# Self-Assessment Questions (SAQs) for Study Session 11

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

## SAQ 11.1 (tests Learning Outcome 11.1)

Match the following words to their correct definitions.

Using the following two lists, match each numbered item with the correct letter.

2. symbiotic relationship

3. waste stabilisation ponds

4. retention time

5. facultative ponds

6. maturation ponds

7. impervious material

8. diffusion

• a.the process by which something moves naturally from a region of high concentration to one of low concentration

• b.material that does not let anything pass through it

• c.a system of ponds to treat wastewater using sunlight and wind

• d.ponds that have oxygen at the top and are without oxygen at the bottom

• e.ponds in which the pathogenic bacteria and viruses in an effluent are eliminated

• f.the time that the effluent spends in an environment

• g.a relationship where two parties live together for mutual benefit

• h.the breaking down of complex materials by micro-organisms

• 1 = h
• 2 = g
• 3 = c
• 4 = f
• 5 = d
• 6 = e
• 7 = b
• 8 = a

## SAQ 11.2 (tests Learning Outcome 11.2)

• a.Zewedu, a pensioner, asks you to help him with ideas on how to reduce his water bill. He does not want to spend money to change his old flush system. Are there ways he can use less water?
• b.Adina and her husband Abenet live in a flat in Dolo Odo. Abenet has bought an aerator fitting for their kitchen tap. If the water use through their kitchen tap is 65 litres a day, what is the maximum saving in water use that they can expect?

• a.Yes, there are several ways Zewedu can save water and hence reduce his water bill. He can put one or two 1-litre bottles of sand in his toilet cistern to reduce the amount of water used per flush. He can also take other steps such as fixing leaking taps; not leaving the tap on when brushing his teeth or shaving; using rainwater for purposes other than human consumption; using greywater for watering the plants, remembering to do it early in the morning or late in the evening to minimise any loss of water by evaporation.
• b.From Table 11.1 we know that the aerator nozzles can give up to 20% savings in water use. Since the current water use from the tap which is to have the nozzle fitted is 65 litres a day, a saving of (20 / 100) ´ 65 = 13 litres a day can be expected.

## SAQ 11.3 (tests Learning Outcome 11.3)

Select the false statement from those below, and give the reason why it is false.

• A.Rainwater can be contaminated due to pollutants in the air.
• B.The roofing material can also add pollutants to the rainwater that is collected from a roof.
• C.It is important to let the first five litres of rainwater from roofs go into the drain.
• D.Rainwater, after sand filtration, is safe for humans to drink.
• E.Untreated rainwater can be used for any purpose that does not involve ingestion by humans.

D is false. After sand filtration there may still be pathogens in the rainwater, and these have to be eliminated to make the water safe for humans to drink.

## SAQ 11.4 (tests Learning Outcome 11.4)

The five statements below are on waste stabilisation ponds. Select the statements that are false and give the reasons why they are so.

• A.Bacteria and algae are both present in the ponds.
• B.The algae in the ponds survive by eating the bacteria.
• C.The ponds need a lot of land but their operation and maintenance costs are low.
• D.The only safety measure needed is to ensure that the treated effluent is used only for non-food crops or for crops that have to be cooked before consumption.
• E.In terms of food production, the only benefit of waste stabilisation ponds is that the treated water can be used for irrigation.