Design & Construction Services for the Biological Nutrient Removal Upgrades at Heritage Village Water Pollution Control Facility
The Heritage Village Water Company retained Weston & Sampson to evaluate, design, and provide construction services for the Biological Nutrient Removal Upgrades to the 0.780 MGD Heritage Village Water Pollution Control Facility located in Southbury, Connecticut.
The facility is located along the Pomperaug River, which the State of Connecticut has classified as a Class A – Trout Stream just upstream of the plant’s discharge point. Limited in area, the site is surrounded by an upscale golf course and FEMA flood zones. Because of the sensitive nature of the site, the facility was required to have one of the most stringent effluent requirements within the state. Additionally, an agreement was reached with the State to accept the flow from their nearby Southbury Training School facility, which allowed the limit to be increased. Weston & Sampson designed the facility to meet effluent Total Nitrogen levels of less than 3.5 mg/L and effluent Phosphorous levels of 0.50 mg/L through the use of the Five-Stage Bardenpho process, making this facility one of the first facilities to utilize this process in New England.
Weston & Sampson utilized existing structures and facilities to the extent allowable, due to the limited area available for expansion. The upgrades included a new headworks facility with fine screening and grit removal; anaerobic and pre-anoxic swing basins; conversion of the mechanical aeration system from mechanical surface aerators to a fine bubble diffused aeration system; conversion of the existing 30-foot diameter secondary clarifiers to post anoxic zones; a new re-aeration basin; two new 55-foot diameter secondary clarifiers; and a new sludge pumping facility with return and waste activated sludge pump systems. The solids handling facilities have also been upgraded with a new 1.0-meter gravity belt thickener and an additional 20,000 gallons of thickened sludge storage. The existing hypochlorite and aluminum sulfate chemical feed systems have been replaced, and a supplemental carbon system has been added for the de-nitrification process.
During the design, the State of Connecticut informed the Heritage Village Water Company that a phosphorus limit of less than or equal to 0.20 mg/L may be imposed over the next 2 to 4 permitting cycles. As such, space was reserved on site for additional phosphorus removal facilities, and the biological process was designed with a great deal of flexibility to allow these modifications to the facility in the future.
The facility upgrades, which were originally estimated at $14 million, were completed at a cost of just over $10 million, thanks in good part to the cooperative relationships between the owner, contractor, and Weston & Sampson. The facility continues to produce an excellent effluent that easily meets all permit requirements.