Built Water Systems

Question 1

What pollutants do we typically want to remove from drinking water?

Answer 1

• Debris and common rubbish, solid stuff, branches, etc.
• Natural organic and inorganic impurities: pathogens, organic substances from decomposing biological material, human and animal waste, minerals, heavy metals, fluoride, arsenic, nitrates….
• Sand and clay
• Pesticides and spill from agriculture
• Man-made pollution for instance from leaks to the ground or emissions to water recipient

Question 2

Key aspects of a water distribution system

Answer 2

-Water distribution occurs in a pressurised system – thus sensitive to damage and leaks

-The distribution system should maintain the quality of the water (no stagnant zones allowing micro-organisms to grow, no intrusion of contaminants, etc.)

-Should be able to distribute relatively large amounts – water is heavy; pumping could be expensive

Question 3

Purpose of water towers in a distribution system

Answer 3

1) Serves as reservoir for water to even out demand fluctuations
2) Keeps stable pressure on local distribution system

Question 4

Purpose of pumps in a distribution system

Answer 4

1) Move water and build up pressure when no water tower
2) Work in parallel to facilitate uneven load and to keep system running if one fails (redundancy)

Question 5

What are the things to treat in wastewater when debris and large solids are removed?

Answer 5

• High organic fraction that cause oxygen depletion in recipient water bodies if not treated
• Nutrients that cause eutrophication
• Harmful substances that influence aquatic life when distributed in the ecosystems and ultimately human health
• Substances that cause odour and reduce the aesthetics
• Turbidity in water could harm aquatic life

Question 6

What are the main components of a generic/simplified municipal water system?

Answer 6

1) Water supply/extraction and treatment

2) Distribution –pressurised

3) Use/the service

4) Collection –normal pressure

5) Discharge/treatment

6) Reuse/recycling

Question 7

What are the main components of municipal waste systems?

Answer 7

1) residential source of waste
2) drop off/redemption centers
3) materials recovery facilities and/or transfer stations
4) waste transformation facility
5) landfill

Question 8

What are the key purposes of municipal waste systems?

Answer 8

1) public health and safety/sanitation
2) material reuse
3) composting
4) energy recovery
5) avoiding environmental pollution
6) climate change mitigation

Question 9

Why do we treat wastewater?

Answer 9

• Pathogens
  – Disease and outbreakes
• Organic matter, BOD
  – Oxygen depletion
• Nutrients, N & P
  – Eutropication
  – Oxygen depletion

Question 10

What are the key steps in sewage treatment (wastewater to river/lake outlet)

Answer 10

Mechanical treatments:
1) screening/grit removal via grit tanks: anything non-biodegradable/useful in sludge

2) primary treatment: gravity-based sedimentation tanks. Creates primary sludge

Biological treatments
1) Secondary reactors: activated sludge (microorganisms)
a. Nitrification (ammonia + oxygen –> Nitrate)
b. Denitrification (Nitrate + denitrifying anaerobic bacteria
–> N2)
c. Neutralizing other organics with microorganisms –> CO2 and H20
2) Secondary clarifiers: activated sludge is removed through sedimentation. Some is reused for its microorganisms, some is sent to treatment.

Chemical treatments
1) Flocculation and coagulation: FeCl or aluminum is added to clump remaining molecules (like phosphorus compounds) together
2) Sedimentation: clumps are separated. This chemical sludge can be sent back to primary treatment

Polishing
1) Multimedia filters (e.g. sand filters, anthracite)
2) Disinfection with chlorine compounds
3) Dechlorination

Cleaned water is released into waterways

Question 11

How does nitrification work in biological treatment of wastewater?

Answer 11

Ammonium from wastewater is exposed to nitrifying bacteria in activated sludge, as well as oxygen, and forms nitrate.

Question 12

How does denitrification work in the biological treatment of wastewater?

Answer 12

Nitrate is exposed to denitrifying bacteria from activated sludge in the absence of oxygen (anaerobic) and turns into N2, which is released.

Question 13

What are the three types of sludge?

Answer 13

Primary sludge, waste activated sludge, and chemical sludge

Question 14

What are the two (broad) types of treatments for sludge?

Answer 14

Thickening (for fertilizer) and digesting (for biogas)

Question 15

What are the steps of sludge treatment?

Answer 15

1. Primary sludge thickening with sedimentation (primary/chemical and activated are in separate chambers)
2. Mechanical sludge thickening (also separate for primary and secondary) –> polymer is added and sludge and water are separated via rotating drum thickener
3. Digestion (all together now!) - some organic material is broken down via anaerobic digestion.
4. Methane and CO2 from the anaerobic digestion are used as biogas to power vehicles or homes, provide heat back to the plant, or are flared.
5. Sludge dewatering: digested sludge is stored and then dewatered by adding a polymer to further separate sludge and water. Dewatering happens by pressing, centrifugation, or other methods.
6. High quality dried sludge is utilized for fertilizer in agriculture or landscaping

Question 16

What are the steps to treat groundwater?

Answer 16

*Aeration to remove gases, such as VOCs and smelly sulphide (H2S), odours, cause oxidation of iron (Fe) and manganese (Mn) (cause brownish colours), to make them possible to separate from the water as solid particles
* Softening (de-mineralisation) in case of need
* Disinfection (from potential pathogens)

Question 17

What are the steps to treat surface water?

Answer 17

• Screening from debris, particles, leaves, etc.
• Coagulation & flocculation to remove suspended solids (see section on solid-liquid separation)
• Sedimentation
• Filtration (typically sand filters and sometimes activated carbon adsorption)
• Disinfection

Question 18

Types of disinfection from pathogens?

Answer 18

• Chlorine or chlorine dioxide (low concentrations that are not supposed(!) to be harmful for human consumption)
• Bromine or iodine (similar to chlorine)
• Ozone (reactive molecule)
• UV rays (high energy, kill pathogens)

Question 19

What is desalination and what are the two common types of performing it?

Answer 19

Desalination is the process of separating out dissolved salts from seawater to achieve water of useful quality. This typically happens through evaporation or membrane systems.