Question

1)Ghana Sewerage Company limited has employed you as a quality control
supervisor in the laboratory. Domestic waste water is brought to the company for
treatment. Before waste water treatment the following data was given to you.
 Weight of a dish = 47.6212
 100mL of sample is placed in the dish and evaporated. New weight of dish
and dry soils = 48.5432g
 The dish is placed in a 550◦C furnace, then cooled. New weight =48.4000g
Fine the
a. Total solids
b. Fixed solids
c. Total volatile solids

2)

a. pH is one of the most important controlling factors for treatment and
chemical analysis of water and wastewater explain.
b. As a water resource engineer for Ghana Water Company why is turbidity an
important in filtration and disinfection processes?
c. Groundwater usually has higher dissolved solids and surface water usually
has higher suspended solids explain.

3)

The current regulation state that all fecal liquid waste must be treated before
discharging into the sea or lagoon. You community has contacted you as a level
400 second semester civil engineering student to design a waste stabilization pond for the community to treat fecal liquid waste in the community. make a sketch of waste stabilization pond and describe to the community the process of treatment

Answer 1

1.) SOLUTION

a) Total solids : All solids are calculated by evaporating the sample and measuring the residue. Hence , here

Total solids = 48.5432 - 47.6212

=0.922gm/100ml = 9.22*10^(-3) mg/l

b) Fixed solids= (48.5432- 48.4000)gm/100ml. = 1.423*10^(-3) mg/l

c) Total volatile solids = (9.22-1.423)*10^(-3)

= 7.797*10^(-3) mg/l

2.) SOLUTION

a) pH is measured by potentiometer in which potential exerted by H+ is measured.

•Permissible value of pH in water is 6.5 to 8.5 and beyond that the water is being rejected

pH=7 indicate neutral water

pH<7 indicate acidic water and

pH>7 indicate basic or alkaline water

•It can also be measured by colour indicators and indicators used are methyl orange and phenolphthalein

•Acidic water causes corrosion and alkaline water causes incrustation of pipe

•Alkaline water causes difficulty in chlorination because at pH>8 effectiveness of disinfectant decrease

•Determination of pH assists in the control of corrosion, determination of proper chemical dose and control of disinfection

•Hence, pH is one of the most important controlling factor for treatment and chemical analysis of water and waste water.

b) Turbidity plays a major role in the process of filtration and disinfection , As-

• Disinfection of turbid water is difficult because yhe suspended solids may partially shield the organisms from disinfectant

• In natural water bodies turbidity interfares with the light penetration and hence with the photosynthetic reactions (which gives oxygen to water)

• In case of filtration if turbidity is not removed in the process of sedimentation then it will decrease the efficiency of filtration even it may chock the filter media

• Turbidity increases the amount of disinfectant needed

Hence there should be a proper control on turbidity of water.

c) In case of ground water , the water available below ground is in contact with minerals like iron , manganese etc. Which are going to be dissolved in the water and all the suspended solids in the water are just removed when water percolate downward under the effect of gravity. These dissolved solids can be removed by the process of aeration.

• On the other hand in case of surface water as water flow in the river it causes erosion of soil and these soil particles remains in suspension in the river . Along with these soil particles many other things like debris, organic matter etc remains in suspension in case of surface water.

3.) SOLUTION

Waste stabilising pond is also known as oxidation pond and it is briefly described below: