BIOLOGICAL WATER QUALITY PARAMETERS

PHYSICAL WATER QUALITY PARAMETERS (click on it)

CHEMICAL WATER QUALITY PARAMETERS (click on it)

Types of Organics

• Organics are further classified into Biodegradable and Non-biodegradable organics
• Biodegradable Organics - Easily decomposed by natural agents like micro-organisms, water, oxygen, ultraviolet rays of the sun, acid rains, etc. Example -  food waste like vegetable and fruit peels, dead plants and animals etc.
• Non-biodegradable Organics - Cannot be broken down or decomposed by natural agents. Example - plastics, polystyrene, toxic organic chemicals, paints etc.
• Biodegradable organics, in water are mostly utilized for food by micro-organisms.
• Reaction in the presence of free oxygen is called  aerobic reaction and reaction in the absence of free oxygen is called anaerobic reaction
• Microbes are majorly classified into 3 categories -

                    1.Aerobic - react in the presence of free oxygen

                    2.Anaerobic - react in the absence of free oxygen
                    3.Facultative - react either in the presence or absence of free oxygen.

• The most important organisms of concern are called pathogens. These are capable of transmitting diseases.
• Examples are bacteria, virus, protozoa and helminths.
• Pathogenic micro-organisms can be tested and counted in laboratory but with great  difficulty. Hence, these tests are not performed generally in routine
• The usual routine tests are generally conducted to detect and count the presence of coliforms, which in themselves are harmless but their presence or absence indicates the presence or absence of pathogenic micro-organisms.
• Coliforms are non- pathogenic indicator organisms.
• Escherichia Coliform (E. Coli) is the predominant member of the coliform group used in the test.

PROPERTIES OF COLIFORMS

1. Gram negative – forms red stain
2. Non-spore forming – no heat resistance
3. Facultative (predominantly anaerobic)
4. Bacillus – rod-shaped
5. Lactose fermenters

Note – Fermentation is a metabolic process in which sugars is converted to acids, gases or alcohol. Coliforms ferment lactose (a type of sugar) to lactic acid, CO2 etc.

TESTING OF COLIFORMS

1. Membrane Filter Technique

• Water sample is poured on the sterile membrane filter.
• Membrane is then put in contact with nutrients (M- endo medium) that permits the growth of only gram negative or coliform organisms. After the incubation for 20 hrs at 35ᵒC, number of visible colonies are counted and related to that of pathogens.
• As per GOI manual, number of visible colonies after incubation of any 100 ml sample should be.  

2.Most Probable Number (MPN) Test

• MPN represents the microbial density which is most likely to be present in the water sample.
• It is also called as multiple tube fermentation test & is determined by statistical methods.
• 3 sets of 5 tubes are taken and a solution of lactose broth is taken in each. The sample added is 10 ml, 1 ml and 0.1ml   in each set respectively. These are called as standard test tubes.
• After incubation at 35ᵒC for 48 hrs, all samples are checked for release of gases (CO2) by checking air bubbles in the tube.
• If gases are evolved, coliforms are present.
• The tubes which contain bubbles are called as positive tubes and are denoted as x-y-z.
• Then referring to the standard table MPN/100ml is noted.
• As per GOI Manual, MPN/100 ml for drinking water should be 
• Standard sample size is 10ml, 1ml & 0.1ml. If ex – 1ml, 0.1ml and 0.01ml sample is taken, then in it, coliforms will also be less, then MPN/100ml from table is multiplied by 10 to get actual values.
• If more than 3 dilution samples are taken, Ex – 100ml, 10ml, 1ml, 0.1ml, 0.01ml, then consecutive 3 are taken and maximum out of them is reported as MPN/100 ml

Water Borne Disease