INTERIM ODOR CONTROLS

The odor abatement program is being conducted in two phases consisting of implementation of interim odor controls, and the design and implementation of the long-term odor control plan. The interim odor controls are non-intrusive approaches have been installed to temporarily mitigate perceived odor problems. Interim odor controls include gel neutralizing agents which were placed in various manholes (MHs), activated carbon filters which were designed to fit into several types of sewer vent structures (VSs) and recently, chemical addition of products to reduce the generation odorous gases. To determine the effectiveness of the interim odor controls, hydrogen sulfide gas levels and the velocity of exhausting air from the sewer were measured before and after the implementation of odor controls in several locations. The passive carbon systems were the most effective with over 99% removal of odors, but resulted in reduced exhaust rates from the sewer vents. Reduced exhaust rates were a primary concern because air trapped inside of the sewer may increase hydrogen sulfide levels and corresponding rates of concrete corrosion, result in the build-up of explosive gases and/or a hazardous atmosphere, and further reduce dissolved oxygen in the wastewater.

The interim odor remedies included either carbon filters or gel neutralizers depending on site accessibility, airflow dynamics, and the proximity of the site to public receptors. Gel neutralizers were hung in 17 structures including MH-1997, 2, 6, 9, 11, 12, 13, 14, 15, 25, 26, 27, 28, 29, 50, 51 and AS-409. Gel neutralizers were hung from the manhole frames using a length of stainless steel (SS) chain that was connected to an eyebolt mounted to a length of SS angle that was bolted into the MH frame. The gel neutralizer in the access shaft at 409 was hung on a SS reinforced bar mounted to existing anchor bolts. Type 316 SS was used for all components that support the gel neutralizer buckets to the MH frames. The picture thumbnails below show a diagram of the gel neutralizer in a MH and actual field pictures of the gels. Click on the thumbnails to view a larger image.

Typical Gel Installation Installed Bucket Used Gel Bucket

Carbon filters were installed in five structures including four at VS-1990, 1995, 204 and 410, and one set of eight filters at AS-31. Existing carbon filters at Site 43 and 52 were maintained as part of the interim odor maintenance plan. Carbon filters were constructed of Type 304 and Type 316 SS in a variety of sizes to securely fit into the vent structures. One-inch wide neoprene rubber strips were used for sealing the carbon filters at VS-1990, 1995, 204 and 410, and masonry sealant was used to seal the filters at AS-31. The thumbnails below show a diagram of the carbon filters in a square park-style VS and field pictures of the type of carbon used and one of the SS carbon filters in place inside of a VS. Click on the thumbnails to view a larger image.

Typical Carbon Installation Installed Carbon Filter Carbon Granules

The design and implementation of the interim odor controls was completed from March through July, 2000. Regular maintenance checks and change-outs have since been performed. The gel neutralizers and carbon filters continue to be maintained and changed on a periodic basis.