Environmental Engineering (Part-4) (General Engineering) (SSC JE)

The following treatment sequence of potable water is prepared from turbid surface water is–
Turbid surface water → coagulation → flocculation → sedimentation → filtration → disinfection → storage and supply.
• Turbidity in drinking water can provide shelter and nourishment for pathogens. Pathogen regrowth in drinking water can cause waterborne disease outbreaks.
Note– The commission has accepted option (d) as correct.

Primary treatment removes about 60-70% of total suspended solids and about 30-35% of BOD dissolved impurities are not removed. It is usually used as a first step before secondary treatment.

Bulking of sludge refers to having f / m < 0.3 / d
• A sludge that exhibits poor settling characteristics is called as bulking of sludge.
Causes–
• Low f/m ratio
• Nutrient deficiency
• Low DO
• Fats, oil and grease.

SO₂ and CO adversely affect functioning of the respiratory system and oxygen carrying capacity of blood respectively.
Effects of SO₂–
• Cardiovascular illness
• Plant damage
Effects of CO–
• Headaches, dizziness • Risk of death

Biological Oxygen Demand (BOD) The approved BOD sampling and analysis procedure measure the DO depletion over a 5 day period under controlled condition (20.6 in the dark).

The test is performed using a specified incubation time and temperature. Test results are used to determine plant loadings, plant efficiency and compliance with NPDES effluent limitations : however, the duration of the test makes is difficult to use the data effectively for process control.

• Standard BOD (5 days) of industrial sewage = Standard BOD (5 days) of domestic sewage per person per day × Population equivalent.

Soft water–Soft water contain a low percentage of carbonic acid, salt or ammonia easily with shop.

Soft water advantage–
• It will not deposit chemicals/residue in pipe and water system for 20 year under normal circumstances.
• This means is cuts down on the cost of replacing water and boiler pipes.
• It saves on the amount of soap used for washing and extends the life of textiles which have to be washed frequently. It improves the conditions under which food is prepared.

Permanent hardness–It is caused by the salt (chloride and sulphate) of Ca and Mg.
• Permanent hardness cannot be removed by boiling of water or hydrated lime.
• It can be eliminate by water softening techniques like Lime-soda process, zeolite, ion-exchange resin reverse osmosis etc.

Temporary hardness–Temporary hardness of water is caused by Ca and Mg bicarbonate. This can be removed by simply boiling of water.

Softening–
• It is process of removal of hardness from water.
• It can be achieved by any of the following method–
(a) Lime soda process
(b) Zeolite method (cation or base exchange method)

If nitrate is present more than 45 mg/l. It affect infant and cause mathemoglobinemia and blue baby disease.
          Acceptable limit = 45 mg/l