Sources of wastewater exist in plenty, ranging right from domestic sources (i.e. wastewater produced as a result of various household activities) to industrial sources (i.e. wastewater produced in various industrial processes). Basically, 'wastewater' refers to any water which has been used for some human activity and thus has been contaminated and left it unsuitable for further use. Though the term 'sewage' is often used for wastewater, it actually refers to water which is contaminated by urine and feces.
Wastewater can cause a great deal of harm to the environment when it is released as domestic, municipal or industrial waste. Taking that into consideration, it becomes all the more important to treat the same before it is disposed off. More importantly, the treatment of wastewater is also helpful when tackling water shortage as this water can be used for a range of activities - including for the purpose of drinking as in case of NEWater in Singapore.
Different Methods of Wastewater Treatment
Wastewater treatment is a process wherein the contaminants are removed from wastewater - both domestic and industrial, in order to produce waste stream or solid waste suitable for safe discharge or reuse. Basically, there exist several different processes of wastewater treatment, all of which can be broadly categorized into three different groups - physical, chemical and biological, on the basis of tasks involved. The extent to which the water is contaminated and what are the contaminants, both play a crucial role in determining which of these three methods to opt for.
When it comes to physical wastewater treatment, physical processes - such as sedimentation, aeration and filtration, are used for the treatment of water instead of resorting to chemicals or biological means. 'Sedimentation', wherein coarse screening of waste water is done to remove contaminating objects after allowing them to settle at the base, is one of the most efficient physical water treatment method used in various parts of the world. When heavy contaminants settle down, the removal of cleared effluent or waste stream becomes relatively easy. Sedimentation is one of the most popular methods, which is often used at the beginning and the end of several other water treatment processes.
Other widely used methods include 'aeration', wherein air is added to the wastewater physically in order to provide oxygen to the contaminated water, and 'filtration', wherein the contaminated water is passed through various filters to separate the contaminating solids from the water. Sand filter is by far the most common filter used in this process. In a number of wastewater treatment methods, semi-solid contaminants - such as grease and oil, are allowed to float on the surface of the water, and are eventually removed physically.
As opposed to physical treatment of water, chemical treatment involves the use of chemicals to get rid of contaminants in it. Of the various methods used to treat water chemically, the most common method is 'chlorination'. In this process, chlorine - a strong oxidizing chemical, is used to kill the bacteria which lead to decomposition of water. 'Oxidization' is yet another chemical water treatment method, wherein oxidizing agents - such as ozone, are used to treat polluted water. These oxidizing agents make water reusable by hampering the biological growth process of bacteria which happens to be the main cause of decomposition of water.
When it comes to industrial wastewater treatment, a chemical process known as 'neutralization' is quite common. This process involves adding acid or base to the water to adjust its pH value and bring it back to neutral level. Lime is one of the best examples of base used in the process of neutralization to neutralize acid wastes. Polyvalent metals, i.e. metals having more than one valence, are very often used as coagulating chemicals in sewage treatment. Iron and other metals containing compounds like ferric sulfate and aluminum sulfate are some of the best examples of coagulants.
There do exist some water treatment processes which can be categorized as physical as well as chemical processes. One of the best examples of this is the use of carbon - which adsorbs contaminants to clean the water.
As of now we stressed on the fact that bacteria decomposes water, and hence one has to get rid of bacteria when it comes to treatment of wastewater. In biological water treatment processes however, bacteria and other such microorganisms are used to biochemically decompose the wastewater and stabilize the end product. Biological water treatment is further categorized into two sub-divisions - aerobic and anaerobic. In the 'aerobic process', bacteria consumes the organic matter and helps convert it to carbon dioxide in the presence of oxygen. In the 'anaerobic process', on the other hand, sludge is fermented at a particular temperature in the absence of oxygen.
More than a billion gallons of wastewater or sewage is produced daily, and disposing that much amount of polluted water in environment can result in a great deal of harm to various lifeforms. It is very important to treat wastewater before it is disposed out into the environment. More importantly, this wastewater has to be transferred to the wastewater treatment plants with utmost care, as any leakage in pipelines carrying it can also result in environmental pollution. At the end of the day, waste disposal is a serious issue which threatens the basic fabric of the environment. The sooner we realize the seriousness of this issue, the better it is for us - as well as the generations to come.