Columbus Discovers a Greener Odor Control Approach

To reduce overflows of untreated wastewater into area waterways, the City of Columbus constructed a large capacity sewer (13-foot diameter) to provide up to 60 million gallons of storage (equivalent to the projected wet weather flow from a 1-year storm event) and connected it to a new headworks facility at the Southerly Wastewater Treatment Plant that was designed to pump and treat over 400-mgd. To address the anticipated high hydrogen sulfide and odor concentrations from the collection system, the new headworks required a proven and effective odor control technology that would reduce any nuisance odors from being perceived off-site. The goals established by the City regarding the odor control system were:No odors at the plant fencelineDesign odor control for the health and safety of the facility operatorsApply a proven odor control technologyProvide redundancy to preclude odor control system down-timeThe odor control challenges were characterizing the sewer and new headworks odor potentials and selecting the most cost-viable technology to comply with these goals.Odor assessment investigations were conducted to characterize odor conditions in the collection system and at the pre-existing headworks area of the WWTP. As a result of the collection system being redesigned to handle and store wet weather flows, it was anticipated the potential for hydrogen sulfide generation and release, due to this greater detention time and deposition of solids, would be increased. Site measurements showed a range of hydrogen sulfideconcentrations from 1 to 160-ppmv. Field measurements and office calculations were used to establish the overall odor control system design average and peak concentrations of hydrogen sulfide as 3.5 and 33-ppmv, respectively. Other reduced sulfur compounds were present, but at considerably lower levels. The volume of air required, to provide effective capture and containment of the odors, was approximately 100,000 cfm.Four odor control technologies were evaluated (wet scrubbing, carbon adsorption, biofiltration, and biotrickling filter) and biotrickling filters were selected based on:lower operating costsno chemicals used/stored/handledno hazardous residualsgreener, sustainable operationless maintenance laboreffective treatment of design odor loadsOnce selected, the City of Columbus installed the largest stand-alone biotrickling filter system (provided by Bioway) for odor treatment in North America. The system was designed to treat 96,000 cfm of odorous air.The biotrickling odor control system consists of ten towers fed by a central fan system. The fan system pulls the odorous air through a carefully designed combination of main and branch ducts and pushes it through the ten towers. The treated air is exhausted through a stack at the top of each of the towers. The multiple towers were designed to manage the varying hydrogen sulfide concentrations and other reduced sulfur compounds associated with raw influent wastewater.Extensive process performance trials were conducted and the biotrickling filter system was found to have exceeded its design performance requirements. The system demonstrated 96% removal of odors, taking the average exhaust odor concentration to less than 300 odor units. The odor control system has proved to be robust and has coped well with the varying seasonal odor loads experienced in central Ohio over the past nearly two years of operation (the new headworks building with odor control system was placed into operation in March 2008).This paper will present the odor control technologies that were evaluated, review the biotrickling filter system and present performance data.