Valley Forge Plant Finds Solution For Odor Control Problem

Valley Forge Plant Finds Solution
For Odor Control Problem

Buchart-Horn and a consultant compiled
plans to eliminate wastewater plant's odor.

After struggling with persistent odor problems at its treatment plant along the Schuylkill River in Chester County, The Valley Forge Sewer Authority adopted an innovative process that relies on wastewater-borne microorganisms to consume odor- causing compounds.

Efforts to reduce odors began in 1988, after the plant was the target of an unusually large number of odor-related complaints. When operational and facility changes failed to produce results, the plant turned to Robert P. G. Bowker, P.E., a nationally-recognized odor consultant.

While members of the Authority and plant operators had assumed the sludge storage area was responsible for odor problems, Mr. Bowker identified the Influent Structure and Primary Clarifiers as problem areas. Subsequently, designs for plant improvement targeted developing a cost-effective method to control hydrogen sulfide emissions with tank covers and air treatment.

The Authority had reservations over the cost and site area demands associated with traditional carbon filters or scrubbers to treat odors. Members also knew that scrubber systems require ongoing purchases of chemicals while carbon filters require periodic replacement of spent carbon.

After concluding that a biofilter treatment system that would send odorous air through piles of compost would require too much area, the Authority selected an innovative biological method that involved diffusing odorous air through the plant's aeration tank.

With assistance from Robert P.G. Bowker & Associates and Buchart- Horn, Inc., The Authority decided that fiberglass or aluminum covers would be best to collect odorous air from the influent structure and the primary clarifiers. The Bowker study indicated that most of the odor from the primary clarifiers occurred in the launders and the influent well areas. Covering only the launder and influent wells involved half the cost of covering the entire tank.

Since construction of a building exceeded budget and space limitations, the design relied upon sound attenuation enclosures to reduce the noise from positive displacement blowers.

The design also called for a dozen air changes per hour inside the covers in order to collect odorous air and not allow hydrogen sulfides to collect and corrode equipment within the enclosures.

The odorous air is diffused through fine bubble diffusers in the aeration tank so that microorganisms in the wastewater consume and volatilize the hydrogen sulfides. In short, the microorganisms have been enlisted for double duty -- to treat the waste and the odor.

The Valley Forge Sewer Authority asked Buchart-Horn, Inc. to prepare contract documents to solicit competitive bids for a design/build contract for the installation of odor reduction equipment. The Authority also chose to bid the project so that each contractor would have to develop an efficient approach and a design.

B-H prepared contract documents based on a developed conceptual design that defined the type of acceptable equipment and materials as well as any size or location constraints necessary to protect the Authority's interests. Bidder response was excellent. This bidding procedure created an innovative team approach through which B-H reviewed the design to protect Authority interests and project goals while the contractor and engineer prepared the design according to the most efficient procedures, equipment and routings.

Eastern Environmental Contractors, Inc. completed the successful odor control project in late '96. While the pungent hydrogen sulfide odors were eliminated, an added benefit was a decrease in energy costs that resulted from a reduction of aerator speeds on the aeration tank. Since the odorous air is diffused with the more efficient fine bubble diffusers, the less efficient surface aerators can be operated at a slower speed that require less horsepower. The 90-horsepower reduction translates to power savings exceeding $60,000 per year.