Industrial Pretreatment Program

Fats, oils, and grease (FOG) cause serious problems in the wastewater collection system and in the plumbing lines of a food service establishment. FOG accumulating in sewer lines can result in raw sewage overflows due to blockages and cause odors, contact with disease causing micro-organisms, and costly cleanup and repair of damaged property.

A hydromechanical grease interceptor (HGI) connected to a plumbing fixture(s) that discharges greasy wastewater is acceptable to meet the code requirements under certain conditions. HGI’s are smaller units typically located inside a building. HGI’s use a flow control device and baffles to slow wastewater flow, allowing solids and FOG to separate.

A hydromechanical grease interceptor needs to be sized correctly to work effectively. Since these units are sized according to flow, make sure the HGI is large enough to accommodate inflow during peak or busy periods. These units should be installed with an indirect connection or air gap. The lid should be easily accessible with enough clearance to remove for cleaning. Make sure your plumber reviews the manufacturer’s instructions for installation since flow control or venting may be required. Food grinders should not connect to HGI’s. Because of their small size, HGI’s need frequent cleaning.

Gravity grease interceptors are large vaults typically made of precast concrete, located outside of a building. Gravity interceptors have one or two compartments that are accessed by manholes. Because of their size and expense, gravity grease interceptors are usually installed during new construction, or when a building undergoes a significant remodel. Multi-tenant buildings may have more than one restaurant that connects to a single gravity interceptor. Cleaning costs are usually divided among tenants.

Depending on interceptor size, menu type, and number of meals served, exterior grease interceptors may require cleaning at least once every 3 months, or when the solids and floating grease contents reach 25% capacity. Business owners may request a waiver from the quarterly pumping requirement based on conditions of use.

Hydromechanical grease interceptors are smaller and need more frequent cleaning. These units should be cleaned monthly or according to manufacturer’s specifications. Menu type and number of meals served will affect the cleaning frequency. Solids and floating FOG should not exceed 25% of the interceptor’s capacity. Business owners with HGI’s may request a waiver from the monthly pumping requirement based on conditions of use.

The code identifies several Best Management Practices to control FOG in wastewater. Food solids that accumulate in grease interceptors leave less room for FOG removal. To keep solids out of wastewater, install strainers or solid separators on all plumbing fixtures including floor drains and sinks. Make compost bins available in dishwash areas and train staff to scrape plates and cookware before washing.

The code also addresses the use of emulsifiers or degreasers. These products are a short-term solution since the dissolved grease will solidify downstream. Emulsifiers and degreasers are not a substitute for regular grease interceptor maintenance.

The Boulder Revised Code gives city staff the authority to request grease interceptor pumping records. The records are used to verify that the interceptor is being pumped on a regular basis. Business owners or property managers should keep records on file for a period of three years.

If possible, observe the pumper at work and make sure the contents of your interceptor are completely emptied. The pumper should check and note any missing parts, such as missing or broken inlet/outlet PVC T’s on a gravity interceptor. The T’s are important since the T on the inlet pipe keeps grease from floating back into your building and the T on the outlet pipe keeps grease from escaping into the city sewer.

If you have an interior interceptor, the pumper should empty the contents and scrape the sides and baffles. All baffles and fittings should be put back in place as per manufacturer specifications.

The pumper should provide a manifest form stating the amount of grease removed, the date, and the grease disposal location.