1. Estimate the particle removal efficiency in a rectangular sedimentation tank with a depth of 4 m, width of 8 m, length of 40 m and process flow rate of 800 m3/h. For the following influent particle settling characteristics compute the overall removal efficiency. Plot the influent and effluent particle concentrations as a function of particle size using histogram. One way to increase the particle removal efficiency is to decrease the overflow rate. How do you propose to do this at the above treatment plant? If the overflow rate is reduced to 2.0 and 1.5 m/h, what are the corresponding particle removal efficiencies?

2. a. As filter bed collects impurities, the increase in the lead loss is directly proportional to the amount of impurities collected. With a uniform quality of feed water, the head loss, h_L in a filter can be written as:

h_L =V_s(a+bV)

where,

V_s - approach velocity of the water (m/s)

V - volume of water filtered through unit area of filter bed since the last backwash (m³/m²)

a, b- constants depending on the size and shape of the filter material and the quality of the applied water; units of and b are s and s/m A filter has a head loss of 0.3 m when newly washed, and 1.3 m after 24 hours. When operating at a rate of 1.5 L/s.m². Estimate the head loss both immediately after backwash and 10 hours later, if the same water is applied at a rate of 2 L/s.m².