Question

You are the water supply manager for an organization that is contracted to supply water to a village with
population 3500 people. The water sources is a river and a pump is used to fill a 10000L tank. The turbidity
of the water is 4.1 NTU, therefore the manger has to determine the most appropriate amounts (mass) and
concentration of chlorine based water treatment chemical and the available chemical is HTH with 60%
chlorine
a) Work out how many grams of HTH you will require to add to one litre of water to a 1% chlorine
HTH solution.
b) You have four buckets, each containing 15 litres of water and added the following volumes of 1%
chlorine HTH solution.
1.0ml to bucket 1
1.5ml to bucket 2
2.5ml to bucket 3
4.0 ml to bucket 4
You wait for 30 minutes and measure the amount of residual chlorine that is in the water and get the
following results
0.0mg/l in bucket 1
0.13mg/l in bucket 2
0.35 mg/l in bucket 3
0.68 mg/l in bucket 4
Based on the Environmental Engineering judgement select the most appropriate chlorine dosage and
bucket and calculate the amount of 1% chorine HTH you will apply to the 10000L tank?
c. How much water will you treat per day if the water consumption is 90l/c/day and distribution losses
are 20%?
d. How much HTH in grams that must be applied in the 10000L tank per month?
e. Calculate the dosage in grams per minute of water purifying chemical, containing 20% (chlorine
based) active ingredients by mass, that will be required to treat a water supply system for a village
of 1500 people, given that water consumption per capita is 80L/day. The pumps and treatment
system are operated for 8 hours per day, required initial maximum chlorine concentration in treated
water at the plant is 4mg/L in the distribution network is 2mg/L. The water loses during distribution
are 15%.
f. After checking the chlorine levels in the village, one area out of 5 was found to have less than 2mg/L
of chlorine, what can you do to increase the chlorine levels for this particular area?

Answer 1