The operation of the Hall Street wastewater treatment plant (WWTP) in Concord, NH has caused the emission of objectionable odors from various liquid and solids treatment processes resulting in periodic odor complaints from its neighbors. The City of Concord retained Fay, Spofford & Thorndike (FST) to conduct a comprehensive odor emissions study at the Hall Street WWTP and to recommend appropriate corrective measures.
An on-site sampling program was developed to quantify and characterize odor emissions from known or potential odor sources at the WWTP. The program involved the sampling and analysis of off-gases from various odor sources in four different sessions. The gas samples were analyzed for odor concentrations, H2S and other reduced sulfur compounds and ammonia.
The assessment of the impact of odors from the WWTP on the community was accomplished by community involvement program and modeling.
Several odor control alternatives were evaluated for the treatment of odorous emissions from the liquid and solids treatment trains. These alternatives were compared based on detailed technical and cost factors. Under the recommended alternatives, the influent channels and screw pump channels in the influent pump station, the primary clarifiers, the biotowers and the biotower effluent channels will be covered using low profile aluminum covers. The odorous air from beneath the proposed covers in the influent pump station and primary clarifiers will be conveyed to the biotowers. The odorous emissions from the top of the covered biotowers and the biotower effluent channel will be collected and transferred to an engineered biofilter.
In the solids treatment train, the odorous air from the RDP process and the associated enclosed conveyors will be conveyed to a dust scrubber followed by an ammonia scrubber. The outlet air from the ammonia scrubber together with the exhaust air from beneath the covered BFPs, BFP/RDP room and sludge loading area will be treated in a multi-stage chemical scrubber.
The Hall Street Wastewater Treatment Plant (WWTP) in Concord, NH was designed in the late 1970’s and went on-line in 1981 to provide secondary treatment for the City of Concord using a biofilter activated sludge treatment system. The process was designed for an average daily flow of 10.1 million gallons per day (mgd) with a peak hourly flow of 25 mgd. In addition to the wastewater flow, the facility receives waste activated sludge (WAS) from two nearby treatment plants as well as significant quantities of septage and leachate from the local landfill. These additional loadings are introduced to the treatment facility at the influent pump station. Figure 1 shows the layout for the Hall Street WWTP.