Plant and Equipment
BACKGROUND
The Town of York has been a summer resort area for many years, and has seen moderate growth in both the year-round and seasonal populations. Since the mid-1980s these populations have increased substantially.
The original secondary treatment plant was constructed at the current site in 1975. It was designed to treat an average daily flow of 1.6 million gallons per day (mgd) and a peak flow of 4.5 mgd. The treatment facility was designed to serve York for approximately 20 years; however, due to the increased population growth of the 1980's, flows to the facility had reached design levels by 1990.
In 1990, the York Sewer District, which owns and operates the treatment facility, obtained the services of Wright-Pierce Engineers to design an upgraded facility at the existing site. In 1994, the new facility went on line, providing treatment for an average flow of 3.0 mgd and a peak flow of 7.5 mgd.
NEW FACILITY
In order for the York Sewer District to provide treatment services to their current users, as well as provide capacity for growth within the Town of York, many components of the treatment facility were replaced with larger, more efficient systems. A new Process Building was also constructed to house the new equipment.
Like the treatment plant constructed in 1975, the new plant incorporates a secondary treatment process to treat the incoming waste water. Biological activity breaks down the various components in the incoming waste system such that over 90% of the biochemical oxygen demand (BOD) and 90% of the total suspended solids (TSS) are removed.
New facilities include: a headworks, where large items in the waste stream are removed by a screening device, and grit is removed by a degritting system; aeration basins, where mixed liquor and oxygen are combined with the waste stream to promote the biological treatment process; clarifiers, where the mixed liquor settles to the bottom of the tank and clean effluent is discharged from the top; and the chlorine contact tank, where liquid chlorine is introduced to kill the bacteria and sodium bisulfite is introduced to remove excess chlorine. In addition, excess mixed liquor (sludge) wasted from the process is dewatered and lime stabilized prior to being applied to farm land as a natural soil amendment. Support equipment for these processes, including several pumps and air blowers, are housed in the Control Building and the new Process Building.
To keep the treatment system operating properly, a Supervisory Control and Data Acquisition (SCADA) system was included in the design. This SCADA system is operated by a computer interface. The SCADA system automatically adjusts equipment speeds to maintain preset levels; provides feedback to the operator as to how the process is operating; provides alarms for equipment malfunction or pending malfunctions; and automatically stores data from the various instruments used to control the process for end of month reporting to the Department of Environmental Protection.