QUESTION Marks$]$

The following design parameters apply to the design of some units of water a treatment plant:$-$

Number of households

Number of persons per household

Per capita water demand

Office space

Water demand for offices per $100m^2$

Retum flow as wastewater

Infiltration

Design horizon

Population growth rate

Shape factor of screen

Spacing between bars

Diameter of bars

Distance from the walls of first and last bar

Number of bars

Angle of inclination of screen to the horizontal

Approach velocity

$=15000$

$=6$ persons

$=\frac{80}{\frac{?}{?}}ca.$day

$=600000m^2$

$=\frac{4001}{d}ay$

$=80\%$

$=15\%$

$=10yrs$

$=2\mathrm{.}5\%$ per annum

$=2\mathrm{.}4$

$=25mm$

$=38mm$

$=40mm$

$=55$

$=60$

$=1\mathrm{.}2\frac{m}{s}$

Compute the following:

a$)$ Current ADWF in $\frac{m^3}{?}$ day for offices and households

b$)$ Population equivalent at current ADWF $($offices and households$)$

c$)$ Projected population equivalent

d$)$ Projected ADWF in $\frac{m^3}{?}$ day at population equivalent

e$)$ PWWF in $\frac{m^3}{?}$ day

f$)$ Head loss through the screen at PWWF$.$

g$)$ The head of water in the grit channel if the throat width is $0\mathrm{.}225$ m

h$)$ The width and length of grit channel at PWWF

i$)$ Depth of grit storage in channel at ADWF if the grit storage time and grit concentration are

$1$ weeks and $0\mathrm{.}01\frac{m^3}{1000}{m}^3$ respectively. Assume a grit storage base width of $50$ cm $.$

j$)$ Sketch the cross$-$section and plan of the grit channel showing all your dimensions

$[10$ marks$]$

Useful formulae

$PF=1+\frac{14}{4+\sqrt[\phantom{2}]{P}},Q_{\text{m}\text{a}\text{x}}=1\mathrm{.}71B{H}_{\text{m}\text{a}\text{x}}^{\frac{3}{2}},W_{\text{m}\text{a}\text{x}}=5\frac{Q_{\text{m}\text{a}\text{x}}}{H_{\text{m}\text{a}\text{x}}}$

$P=P_o(1+r{)}^n,h_l=(\frac{w_b}{b}{)}^{\frac{4}{3}}\frac{v^2}{2g}$Sin$,PF=\frac{5}{P^{\frac{1}{4}}}$

Depth $of$ storage required $in$ grit channel $=\frac{\text{G}\text{r}\text{i}\text{t}\text{v}\text{o}\text{l}\text{u}\text{m}\text{e}}{\text{G}\text{r}\text{i}\text{t}\text{c}\text{h}\text{a}\text{n}\text{n}\text{e}\text{l}\text{b}\text{a}\text{s}\text{e}\text{w}\text{i}\text{d}\text{t}\text{h}\text{l}\text{e}\text{n}\text{g}\text{t}\text{h}}$

The grit volume

$=$ ADWF $x$ storage time x grit concentration