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Drinking water:
Drinking water quality is regulated. In many jurisdictions, standards
are set for approximately 90 contaminants in drinking water. For each of these
contaminants a legal limit, called a maximum contaminant level, is set and if
that limit is exceeded, it requires a certain treatment. Water suppliers will
not provide water that doesn't meet the drinking water standards. Water that
meets these standards is safe to drink and every water utility providing
drinking water sees that this standard is maintained.
Water Treatment Plant:
A water treatment plant should produces drinking water that is free of
bacteria, sparkling clean and without an objectionable taste or odor. Depending
on the location of the well water or reservoir, the quality of the untreated
water, and the local codes and standards for water quality, the plant may put
the water through several treatments. Although treatment processes vary from
plant to plant, there are three basic processes: coagulation and settling,
filtration and disinfection. There are a number of ways to purify water.
Chemical purification of above ground water is mandatory in all states. Since
most areas lack alternate filtering mechanisms, such as ozone treatment,
chlorine is used as the most common sterilizing agent.
Wastewater Treatment Plant:
The process carried out in treatment of wastewater is briefed below:
a. Screening:
Wastewater entering the wastewater treatment plant includes items like
wood, rocks, even dead animals. If they are not removed, they could cause
problems later in the treatment process. Most of these materials are sent to a
landfill.
b. Pumping:
Wastewater treatment plants are located on low ground, often near a
river into which treated water can be released. If the plant is built above
ground level, the wastewater has to be pumped up to the aeration tanks. From
here on, gravity takes over to move the wastewater through the treatment
process.
c. Aerating:
One of the first steps that a wastewater treatment facility can do is
to just shake up the sewage and expose it to air. This causes some of the
dissolved gases (such as hydrogen sulfide, which smells like rotten eggs) that
taste and smell bad to be released from the water. Wastewater enters a series
of long, parallel concrete tanks. Each tank is divided into two sections. In
the first section, air is pumped through the water. In the second
section…(please finish the point).
As organic matter decays, it uses up oxygen. Aeration replenishes the oxygen.
Bubbling oxygen through the water also keeps the organic material suspended
while it forces 'grit' (sand and other small, dense particles) to settle out.
Grit is pumped out of the tanks and taken to landfills.
d. Sludge removal:
Wastewater enters the second section or sedimentation tanks. Here, the
sludge (the organic portion of the sewage) settles out of the wastewater and is
pumped out of the tanks. Some of the water is removed in a step called
thickening and then the sludge is processed in large tanks called digesters.
e. Scum removal:
As sludge settles at the bottom of the sedimentation tanks, lighter
materials floats up to the surface. This ‘scum’ includes grease, oils,
plastics, and soap. Slow-moving rakes skim the scum off the surface of the
wastewater. Scum is thickened and pumped to the digesters along with the
sludge. Filtration is also used in sewage treatment in many cities.
The liquid sewage is filtered through a substance, usually sand, by the action
of gravity. This method gets rid of almost all bacteria, reduces turbidity and
color, removes odors, reduces the amount of iron, and removes most other solid
particles that remained in the water.
f. Killing bacteria:
Wastewater flows finally into a 'chlorine contact' tank, where the
chemical chlorine is added to kill bacteria, which could pose a health risk.
The chlorine is mostly eliminated as the bacteria are destroyed, but sometimes
it must be neutralized by adding other chemicals. This protects fish and other
marine organisms, which can be harmed by the smallest amounts of chlorine. The
treated water (called effluent) is then discharged to a local river or the
ocean.
Desalination
Desalination is the process of converting saline water into fresh,
drinkable water. Seawater desalination is a process that removes salts and
other impurities from seawater. This process is used in many areas of the world
where fresh water is scarce. Seawater desalination produces very safe,
high-quality water suitable for drinking and other potable water uses. The
future seawater desalination facilities will use reverse osmosis technology,
regarded as the most efficient and cost-effective desalination process. Reverse
osmosis uses semi permeable membranes to separate fresh water from seawater.
Reverse Osmosis
Reverse osmosis is often used in commercial and residential water
filtration. It is also one of the methods used to desalinate seawater.
Sometimes reverse osmosis is used to purify liquids in which water is an
undesirable impurity. Reverse osmosis occurs when the water is moved across the
membrane against the concentration gradient, from lower concentration to higher
concentration. To illustrate, imagine a semi permeable membrane with fresh
water on one side and a concentrated aqueous solution on the other side. If
normal osmosis takes place, the fresh water will cross the membrane to dilute
the concentrated solution. In reverse osmosis, pressure is exerted on the side
with the concentrated solution to force the water molecules across the membrane
to the fresh water side.
Water Meter
A water meter measures the quantity of water passing through a
particular outlet. The readings from your water meter determine the amount you
are charged every month on your water bill. There are two basic types of water
meters - straight reading and circular reading. The straight reading meter
records the cubic feet of water used in much the same way that a car's odometer
records miles. The dial with a single hand measures tenths of a cubic foot. The
circular reading meter uses a series of circular dials to record cubic feet of
water used. To read this type of meter, start with the 100,000 circle, then
read the 10,000 circle, and so forth on down to the circle that reads in 1
cubic foot increments. If a hand is between two numbers, always read the lower
number.
Major American and UK
water utilities
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