Test: Environmental Engineering & RCC- 2 - GATE MCQ

Since the area is limited and there is no time period specified for population estimation, therefore logistic curve method will be the best.

1 JTU= The standard turbidity produced by one mg of silicon dioxide(silica) in one litre of distilled water.
1 FTU= The standard turbidity produced by one mg of formazine in one litre of distilled water.
Nephlometer measures turbidity in NTU and both NTU and FTU measures turbidity of instrument which uses scattering principle.

Water with hardness upto 75 ppm are considered soft while those with 200 ppm and above are considered hard. In between the waters are considered as moderately hard.

Eriochrome black T is used to measure hardness. Phenolphthalein is used to measure alkalinity. Blue litmus is used to measure acidity of water.

Threshold odour number represents the dilution ratio at which the odour is hardly detectable

Hardness is measured by the titration process. The titrant used is EDTA solution also known as versonate solution. Indicator used is EBT (Erichrome Black T Indicator) and the titration is assumed to complete when the colour changes from blue to red.

A fluoride concentration of less than 0.81.0 ppm may be harmful and may cause dental caries (tooth decay) due to the formation of excessive cavities in the teeth of young children during calcination of their permanent teeth. Higher fluoride concentrations, greater than 1.5 ppm or so, may again be harmful, causing spotting and discolouration of teeth, (a disease called fluorosis), which with continued excessive consumption of fuorides, may even cause deformation of bones.

MPN (most Probable Number) is used to measure total coliform in water sample.

BOD₅ = Loss of oxygen in mg/l x Dilution ratio
BOD₅ = (7 - 0) x 100 = 700 mg/l

The detention period (t) of a settling tank may be defined as the average theoretical time required for the water to flow through the tank length. It is that time which would be required by the flow of water to fill the tank, if there were no outflows. In other words, it is the average time for which the water is detained in the tank. Hence, it is the ratio of the volume of the basin to the rate of flow (or discharge) through the basin
∴ Detention time t for a Rectangular tank

Lime helps in removing the entire carbonate hardness (i.e. carbonate hardness caused by Ca as well as that caused by Mg), and it reacts with noncarbonate hardness of Mg to convert the same into non-carbonate hardness of Ca. The non-carbonate hardness of Ca is finally removed by Soda. Lime also helps in removing the free dissolved carbon dioxide, if and when it exists in the given
water

Common problems associated with
filtration of waste water are:
(i) Air binding
(ii) Turbidity break through cracking of sand bed
(iii) Mudball formation
(iv) Buildup of emulsified grease
(v) Loss of filter medium due to backwashing
(vi) Gravel moulding or bumping of filter beds.

The turbidity denotes the concentration of colloids. Alkalinity is used for restoring pH after alum (coagulant) addition.
In the case of low turbidity small number of colloids make the coagulation difficult. If the alkalinity is high, moderate alum doses will result in the formation of AI(OH)₃ which is amorphous and gelatinous. So sweep coagulation takes place.
High turbidity-low alkalinity: With relatively small doses of coagulant, water can be coagulated by adsorption and charge neutralization. Depression of pH makes this method more effective because aquometallic ions are more effective at low pH.
High turbidity-high alkalinity: The pH will be relatively unaffected by coagulant addition. Because of high alkalinity, adsorption and charge neutralization will be less effective than in waters of low alkalinity. Higher coagulant dosage should be used to ensure sweep coagulation.