Tag: personal and public cleanliness

The sedimentation process involves the settling down of particles suspended in water under the effect of gravity. The particles that settle down are known as sediment. In purification of water sedimentation process helps in reducing the concentration of particles in suspension. It is the first step used in the primary treatment of sewage water. 

The sewage water can be treated in the treatment plants with the use of microbes. The bacterial cells, fungal cells and algae are the common microbes which are used for the cleaning of the waste. The microbes have the ability to feed and decompose on the organic matter and convert it to simpler non-toxic forms. The organic matter of the wastewater can be reduced and the water can be purified. 

Carbon dioxide, CO$ _2$, is gaining acceptance for pH control in water treatment plant. It reduces high pH levels quickly. It is not stored as an acid solution so it is considered safer than sulfuric acid. It is non-corrosive to pipes and equipment. It requires less equipment and monitoring costs. It requires no handling costs. It can be utilized via a completely automated system. 

Primary treatment basically involves physical removal of particles large and small from the sewage through the filtration and sedimentation. These are removed in stages initially floating debris is removed by sequential filtration.

Chlorine is used for municipal drinking water purification. It is a strong oxidizing agent, hence it kills pathogenic bacteria by oxidation of organic molecules. Chlorine on hydrolysis produces hypochlorous acid that penetrates the pathogenic surface and disintegrates lipids in its cell wall. It also reacts with intracellular enzymes and proteins and deactivates them. Hence chlorination is used to prevent the spread of waterborne diseases such as cholera, dysentery and typhoid. Thus the correct answer is option B.

The polluted water can be purified using the treatment plants. Activated sludge method refers to floc of microorganisms like bacteria and fungi which are used in the process to break down organic matter into carbon dioxide, water, and other inorganic compounds. There are microbes which grow in the water forming mass or flocs and help in the clearing of the water. These flocs are used in the next round of treatment plants for efficient removal of wastes.

Sewage pollution can be prevented by treating sewage, in sewage or effluent treatment plant, before passing into water course. The treatment comprises of primary treatment, secondary treatment and tertiary treatment.
Primary treatment consists of shredding, churning, floatation, screening and sedimentation.
In secondary treatment organic matter is decomposed through sewage fungus by passing sewage through water hyacinth pond, or trickling filter method if passing sewage through thick bed of gravel, or activated sludge method i.e., passing sewage through aerated or oxidation tanks. In activated sludge method, aeration helps in oxidation of sludge or biosolid. The aerobic bacteria can be recycled. The cleared water is now chlorinated with chlorine or perchlorate salts, ozonised or irradiated with ultraviolet light to kill pathogens.
The activated sludge process is a process for treating sewage and industrial wastewaters using air and a biological floc composed of bacteria and protozoa.
The tertiary treatment is physico-chemical treatment for removing turbidity and dissolved substances. Alum, ferric chloride and lime are used for their precipitation.
Therefore, the correct answer is option B.