Wastewater
Wastewater Treatment
Water is the basis of life on earth. No creature or plant on this planet can survive without. As far as humans go, then we need hundred times more water than any other species. We use it for irrigation, drink, cook food and clean ourselves and our surroundings. In the process, we waste a lot of fresh water.
Even though 75% of earth is covered with water, the reserves for freshwater are very limited. Thus, treatment and recycling of wastewater is essential for survival of modern human civilization.
That’s why, scientists and experts have developed various methods to treat wastewater and make it reusable. Wastewater treatment is the process of eliminating all the impurities and contaminants from household sewage and wastewater. The process removes all the biological, physical and chemical pollutants from the water through a number of processes. Its objective is to create a steady flow of fresh water for day to day domestic and commercial usage.
Wastewater can be first treated close in its primary storage area like
in septic tanks and aerobic treatment systems. The water can be collected
there and then transported to various water treatment plants through water
pipes.
There are basically six different methods through which wastewater is cleaned
and turned into reusable water. These methods used various techniques to
clean water and their results vary according to the quality of water.
Let’s discuss the process:
1. Preliminary Treatment
The Preliminary treatment of water is done to protect the pumping equipment
from getting jammed by all the slime and dirt in the water. This method
removes and reduces the large floating particles, inorganic solids and pollutants
like oil and grease from the water. This is the first step of wastewater
treatment and facilitates further decontamination of the water.
In this stage, solid waste particles are removed from the water with the
help of devices like Screens, grinders, cutters, grit chambers and pre-aeration
tanks. All of these devices are very carefully designed and applied on wastewater
from different resources.
2. Primary Treatment
In the second method, all the heavy solids are from the wastewater through
the process of sedimentation. Sedimentation is the process in which waste
water goes through big tanks called primary sedimentation tanks. All the
sludge in the water gets can settled on the bottom of this tank and all
greasy substance like oil rises to the surface. The oil on surfaces is skimmed
off and sludge is removed and sent to be processed separately, through special
scrapers fitted inside the tanks. The purpose of this treatment is to decrease
the speed of wastewater to allow the solids to settle down and light particles
to surface. The water treated through this process is like the water gone
through stream.
3. Secondary Treatment
This kind of treatment depends on aerobic organisms which biochemically
rot organic solids to inorganic particles. In this treatment, water is passed
through four different types of devices. At first, it goes through trickling
filters to secondary settling tanks. Then, the water is accumulated in final
settling tanks to remove additional sludge. The treated water then goes
through intermittent sand filters. The water is then, finally filled in
a stabilization pond where it goes through the process of chlorination.
Even though, this process is performed at every step of wastewater purification,
but it becomes much more important in the later stages.
Chlorination helps in disinfecting the water, prevents wastewater decomposition and controls the odour. Even though chlorination is most commonly used methods of wastewater disinfection, there are some other methods used also which can be used for this purpose, for example, the ozone method. This method is much safer for fish and other living forms. It also doesn’t add any peculiar smell or taste to the water like chlorine does.
4. Tertiary Wastewater Treatment
Tertiary treatment has been added to wastewater treatment process since
1970's. Tertiary treatment involves additional treatment rendered to wastewater
after the secondary treatment. Many times, this only involves extra sand
filters to remove increased suspended solids. Sometimes, tertiary treatment
may also include removing plant nutrients, nitrogen and phosphorous from
the water to improve its purity.
Tertiary treatment has come into practice because of improvement in wastewater treatment units and awareness about environmental effects of the purified wastewater. Tertiary wastewater treatment is also sometimes known as the advanced water treatment. This is the highest degree of water treatment and may include chemical and physical methods to produce high quality of water.
5. Sludge Treatment
Even though sludge treatment is not directly connected to the process of
procurement of fresh water to consumers through wastewater treatment, it
is an important step. Sludge is solid waste removed from the wastewater
in treatment units. It is essential to treat this sludge to some to prepare
it for final disposal. The main objective of sludge treatment is to remove
all the water from it and decompose the organic solids into mineral solids
or at least in more stable organic ones. Sludge treatment process can be
done by the following methods: This is accomplished by a combination of
two or more of the following methods:
1. Conditioning with chemicals
2. Centrifuging
3. Digestion with or without heat
4. Elutriation
5. Heat drying
6. Incineration
7. Thickening
8. Drying on sand bed -- open or covered
9. Vacuum filtration and
10. Wet oxidation
After the purification, the treated wastewater becomes almost as pure
ad normal water and is ready to be reused for various purposes. Even though,
most countries don’t provide this water for drinking purposes, but it has
become a major source for irrigation and commercial purposes. Treated wastewater
has also helped cities in restoring the depleting underground water levels.
The National Association of Clean
Water Agencies
WateReuse Association
Integrated Water Strategies
Texas Water Resources Institute
Indian
Chemical Portal
U.S EPA
India Water Portal
World
Health Organization
Water and Wastewater
New
Zealand's Ministry for the Environment
Canadian Water & Wastewater Association
Purdue
University
USGS
Queensland
Government
Waste Water
Treatment from Humboldt County California