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can you please solve these questions in the file below ? and make sure to send it as wordModule VI Homework
Material Balance
1. A river 400ppm of salts and an upstream flow of 25.0m3 /s receives an agricultural discharge
of 5.0 m3/s carrying 2000 mg/L of salts. The salts quickly become uniform distributed in the
river. A municipality just downstream withdraws water and mixes it with enough pure water (no
salt) from another source to deliver water having no more than 500 ppm salts to its customers.
What should be the mixture ratio F of pure water to river water?
500 ppm
FQ m3/s
25.0 m3/s
400 ppm
Q m3/s
5.0 m3/s
2. Consider a hilly area in which new homes are being constructed. As rain falls on the site , the
runoff water will carry mud and dirt into a nearby creek-polluting it badly. A detention pond was
built to catch the runoff and allow the mud to settle before the water flows into the creek. For
simplicity, assume the rain is steady, and ignore any transient effects on the pond water
The runoff generated by the rainstorm is 10 m3/s, and has a particle concentration of 5.0
g/L. The creek flows at 200 m3/s and normally has a concentration of 15.0 mg/L of solid
particles. The detention pond will catch and remove most of the mud, leaving the overflow water
with a concentration of 400 mg/L. assume that 5% of the water that comes into the pond will
seep down through the bottom (filtering out all particles), while the rest will over flow into the
Calculate the mass of mud accumulated in the detention ponds after three hours
of this rainfall/runoff.
Calculate the concentration of particles in the creek after mixing with the
overflow from the pond.
3. Sludge is wet solids that result from the processing in Municipal sewage systems. The sludge
has to be dried before it can be composted or otherwise handled. If a sludge containing 70%
water and 30% solids is passed through a drier, and the resulting product contains 25% water,
how much water is evaporated per unit ton of sludge sent to the drier
4. A package water treatment plant consists of filtration and settling, both designed to remove
solids, but solids of different sizes. Suppose the solids removals of the two processes are as
Settling Tank
Small solids (%)
Large solids(%)
If the two types of solids are each 50% by weight, would it be better to put the filter before the
settling tank in the process train? Why? (Vesilind 3.13 p 108)
5. A slurry containing 20 % by weight of limestone (CaCO3) is processed to separate pure
dry limestone from water. If the feed rate is 200kg/h, how much CaCO3 is produced per
hour? (Ans. 400kg/h
6. Each day 3780 m3 of wastewater is treated in a municipal wastewater treatment plant.
The influent contains 220 ppm of suspended solids. The “clarified water has suspended
solids concentration of 5 ppm. Determine the mass of sludge produced from the clarifier.
7. An Aqueous solution of sodium hydroxide contains 20.0% NaOH by mass. It is desired
to produce an 8.0% NaOH solution by diluting the stream of 20% solution with a steam
of pure water . Calculate the ratio (liter H2O/kg of feed solution) and kg product
solution/kg feed solution). (Ans. 1.5 Liter H2O/Kg feed solution; 2.50 kg product/kg

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