# GATE Questions & Answers of Basic unit processes and operations for water treatment

## What is the Weightage of Basic unit processes and operations for water treatment in GATE Exam?

Total 6 Questions have been asked from Basic unit processes and operations for water treatment topic of Water and Waste Water subject in previous GATE papers. Average marks 1.67.

A flocculation tank contains 1800 m3 of water, which is mixed using paddles at an average velocity gradient G of 100/s. The water temperature and the corresponding dynamic viscosity are $30^\circ C$ and $0.789\times10^{-3}$ Ns/m2 , respectively. The theoretical power required to achieve the stated value of G (in kW, up to two decimal places) is ______

At a small water treatment plant which has 4 filters, the rates of filtration and backwashing are 200 m3/d/m2 and 1000m3/d/m2 , respectively. Backwashing is done for 15 min per day. The maturation, which occurs initially as the filter is put back into service after cleaning, takes 30 min. It is proposed to recover the water being wasted during backwashing and maturation. The percentage increase in the filtered water produced (up to two decimal places) would be ______

A municipal corporation is required to treat 1000 m3/day of water. It is found that an overflow rate of 20m/day will produce a satisfactory removal of the discrete suspended particles at a depth of 3 m. The diameter (in meters, rounded to the nearest integer) of an circular settling tank designed for the removal of these particles would be ____________

Match the items in Group – I with those in Group – II and choose the right combination.

 Group - I Group - II P. Activated sludge process 1. Nitrifiers and denitrifiers Q. Rising of sludge 2. Autotrophic bacteria R. Conventional nitrification 3. Heterotrophic bacteria S. Biological nitrogen removal 4. Denitrifiers

A water supply board is responsible for treating 1500 m3/day of water. A settling column analysis indicates that an overflow rate of 20 m/day will produce satisfactory removal for a depth of 3.1 m. It is decided to have two circular settling tanks in parallel. The required diameter (expressed in m) of the settling tanks is __________

Consider a primary sedimentation tank (PST) in a water treatment plant with Surface Overflow Rate (SOR) of 40 m3/m2/d. The diameter of the spherical particle which will have 90 percent theoretical removal efficiency in this tank is ________ $\mu$m. Assume that settling velocity of the particles in water is described by stokes’s Law.

Given: Density of water = 1000 kg/m3; Density of particle = 2650 kg/m3; g = 9.81 m/s2; Kinematic viscosity of water (v) = 1.10 X 10-6 m2/s.