Designing a Flocculator: A water treatment plant is being designed to process 50,000 m3/d of water. Jar testing and pilot-plant analysis indicate that an alum dosage of 40 mg/L with flocculation at a Gt value of 4.0 x 104 produces optimal results at the expected water temperatures of 15o C. Assume the average G value is 30 s-1. Determine: (1) The monthly alum requirement in kg/month (2) The flocculation basin dimensions if three cross-flow horizontal paddles are to used. The flocculator should be a maximum of 12 m wide and 5 m deep in order to connect appropriately with the settling basin. (3) The power requirement. (4) The paddle configuration. 1. Monthly alum requirement: 40 mg/L x Q x time = _______________________ kg/month 2. Basin dimension: (a) Calculate detention time Then Gt = 4 x 104 t = 4 x 104 / G x (1 min/60 s) = __________________ min. (b) Volume of tank is V = Qt = 50,000 (m3/d) x t = _____________________ m3 (c) The tank will contain three cross-flow paddles so it length will be divided into three compartments. For equal distribution of velocity gradients, the end area of each compartment should be square, i.e., depth equals 1/3 length. Assuming maximum depth of 5 m, length is: 3 x d = _______________ m Width is d x L x w = V W = _________________ m (d) Draw the configuration of the tanks with paddles: 3. Power requirements: (a) Assume G value tapered as follows: (remember, the average of all three must be what you assumed earlier) First compartment, G = ________________ s-1 Second Compartment, G = ________________ s-1 Third compartment, G = ________________ s-1 (b) Power requirement for compartment 1, 2 and 3 P = G2 V m Where Vcompartment = V/ 3 = _______________________ m3 At 15o C m = ___________________ Pa*s or N*s/m2 P1 = _____________ W = _______________ kW P2 = _____________ W = _______________ kW P3 = _____________ W = _______________ kW 4. Paddle configuration (a) Assume each paddle has four boards 2.5 m long and w wide. There are three paddle wheels per compartment. (b) Calculate width of paddle (w) from power input and paddle velocity: At 15o C, r = ___________________ kg/m3 (Table A-1) assume paddle velocity in the middle of design range (above) = _______________ m/s CD = __________________ (reference table above) Ap = length of boards x (w) x number of boards 3 paddles at ________________ boards per paddle = ______________ boards Ap = ____________ boards x 2.5 m (length) x (w) P (in terms of (w)) = _________________________ Set equal to average power found above: Solve for width of paddle: w = ________________ m Solution 1. Quantity of water to be processed for a month, Q= 50,000 m3/day x 30 days = 1,500,000 m3 = 1,500 L Monthly alum dosage required = 40 mg/L x 1500 L = 60,000 mg = 60 kg 2. a) Gt = 4 x 104 G=30 s-1 Retention time required = Gt/G = (4 x 104)/30 = 1333.33 seconds = 22.22 mints b) Quantity of water to be processed, Q= 50,000 m3/day = 34.72 m3/min Volume of the tank should be, V = Q x retention time, t.