Odor Control in Collection Systems

Hermitage, Pa. is an upper-middle class community whose water pollution control plant had received numerous odor complaints from a resident.The odor problem was mainly in the resident’s bathroom.The hydrogen sulfide (H2S) gas was liberating out of the influent stream from a forced main on the resident’s property, caused by the agitation of the influent when the circulation pumps at the Sample Road collection station were in operation. The problem was so severe that the resident complained of headaches and dizziness stemming from the odor.

The collection station’s flow rate is 180,000 gal per day (gpd), feeding a 14-in. forced main, which is located near the resident’s property.

Hickory Engineering of Hermitage, Pa.,was commissioned to examine the problem. Sampling of the influent was done both in liquid and vapor phases to determine the level of H2S.This was done using Gastec S2 sulfide liquid detection tubes and a Mine Safety Appliance gas detection unit. Random sampling was conducted for 30 days in October 2004 in order to take into account varying weather conditions and a range of times of day to determine the average level of H2S.

The corrosion rate was determined by installing corrosion coupons into the collection system at the Sample Road collection station. The coupons remained in the system for 30 days and were replaced in the collection station prior to treatment for the removal of the H2S. A comparison of the weight of the coupons was measured at the conclusion of the test to determine if the corrosion rate was reduced.

 

Polymeric amine solution

By adding a polymeric amine, H2S levels and solids buildup would be reduced. The combination of multiple amine sites and organophilic properties allows for fast, efficient abatement of these problem compounds. It also absorbs and reacts with the H2S and mercaptans to form water-soluble and nonvolatile polysulfides that are easily consumed in the downstream waste treatment process. These spent reaction products also help to reduce corrosion and solids, eliminating the additional expense of corrosion control and degreasing compounds.

The reason for the selection of the polymeric amine was due to the fact that it actually converts the sulfide molecule into a friendly sulfate. Similar products simply raise the pH level of the influent, causing the H2S to remain in liquid state. The polymeric amine is selective only to sulfide molecules.

The polymeric amine was introduced at the collection system using an LMI chemical feed pump at a determined flow rate.The H2S level at the resident’s home was reduced from as high as 100 ppm down to less than 5 ppm.

 

Conclusion

The polymeric amine is an effective way to safely eliminate H2S, reduce solids buildup and reduce the rate of corrosion in a collection system. The Hermitage WPC Plant has been treating with polymeric amine at two of its collection stations, accounting for more than 70% of the entire collection system since May 2005. It has been budgeted to treat the remainder of the system in 2006.

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