Sequentially arrange the steps involved in laying a sewer line:
A. Transferring the center line of the sewer to the bottom of the trench.
B. Setting sight rails over the trench.
C. Driving pegs to the level of the invert line of the sewer.
D. Placing the sewer in the trench.
Choose the most appropriate answer from the options given below:
Step 1: Setting sight rails.
The first step is to establish reference sight rails above the trench (B).
Step 2: Driving pegs.
Next, pegs are driven to the level of the invert line of the sewer (C).
Step 3: Transferring center line.
The sewer's center line is then transferred to the bottom of the trench (A).
Step 4: Placing sewer.
Finally, the sewer is placed in the trench (D).
Step 5: Conclusion.
Thus, the correct sequential order is B → C → A → D. Hence, the correct answer is (D).
An activated sludge process (ASP) is designed for secondary treatment of 7500 m\(^3\)/day of municipal wastewater. After primary clarifier, the ultimate BOD of the influent, which enters into the ASP reactor, is 200 mg/L. Treated effluent after secondary clarifier is required to have an ultimate BOD of 20 mg/L. Mix liquor volatile suspended solids (MLVSS) concentration in the reactor and the underflow is maintained as 3000 mg/L and 12000 mg/L, respectively. The hydraulic retention time and mean cell residence time are 0.2 day and 10 days, respectively. A representative flow diagram of the ASP is shown below.

The underflow volume (in m}^3\text{/day, round off to one decimal place) of sludge wastage is \(\underline{\hspace{1cm}}\).


