Over the past decade, we have seen a huge turn in the interceptor market — the adoption of HDPE (plastic) interceptors. There are several advantages using an HDPE interceptor, with the biggest benefit being the longevity of the unit compared to a concrete alternative.
As can be surmised, a concrete unit will fail — it is not a matter of if it will fail, it is a matter of when it will fail. Once grease has been sitting in an interceptor for over two weeks’ time, it gets to a pH level of <5, meaning it is highly acidic. At this point, the grease starts to eat away at the concrete, destroying the unit. Although a concrete unit typi-cally has a 4-inch thick wall, there is rebar halfway in between the wall to give it structure. Once this rebar is exposed, the unit begins to collapse inward on itself. So, even though the unit is 4 inches thick, in reality it only has 2 inches of effectiveness.
Concrete is inherently porous. Why would we use it to store highly acidic material (FOG) that is required to be neu-tralized by the EPA? Neutralization tanks are not made of concrete; they are made of high-density polyethylene (HDPE).
The common reason for installing a concrete unit is simple: The unit has a lower upfront cost, so it will stay within the tight construction budget; however, what saves a dollar today, costs more tomorrow. There is no debating a con-crete gravity interceptor costs less than a comparable gravity HDPE interceptor, but a HDPE interceptor has a much larger advantage — they come with a lifetime warranty.
After 10 to 20 years, a concrete interceptor will succumb to corrosion and need to be replaced. Not only will a new unit need to be purchased to replace the old one, but due to having hazardous material in the chamber, the corroded concrete unit will need to be disposed of properly at an EPA protected site — this is very costly. Additionally, the loss of revenue incurred while the business is closed to replace the unit must be taken into account, along with the cost of the labor to dig-up the old unit and connect a new unit.
If the overall lifetime cost of the interceptor were considered from the onset, an owner looking to hold the building for more than a decade would never knowingly select a concrete option. We call this “total-installed cost.” Once an HDPE interceptor is installed, funds never need to be allocated for the unit to be replaced. That concrete interceptor price suddenly doesn’t look very attractive.
One other major advantage of an HDPE interceptor is they are offered in either a hydromechanical or gravity setup. The ability to install a HDPE hydromechanical unit provides a more budget-friendly number, along with lower operating costs as gravity interceptors are required by code to be pumped out when only 25% full. The difference between the two is that gravity style acts as a giant holding tank giving the grease water time to rest for separation, whereas hydromechanical units utilize a flow restrictor along with an inlet diffuser.
This combination slows down the pace of the water, and then directs the incoming effluent away from the outlet. The grease in a hydromechanical unit separates from the water much more efficiently, allowing the unit to hold more grease per volume before needing to be pumped out. Steel units are generally this type of setup. Also worth noting, steel units have an even shorter life expectancy than concrete, and HDPE interceptors comparable in size are about the same cost as steel, but come with a lifetime warranty.
Another advantage of using a HDPE interceptor is the overall weight of the unit. When concrete units are purchased, part of the purchase price is the delivery of the unit to the site using a boom lift. If the con-tractor is running behind and the flatbed arrives with the concrete interceptor before the hole is dug, the shipment is rescheduled, throwing off the construction timeline or the contractor may need to rent a crane to keep on track. With an HDPE Gravity unit being so light, in the same situation, a boom truck would not be needed. A backhoe onsite would be able to take the unit off the truck until the hole was dug, not re-quiring any extra planning. For example, a typical 2,000-gallon concrete gravity interceptor weighs around 21,250 pounds; comparatively, a 2,000-gallon HDPE gravity interceptor weighs around 1,350 pounds.
Another available option would be to specify a HDPE hydromechanical unit. Most of the HDPE units in the market are light enough to be lifted into place by two people. They also are offered in widths less than a doorway, which make them perfect for retrofit applications inside of a building that cannot be accessed by a boom truck or backhoe.
Lastly, when considering a HDPE interceptor solution, investigate the manway extensions when burying the unit. Some manufactures offer their proprietary extensions that will add unneeded expense to the project budget, while also introducing additional gaskets to connect the risers the further the unit is buried. More gaskets means more potential weak points.
Although most AHJs around the country are open to an HDPE unit, not all are open to a hydromechanical option because they are comfortable with the process they have always used. When specifying a grease interceptor, the AHJ always has the final say — please check the local codes first.
Interceptor manufacturers can be leaned on for assistance as they have experience helping update local codes and educating the AHJs on the benefits of HDPE interceptors — both gravity and hydromechanical.