The Keene Wastewater Treatment Plant (WWTP) is owned by the City of Keene and is operated by the city’s Department of Public Works. It is a Grade IV secondary treatment, activated sludge facility. Located on Airport Road, behind the airport, the WWTP currently treats the domestic and industrial wastes from the communities of Keene, Marlborough, and some sections of Swanzey with a combined population of 35,000. It also accepts septage waste from the region.

The treatment plant is an activated sludge process, with biological nitrification, permitted for the discharge of an average daily flow of 6 million gallons. Peak design capacity is 15 million gallons per day. Treatment consists of grit removal, primary settling, secondary aeration, flocculation, final settling, and disinfection by ultraviolet light. The plant effluent is discharged into the Ashuelot River. Solids collected from the primary and secondary systems are thickened and combined, then dewatered using belt filter presses. The dewatered solids are then landfilled.

The city is permitted, through its NPDES Discharge Permit issued by the U.S. Environmental Protection Agency and the State of New Hampshire, to treat and discharge 6 million gallons per day. The actual average daily flow is approximately 3 million gallons per day. Effluent flow to the river must have a monthly average of less than 30mg/L total suspended solids (TSS) and 25 mg/L carbonaceous biochemical oxygen demand (CBOD). Keene has averaged greater than 95-percent removal of both of these parameters since 1990.

Long-term wastewater strategies include identifying ways to use wastewater as a resource, adopting environmentally responsible wastewater treatment and disposal strategies, and working towards a strong water-conservation program.

The City of Keene should make it a policy to install only low-flow fixtures in city projects, and encourage all private projects to do the same. The city should also explore the potential for using waterless urinals and composting toilets in appropriate situations.

Many advances have also been made in natural systems-based, decentralized wastewater treatment systems that are energy efficient and provide high-quality discharge. These systems harness native plants and micro-organisms in constructed wetland systems to safely treat waste underground and discharge water that can percolate into the ground, or be used for irrigation. These “living machines” can even be used to grow harvestable plants and help develop alternative opportunities for new businesses that use the nutrient rich by-products.