The main purpose of the tertiary treatment is to ensure that the treated water which is to be released on to the environment is biologically accepted by all other fresh water organisms such as weeds and algae. This part of the treatment includes processes like physical water treatment, lagooning, and excessive nutrient removal processes.to ensure that the discharged water is raised in effluent quality before proceeding to the final stages.
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In physical water treatment, much of the residual suspended matters are removed using only physical processes such as sedimentation method and the infamous filtration method. In the sedimentation method, the water is place in a certain tank to allow all the remaining heaver objects to sink down to the bottom of the container. After few hours went most of the dense object are separated from the water, the cleared effluent or waste stream is removed. Sedimentation is one of the most common methods, quite often used at the beginning and the end of many water treating processes. Another physical method that is commonly used in the sewage water treatment system is the filtration method. In filtration, the water is allowed to pass through filters to separate the contaminating solids from the water. Sand filter is a common filter used in this process. In a number of wastewater treatment methods, semi-solid contaminants like grease and oil are allowed to float on the surface of the water, and then they are physically removed.
Besides the in lagooning where lagoon is a stationary system having a continuous flow: several ponds working in parallel in which the inlet flow and the outlet flow are equals form lagoon plants. The lagooning technique is a natural and very efficient technique that consists in the accumulation of wastewater in ponds or basins, known as biological or stabilization ponds, where a series of biological, biochemical and physical processes take place. In these ponds or lagoons, certain types of the microorganism are actually supported as these “biological agents” help in treating the water further by removing the fine particulates. These types of biological ponds are usually classified as anaerobic ponds or oxidation ponds depending on the shape, depth, organic rate, level of treatment of that particular lagoon itself.
The excessive nutrient removal is the most viral step in the last stages of the water treatment before the water is released to the environment. When the previously treated water comes to this area of the system, the nutrients level mainly nitrogen and phosphorus in the water is checked. Where if found in excess, the excessive nutrient removal step is carried out. This is because if the unchecked water supply is to be released into the natural water system (river, pond, etc.) it will cause a sudden increase in the native microorganism population of that certain water system. Some of the native microorganisms which are commonly found in ponds today are usually weeds, algae, and cyanobacteria. Therefore, after the sudden rapid grown in the population of these microorganisms, the number of algae for example, becomes unsustainable which causes most of them to die and eventually decay. The following decay process would substantially increase the biochemical oxygen demand (BOD) in that particular pond, which would cause the other fresh water living organism such as fishes to die as well.
Firstly, the nitrogen removal process is carried out. There are various methods of removing nitrogen, each with advantages and disadvantages. However, the biological treatment method is used most commonly. With this method, organic nitrogen and ammonia nitrogen is converted into nitrous and nitrate nitrogen in an aerobic environment, and is dispersed into the atmosphere as anaerobic nitrogen gas. Therefore the gas is removed from the water and released to the atmosphere. And as there is no secondary pollution, this can be called an effective method.
In the removal of phosphorus is usually carried out using a method called enhanced biological phosphorus removal (EBPR). The first process in EBPR is the mainstream biological treatment process. Where the utilizing of aerobic and solids separation zones and the provision of return activated sludge are carried out. The next is a first side stream process for anoxic/anaerobic “selection” of desirable BPR organisms such as the polyphosphate accumulating organisms (PAOs). Finally, a second side stream process serves to ferment organic material in some of the return activated sludge to produce food utilized in the first side stream selection process. The system permits the three processes to be separated from each other by creating two side streams, allowing all three processes to be controlled separately and optimized in satisfying their own specific goals. Besides this biological method, the removal of phosphorus can also be done via chemical precipitation, usually with salts of iron, aluminum, or lime. Chemical precipitation is usually more reliable, easier to operate, and requires smaller equipment footprint than biological removal. But the main back draws of this chemical method is that it may form excessive sludge production as hydroxides precipitates and the chemical used in this method might be considered expensive.
The importance of Wastewater Treatment in our society
Water scarcity is the major problem that is faced all across the world. Although 2/3rd of the earth’s crust is made up of water but all this water is not available for drinking and for other human activities as either it is locked in the form of ice or present in the form of vast saline oceans and seas. It has been found out that 97% of the total water is salty that is of no use to human and animals (except marine animal) and the remaining three percent is available as freshwater. More than half of this three percent is locked in glacier and less than 0.01% is available as fresh water. So water resources are less as compare to human demand for water.
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Above this, the major part of water that can be consumed is getting polluted because of human activities. This polluted and untreated water is causing abundant water borne diseases. Then the world is facing a huge climatic change which is further aggravating the water problem. Some of the regions are getting more rain water than earlier and some are getting almost negligible. Experts even believe that the next World War would not be for oil or land but it will be for water.
Also because of improper use of water and lack of water treatment, the problem of water crisis will further increase where 884 million people are already not getting easy access to safe drinking water. And a further 2.5 billion people are getting difficult access to water for disposable and sanitation. Agriculture is also overusing and polluting the ground water thus depleting the natural source of water. So here water treatment plants will play important role.
Water crisis at present is the biggest problem according to the United Nations. Almost 25 countries of Africa, parts of China, Peru and Brazil in Latin America, some parts of Middle East like Iran, Chile, Mexico, and Paraguay are some of the countries that are facing the water crisis. Even other parts of the world are facing the varied levels of the water crisis. Because of acute shortage of water, the food problems are getting aggravated. About 40 million people in Africa are facing the problem of food shortage. It is expected that if the similar conditions will persist then there will be 500 million till 2025 who will suffer from these problems. Nature has its role but the major water problem is arising because of its increasing consumption and faulty usage. Major chunk of the problem can be solved if the wastewater treatment is taken very seriously and precautions at every step are taken to improve the water quality.
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