Ionization Tubes Used to Control Odors at the Source

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Two treatment facilities have conducted tests on a new odor control technology that uses ionization to oxidize odors at their source, which could reduce the need for equipment to collect and treat odor-laden air.

The Bentax Air Purification System connects directly to the HVAC system of a facility, such as a Sludge Dewatering Building, and elevates the natural oxidation potential of the indoor air without creating ozone.

The system features a set of ion tubes that produce a measurable and controllable quantity of negative and positive ions. When outside air is passed over the tubes, the ions attach themselves to the oxygen molecules, creating uneven polarity and forming clusters of 10 to 60 oxygen molecules clinging together. Typically one to two million clusters are formed per liter of air passing by the ion tubes. These higher energy molecules start immediately to disinfect the air, kill bacteria, and neutralize odors.

Because the process employs ionization, the longer the system operates the more effective it becomes, as walls and structures in the room become more charged with ions.

Power costs for the system are minimal. In many cases less energy is required to power the ionization process than is required to light the building. The only maintenance associated with this process is cleaning of the ion tubes about four times per year. The payback on replacing existing wet odor control systems is typically five years or less.

Process Demonstrations

The Allegheny County Sanitary Authority (ALCOSAN) conducted the first North American demonstration of the technology. In the project, baseline odor levels measured in the district’s sewage sludge dewatering building were reported at 1 ppm hydrogen sulfide and 8-9 ppm ammonia.

Process Demonstrations

A demonstration scale facility with an 1100 cu. ft. chamber was used to model the dewatering building at 6 air changes per hour. Raw municipal sludge covered the bottom of the chamber. Fresh air was drawn across the ion tubes and ducted into the air tight chamber. The only change that was made from baseline to active ion testing was to turn on the ion tubes. Flushing air rate remained constant at 120 cubic feet per minute (CFM).

Process Demonstrations

All data was recorded by Industrial Health Foundations Inc., an independent and OSHA approved laboratory. The ammonia and hydrogen sulfide were continuously monitored at the exhaust stack with an Industrial Scientific LTX310 and Gas Tech GT402, respectively.

Process Demonstrations

When testing began, baseline ammonia levels were stable at 26 ppm. When the ion tubes were engaged the ammonia levels dropped to non-detect. The sludge that was being used was producing low levels of hydrogen sulfide, (less than 1 ppm). Bottled ammonia gas was briefly turned on and off to test instrumentation response. Later a more sulfide active sludge was added to the chamber. The system initially lined out with ammonia in the 10-12 ppm range and hydrogen sulfide at 3 ppm. When the odor control system was engaged a second time, both contaminants were oxidized to non-detect on the CEMs.

Process Demonstrations

A second demonstration was run in April 1998 at the Harbour Remediation & Transfer Company, in Toronto, Canada, which operates a biosolids treatment facility for the City of Toronto.

Process Demonstrations

In this process, lime was added to dewatered sludge to stabilize the sludge prior to landfill. The plan was to measure total odor units, or dilutions to threshold, with drawn samples sent to an odor panel.

Process Demonstrations

Gases, heavy with ammonia and Total Reduced Sulfur (TRS) were ducted from a freshly processed and fuming sludge mound in the sludge storage building to a test chamber with Bentax operating. Odor samples were drawn at both the inlet and outlet ducts of the chamber. The emission criteria was set at 100 odor units or less. The system was able to reduce total odor units by about 90 percent, and meet the criteria of 100 odor units or less. Ammonia levels had decreased to non-detect as well, reporting 99 percent ammonia removal.

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