Objectives: Students will be able to describe the
water treatment plants in New Haven.
The South Central Connecticut Regional Water Authority is a non-profit public corporation that supplies water to the greater New Haven area. If you live in New Haven, your water probably comes from one of the following systems: Lake Whitney, Lake Saltonstall, Lake Gaillard or The West River Water Treatment plants. All of the systems are very similar, there are only subtle differences between them.
Up until 1903, New Haven’s water supply came directly, untreated, from local water sources such as Lake Whitney. In 1901 there was a great outbreak of typhoid which sickened more than 400 people. Epidemiologists traced the out break to the untreated water. This event led to the construction of the Lake Whitney Slow Sand Filtration Treatment Plant. The filter was the first “modern” functionalist structure in Connecticut, by using reinforced concrete.
There are 12 sand beds at Lake Whitney. The bottom of the beds are covered to a depth of 8 inches, with a layer of gravel or broken stone from 1 to 3 inches in diameter; on top of this layers of gravel and course sand of gradually increasing degrees of fineness are place successively to a depth of 16 inches. Filter sand is on the very top vary in depths between 2 and 3 feet.
Raw water comes into the plant and travels up through the layers of gravel and sand. It is then allowed to filter back through the sand and gravel virtually free all contaminants. Bacteria is also encouraged to grow on top of the sand. This bacteria is “good” bacteria because it destroys “bad” bacteria such as those responsible for the typhoid epidemic in 1901.
In the Lake Saltonstall system, located in Branford just off of I-95. Untreated water is first pumped into the plant and then into the flash mixing tank. Chemicals may be added to the flash mixing tank to disinfect the water. Alum is also added to help remove solids, dissolved particles and colloids.
The alum which form a gelatin film is clumped by adding a polymer which acts like a glue to make larger floc particles which can be more easily filtered out of the water. Chlorine can be added again to the system before filtering.
Each of the dual filters has approximately 20 inches of anthracite (coal), 10 inches of sand, and 12 inches of support gravel. Activated charcoal has an enormous surface area, approximately one million square centimeters per gram in some samples. Hence, charcoal is very effective in selectively adsorbing polar molecules from water. Bacteria and other organisms are removed by organisms that are attached to the gravel.
After filtration, the water is treated again with chlorine to disinfect, and the pH is also adjust by the base NaOH. The water is then stored until it is ready to be pumped into the system.
Before going into the system, the water is first treated with fluoride, to prevent tooth decay; and phosphates are also added to help prevent corrosion in the pipe lines and in our homes.
The Lake Gaillard Plant is located in North Branford and supply approximately two-thirds of South Centrals water. Lake Gaillard is the largest reservoir system. Water in Lake Gaillard may come from Lake Hammonasset or Lake Menunkatuc; the water travels through tunnels cut through nearby mountains.
The Gaillard system has a few variations from the Saltonstall plant. First raw water comes into the plant and flows through a turbine to generate approximately 10 percent of the power needed to run the plant.
Alum and chlorine are added just before the water goes into the static mixer. The static mixer disperses the treatment chemicals throughout the water. Fixed baffles inside the mixer stir the water as it flows through. Mixing continues in the flocculation chambers. Here, chemical coagulants draws particles together to form larger particles which are removed in the filters.
Note: all filters are cleaned by backwashing or sending water backwards up through the filter bed. Solids removed from the filters go into the sanitary sewer while water is recycled.
From the filters, water is stored and treated similarly to Saltonstall’s method prior to leaving the plant (see diagram)
The West River Water System draws water from a network of reservoirs in Bethany and Woodbridge, and the system supplies an average of 15 percent of South Central’s water.
At West River, raw water comes through an intake pump, chemicals such as alum and chlorine are added, which then goes into the contact tank. The contact tank is made up of a dynamic mixer and two static mixers. Potassium permanganate is often added to remove metals such as iron and magnesium. Sodium hydroxide is also added to raise the alkalinity of the water which helps the alum react.
The water then enters the flash mixing tank, also known as the rapid mix, alum and two types of polymers are added here so that large floc particles are mad and then the water enters the filters (see diagram).
If you wish to visit one of these plants I recommend West River because it is completely enclosed and they also have a working miniature of the plant just call the Water Authority to set up a tour.
Problem:
A resident in New Haven received a bill from the water company recently. A man and his wife used 2800 cubic feet of water in three months. How many gallons of water did they use each day? Note: one cubic foot of water contains 7.48 gallons.
answer:
lcubic foot = 1.48 gallons
1
month
= 30
days
(figure available in print form)
Locate the water meter in your house or apartment building Find out how to read your meter by asking someone from the utility company. Heat the water meter in your house or apartment. After 24 hours reat the meter again. By subtracting the two sets of numbers, you will find out how many gallons of water your household uses a day. How many liters of water does your household use a day?
(figure available in print form)
(figure available in print form)
(figure available in print form)
