Insertable Filtration System Controls Manhole Odors

Odor complaints from manholes are a familiar problem, especially in receiving or drop manholes. The most common component of odor in sewer gas is hydrogen sulfide with lesser concentrations of other odorous compounds. A new insertable air filtration system can help control the odors.

Odor Sentry is a new high-capacity manhole odor control insert from Sulfa Treat. The system incorporates a stainless steel filter insert, with a three cubic foot capacity, filled with the company's Enforcer™ odor control media. The media-filled unit is installed below the manhole lid, out-of-sight.

Sulfide corrosion of concrete and metal steps is aggravated by sealing of manhole lids.

The cylindrical media basket is held in the manhole or wetwell with a tub-type holder that can be manufactured to fit any size or shape of manhole or wetwell entry.

Because of the system's lightweight components and simple design, one person can install the insert in less than 20 minutes. The inserts are constructed of stainless steel and other corrosion resistant materials. A bottom swing-open trap door allows media removal, in or out of the manhole.

The system passively treats vented sewer gas at spike flow rates as high as 35 cfm and H2S levels of several hundred ppm or more.

The Enforcer™ odor control media is a mix of non-hazardous solid organic and inorganic odor counteractants. Hydrogen sulfide and light mercaptans are safely and irreversibly reacted away while attacking other odors present.

The media contains no caustics or oxidizer and is safe to handle. The media thrives on varying moisture levels commonly encountered in manholes and wetwells, achieving a H2S loading of up to 25 percent by weight. The system is designed to allow an outflow and inflow of air so the manhole can breathe.

The media can be stored in unopened pails for a year or more. No special storage, inventory or handling procedures are required. The media should properly fluff during filling for a consistent and low pressure drop. The used media can be vacuumed or dumped into a trash container for disposal in common Class II non-hazardous landfills.

Case Study

In a major mid-western city, odor complaints were frequent where an underused force main entered a gravity system running through a subdivision. Odors escaped from the manholes causing complaints throughout the area. Sealing the manholes forced the odors through some roof vents. The sealed manholes also experienced rapid deterioration of the manhole lining and steps.

The local sewer district company repeatedly responded to calls from homeowners despite using several methods to treat the odor, including liquid additives and counteractants. Testing of the air in the manholes showed 2.5 ppm H2S.

An Odor Sentry® system was placed in a manhole at the top of a hill just downstream of the receiving manhole and two more in manholes near homes along the line down in the valley. The units have been in operation for one year with no consumer callbacks due to odor.