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Everything you need to know about water and wastewater microbiology. Some of the most frequently asked questions are as follows:-
Q.1. Why do ocean estuaries fed by rivers have higher microbial counts than other shoreline waters?
Ans: Ocean estuaries have a higher nutrient level.
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Q.2. Give two main characteristics of aquatic bacteria.
Ans: (1) Bacteria whose main habitat is water usually possess appendages and hold fasts, e.g., Caulobacter.
(2) Some of them have gas vacuoles which they can fill and empty to maintain buoyancy.
Q.3. What is a littoral zone?
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Ans: This is the region along the shore of an inland body of water where there is considerable vegetation and where light penetrates the vegetation up to the bottom.
Q.4. Define a limnetic zone.
Ans: The surface zone of an inland body of water away from the shore.
Q.5. What is pro-fundal zone?
Ans: Pro-fundal zone is deeper water in the area of the limnetic zone. It falls below the limnetic zone.
Q.6. What is the benthic zone?
Ans: The sediment at the bottom of a water-body is called benthic zone.
Q.7. Which are the microorganisms found in limnetic zone with sufficient oxygen?
Ans: They are pseudomonads, Cytophaga, Caulobacter and Hyphomicrobium.
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Q.8. Which zones in an ocean are poor in oxygen and light?
Ans: The pro-fundal zone which is below the limnetic zone and the benthic zone which is the lower most zones are both poor in oxygen and light. Both these zones are in deeper waters.
Q.9. Which are the bacteria found in the waters of pro-fundal zone?
Ans: Purple and green sulphur bacteria.
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Q.10. Which are the common bacteria in the sediments of benthic zone?
Ans: Desulphovibrio which use sulphates (SO2-4) as an electron acceptor and reduce it to hydrogen sulphide, giving a “rotten-egg smell” to lake mud. The bottom sediments may also contain methane producing bacteria and Clostridium.
Q.11. The ocean waters mainly consist of photosynthetic diatoms and other algae. What are these suspended organisms called?
Ans: Phytoplankton.
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Q.12. Give the types of organisms comprising the food chain in the ocean.
Ans: The protozoa feed on bacteria and the smaller phytoplankton. In turn the krill that are shrimplike crustaceans feed on the phytoplankton, and in turn the krill turn out to be the food of larger animals of sea.
Q.13. What is microbial luminescence in deep sea?
Ans: Certain bacteria produce light flashes when they are agitated by the movement of water in wave action.
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Q.14. Name the fish that establishes symbiotic relationship with luminescent bacteria at the bottom of the ocean in the benthic zone.
Ans: Photoblepharon palpebratus, the flashlight fish uses the flow of its resident bacteria as an aid in attracting and capturing its prey in complete darkness on the floor of the ocean.
Q.15. How do luminescent bacteria emit light?
Ans: The luminescent bacteria have an enzyme known as luciferase which picks up electrons from flavoproteins in the electron transport chain and then emits some of the electron’s energy as a photon of light.
Q.16. Give some of the common diseases spread by water contaminated with human or animal faeces.
Ans: These are typhoid fever, cholera (bacterial) and hepatitis A (caused by a virus). The ingestion of cyst of protozoa Giardia lamblia may cause diarrhoea, and that of Entamoeba histolitica may cause amoebic dysentery.
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Q.17. What harm can be there to water bodies on addition of phosphates?
Ans: Phosphates can cause eutrophication (eu = means true or well, troph means nourish) that is an overabundance of nutrients resulting in overgrowth of algae or cyanobacteria, consequently causing death to other organisms.
Q.18. What is bioremediation?
Ans: It is the use of microorganisms to get rid of environmental pollutants, e.g., oil is rich in carbon and sulphur but low in nitrogen and phosphorus which are essential for the growth of microorganisms. Therefore, if an oil soluble fertilizer having these nutrient factors is spread over oil spills mixed with the adapted bacteria the oil is metabolized very fast.
Q.19. How does Thiobacillus ferroxidans help to lower the pH of water on receiving coal mining wastes containing iron sulphide (FeS2).
Ans: The bacterium Thiobacillus ferroxidans obtaining energy from oxidation of the ferrous ion (Fe2+) converts the sulphide to sulphate, and consequently sulphate enters the water lowering the pH and causes harm to aquatic life.
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Q.20. What do the yellow precipitates in streams polluted with coal-mining wastes indicate?
Ans: They indicate the formation of iron hydroxides which is promoted due to low pH.
Q.21. Name an indicator organism that can be used for testing the purity of water against contamination of faecal (US fecal) matter.
Ans: Escherichia coli.
Q.22. What are the diseases caused by some strains of coliforms?
Ans: Diarrhoea and opportunistic urinary infection.
Q.23. What are the criteria for an indicator organism for detection of faecal contamination?
Ans: (1) The organisms should be present in human faeces in substantial numbers.
(2) The indicator organism should be able to survive in water for sufficient time.
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(3) The indicator organism should be detectable by simple tests.
Q.25. How is it convenient to detect coliforms specifically Escherichia coli by using media containing O-nitrophenyl- (3 -D-galactopyranoside (ONPG) and 4-methylumbelliferyl- P -D-glucuronide (MUG)?
Ans: The coliforms produce enzyme P -galactosidase that acts on ONPG and shows yellow colour indicating their presence in the sample. E. coli is quite distinct among coliforms and produces the enzyme, P -glucuronidase which acts on MUG to form a fluorescent compound which glows blue in long wavelength ultraviolet light. These simple tests can be used to determine the presence or absence of coliform or E. coli in a sample.
Q.26. How does one get rid of cysts of Giardia lamblia and Cryptosporidium which are resistant to chlorination?
Ans: By filtration.
Q.27. What is flocculation?
Ans: During water treatment, the removal of colloidal substances by addition of a flocculent chemical such as aluminium potassium sulphate (alum), which causes colloidal particles to coalesce resulting in aggregations of finely suspended particles called floe.
Q.28. Give the steps of water treatment in a typical municipal water purification plant.
Ans: It comprises the following main steps:
(1) Sedimentation tank or the raw water reservoir to allow particles to settle down.
(2a) Mixing tank in which water is mixed with flocculent.
(2b) Flocculation tank in which aggregates of floe settle down.
(3) Filtration process in which water undergoes filtration.
(4) Disinfection: The water is disinfected by chlorination, ozone treatment or exposure to UV light.
(5) Storage tanks: The water is stored before use by the consumer.
