What is the key difference between primary and secondary sewage treatment?

(i) Microbes are the major components of biological systems on this Earth.

(ii) All microbes are not pathogenic. Many microbes play an essential role in the welfare of human society.

(iii) Microbes and microbially derived products are used almost every day.

2. Microbes in Household Products:

(i) Microbes such as Lactobacillus and others commonly called lactic acid bacteria (LAB) grow in milk and convert it to curd.

(ii) The dough used to make bread is fermented by the yeast Saccharomyces cerevisiae.

(iii) Certain dishes, such as idli and dosa, are made from dough fermented with the help of bacteria.

(iv) Yoghurt is a preserved milk product made by bacterial fermentation of milk.

(v) Probiotics are beneficial forms of gut bacteria that help stimulate the natural digestive juices and enzymes that keep our digestive organs functioning properly.

3. Microbes in Industrial Products:

(i) Microbes produce industrial products like lactic acid, acetic acid, and alcohol.

(ii) Penicillin was the first antibiotic to be discovered by Alexander Fleming in $1928$.

(iii) Antibiotics like penicillins produced by certain fungi are used to kill disease-causing harmful microbes.

(iv) Antibiotics have played a major role in controlling infectious diseases like diphtheria, whooping cough and pneumonia.

(v) An antibiotic that acts on a variety of pathogenic organisms is called a broad-spectrum antibiotic.

(vi) An antibiotic that acts on selected or specific pathogenic organisms is called a narrow-spectrum antibiotic.

(vii) Streptokinase produced by Streptococcus is used as a ‘clot buster’ for removing clots from the blood vessels of patients who have undergone myocardial infarction (heart attack).

(viii) Cyclosporine A, produced by the fungus Trichoderma polysporum, is used as an immunosuppressive agent in organ-transplant patients.

(ix) Statins produced by the yeast Monascus purpureus is used as blood-cholesterol lowering agents.

4. Microbes in Sewage Treatment:

(i) The municipal waste-water, including human excreta, is called sewage.

(ii) Microbes are used for sewage treatment by the process of activated sludge formation, which helps recycle water in nature.

(iii) Sewage is treated in sewage treatment plants by the heterotrophic microbes present in the sewage, before being disposed of in water bodies.

(iv) The sewage treatment is divided into three steps, primary treatment, secondary treatment, and tertiary treatment.

(v) Biological oxygen demand is the amounts of oxygen that would be needed if bacteria oxidised all the organic matter in one litre of water.

5. Microbes in Production of Biogas:

(i) The excreta (dung) of cattle, commonly called gobar, is rich in methanogenic bacteria, and it can be used for the generation of biogas, widely called ‘gobar gas’.

(ii) Biogas produced by microbes is used for cooking and lighting in rural areas.

6. Microbes as Biocontrol Agents:

(i) Biocontrol refers to using biological methods to control plant diseases and pests.

(ii) Biocontrol measures help us to avoid the heavy use of toxic chemical pesticides for pest control.

7. Microbes as Biofertilisers:

(i) Biofertiliser is a substance that contains living microorganisms.

(ii) The main sources of biofertilisers are bacteria, fungi and cyanobacteria.

(iii) Farmers have started using biofertilisers instead of chemical fertilisers.