I$7\mathrm{.}9$ A single$-$stage high$-$rate trickling filter plant

treats a municipal wastewater from a population of

$10,000$ persons. The plant has a polishing pond

downstream from the final clarifier. Pertinent data

are: wastewater flow $=100ga\frac{l}{c}ap-$day $/$cap$-$

day$),$ influent $BO{D}_5=200m\frac{g}{l},$ BOD ${?}_5$ removal by the

primary clarifier $=33\%,$ recycle ratio $=2\mathrm{.}5,$ filter

depth $=5$ to to $2\mathrm{.}13m,$ and eflluent $BO{D}_5$

$=25m\frac{g}{l}.$ Determine, using USCS units and the

NRC equation:

a$.$ The theoretical filter diameter if a depth of $6ft$ is

assumed.

b$.$ The design diameter if rotary distributors are

available in $5-ft$ increments in diameter.

c$.$ The filter deoth.

d$.$ Prepare a spreadsheet using the calculated

diameter in part $b$ and depth in part $c,$ to find the

effluent $BO{D}_5$ for different recirculation ratios.

Plot and note if there is a point of diminishing return.

Notes for $17\mathrm{.}9$

Note the BOD loading has the volume of

the reactor embedded within the vale

$($lb$/$day$/1000$ ft ${?}^3)$

$,$ Vol $=$ surface area $x$ depth

Once diameter is calculated, round up in

increments of $5$ feet and calculate the new

depth.