Environmental Engineering (Part-3) (General Engineering) (SSC JE)

The national ambient air quality standards in India were first notified in 1994 under the Environment (Protection) Rules, 1986.

As per CPCB : Indian National Air Quality Standards what is the standard permissible value for PMₗ₀ is 100 µg/m³ for average 24 h value.

Vitrified clay pipes is not often use as pressure pipe, but is widely use in sewerage and drainage for flow at partial depth, vitrified sewer pipe are used for small length with small diameter.

• The main advantage of vitrified clay pipe is that it is virtually corrosion-free, has a long life, and its smooth surface provide high hydraulic efficiency. It is highly impervious.

Tubewells– Tubewells can be easily in such soils and are very useful for irrigation. The general average yield from the standard tubewell is however of the order of 40 to 45 litre/sec.
• Deep tubewells are as deep as 70 to 300 m and tap more than one aquifer. They are usually constructed in over country by the state government and and are called the state tubewell & such wells may yield as high as 200 to 220 liters/sec.
• Shallow tubewells having 20 to 70 m upon and tapping only one aquifer are also constructed, usually by private individual former. Such wells may yield as high as 15 to 20 liters/sec, if located at proper place.

Aquifer– An aquifer is a saturated formation of earth material which not only stores water but yields it in sufficient quantity. Thus an aquifer transmits water relatively easily due to its high permeability. Example– Sand, grave.

Aquitard– It is a formation through which only seepage is possible and thus the yield is insignificant compared to an aquifer. It is partly permeable. Example–Sandy clay.

Aquiclude– It is a geological formation which is essentially inpermeable to the flow of water. Example– Clay. Aquifuge– It is a geological formation which is neither porous nor permeable. Example–Rock.

The sewer pipe lengths are usually laid from the lowest point with their sockets facing up the gradient on desired feeding. Thus the spigot end of new pipe can be easily inserted on the socket end of the already laid pipe.

Laying of sewer–
(i) Marking of the alignment
(a) By reference line
(b) By sight rail
(ii) Excavation of trench
(iii) Dewatering of trench
(iv) Bracing of trench
(v) Laying and joining of pipes
(vi) Testing of leakage
(a) By air test - for long pipe
(b) By water test - for small pipe.
• After bedding concrete is laid in required alignment and levels.
• The sewer pipes are than lowered down into the trench either manually or with the help of machines.

When the ratio of flow to vertical diameter is 0.95 the maximum flow occurs in an egg shaped sewer.
• Condition for maximum velocity for egg-shaped sewer– D 0.81d
• Wetted perimeter (P) = 2.65 d

The most harmful constituent of water is bacteria.
Water borne diseases–
Bacteria– Typhoid fever, cholera, bacillary dysentry etc. Protozoa– Amoebic dynsentry
Virus– Jaundice, poliomyelities, infectious

The temporary hardness of water is due to presence of bicarbonates of calcium and magnesium. The treatment for removing the hardness or dissolved impurities from water is known as softening of water.

Permanent hardness–The hardness due to the presence of sulphates chlorides and nitrates of calcium and magnesium is known as permanent hardness.

Note–The temporary hardness may be removed by boiling the water or by adding lime water in water which is called lime process.
• The permanent hardness of water may be removed by lime soda process, zeolite (silicate of sodium) or base exchange proces (also known as cation exchange method).

Rapid sand filter–
• Uniformly coefficient Cᵤ= 1.2 to 1.8
• Effective size of sand Dₗ₀ = 0.35 to 0.55 mm
• Rate of filtration of R.S.F. ⇒ 3000–6000 ℓ/m² /hr
• Area of tank (RSF) ⇒ 10–100 m² /unit
• Its clean through back washing, using 2-5% of total water filter.
• Removal of turbidity upto 40 ppm
• R.S.F. is highly efficient in colour removal when used with conjugate sedimentation. It is bacteria removal 80- 90%.