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Superintendent:
Larry Anderson
Administrative Assistant: Evelyn Gendron
564 Nashua St.
Milford, NH 03055
phone: 249-0660
fax: 672-1071
facility hours:
7:00a-3:30p
Information
Service
App.
Treatment Process
Effluent Standards
Industrial Pretreatment
Composting
Plant Statistics
Treatment
Process |
Milford Wastewater
Treatment Facility
Milford constructed its advanced secondary treatment facility in 1982 to serve Milford and neighboring Wilton. The project included installation of approximately 14.5 miles of sewers. Construction costs for the collection system and treatment facility totaled $14.2 million. The Environmental Protection Agency (EPA) and the New Hampshire Water Supply and Pollution Control Commission covered most of the cost with grants totaling $13.2 million. The Farmers Home Administration provided additional assistance in the form of a loan.
For After Hour Emergencies
Please Call
673-1414
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 Treatment Process
Milford's treatment facility was designed to handle an average daily flow
of 2.15 million gallons per day (MGD) and a peak flow of 6.45 MGD. It uses
a conventional activated sludge treatment process. The process begins with
influent wastewater screening, followed by grit removal, and then primary
clarification. Next, the wastewater is aerated in a system of six tanks fitted
with fine bubble membrane diffusers. A combination of 60, 100, and 200 horsepower
centrifugal blowers provide air to the system. The fine bubble system replaced
the original coarse bubble diffuser system and has resulted in considerable
energy savings. Following aeration, the wastewater passes through the secondary
clarifiers for final solids settling and removal. The treated effluent then
flows through an ultraviolet disinfection system before being discharged to
the Souhegan River. The UV system replaced the chlorine disinfection system.
Milford converted to UV disinfection to improve overall treatment performance
and meet the more stringent limits imposed since 1993.
Effluent Standards
Milford's wastewater treatment facility was
designed to meet an effluent standard of 20 milligrams per liter (mg/l) for
biochemical oxygen demand (BOD) and 30 mg/l for total suspended solids (TSS).
The facility was also required to limit discharge of nitrogen to 1.0 mg/l
during warm weather months.
Discharge limitations for the treatment facility tightened in 2000 to require
no more than 7 mg/l of bod in warm weather months and 10 mg/l of BOD during
the remainder of the year. The changes resulted from a program undertaken
by the Department of Environmental Services (NHDES) to improve water quality
throughout the state. NHDES set Milford's TSS limit at 15 mg/l, and imposed
a year-round limitation on ammonia nitrogen varying from 7.3 to 19.4 mg/l.
The treatment system requires the addition of chemicals to assist in keeping
operations within permit limits. Magnesium hydroxide, the key chemical in
the operation, is added to the aeration tanks to provide the proper conditions
to allow the biological treatment process to work. Since the plant must reduce
the level of ammonia nitrogen in the effluent, the pH must remain in a certain
range to support the ammonia-nitrogen reaction. Without the magnesium hydroxide,
pH would drop and the facility would have difficulty meeting its permit requirements.
The Milford Wastewater Treatment Facility has stringent limits for three metals:
lead, cadmium, and copper.
Industrial Pretreatment
The staff also operates an industrial pretreatment program which requires
certain industries in Milford and Wilton to limit the discharge of some pollutants
that have a harmful effect on the treatment facility and the Souhegan River.
Pretreatment personnel inspect and monitor industrial discharges on a regular
basis. Industries must correct any violations of their discharge permit or
face penalties.
Composting
Biosolids generated during the treatment process are dewatered on the belt
filter press through a combination of gravity drainage and pressure belts
passing through a series of rollers. The process also uses polymer to assist
in dewatering. Following dewatering, the biosolids are mixed with wood chips
and wood ash, then piled over perforated plastic pipes through which small
blowers provide air for ventilation. The natural aerobic decomposition that
occurs during composting raises the temperature of the chip/biosolids/ash
mixture to above 130 degrees Fahrenheit. Over three to five days, most bacteria
is killed. In the process, moisture is driven from the biosolids mixture leaving
a dark, fine material resembling peat moss.
Milford's composting facilities also include an equipment building that holds
screening equipment, a loader, and a dry compost storage building.
Plant Statistics
Design Daily Flow 2.15 MGD
Peak Design Capacity 6.45 MGD
Average Daily Flow 1.2 MGD
BOD Loading 3,350 lbs./day
Suspended Solids Loading 4,000 lbs./day
Total Kjeldahl Nitrogen Loading 450 lbs./day
Population Served 12,800 persons
Treatment Facility Components
Main Pump Station - three 60 hp variable speed pumps 2250 GPM
Headworks - Two comminutors, one manual bar rack, two aerated grit chambers
Primary Clarifiers - two 45' diameter circular center feed clarifiers
Aeration - Two 3-celled tanks with fine bubble diffusers
Secondary Clarifiers - Two 55' diameter circular center feed clarifiers
Disinfection - - Three-bank ultraviolet radiation
Post Treatment - Aeration cascade for oxygenation
Sludge Compost Facility - 1.8 dry ton per day utilizing the aerated static
pile process
Process Equipment
Grit Removal - Screw conveyor and washer
Blower Systems - Two 100 hp 1600 SCFM centrifugal blowers, Two 60 hp 860 SCFM
centrifugal blowers, One 200 hp 3700 SCFM centrifugal blower
Major Pumping Systems - Return activated sludge: three 15 hp variable speed
pumps supplying 750 gpm; Waste activated sludge : two 10 hp pumps supplying
110 gpm; Thickened sludge pumps: two 7.5 hp pumps and one 5 hp pump supplying
95 gpm; Primary sludge pumps: four 5 hp constant speed plunger pumps supplying
96 gpm; Water pumps: two 15 hp constant speed pumps supplying 300 gpm
Sludge Thickening and Dewatering - Two 15' diameter circular center feed gravity
sludge thickeners; one 1.5 meter two belt multi-zone belt filter press with
polymer feed
The Milford Wastewater Treatment Facility completed installation of a Supervisory
Control and Data Acquisition (SCADA) system. The system allows facility personnel
to acquire information from remote areas of the facility from a computer work
station. The system monitors pumping rates, influent/effluent flows, tanks
levels and process control parameters. |
