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City reports success in pilot odor-control program for County Line trunk sewer; plans expansion
Summary
Utilities staff said a biological/chemical/mechanical pilot to reduce sewer odors on the County Line trunk sewer has cut H2S and odor calls; staff described a combined biochem treatment and odor-scrubbing units installed earlier this year and proposed additional installations.
City utilities staff presented a status update on a multi-pronged odor-control pilot targeting the County Line trunk sewer and lift-station network.
The presenter, identified in the meeting as a utilities staff member, said the pilot uses biological augmentation (“Biochem”), targeted mechanical lift-station improvements, and commercial odor-control scrubber units to reduce hydrogen sulfide and other malodors. The presenter said the system covers roughly 600 miles of sanitary sewer in city service area, with the farthest upstream sewer stretching about 13.5 miles to the wastewater treatment plant; in the County Line area roughly 19 lift stations feed the top 3–3.5 miles of force main, which has generated most odor complaints.
Staff described Biochem as a cultured bacterial product that replaces the “bad” biofilm in pipes, reduces grease and H2S production and, according to staff, improved treatment-plant loadings. The presenter said the city temporarily turned the biochem dosing off during a test and saw an immediate increase in H2S and other loadings, which staff cited as evidence the product reduced odors and plant influent. “We turned it off in 30 days,” the presenter said of an early test period, and then restored dosing after H2S and load increases were detected.
Staff also described deploying higher-capacity odor-scrubbing units (referred to in the presentation as “wager units”/odor control units) at key locations. One such installation—placed in February—cost about $175,000 to install and carries an annual operating cost the presenter estimated at about $15,000. Staff said the new units “allow the system to breathe” by allowing gases to vent through the scrubbing units and by reducing system pressures; since installation staff reported no odor calls from the nearby neighborhood and materially lower H2S readings near Fire Station 3.
Utilities staff recommended expanding the combined biological/chemical/mechanical approach into additional County Line locations and other hotspot areas and said the program has reduced the need for the previous caustic chemicals the city used. No regulatory changes or new charges were proposed; staff framed the item as a capital/operations investment to reduce complaints and protect treatment-plant compliance.
