SAQs

Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering these questions.

Classify the following examples of water pollutants using the categories shown in the table below:

  • copper
  • insecticides
  • sand
  • protozoa
  • nitrates
  • bacteria
  • lead
  • silt
  • phosphates
  • faecal matter
  • intestinal worms
Category of water pollutant Examples
Sediments and suspended solids
Organic matter
Biological pollutants
Plant nutrients
Other chemical pollutants

Show answer

The answer is as follows:

Category of water pollutant Examples
Sediments and suspended solids sand, silt
Organic matter faecal matter
Biological pollutants bacteria, protozoa, intestinal worms
Plant nutrients nitrates, phosphates
Other chemical pollutants copper, lead, insecticides

The following are pollution sources. Give two specific pollutants for each source.

A residential area: ………………………………………………

A metal plating plant: ………………………………………………

Agricultural activities: ………………………………………………

An uncontrolled landfill site: ………………………………………………

Urban surface water run-off: ………………………………………………

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There are several possibilities, listed below.

A residential area: human excreta, wastewater containing dissolved and suspended organic matter, suspended inorganic matter, pathogenic micro-organisms
A metal plating plant: cyanides, heavy metals
Agricultural activities: nitrates, phosphates, pesticides
An uncontrolled landfill site: leachate containing dissolved organic matter, inorganic components and heavy metals
Urban surface water run-off: sediment, metals, hydrocarbons, rubber, detergents, litter

Read Case Study 4.1 and then answer the questions that follow.

Case Study 4.1

Mekanisa is a place in the southern part of Addis Ababa where urban agriculture is practised. A group of farmers grow different varieties of vegetables and sell them to people in the city. The farmers use water from the nearest river (the River Kera) for irrigation. They mostly grow leafy vegetables, with two harvests a year.

The Kera River originates a few kilometres from Mekanisa and passes through residential, commercial and industrial areas before reaching Mekanisa. Along its way, human excreta and industrial wastes are indiscriminately discharged into the river. One of the prominent polluters of the river is the city’s biggest slaughterhouse, located at the side of the river. Untreated wastewater from the slaughterhouse is discharged into the river giving a blue-black colour to the water. Farmers like this type of water for irrigation as it helps their crops grow.

One of the authors of this Module undertook research assessing the level of pollution of the river water. The results are shown in Table 4.2.

Table 4.2 Analysis of water from the River Kera.

Parameters FAO* Guideline Concentrations for components in irrigation water (Pescod, 1992) River water
Faecal coliforms <1000 per 100 ml >2500 per 100 ml
Copper 0.2 mg l-1 25.5 mg l–1
Zinc 2.0 mg l-1 56.3 mg l–1
Iron 5.0 mg l-1 71.0 mg l–1
Lead 5.0 mg l-1 19.0 mg l–1
Manganese 0.2 mg l-1 37.0 mg l–1
*FAO is the Food and Agriculture Organization of the United Nations.

  1. What nutrients in the river water do you think benefited the crops grown by the farmers?
  2. State which components in the river water might be harmful to people and give your reasons.
  3. Suggest what should be done regarding the pollution of the River Kera.

Show answer

  1. There are likely to be nitrates and phosphates in the river water which are vital to plant growth.
  2. The presence of a high number of faecal coliformsindicates that the water is unsafe, and also that other micro-organisms, which may be pathogenic, may be present. The concentrations of copper, zinc, iron, lead and manganese in the river water are all greater than the guideline values recommended by the FAO. This implies that they are harmful.
  3. Pollution control at source is required. This would entail treating the sewage, industrial effluents and slaughterhouse wastewaters before they are discharged into the river.

Which of the following statements is false? In each case, explain why it is incorrect.

  1. Latrines should be sited up-slope of a water source so that they don’t get flooded.
  2. For the protection of springs, a fence, a diversion ditch, a watertight concrete box, and a tight-fitting cover are enough.
  3. Farmers should use the minimum amount of fertiliser that is necessary for their crops, and apply it after rain.
  4. Catchment management involves several different activities to ensure that the integrity of a water source is maintained.
  5. To save time water pollution control legislation is best drawn up by one ministry.

Show answer

1 is false. Latrines should be below a water source on sloping ground otherwise seepage from the pit could flow down into the water source.

2 is false. The protection measures are correct but the cover should have a lock.

5 is false. Water use is relevant to several different ministries, all of which should be consulted when legislation is being prepared.

Last modified: Monday, 3 October 2016, 5:23 AM