you when the grease needs to be removed. Plumbing & Drainage Institute (PDI) has recently released standard PDI- G102, which establishes performance requirements for sensing and alarm devices. These devices sense the level of the grease layer inside the unit and transmit an audible and visual signal to alert personnel that it is time to remove the grease. This eliminates the need to open the unit to check the
Clean Water Outlet — An actual installation with cover removed. Separated grease on the left and clean water exiting outlet on the right.
maximum flow (full bore). Even if the pipe was sized using fixture units, a pipe diameter is selected to flow only about ½ full, so periods of peak flow can still be handled, and the interceptor will be correctly sized to handle those flows. Solids are typically food particles
and can float or sink once inside an interceptor. The horrible odors associated with non-maintained grease interceptors can usually be traced back to decaying solids. It is best to keep as many solids out of a grease interceptor as possible. Good solutions are to install a solids interceptor just upstream of the grease interceptor and to establish business practices of wiping dirty plates into a garbage can before washing and using strainers in sink outlets.
Advancements The principle of grease separation
resulting in an upper layer of grease inside an interceptor still holds true for the advancements discussed below. As is common with innovation, the industry has tried to answer historical issues associated with grease containment. Cleaning out a grease interceptor is usually not the most desired job in a facility, and the issues previously discussed regarding personnel turnover and lack of maintenance are all problems worth being solved. Because an interceptor is a neatly
grease layer thickness and avoids having to clean the unit more often than is actually needed. There are also grease removal
devices available. These units are sometimes misleadingly referred to as automatic units. A standard for grease removal devices is ASME A112.14.4. The removal of grease is automatic, but periodic maintenance to clean and remove solids is still necessary. Based on a timer setting or grease layer thickness sensor, the top layer of separated grease is removed to an external container without removing the cover. Some of these units may require a small opening in the interceptor shell to get the grease out, which is a concern to some regarding possible odors. Also, methods of grease removal are different; some perform better than others regarding those floating solids. These are some things to consider
before specifying or installing a grease interceptor, but I imagine some topics are missing. There are many sources for more information, including reputable manufacturers who would be happy to help you select the right product for your next project. Spending a little time planning and considering factors will pay dividends for you, your customers and the environment, for years to come. l
Brian Tubaugh is the director of engineering for the Josam Company.
phc may 2011
www.phcnews.com
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