Instruction: Assume suitable data required for design clearly stating the same. Number in the

parenthesis, to the right, indicates full marks.

Q$.1.($a$)$ BOD of the sewage incubated for $3$ days at $27C$ is $120m\frac{g}{L}.$ Calculate BODs at $20C$ and

ultimate BOD. Assume $K=0\mathrm{.}23$ per day $($base e$)$ and $=1\mathrm{.}047.$

$($b$)$ A $30$ cm diameter sewer having an invert slope of $1$ in $150$ was flowing full. What would be

the velocity of flow and discharge? Consider $n=0\mathrm{.}013.$ Is the velocity self$-$cleansing? What

would be the velocity and discharge when the sewer is running $0\mathrm{.}8$ times its full depth? For

$\frac{d}{D}=0\mathrm{.}8,$ the proportionate velocity $(\frac{v}{V})=1\mathrm{.}14$ and proportionate discharge $(\frac{q}{Q})=1\mathrm{.}067.$

$($e$)$ A watershed of total area of $18$ hectares comprises of upstream non$-$residential area of $10$

hectares and remaining downstream residential area of $8$ hectares having existing storm water

drain of $1\mathrm{.}8$ km in length. The time of concentration for non$-$residential and residential area

are $22$ min and $20$ min and overall runoff coefficients are $0\mathrm{.}36$ and $0\mathrm{.}64,$ respectively. For

rainfall frequency of once in $5$ years the intensity duration has relation $I=82e^{-0\mathrm{.}02816},$

where tc is time of concentration in min and I is $m\frac{m}{h}.$ The velocity of flow in existing storm

water drain is $0\mathrm{.}90\frac{m}{s}.$ Estimate the design flow for storm water drain for non$-$residential

area of catchment contributing the storm flow at the entry of the existing storm water drain

and at the end of the $1\mathrm{.}8$ km of existing length of the drain, when whole catchment is

contributing. What will be design discharge for this drain?

Q$.2($a$)$ Determine the head loss through a bar screen when it is cleaned and when $50\%$ of the flow

area is blocked off by the accumulation of floating coarser solids. Consider following

conditions:

Approach velocity $=0\mathrm{.}6\frac{m}{s}$;$,$ Velocity through the clear bar rack $=0\mathrm{.}8\frac{m}{s}$

Open area for flow through clear bars $=0\mathrm{.}186m^2$;

Consider head loss $=(\frac{1}{0\mathrm{.}70}{)}^{*}\frac{V^2-v^2}{2}g$

$($b$)$ Design a horizontal flow grit chamber with rectangular cross section for treating average

sewage flow of $6$ MLD and maximum sewage flow of $12$ MLD$.$ Consider the settling

velocity of smallest particle to be removed equal to $2\mathrm{.}4c\frac{m}{sec}$ and critical horizontal

velocity $22\mathrm{.}7c\frac{m}{sec}.$

$($c$)$ What is purpose of providing separate grit chamber and primary sedimentation tank in

sewage treatment plant? State the design guidelines for primary sedimentation tank.

Q$.3.$ Explain the following: $($Any three$)$

i$)$ Describe oxygen sag analysis and state parameters affecting self$-$purification

ii$)$ Describe different types of Manholes used in sewerage network. State the purpose for

which these are provided.

iii$)$ Describe different variant of activated sludge process used in sewage treatment

iv$)$ Describe MBBR$.$ What advantages it offers over activated sludge process?

v$.$ Sewer shape and materials used for construction.

vi$)$ Describe self$-$cleansing and limiting velocity for sewer design.