IFM was approached in the summer of 2004 by a local Water and Sewer Authority to determine an economical method to manage odors originating from a drop manhole near a residential and business area. Working with existing staff, IFM initially surveyed and sampled the problem manhole and numerous points upstream of the problem area. Hydrogen Sulfide was present, indicated by corrosion of the manhole lid and previous rehabilitation efforts by the Water and Sewer Authority.
IFM determined from the initial visit and sample results that the odors could be reduced, but may require pretreatment at the pumping station and also a polishing treatment within the problem manhole. This two-fold approach was necessary to reduce the formation of corrosive hydrogen sulfide gas in the force main (which has an average detention time of 24 hours), but also minimize the demand for odor controlling products downstream at the problem drop manhole.
IFM utilized AOS 2008 (IFM's Alternate Oxygen Source product) upstream at the main pumping station at rate determined based on field sampling and analysis. The addition of AOS 2008 reduces the formation of hydrogen sulfide in the force main by providing an intermediate form of oxygen (NO3-) that sulfide forming bacteria prefer over sulfates (SO4-2). By providing substantial forms of nitrate molecules, the sulfide forming bacteria reduce sulfate reduction, ultimately eliminating the formation of hydrogen sulfide gas.
Also utilized in this pilot was the addition of ONM 2015 (IFM's Odor Neutralizing Microbes) misted into the top of the manhole. This product neutralizes odors such as mercaptans, amines, ammonia and hydrogen sulfide that are present in the air and also contain bacteria to provide long-term odor control. IFM constructed a temporary housing at the problem manhole which contained a 55-gallon drum of ONM 2015 and the 12-volt timed relay dosing system that was required for this application. The pump was set to dose the manhole with a misting spray for 35 seconds every hour, providing 24/7 treatment.
Not only did this combination of products alleviate the odor problems in this area, it maintained the sulfide levels below 1.0 mg/l (aqueous sulfide), which will extend the life of the manhole. For this application, it was found that 15 gallons of AOS 2008 per day and Â½ gallon per day of ONM 2015 adequately controlled hydrogen sulfide and other malodors to acceptable levels. Currently, the Water and Sewer Authority is continuing to feed AOS 2008 at the main pumping station and plans are underway for a permanent housing and feed system for the Odor neutralizing Microbes application.