Test: Environmental Engineering- 1

Biological treatment of sewage treatment is basically an oxidation and reduction process both, it depends whether the treatment is aerobic or anaerobic.

In aerobic process: Nitrogenous organic matter is converted into NH₃ by oxidation process.

In anaerobic Process: Nitrogenous organic matter is converted into acids, alcohols gases by reduction process.

The Bureau of Indian Standards (BIS) fixes the upper limit of TDS in drinking water at 500 ppm. A RO water filter should provide you with an output water content of TDS around 50 ppm. A TDS level of 35 - 175 ppm is recommended for long term direct consumption.

Generally, the specific gravity of municipal sewage lies between 1.2 to 1.4 which is slightly greater than 

A trap is a device which has a shape that uses a bending path to capture water to prevent sewer gases from entering buildings, while allowing waste to pass through. Trap Should be made of non-adsorbent material. Depending upon the shape, Traps are classified as:

1. P - Type

2. Q - Type

3. S - Type

In kitchen and Bathrooms, a gully trap is provided at the junction of roof drain and other drain.

Check Valve: These valves are used to check the flow of water in reverse direction. These are generally provided on the delivery side of the pump. These valves work automatically.

Pressure reducing valve:  In hydraulics, a pressure reducing valve serves the same purpose as a "pressure regulator" valve in a compressed air system. It is one of a variety of pressure control valves available for hydraulic circuits. It is always used in a branch circuit and never in the full pump flow line.

Air Relief Valve: it is a type of safety valve used to control or limit the pressure in a system, pressure might otherwise build up and create a process upset, instrument or equipment failure, or fire. The pressure is relieved by allowing the pressurised fluid to flow from an auxiliary passage out of the system.

Scour valve: This valve is used to drain the water out of the pipe system.

Sluice valve: These valves are used to regulate the flow of water in the pipe system by dividing into number of sections.

Design discharge of pond is (Q_o) = (10000 × 200)

Q_o = 2 × 10⁶ liters/day

Organic loading rate = 300 kg/day/hectare

Applied Bod (S_o) = 300 mg/liter = 300 × 10^-6

Area of oxidation pond required = 

Corrosion in concrete sewers is mainly caused by Hydrogen sulphide gas which is formed due to Anaerobic decomposition of sewage. During Anaerobic Decomposition of sewage Acids, Alcohols and gases are formed and Hydrogen sulphide is one of the formed gases.

It is the laboratory method in which water sample is immersed in metallic container having glass bottom placed over the ignited frame and the height of water in the container at which image of flame ceases to be seen is noted to give the turbidity of water sample in standard units (STU). The principle utilised in this method is adsorption principle in which longer is the length of the path travelled by light, smaller is the turbidity and vice versa.

Operational Troubles in Standard rate Trickling Filter are:

1. Fly nuisance: Due to the presence of insects over the filter media, the entire media is flooded with flies which makes the operation of filter difficult. Moreover, theses flies moves along with waste water in the filter medium leading to choking of filter, thereby affects the working of trickling filter.

2. Ponding Problem: Due to growth of algae and fungi in the voids of the filter media that leads to ponding of the waste water over the filter media.

3. Odour problem: This problem is generally found if spray nozzle method of distribution method is adopted.

Water Borne diseases are conditions caused by pathogenic micro-organisms that are transmitted in water. Disease can be spread while bathing, washing or drinking water, or by eating food exposed to infected water.

1. Cholera: Cholera is a waterborne disease and is diarrhoeal in nature.

2. Typhoid: It is another disease that gets transmitted by drinking contaminated water that carries ‘Salmonellae Typhi bacteria’.

3. Diarrhoea: Diarrhoea is one of the most common waterborne diseases that mostly affects children under the age of 5.

4. Hepatitis A: Another type of waterborne disease is Hepatitis A and it is caused by Hepatitis A virus, which affects the liver.

5. Malaria: Malaria is a mosquito-borne infectious disease affecting humans and other animals caused by parasitic protozoans belonging to the Plasmodium type.

Alkalinity is the total amount of those substances present in water which tend to increase the concentration of OH^- ions either directly or indirectly. It is the ability of water to neutralize acids. Different types of alkalinity are present in water which is further difficult to show collectively, so to express all the different type of alkalinity in one single way, we expressed it as equivalent of Calcium Carbonate (CaCo₃).

Soluble organic ingredients are bacteria that are functional in some biological treatment processes, which depend on microbial decomposition using dissolved oxygen. These include carbohydrates, proteins and lipids.

The sound pressure of the faintest sound that can be heard by a normal healthy individual is about 20 μPa. Hence, this pressure is used as reference pressure in determination of sound pressure level.

Chlorine required for the city = Dose × Discharge

∴ Bleaching powder required 

The sewer which transports the sewage to the point of treatment is called outfall sewer.

For separation of dry dust of 10 to 100 μm size, wet scrubber is used.

[H⁺] ion in mol/l = 0.1008 x 10^-3

As per IS 2470 (part 1) - 1985, clause 3.4.5.1

Septic tank shall have minimum width of 750 mm, minimum depth of one metre below water level and a minimum liquid capacity of 1000 litres.

ZONES OF POLLUTION: A polluted stream undergoing self-purification presents the following four distinct zones of pollution

(1) ZONES OF DEGRADATION: This usually occurs below the output sewer when discharging its contents into the stream. The zone is characterized by water becoming dark and turbid with the formation of sludge deposits on the bottom. Dissolved oxygen gets reduced to 40%.

(2) ZONES OF ACTIVE DECOMPOSITION: This is marked by heavy pollution. It is characterized by the absence of dissolved oxygen; water is grayish and darker with active anaerobic organic decomposition accompanying and with the evolution of methane (CH₄), Hydrogen sulphide (H₂S), Carbon dioxide (CO₂) and Nitrogen (N₂), bubbling to the surface with masses of sludge forming black scum. Fish life is practically absent, fungi and bacteria disappear. As the organic decomposition slackens, reaction sets in and D.O. again rises to its original level (i.e. 40%).

(3) ZONE OF RECOVERY: In this zone, the stream tries to recover its former appearance. Most of the organic matter has been settled as sludge, B.O.D. falls and the D.O. content rises above 40% microscopic aquatic life reappears. Water becomes clearer, fungi decrease and algae reappear. Mineralization is active and products such as nitrates, sulphates, and carbonates are formed.

(4) CLEAR WATER ZONE: In this, the natural stream condition is restored, the D.O. is higher than the BOD. Oxygen balance is attained and recovery is said to be complete. Water becomes attractive in appearance. Some pathogenic organisms may, however, be present.