In your water treatment plant, a lime water softening process produces 20 tonnes
ID: 1711276 • Letter: I
Question
In your water treatment plant, a lime water softening
process produces 20 tonnes of sludge per day. This
sludge, which is mainly CaCO3
, with some magnesium
precipitates, is 15 % solids by weight and has a specific
gravity of 1.05. The CaCO3
can be converted to CaO
for reuse by calcining (burning) sludge. Before
calcining, the sludge is thickened with a centrifuge that
captures 70 % of the solids fed to it. The thickened
sludge discharged from the centrifuge is 55 % solids by
weight. This is fed to the calcining furnace. How
many m3 per day of sludge are fed to the furnace?
Explanation / Answer
1.Total Sludge=20 tonnes per day
2.CaCo3 mainly solids=0.15x20=3 tonnes, 3. Sp gravity=1.05 so volume= 3/1.05=2.86 m3
4.Centrifuge captures 70% of solids=0.7x2.86=2 m3
5. So sludge thickened discharged from centrifuge=2.86-- 2.00=0.86 m3
6. It is 55% solids. So solids =0.55x0.86=0.47m3
7. This 0.47 m3 is fed to calcining furnace.
8. So answer is 0.47 m3per day of sludge