Self-Assessment Questions (SAQs) for Study Session 6
Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering these questions.
SAQ 6.1 (tests Learning Outcome 6.1)
Match the following words to their correct definitions.
Using the following two lists, match each numbered item with the correct letter.
drainfield
Sludge Gulper
anaerobic ponds
septic tank
facultative ponds
comminutors
Vacutug
soakaway
maturation ponds
retention time
desludging
sustainable drainage systems
faecal sludge management
a.a watertight tank installed underground that collects sewage in areas where there are no sewers
b.ponds that are used at the end of a waste stabilisation system to reduce the level of pathogens in the wastewater
c.drainage systems that encourage infiltration of rainwater without special equipment
d.a network of perforated pipes through which the outflow from a septic tank goes into the ground
e.a small vacuum truck designed for pit latrine emptying in crowded areas
f.ponds that have oxygen at the top and no oxygen at the bottom
g.a manually operated pump for desludging pit latrines
h.first stage of waste stabilisation pond system treating highly polluted wastewater
i.an item of equipment that is used to cut up paper and rags in wastewater flowing into a treatment plant
j.combined processes for safely disposing of sludge from pit latrines and septic tanks
k.the process of removing sludge from a place
l.a pit into which the wastewater from a septic tank goes for disposal
m.the time that is spent in a given environment
- 1 = d
- 2 = g
- 3 = h
- 4 = a
- 5 = f
- 6 = i
- 7 = e
- 8 = l
- 9 = b
- 10 = m
- 11 = k
- 12 = c
- 13 = j
SAQ 6.2 (tests Learning Outcome 6.2)
Outline the main advantages and disadvantages of vacuum trucks, the Vacutug and the Sludge Gulper as options for pit emptying.
Answer
Vacuum trucks are quick and efficient, but because they are large vehicles are not suitable in some urban areas where roads and passageways are too narrow for them. Vacutugs are smaller and therefore can access places that trucks cannot reach. In places with very limited space a Sludge Gulper or similar hand-operated pump may be a better option. These are very simple tools, but it may be difficult to ensure the safety of the operator and effective containment of sludge throughout the process.
SAQ 6.3 (tests Learning Outcome 6.3)
- a.List the points where sludge is produced in the different treatment processes described in this study session.
- b.State briefly the options for treatment and reuse of the sludge.
Answer
- a.Sludge is found in pit latrines, septic tanks, anaerobic ponds in waste stabilisation pond systems, and in primary and secondary sedimentation tanks in mechanical-biological treatment plants.
- b.Some options for treatment and reuse are:
- direct application onto land as a soil conditioner after two years of storage
- drying out the sludge
- composting the sludge with vegetable matter
- anaerobically digesting the sludge to produce biogas.
SAQ 6.4 (tests Learning Outcome 6.4)
The table below has several statements applicable to different wastewater treatment systems. Allocate each of them to one of the following wastewater treatment options:
- Septic tank
- Waste stabilisation ponds
- Reed beds
- Mechanical-biological treatment.
| Is expensive due to tanks and equipment involved | |
| Can be used to treat wastewaters containing pesticides | |
| Relies on sunlight and wind for treatment | |
| Need a lot of space | |
| Requires skilled personnel for operation | |
| Used for houses with water-flushed toilets in areas without sewers | |
| The area around the roots and rhizomes contains aerobic and anaerobic bacteria | |
| A vacuum truck is used to suck sludge out of it | |
| Consists of many different stages of treatment | |
| Partially treated wastewater goes to a soakaway or drainfield | |
| A symbiotic relationship exists between the bacteria and algae in this system | |
| Use plants for treatment of sewage |
Answer
| Is expensive due to tanks and equipment involved | Mechanical-biological treatment |
| Can be used to treat wastewaters containing pesticides | Reed beds |
| Relies on sunlight and wind for treatment | Waste stabilisation ponds |
| Need a lot of space | Waste stabilisation ponds |
| Requires skilled personnel for operation | Mechanical-biological treatment |
| Used for houses with water-flushed toilets in areas without sewers | Septic tank |
| The area around the roots and rhizomes contains aerobic and anaerobic bacteria | Reed beds |
| A vacuum truck is used to suck sludge out of it | Septic tank |
| Consists of many different stages of treatment | Mechanical-biological treatment |
| Partially treated wastewater goes to a soakaway or drainfield | Septic tank |
| A symbiotic relationship exists between the bacteria and algae in this system | Waste stabilisation ponds |
| Use plants for treatment of sewage | Reed beds |
SAQ 6.5 (tests Learning Outcome 6.5)
You are walking in an alley in an unsewered part of town when you are nearly drenched by washwaters from clothes washing thrown over a fence. What would you do to advise the householder about proper disposal of their wastewater?
Answer
After recovering from my shock, I would approach the house where the water came from and gently explain to the person who threw the water that it is not advisable to dispose of such waters (sullage) by throwing it away as they did because:
- an innocent person could get soaked with dirty water
- the washwaters on the ground could become a breeding place for mosquitoes, and flies and rats could also be attracted to it as a water source
- the washwaters would make the alleyway wet and unpleasant.
I would suggest that the best way to dispose of the sullage would be to pour it into a hole that has had gravel or sand put into it.
SAQ 6.6 (tests Learning Outcome 6.6)
Name three ways in which the risk of flooding from stormwater can be reduced.
Answer
Flood risk can be reduced by
- building storm drains that are large enough to cope with large volumes of water
- constructing ponds that will temporarily hold the stormwater
- using broken stones and gravel rather than solid concrete in roadside ditches and other places where rainwater builds up so that water can infiltrate into the ground.
Summary of Study Session 6