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Water and Wastewater Plant Directory
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Nashua, New Hampshire, USA
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Nashua Wastewater Treatment Facility
Sawmill Road
Nashua, New Hampshire, 03060
USA
Contact Information:
Contact: Richard Seymour, Deputy Director
Email:
Telephone: 603-589-3560
Fax: 603-594-3474
Plant Operation: Municipal
Processing: Wastewater
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Web site:
http://www.gonashua.com/defaulto.asp?url=/wwtf/default.asp
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Plant/Process Description:
Every day approximately 13 million gallons of
wastewater flows from Nashua and Hudson into the
Nashua Wastewater Treatment Facility. Wastewater
is sent from homes, businesses, and industries
into Nashua’s sewer/collection system. At the
facility, the wastewater is channeled through
several different treatment processes to remove
pollutants before being discharged into the
Merrimack River.
In preliminary treatment, two mechanical bar
screens are used to remove large solids and other
coarse debris that might damage downstream pumps
and other equipment. The flow then proceeds to
aerated grit chambers where the grit and sand is
allowed to settle. This material is washed and
loaded into trucks for disposal at the city’s
landfill.
In the next phase, known as primary treatment,
the wastewater flows to primary sedimentation
tanks where settleable and floatable solids
separate out naturally. In this step,
approximately 50 percent of the solids and 30
percent of the organic material are removed from
the wastewater in the form of primary
sludge.
In secondary treatment, the wastewater flows into
four large aeration tanks where bacteria and
other simple organisms grow and multiply,
digesting the organic matter as food. This mass
of organisms and solids is then allowed to
separate from wastewater in the secondary
clarifiers, resulting in a purified liquid known
as effluent. The separated excess biological
organisms are called secondary sludge. At the
end of the secondary process, more than 90
percent of the organic materials and solids have
been removed from the wastewater.
In the final step, Sodium hypochlorite a strong
bleach is then added to the effluent to kill any
remaining harmful bacteria. The disinfected
effluent is then completely neutralized to remove
excess hypochlorite in order to protect aquatic
wildlife in the river.
The sludges created in primary and secondary
treatment processes are thickened to remove the
majority of the water they contain. Tanks called
gravity thickeners are used to thicken primary
sludge, while mechanical devices known as belt
thickeners are used to thicken the secondary
sludge.
The thickened sludges are then sent to the new
anaerobic digester complex. In the 1.3 million
gallon egg shaped primary digester, the sludge is
held for 20 days. Here the solids are further
broken down into carbon dioxide, water and
methane gas. The methane is sent to a generator
to produce electricity and to a boiler to produce
heat for the digestion process. Anaerobic
digestion eliminates between 50% to 50% of the
sludge that needs to be disposed of and this
amounts to a reduction from 19,000 tons/year pre-
digestion to less than 10,000 tons/year with
digestion on line.
After leaving the digester complex, the digested
sludge is sent to three belt filter presses for
dewatering, creating a material similar in
consistency to damp soil. Presently the
dewatered sludge is discharged to conveyors,
loaded onto trucks, and hauled by White Mountain
Resources to farms as a soil enhancer.
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Owner:
City of Nashua
Web site:
http://www.gonashua.com/
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Operating Company:
City of Nashua
Web site:
http://www.gonashua.com/
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Directions:
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Disclaimer:
Water and Wastewater.com provides the information on
this page for reference purposes only. We do not certify
the accuracy of the information provided by third-party
individuals for this listing.
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