List of top Water & Wastewater Treatment and Management Questions asked in GATE ES

A 10 million litres per day (MLD) sewage treatment plant (STP) is based on the Activated Sludge Process (ASP). First, the sewage undergoes primary treatment and the resulting treated sewage has BOD$_5$ of 140 mg/L concentration. This is further passed through a 1500 m\(^3\) capacity aeration tank (in ASP), where the mixed liquor volatile suspended solids (MLVSS) concentration is maintained at 3000 mg/L. The concentration of BOD$_5$ of the treated sewage is 5 mg/L. The Food to Microorganisms ratio (F/M) of the ASP is _______ day\(^{-1}\) (rounded off to two decimal places).
In a field test of a geological formation of permeable soil (porosity = 20 %), the hydraulic gradient was found to be 2 %. The actual seepage velocity of the flow was found to be 0.0025 m/s. Assume that the flow is in the laminar regime. The permeability \( K \) of the aquifer is _______ m/s (rounded off to three decimal places).
In the context of water quality, which of the following is/are correct for the most probable number (MPN) of a water sample?
The characteristics of a water sample are as follows: Na\(^+\) = 92 mg/L, K\(^+\) = 19.5 mg/L, Ca\(^{2+}\) = 40 mg/L, and Mg\(^{2+}\) = 24 mg/L. What is the sodium adsorption ratio (SAR) of the water sample which may be considered for irrigation purposes?
A sewage treatment plant (STP) receives sewage at a flow rate of 20000 m\(^3\) per day. The sewage has 200 mg/L of suspended solids. Assume 60% suspended solids are removed in the primary clarifier. The underflow (i.e. sludge) removed from the clarifier contains 5% solids (by weight).
The daily volume of the sludge generated will be ________ m\(^3\) per day.
Assume sludge density = 1000 kg/m\(^3\).
A flocculation tank used for water treatment has a velocity gradient (G) of 800 s\(^{-1}\). The volume of the tank is 40 m\(^3\). The dynamic viscosity of water is \(9 \times 10^{-4}\) N.s/m\(^2\). The theoretical power required to maintain the given velocity gradient is _______ kW (rounded off to the nearest integer).
A water jet discharging from a 4 cm diameter orifice has a diameter of 3.5 cm at its vena contracta. The coefficient of velocity is defined as the ratio of the actual velocity of the jet at vena contracta to the theoretical velocity of the jet. If the coefficient of velocity is 0.98, the coefficient of discharge for the orifice will be _______ (rounded off to two decimal places).