Following observations were made on a 4% dilution of waste water: DO of aerated water used for dilution = 4 mg/lt. DO of diluted sample after 5 days of incubation = 0.8 mg/lt. DO of original waste water sample = 0.5 mg/lt. What is the value of ultimate BOD? (Take Kp (at base 10) = 0.12 day %3D

What diameter would a circular clarifier have to be to remove 50 μm particles with 75% efficiency from a 4 MGD (million gallon per day) flow?  Assume the particle specific gravity is 1.5 and the temperature is 10°C.  Answer: 18 m

From water sample, 25 mg/L HCO3" as CacO3, 10 mg/L C032 as Caco3 and 50 mg/L Ca* as CaCO3 were measured. pH was near neutral. What is alkalinity? () mg/L as Cac03 (*Answer in whole number only)