Tag: wastewater treatment - need and methods

Sewage treatment is done in three stages: primary, secondary and tertiary treatment. Secondary treatment removes dissolved and suspended biological matter, using microorganisms in a controlled environment. Most secondary treatment systems use aerobic bacteria, which consume the organic components of the sewage (sugar, fat, and so on). Some systems use fixed film systems, where the bacteria grow on filters, and the water passes through them. Suspended growth systems use activated sludge, where decomposing bacteria are mixed directly into the sewage. Because oxygen is critical to bacterial growth, the sewage is often mixed with air to facilitate decomposition.

Methanobacterium  are anaerobic organisms.
Biogas refers to a mixture of different gases produced by the breakdown of organic matter in the absence of oxygen.
Activated sludge-sediment in settlement tanks of sewage treatment plant is a rich source of aerobic bacteria.
Biogas can be produced by anaerobic digestion with anaerobic bacteria.
Thus, the correct answer is option (C), 'Activated sludge-sediment in settlement tanks of sewage treatment plant is a rich source of aerobic bacteria'.

Proper disposal of the domestic waste before it goes in to the lakes and oceans is useful in preventing water pollution. Domestic sewage which is the waste water that goes out into the environment through several routes should be treated before being released. It contains soaps, detergents, toilet paper, household refuse all of which causes water pollution. All this sewage should be properly collected and treated in which contaminants are removed from sewage to produce sludge suitable for discharge into the environment. 

Domestic sewage primarily contains biodegradable organic matter, which readily decomposes by bacteria and other micro-organisms, which can multiply using these organic substances as substrates and hence utilise some of the components of sewage. It is possible to estimate the amount of biodegradable organic matter in sewage water by measuring biochemical oxygen demand (BOD). It can be purified treating with with micro-organisms.

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.