There are two identical trickling filters operating in parallel after primary clarification, both

without recirculation. The total flow is evenly distributed between the two filters. Plastic

packings are used in both filters. The primary effluent wastewater characteristics are given

below, and the goal is to achieve a $60\%$ removal in $BO{D}_5.$ It can be assumed that the

production of cell debris within the filters is negligible.

Calculate the following: $(18$ points$)$

$($a$)$ The hydraulic application rate for each filter $($in $\frac{L}{m^2}\frac{?}{s}).$

$($b$)$ The amount of biomass produced in each filter $($in $mgVS\frac{S}{L}).$

$($c$)$ The concentration of oxygen required in each filter, as determined using a COD mass

balance $($in $m\frac{g}{L}).$

A reverse osmosis system employs a cellulose$-$based membrane to eliminate total dissolved

solids $($TDS$)$ from wastewater. The system's properties are provided below.

Calculate the following:

$($a$)$ The required minimum membrane area $($in $m^2)$ to achieve the desired permeate TDS

concentration. $(22$ points$)$

$($b$)$ The rejection rate $(\%).(5$ points$)$

$($c$)$ The concentration of TDS in the concentrate stream $($in $k\frac{g}{m^3}).(10$ points$)$