Lecture 11: Wastewater treatment

Question 1

What actually is water quality?

Answer 1

expresses the suitability of water for various uses or processes: drinking water; irrigation water…

Question 2

What is Dissolved oxygen content (DO)

Answer 2

Amount of dissolved oxygen available in the water to be used by animals and micro-organisms

Question 3

What is Biological oxygen demand (BOD)?

Answer 3

Amount of dissolved oxygen consumed by aquatic microorganisms

Question 4

What is conductivity?

Answer 4

Conductivity is the measure of the ease at which an electric charge or heat can pass through a material. How easily water flows through something. Mostly different aquifers in this case.

Question 5

What does turbidity do?

Answer 5

It reduces the transmission of light into water

Question 6

How does waste lead to development pressure?

Answer 6

Relocation of people into ‘mega-cities’ increases uses of energy and generation of waste. Increases on the world population causes an increase on industrial and agricultural activities that generate pollution.

Question 7

Difference between chemical pollutant and contaminant?

Answer 7

Chemical pollutant: substance that has a harmful effect on the health, survival or activities of humans/other organisms

Contaminant: substance that cause deviations from the normal composition of an environment. Are not classified as pollutants unless they have a harmful effect

Question 8

Different industries generate different pollutants. Food processing plants generate … and paper mills generate …

Answer 8

Food processing plants: high BOD
Paper mills: high BOD and toxic compounds

Question 9

Definition, advtanges of Phytoremediation

Answer 9

Plants live in conjunction w/ bacteria. They transport and store harmful chemicals.

Advantages:
* Root system absorbs substances efficiently
* Plant diversity tolerates high levels of pollutants

Question 10

Definition, advtanges and disadvantages of phytoextraction

Answer 10

Uptake of contaminants by plant roots, movement to above ground parts of the plant

Advantages:
* Cost effective
* Contaminant permanently removed
* Amount of waste decreased by 95%

Disadvantages:
* Metals released in the rhizosphere

Question 11

Definition, advtanges and disadvantages of phytostabilisation

Answer 11

Immobilisation of contaminants in soils through absorbing and accumulating by the roots

Advantages:
* No hazardous waste
* Rapid and effective

Disadvantages:
* Contaminants remain in situ
* Extensive fertilisation is necessary
* Need for monitoring

Question 12

Definition, advantanges and disadvantages of phytotransformation

Answer 12

Breakdown of contaminants by plants

Advantages:
* Environmentally friendly
* Cost free

Disadvantages:
* Takes time to set up (multi-seasonal)
* Contaminants can re-enter, i. e. through animals that eat the plants

Question 13

Definition, advtanges and disadvantages of phytovotalisation

Answer 13

Plants take up contaminants from water, transpiring them after transformation

Advantages:
* Contaminants changed into non-harmful substances

Disadvantages:
* Released contaminants likely to recycle by precipitation, redepositing them into lakes and oceans

Question 14

Why would we clean wastewater?

Answer 14

Contributes to eutrophication (more nutrients)
 High oxygen demand via organics
 High nitrogen and phosphorous content
 Low dissolved oxygen

› Carries pathogenic organisms

Question 15

What’s the con with normal wastewater treatment plants?

Answer 15

• they are expensive
• require highly trained operators onsite all of the time
• can be difficult to operate because of ecological changes in microbes.

Question 16

What’s a better alternative that is cheaper?

Answer 16

Natural wetlands –> have been used to treat waste in the past. Typically occur in low lying areas that are inundated by surface and groundwater. Known nutrient sinks and transformers.

Question 17

Explain the classification of soil filters: difference between unplanted filters and planted filters

Answer 17

Unplanted –> subsurface biofilters, percolation beds, infiltration beds

Planted –> constructed wetlands

Question 18

What are prerequisites for wetlands?

Answer 18

› Wastewater not too toxic for bacteria and plants
› Sufficient incident light to allow photosynthesis
› Temperature not too low
› Adequate quantities of nutrients to support growth
› Detention time long enough

Question 19

Pros of a natural wetland

Answer 19

› Site location flexibility
(compared to natural wetlands)
› Simple operation and maintenance
› Can be integrated attractively into landscaping

Question 20

Disadvantages/challenges of the natural wetlands

Answer 20

› Mosquitos (in Free Water
Surface Systems)
› Start-up problems
› Space requirement
› Variable performance possible

Question 21

Constructed wetlands can be based on … characteristics and …. characteristics

Answer 21

water flow characteristics (surface flow or subsurface flow?)

plant species characteristics (floating plants, submerged plants, emerged plants)

Question 22

Role of aquatic plants in free water surface constructed wetlands

Answer 22

• nutrient uptake
• heavy metal accumulation in plant tissue
• habitat for wildlife
• aesthetics

Question 23

Mosquitos can bread in free water flow constructed wetlands. Solutions?

Answer 23

There is less mosquito breeding if the biodiversity and complexity of food web is high
* no above ground flow
* pretreatment to reduce organic loading rate
* temporary drying of the beds will eradicate larvae