Pacific Sales NW

1000 gallon gravity vs 125 gallon Schier GB-75 equal; really?

2009-12-21T11:11:00.000-08:00

One of the most common questions I get is "how are your much smaller Great Basin units equal to large volume gravity interceptors?".

Most if not all jurisdictions have existing ordinances that require a minimum of a 1000 gallon concrete gravity interceptor for outdoor installations. When we submit a Great Basin GB-75 as equal to that many AHJ's immediately are thrown off by the size of the unit by comparison. A GB-75 only contains 125 gallons of water compared with the 1000 gallon gravity interceptor. So naturally the question arises, how are these units equal?

The purpose of a grease interceptor is to separate and store fats, oils, and grease (FOG) from a food service establishment (FSE) preventing the FOG from clogging waste lines downstream. The real question should be how much grease does that gravity interceptor hold versus the Great Basin? That should be the basis of comparison, not how much water they each hold.

This can be a difficult question to answer. Why? The Uniform Plumbing Code does NOT require gravity interceptors to be tested for performance. A certified gravity interceptor must simply meet IAPMO Z1001-07 which is nothing more than a design standard. In other words the IAPMO standard tells a manufacturer how to build an approved unit. There is NO performance test requirement in the standard. So how much grease will a 1000 gallon gravity interceptor separate? No one actually knows for sure.

What do we know about the performance of gravity grease interceptors? IAPMO wanted to know that as well and funded a study by the Water Environment Research Foundation (WERF) to investigate a variety of known gravity interceptor construction designs to determine which was the most efficient design. WERF discovered two (2) performance problems with all of the designs they tested. The most significant problem they discovered was that turbulence in the entering effluent was not easily disapated in the unit causing a significant amount of FOG to stay entrained in the effluent as it moved through the interceptor. The second problem they discovered was that the existence of a baffle wall had a negative effect on performance in each of the designs tested. Each of these problems alone were significant but combined they were potent in their effect on performance.

In short the turbulence in the entering effluent combined with the existence of a baffle wall created what WERF called "the short circuit effect". As the entering effluent traveled across the interceptor the turbulence would keep a significant amount of FOG entrained while the baffle wall seemed to direct the flow path into the second chamber and ultimately out of the unit. None of the designs that were tested successfully dealt with these two problems.

The best we can do in determining how much FOG a gravity interceptor can separate and store is to evaluate comparably sized metal baffle type interceptors. Taking an average of 5 manufacturers we can deduce that a 1000 gallon gravity interceptor "may" be able to separate and store up to 933 lbs of grease.

So what about a Schier Great Basin, how do they work? Schier's own research indicated that a wide open vessel was more effective than one with a baffle wall. With the baffle wall removed all that needed to be dealt with was the turbulence from the entering effluent. This problem was solved by the inlet Diffuser. As the effluent enters the unit the diffuser captures and dissipates the energy creating a smooth flow path across the unit. FOG naturally and quickly floats to the top when you remove the turbulence and any obstructions in the unit.

The Schier GB-75 was tested by NSF to the ASME A112.14.3-2000 standard as required under the code for a hydromechanical device and was certified to separate and store 616 lbs of grease. As noted above that is 317 lbs less grease storage capacity than the 1000 gallon gravity interceptor. However, one must also consider the real world. Virtually all jurisdictions require gravity interceptors to be pumped and serviced at a maximum of 25% of capacity (between FOG and solids). It is well known that these interceptors become inefficient with as little as 10-25% of capacity. A Schier interceptor maintains its optimum efficiency up to its rated capacity.

For comparison sake the 1000 gallon interceptor must be pumped at 25% of capacity which equals 233 lbs of grease. The GB-75 is still operating at peak efficiency at 90% of capacity which is 554 lbs of grease.

The Schier GB-75 is not only a code approved equal to a 1000 gallon gravity interceptor in terms of sizing, but exceeds the performance of the comparable gravity interceptor by a substantial amount.

Grease Interceptors - Hydromechanical, what does it mean?

2009-11-16T11:39:00.000-08:00

The 2006 Uniform Plumbing Code made some interesting changes in chapter 10 relating to grease traps that have some people confused. Lets clear it up.

For years the term "Grease Trap" was used to define "A plumbing appurtenance or appliance that is installed in a sanitary drainage system to intercept nonpetroleum fats, oil, and greases (FOG) from a wastewater discharge." The device was commonly used as a point of use interceptor servicing a specific fixture. Until the 2006 code changes these devices were limited to a maximum of 4 drainage fixtures.

Now we have a new term "Hydromechanical Grease Interceptor". It is defined as "A plumbing appurtenance or appliance that is installed in a sanitary drainage system to intercept nonpetroleum fats, oil, and greases (FOG) from a wastewater discharge and is identified by flow rate, and separation and retention efficiency. The design incorporates air entrainment, hydromechanical separation, interior baffling, and / or barriers in combination or separately..." These devices are required under the code to control the flow rate entering the device with either an external flow control or a built-in flow control (non-external), either directly connected or indirectly connected to the sewer system. These devices are allowed a maximum of 720 drainage fixture units (DFU) according to Table 10-2 of the code.

That definition may need a bit of explaining. Lets simplify it. A Hydromechanical Grease Interceptor is a device that separates and stores grease (FOG) and is commonly used inside a restaurant for point of use grease separation. These devices are "generally" installed inside.

Are all Hydromechanical Grease Interceptors alike? The short answer is no.

For years manufacturers have used the same old technology for grease traps. The basic design is a metal container with baffles inside staged in such a manner as to lengthen the flow path. An external flow control is provided to restrict the flow rate entering the unit to its certified capacity. This external flow control requires a "vent" or better stated an air-intake. A certified device is required to separate and store twice as much FOG in pounds as its rated flow capacity. For example a 25 gpm unit is required to separated and store 50 pounds of grease.

Schier Products manufacturers a Hydromechanical Grease Interceptor, however this is not the same old technology. Schier has revolutionized the industry by eliminating internal baffles and placing the flow control device inside the unit. The new technology is far superior and much more efficient than traditional grease traps. This is accomplished by the Diffusion Flow technology. This technology utilizes a wide open container in combination with an inlet Diffuser that captures and dissipates the energy and turbulence in the entering effluent. The net effect is a smooth flowing waste stream which allows the FOG to separate naturally and very quickly. In fact this technology is so effective that our 25 gpm unit will actually separate and store 98 pounds of grease. Thats nearly twice the capacity of a traditional design.

Hydromechanical Grease Interceptors; the new term for a grease trap. Although these are commonly available today remember that not all designs are alike. Consider the advantages of a Schier Products Hydromechanical Grease Interceptor for your next project.

Grease Interceptors - Materials of construction, does it matter?

2009-11-12T17:45:00.000-08:00

Schier Products manufacturer's all of their grease interceptors out of HDPE (high density polyethylene). This material has excellent properties ideally suited for grease interceptors. Consider these advantages:

- The material is completely inert to whatever may come down a commercial kitchen waste line. Because of this Schier is proud to be the ONLY manufacturer in the industry to offer a LIFETIME warranty on all of its grease interceptors, solids interceptors, oil separators and even their chemical waste tanks.

- The material is lightweight making installations much easier, faster, and less expensive than other materials of construction.

- The material is durable allowing it to take a high degree of physical abuse without deteriorating.

What about concrete?
The Portland Cement Association produced an article titled: "Effects of Substances on Concrete and Guide to Protective Treatments" (2001). In this article they listed a variety of media that will deteriorate concrete ultimately leading to a failure unless a protective coating is used. Among the types of media listed that are harmful to concrete are: fats, fatty acids, vegetable oils, salts, sugars, acids, bleach and water. All of these are commonly found in the waste effluent in a normal commercial kitchen.

Concrete gravity grease interceptors are guaranteed to fail and in fact they are being replaced all the time. On average a concrete gravity interceptor will last approximately 8 years. Schier recently replaced a concrete gravity interceptor in Beaverton Oregon. The restaurant's 1000 gallon concrete gravity grease interceptor had a large hole in the bottom. The city required them to replace the failed unit and approved a Schier GB-250 as the replacement unit. The Schier unit was successfully installed inside the existing gravity interceptor substantially reducing the replacement cost and providing the restaurant with a far superior product. The Schier unit will be there for the life of the plumbing system giving peace of mind to the restaurant and the city.

Metal is also a poor choice for a grease interceptor. Most grease interceptor manufacturers still use metal today with a "corrosion resistant" coating in the interior of their units. Unfortunately the process for pumping out and cleaning these devices invariably scratches the coating leaving bare metal exposed. These exposed areas are susceptible to corrosion. The average lifespan of a metal grease interceptor is approximately 5 years.

When you have a choice on what to recommend or specify for a project, consider the materials of construction involved - it really does matter!