For a small community, Greenfield, Mo., was plagued with what appeared to be major inflow and infiltration (I&I) problems. The sewer pipes...
Upgrade will help protect water quality for 9 million New Yorkers
Environmental Protection Commissioner Carter Strickland announced the completion of a $7.4-million project to upgrade a city-owned wastewater treatment plant at Margaretville, Delaware County. Upgrade work began in 2009 and will help protect water quality in the Delaware watershed, which supplies more than half of the city's daily drinking water needs. With the construction of the expanded state-of-the-art microfiltration system, peak flow treatment capacity has increased to 1.2 million gal per day (gpd) from 860,000 gpd.
The expansion also will enable a previously planned extension of the sewer collection system to serve certain residents now served by individual septic systems. These individual systems are considered at risk of contaminating source waters and are subject to enforcement costly to both residents and regulatory agencies, in case the systems fail. Microfiltration is an advanced treatment process in which treated wastewater, or effluent, passes through a membrane filter removing pathogens and contaminants prior to final disinfection.
The Margaretville Wastewater Treatment Plant serves about 1,300 residents and businesses. It was built by the Department of Environmental Protection in the 1950s and upgraded in 1998 at a cost of $30 million and provides sewerage disposal free of any cost to local citizens, local businesses, or local governments in the area.
"Protecting the drinking water of 9 million New Yorkers requires continuous investments ranging from land acquisition to local wastewater treatment plant upgrades," Strickland said. "Upgrading the Margaretville Wastewater Treatment Plant to help maintain our high water quality helps to ensure that New York City remains one of only five large cities to have an unfiltered water supply."
Wastewater treatment includes physical, chemical and biological processes that remove pollutants and disease-causing pathogens from wastewater. Each step of wastewater treatment removes pollutants and impurities. The first step of the process at the Margaretville Wastewater Treatment Plant is preliminary treatment, where a series of grates called bar screens remove solid objects—such as rags and household debris found in wastewater. Pumps then raise the wastewater to a series of settling tanks for primary treatment, another physical process in which the flow is reduced from a speed of 2 ft per second to about 1 ft per minute to allow heavy waste to settle to the bottom and lighter waste to rise to the top. Slow-moving bars skim the waste from the top and bottom.
Suspended material, which neither sinks nor floats, moves to another series of tanks for secondary treatment, also known as the suspended growth process. Much like bacteria breaks down food during digestion in a human body, in this process good bacteria consume the suspended material in an oxygen-rich environment. The bacteria are mixed with chemical coagulants so small fine particles and phosphorus that can damage the reservoirs form sticky heavy particles, and, as they become heavier, settle to the bottom of another battery of tanks where they are then removed. The remaining flow first goes through fine mixed media filtration, and then through microfiltration. Microfiltration is an advanced treatment process required on all wastewater treatment plants in the watershed in which treated wastewater passes through a membrane filter that removes remaining pathogens and contaminants. The remaining flow is further disinfected with ultraviolet light before release into the East Branch of the Delaware River, which flows into the Pepacton Reservoir.
The project was required by the State Department of Environmental Conservation to address inflow and infiltration issues caused during local storm events and snow melts.