Biofilter array ends odor complaints from sewage transfer line - Case Study


Courtesy of Biorem Technologies Inc.

Management at Jefferson County (AL) Environmental Services reports it has solved a long-running odor problem by tapping a 30,000 din-capacity biotilter array into a 14 mgd average, 55 mgd maximum sewage, transfer line. The 6-unit BASYS array was manufactured by Biorem Technologies Inc. of Guclph, Ontario.

The array handles hydrogen sulfide at average concentration of 5 ppm, and maximum of 25 ppm, as well as other odor-causing compounds, such as methyl mercaptan, dimethyl sulfide (DMS), dimethyl disulfide (DMDS), and odier Total Reduced Sulfur (TRS) compounds. The county has ordered five additional systems from the manufacturer for one of its wastewater treatment plants.

A long-running odor problem was solved by tapping a 30,000 cfm-capacity biofilter array into a 14 mgd average, 55 mgd maximum sewage transfer line. The line discharges into an underground junction box, with the odor control system's main collection duct evacuating box head-space air above ground for humidification and biofiltration before discharge to atmosphere through fan stacks.

'Our main purpose was to stop the dozens of odor complaints we received over four or five vears where the transfer line ran near a shopping mall and a residential area,' said Clyde C. Osborne, wastewater treatment plant superintcndcnt. 'Helping to reduce corrosion that was found during a routine inspection was a welcome byproduct. When you go to that site now, you don't smell anything.

Once the system became frilly operational, the complaints stopped.'

Osborne said a high-stack exhaust fan had apparently been solving the problem up- and downstream of the sensitive area for about seven years, but complaints had persisted in the immediate area, stimulating a search for an alternative solution.

'We considered activated carbon towel's, which we had used at a pre-treatment facility upstream, but we didn't like the expense of having to change media every three or four years, or the need to dispose of a hazardous material,' he said. 'That led us to biological filtration, with presentations from three vendors. Biorem was chosen because their media was more uniform, and didn't seem to present risks of filter clogging or attracting rodents.'

Dampers on inlets and outlets to modular biofiltration units allow for isolation of each unit. Biofiltration media was designed specifically to handle a wide range of odor-causing compounds, including TRS and others, versus the traditional focus on hydrogen sulfide only.

'Construction started early in 2002, with a local contractor able to handle the installation. Startup was in August 2002, with media expected to last for 10 years. We're expecting a low-maintenance, long-runring solution ro the problem. They provided sample testing three or four times the first year, and then we contracted for more, and haven't seen any problems.' The 60 inch, 35-mile concrete transfer line, built in 1987, receives effluent from about one-quarter of the system's 164 pump stations, which range in capacity from 100,000-5,000,000 gpd. Corrosion had been enough of a problem to require activated sludge pretreatment, upstream from the odor complaint area, that was related to input from dairy product and soft drink plants.

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