ods 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 flowrate. This may be easier than expected at first thought. Sources are available that provide tables showing maximum flowrate in “horizontal” gravi ty flow pipes for different slopes and pipe diameters. The plumbing system engi- neer 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 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 intercep- tor 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 associ- ated with non-maintained grease inter- ceptors 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 wip- ing 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 indus- try 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 dis- cussed regarding personnel turnover and lack of maintenance are all prob- lems worth being solved. Because an interceptor is a neatly sealed box that no one really wants
Plumbing Engineer
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 establish- es 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 per- sonnel that it is time to remove the grease. This eliminates the need to open the unit to check the 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 open- ing in the interceptor shell to get the grease out, which is a concern to some regarding possible odors. Also, methods of grease removal are dif- ferent; some perform better than oth- ers 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, includ- ing 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 envi- ronment, for years to come. n
Brian Tubaugh is the director of engineering for the Josam Company.
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May 2011/Page 55
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