Indiabix: wastewater

15 cm

The minimum recommended diameter of sewers

Aerobic bacterias

flourish in the presence of free oxygen consume organic matter as their food oxidise organic matter in sewage

30 litres/person/year

The rate of accumulation of sludge in septic tanks is recommended

250 рpm

If 2% solution of a sewage sample is incubated for 5 days at 20°C and depletion oxygen was found to be 5 ppm, B.O.D. of the sewage is

1.75 D

If D is the diameter of upper circular portion, the overall depth of a standard egg shaped section

1 in 120

the diameter of sewer is 225 mm, the gradient required for generating self cleansing velocity

correct statement

pH value indicates acidity and alkalinity of sewage; In acidic sewage, the pH value is less than 7; In alkaline sewage, the pH value is more than 7 ;Fresh sewage is generally alkaline

centrifugal pump

non-clog pump which permits solid matter to pass out with the liquid sewage

Both A and R are true and R is the correct explanation of A

Assertion (A) : Discharging the effluents from the oxidation ponds just up stream of lakes or reservoirs is undesirable. Reason (R): The discharged algae get settled in the reservoirs and cause anaerobic decomposition and other water qualities.

1.36 m

The width of a rectangular sewer is twice its depth while discharging 1.5 m/sec. The width of the sewer is

correct statement

In treated sewage, 4 PPm of D.O. is essential ,

Only very fresh sewage contains some dissolved oxygen ,

The solubility of oxygen in sewage is 95% that is in distilled water

horse shoe shaped

olden days the type of section adopted in trunk and out fall sewers was

4 PPm

For the survival of fish in a river stream, the minimum dissolved oxygen is prescribed

fully mechanised composting plant, involves

mechanized receipt, mechanized segregation, mechanized pulverising of refuse

Self-cleansing velocity is

velocity at which no accumulation remains in the drains

4 hours

If the over land flow from the critical point to the drain is 8 km and the difference in level is 12.4 m, the inlet time is

three pipes

An inverted siphon is designed generally for

C. 5

rainfall may be classified as acidic if its pH value is less or equal to

slightly less than 5% of the design discharge

When drainage to sewage ratio is 20, the peak dry weather flow is

sedimentation tank and an activated sludge treatment plant

For treating the sewage of a large city, you will recommend

216 cu m

The dimensions of a rectangular settling tank are : length 24 m, width 6 m and depth 3 m. If 2 hour detention period for tanks is recommended, the rate of flow of sewage per hour, is

at an angle 30° to 60° to the direction of flow

The screens are fixed

2.65

In primary sedimentation, the 0.2 mm inorganic solids get separated if specific gravity is

Inlets are generally provided in all sewers

in-correct statement

greasy and oily matters

Clogging of sewers, is caused due to

0.45 m/sec

A sewer pipe contains 1 mm sand particles of specific gravity 2.65 and 5 mm organic particles of specific gravity 1.2, the minimum velocity required for removing the sewerage, is

ferric chloride

The coagulant widely used for sewage treatment, is

Glazed stonewares.

House connections to the laterals is generally made by

2.0

The ratio of maximum sewage flow to average sewage flow for mains up to 1 m in diameter, is

when diluting water is used for water supply near the point of sewage disposed

Dilution method of disposing off sewage, is not preferred to

1 in 60

For house drainage minimum gradient is

1095 mm.

the side of a square sewer is 1000 mm, the diameter of a hydraulically equivalent circular section, is

1/3

The ratio of minimum hourly flow to the average flow of sewage is

initial demand , first stage demand & carbonaceous demand

Bio-chemical oxygen demand (BOD) for the first 20 days in generally referred to

glazed bricks sewers

For non-scouring velocity 5 m/sec, the type of sewers generally preferred to, is

dilution

Disposal to sewage in large cities, is done in

H2SO4

For the COD test of sewage, organic matter is oxidised by K2Cr207 in the presence of

0.25

R.C. sewer pipes, the percentage longitudinal reinforcement to the cross- sectional area of concrete is kept

vertically

The asbestos cement pipes are generally laid

bacterias

Chlorination of water is done for the removal of

an Imhoff cone.

For evaporation and measurement of settlable solids, the apparatus used, is

watts

In Sl units the power of sound is represented in

sanitary sewage

rain sanitary sewer is constructed to carry

from low lying areas ,from flat areas, from basements ,across a high ridge

The sewage is pumped up

skimming

Removal of oil and grease from sewage, is known

methane

The gas which may cause explosion in sewers, is

bottom side

In sewers the effect of scouring is more on