Odor Control
Controlling odor from a wastewater pumping system requires both careful design and the use of various chemicals added to the fluid or ozone treatment of the atmosphere within the wet well.
Odor in a wastewater collection system is usually caused by the release of hydrogen sulfide gas (H2S) from the sewage. The source of the “rotten egg” smell, H2S is highly toxic. Several factors can affect the release of H2S: 1) Time – the longer the fluid remains in the wet well of force main, the greater the chance it will begin to off-gas H2S; 2) Agitation – gas is more likely to be produced if the influent fluid splashes or is dumped into the wet well rather than being directed into the wet well without agitation; 3) Chemical Constituency – some sewage is more likely to produce H2S, due to its chemical makeup.
Chemical Injection – The most common method for reducing the production of H2S is by the injection of one or more chemicals into the wet well. The addition of Bioxide® solution, a product of the Siemens company, introduces nitrate oxygen into the waste stream and creates an environment in which certain naturally occurring bacteria thrive. These bacteria utilize the dissolved hydrogen sulfide which is present as a part of their metabolism, thereby removing any dissolved hydrogen sulfide from the wastewater.
Ozone Treatment – Another odor control method is ozone (O3) treatment of the atmosphere within the wet well. Ozone is a strong oxidizer. An ozone generator with a contact chamber is located near the wet well. Air is circulated from the wet well to the contact chamber where it is exposed to a predetermined concentration of O3. The H2S is oxidized to a sulfate, thereby reducing odor within the wet well and force main.
Air Injection in Force Main – Formation of H2S can occur in the force main exiting the pump station. This is prevalent in long force mains, due to the length of time that the effluent remains in the force main. One method for reducing the formation of H2S is the injection of compressed air in the force main to improve the dissolved oxygen concentration, thus preventing downstream formation of sulfides and helping to oxidize existing sulfides. A typical force main air injection system consists of an air compressor and associated valves, sensors and controls.