Tag: chemistry

Explosive growth of plants and algae is a response to the addition of excess nutrients, mainly phosphates, which induces, the decaying of which consumes oxygen from the water causing water pollution. Phosphates are among the major nutrients that is required by plants for growth. 

Biochemical oxygen demand is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over a specific time period. The BOD value is most commonly expressed in milligrams of oxygen consumed per litre of sample during 5 days of incubation at $20^{\circ}C$ and is often used as a surrogate of the degree of organic pollution of water.

BOD is similar in function to chemical oxygen demand (COD), in that both measure the amount of organic compounds in water. However, COD is less specific, since it measures everything that can be chemically oxidized, rather than just levels of biodegradable organic matter

In general, all common methods of sewage purification use sedimentation processes by which solids (sludge) sink to the bottom – in some cases this primary sludge is removed for further treatment.

After this comes the secondary or biological treatment of sewage purification, this involves biological processes and the use of microorganisms that “eats” away a lot of the hazardous contaminants. Use of oxygen by various implementation techniques is very important.

After the secondary stage of sewage purification comes final settlement of biological solids and then a tertiary treatment that removes even better the rest of the biological and organic materials in the water. 

Potassium permanganate is an inorganic chemical compound and it is a strong oxidizing agent. Potassium permanganate is used in water treatment to remove odor-causing compounds and is also used to remove iron and manganese in water.

Sodium carbonate, $Na _2CO _3$, is also known as washing soda. It can remove temporary and permanent hardness from water. Sodium carbonate is soluble but calcium carbonate and magnesium carbonate are insoluble. The water is softened because it no longer contains dissolved calcium ions and magnesium ions.

Factors responsible for the depletion of water table-

1. Polar stratospheric clouds (PSCs) are the medium on which reservoir chlorine compounds are converted into ozone-destroying chlorine radicals, they are essentially two types of  PSC known as type 1 and type 2.
2. Polychlorinated biphenyl (PCBs) is a group of organic compounds used in the manufacture of plastics, as lubricants, in transformers, adhesives and so forth. They are highly toxic to aquatic life and persist in the environment for long periods of time. They can accumulate in food chains and may produce harmful side-effects at high concentrations.
3. Biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed (i.e demanded ) by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time period.
4. Chemical oxygen demand (COD) is defined as a  measure of the oxygen equivalent of the organic matter content of a sample that is susceptible to oxidation by a strong chemical oxidant. Therefore, BOD is a measurement of water pollution.

Option (C) is correct.

In COD, the degradation is affected by an oxidizing agent, $K _2 Cr _2 O _7.$ COD  is a measure of amount of oxygen , required to degrade or breakdown the organic matter. 

Clean water has BOD which is less than 5 ppm. If it is equal to or more than 12 ppm, then the water is considered as polluted. So this indicates water be rich in dissolved oxygen, that helps the microorganisms to oxidize inorganic and organic materials.