Environmental Engineering (Part-5) (General Engineering) (SSC JE)

A portion of a confined aquifer in which the piezometric surface is not only above the ceiling of the aquifer but also have ground surface is referred to as an artesian aquifer.

The confineed acuifer is also known as pressure aquifer or artesian aquifer. The top and bottom layers of a confined aquifer are generally impervious.

The pH value indicates the hydrogen-ion concentration in water. The hydrogen-ion concentration is an atom or group of atoms that carries an electric charge.

Rapid sand filter–
• Coefficient of uniformity – Cu = 1.2–1.6
• Effective size D10 = 0.35 – 0.55 mm
• Cleaned through back washing and process takes 15- 30 minutes.
• Base material is gravel.
• Rate of filtration (3000–6000) l/m²/hr
• Maximum loss of head - 2.5 to 3.0 m
• Washing period is 24-48 hrs.
• RSF is highly efficient in colour removal.
• Its construction is complicated and skilled labour required.
Slow sand filter–
• Coefficient of uniformity Cu = 3–5
• Effective size Dₗ₀ = 0.2–0.3 mm
• Frequency of cleaning = (1–3) months
• Design period = 10 years
• Rate of filtration = 100 - 200 l/m²/hr
• Efficiency = 98–99%
• Plan area required is = 100 – 2000 m²
• For cleaning layer of sand is scraped and top = 1.5 to 3 cm of sand is removed.
• Period of cleaning = 1–3 months.

Bio-Chemical Oxygen Demand–It is use for measurement of the quantity of oxygen required for oxidation of bio-degradable organic matter present in water sample by aerobic biochemical action.
• Sample is diluted with dilution water in such a way that sufficient oxygen is available for the incubation period of 5 day at 20ºC.
• BODₛ = 2/3 BODᵤ and BOD for municipal sewage is 100-200 ppm.
• Drinking water should have zero BOD.

Water is one of the abundantly available substance in nature. It is an essential constituent of all animal and vegetable matter and forms about 75% of the matter of earth's crust.

• Rainwater is a purest form of naturally occurring water. • Water is distributed in nature in different forms such as rain water, river water, spring water and mineral water.
• The rain water however is associated with dissolved gases such as CO₂, SO₂, NH₃ etc.

The most commonly used disinfectant for drinking water throughout the world is chlorine. The process of applying chlorine or chlorine compounds in small quantity to water to disinfect it is known as chlorination.

• The time of contact for chlorination should be at least 20 minutes.
• UV light disinfection is a method used to clean water by exposing it to ultraviolet radiation. This process kills micro-organism such as bacteria, viruses and other pathogens that can make drinking water unsafe.
• UV light disinfection is a chemical free process that does not after the taste or odor of the water.

Ozonization– It is a chemical water treatment technique based on the infusion of ozone into water.

Hydrogen sulphie (H₂S), sulphur dioxide (SO₂) and nitrogen oxides are three polluting gases that pose a threat to the Taj Mahal coming from the oil refinery near Mathura.
The marble of the Taj Mahal gets corrected due to acids. Acid rain is caused by an increase in sulphur dioxide and nitrogen oxides in the atmosphere.

Wastewater treatment– It is well known that there are various common ways to treat wastewater such as physical water treatment, biological water treatment, chemical treatment and sludge treatment.

Physical water treatment–For cleaning of wastewater physical method are used in this type of treatment.
• The removal of solid material different processes like screening, sedimentation and skimming are employed in this type of treatment.
• The most important technique of physical wastewater treatment is sedimentation in which insoluble and heavy particles get suspended from the wastewater.
• We can easily separate the pure water settling down of insoluble material at the bottom.

Typhoid fever is caused by the bacterium salmonella typhiod. Typhoid can be caused by the consumption of contaminated water and food.

• Cholera is bacterial disease caused by vibrio cholera bacteria.
• Malaria is mosquito-borne parasitic infection spread by anopheles mosquitoes, it is not water borne disease.
• Typhoid, dysentery and cholera is water borne disease.

According to IS 10500 : 2012, The maximum permissible limit of fluoride in drinking water is 1.5 ppm.