Raw primary sludge at a solids concentration of 3% is mixed with waste activated

Question

Raw primary sludge at a solids concentration of 3% is mixed with waste activated sludge at a solids concentration of 6,000 ppm. The flows are 20 and 25 gal/min, respectively. What is the resulting solids concentration? This mixture is next thickened to a solids concentration of 80,000mg/L solids. What are the quantities ( in gallons per minute)of the thickened sludge and thickener overflow (water) produced ? Assume perfect solids capture in the thickener. Also, draw a blackbox diagram for this problem. Show all work

Explanation / Answer

total flow = 44 gal/min

tocal solid = 20*.04+24*.005 = 0.92

resultant conc. = .92/44 *100= 2.091%

thickened sludge = .92/0.08 = 11.5 gal/min

Overflow = 44-11.5 = 32.5 gal/min

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