Design percolating filters with conical humus tanks for treating 7 million litres of sewage per day.

• We will design conventional trickling filters, with a hydraulic loading, say, 28 ML/ha/day [i.e. between 22 to 44].

  • Surface Area of the filter bed required

= 7/28 ha= 7 /28 *10^ 4 m^ 2 =2500 m^ 2

Using two equal sized circular tanks, we have the dia of each tank

= sqrt 2500 2 * 4 pi =39.9 m; say 40 m Hence, use two trickling filters, each of 40 m dia. A third extra unit as standby unit, may also be provided. The depth of the filter provided may be kept 2 m or so. Humus Tank Design of Conical Humus Tank = 7 24 1.5 M.L=0.437* M.L=437 cu.m

The volume of each conical tank, such as shown in figure, is given by V= παζ x Depth Using 4 Nos. with 7.5 m depth of each tank, we have the total surface area required for all 4 tanks = 437 7.5 m^ 2 =58.27 m^ 2 .. Dia of each tank (d) is given by 1/3 * (pi * d ^ 2)/4 = 1/4 * (58.27)

or d = sqrt((58.27 * 4 * 3)/(4x)) = 7.46m / s * ay * 7.5 Hence, use 4 tanks with dia 7.5 m and height also as 7.5 m. One additional tank as stand by unit may also be provided; thus, using 5 tanks in all.