Questions 2

Question 1

1. Describe the principle of TSAAD and explain advantages compared to anaerobic
   degradation in a typical landfill containing organic waste.

Answer 1

The acidogenic stage is promoted and utilised as a treatment. Food waste -> acid fermentation (big cell) -> strong leachate -> methane production (small cell).
Recirculation within the steps.

Advantages: Reduced methane emissions during acidogenic degradation. Controls methane formation. Immobilization of hazardous compounds. Saves space.

Question 2

2. Describe briefly the different degradation phases occurring in a landfill containing
   biodegradable waste.

Answer 2

Aerobic degradation – microorganism uses oxygen to decompose the waste. Heat is released.
Acidogenesis – hydrolysed compounds first converted into organic acids and alcohols and then even smaller compounds. pH decreases. A lot of leachate is formed.
Methanogenesis – the organic acids converted into methane and carbon dioxide.

Question 3

3. The aerobic, acidogenic and methanogenic degradation states are three characteristic degradation states of landfilled organic waste that are controlled by biological degradation processes. How do they affect leachate quantity and quality?

Answer 3

Aerobic – Low quantity. Quality: High Cl. Rather high sulfate. Neutral pH. Heavily polluted.

Acidogenic – High quantity. Quality: Metal emissions (Zn, Fe). Low pH. High ammonium and sufate. High volatile fatty acids. High protein/organic matter percentage.

Methanogenic – Low quantity, could be more quantity due to saturated waste. Quality: low metal emission. High HCO3-. Low redox potential and neutral pH.

Question 4

4. Discuss advantages of using ratios of variables e. g. BOD/COD, N/P or CH4/CO2 compared to using each variable separately. When would you use what (ratio or single)?

Answer 4

BOD/COD – which phase of the landfill is in. Indicates the amount of organic matter that is biologically degradable.
N/P – seeing which nutrient that is dominating. One nutrient might be limiting. Indicates which stage of degradation the landfill is in, mobilization of phosphorus low in methanogenic phase.
The ratio makes it possible to compare different waters. Use a single variable when you want to know the concentration for eg treatment.

Question 5

5. You are responsible for the operation of a landfill receiving large amounts of easily degradable organic material. If you want to avoid the acidogenic degradation phase, what strategy can be used to achieve this?

Answer 5

Pre-treated layer in the bottom that contains microorganisms. The microorganisms take care of the new leachate which means that there is a quicker transformation to the methanogenic phase. Decreases the BOD.

Question 6

6. Argue for separated treatment of municipal wastewater and landfill leachate.

Answer 6

The effects are often poor. Wastewater has stronger variations in flow and quality due to depending on seasonality, precipitation and irrigation. Leachate has higher contents of COD, AOX, NH4, metals (Fe, Mn) and salts. Lower amounts of P and particles. The quality also depends on degradation phases.

Question 7

7. Why is it important to make analyses immediately after sampling?

Answer 7

There can be reactions in the leachate that changes the composition. Oxidation of the leachate. Change of pH, redox and suspended solids.

Question 8

8. In what ways can nitrogen be reduced in leachates?

Answer 8

• Incorporation into the biomass (area and time dependent)
• Oxidation of NH4+ to NO3- with reaction to N2 (demand of energy, reducing agent, time, area, sensitive micro organisms)
• Anammox = anaerobic ammonium oxidation, carried out by bacteria (low cost but not used that much)

Question 9

9. A natural treatment system consists of three active parts. Name them and briefly describe the function of each part.

Answer 9

Soil particles that filtrate and cause retention.
Soil organisms that cause biodegradation (C) and transformation (N)
Plants: incorporation, filtration, carbon source, surfaces for bacteria, wind protection, O2 source below water surface due to photosynthesis etc

Question 10

10. What are the main pathways for carbon during aerobic and anaerobic waste degradation?

Answer 10

Water or gas emissions.
Aerobic degradation -> gas emissions.
Anaerobic degradation -> water emissions, strong leachate.

Question 11

11. Explain why landfills may emit material?

Answer 11

There are reactions in the waste. Diffusion etc. There is a concentration gradient between the landfill and the environment. If the landfill is not mechanically stable (landslides etc) there can also be emitted materials.

Question 12

12. Why does the leaching of lead decrease when the degradation state of a landfill shift from acidogenic to methanogenic conditions?

Answer 12

Because the pH rises, causing the lead to become immobilized.

Question 13

13. The BOD/COD ratio of a leachate is often used to characterize the degradation state of a landfill:
    - What do the abbreviations stand for?
    - What is the relevance of a quotient in the range of 0.05-0.1 with regard to the degradation processes in landfills and the consequences with regard to leachate treatment?

Answer 13

Biological oxygen demand. Chemical oxygen demand. The biochemical oxygen demand (BOD) represents the amount of dissolved oxygen (DO) consumed by biological organisms when they decompose organic matter in water. The chemical oxygen demand (COD) is the amount of oxygen consumed when the water sample is chemically oxidised.
A value of below 0.4 says that the degradation has passed the acidogenic stage and gone into the methanogenic phase. There will be less metal emissions in the leachate.

Question 14

14. Name and briefly describe three decisive (important) factors for the amount of leachate that can be expected from a landfill. When in the life-time of a landfill can you expect most leachate?

Answer 14

The climate. How much water that comes in. Rain.
The landfill geometry (if it is deep in the ground -> more water entering)
How the groundwater pressure is (discharge area -> higher pressure -> more water entering)
The technical measures (how it’s designed).
The most leachate comes when the waste is saturated, in the middle or towards the end of a landfill.

Question 15

15. During aerobic degradation the share of the substrate that goes into new biomass is up to about 40%, yielding a BOD/COD of 0.6. If you see a BOD/COD of 0.1, what can that mean?

Answer 15

A low degradable substrate or that something hinders the degradation (e.g toxins that kill the bacteria and reduce BOD, agents that affect the COD and increase it).

Question 16

16. Why does aerobic pre-treatment before landfilling promote a faster establishment of methanogenisis?

Answer 16

Because there are microorganisms in the waste that can take care of the leachate and cause a faster transition to methanogenesis.

Question 17

17. Why is it that the gas permeability in a landfill is higher in the horizontal direction than in the vertical?

Answer 17

There are layers of waste due to compaction and the pressure of the waste. There is overlapping of the layers -> The vertical permeability is not very good. It is easier for gas and leachate to go horizontally.

Question 18

18. Name two different methods for dividing a sample into representative sub samples. Explain one of them.

Answer 18

Riffle splitter
Quartering

Question 19

19. What constituents/pollutants occur typically in landfill leachate and have to be treated?
    Nitrogen/ammonium?
    Suspended particles?
    Fe, Mn?
    Salts?
    Phosphorus
    COD?

Answer 19

nitrogen/ammonium -YES
suspended solids (particles) – NO (due to filter)
iron and manganese – YES (compared to waste water)
salts - YES
phosphorous – NO
COD - YES

Question 20

22. LFG is often assumed to contain 50% CH4 and 50% CO2. * Is this a reasonable assumption?
    * Will it change over time?

Answer 20

Undiluted biogas can have approximately 50% CH4 and 50% CO2. However, collected landfill gas is diluted with air and therefore have lower concentrations of CH4 and CO2. It also depends on the time of collection as the CO2 is at its highest of around 70% in the acidogenic phase. However, after the landfill is stable the values are approximately 50-50. The composition of the waste can change the LFG, a higher fat level gives more CH4.

Question 21

24. Why are clays suitable as liner materials in landfill constructions?

Answer 21

Because it has very low permeability. It also gets very compact.

Question 22

25. What is CEC and why is it important for a contaminant transport in soil?

Answer 22

Cation exchange capacity. Most metal are cations (+). The soil/clay is negative and can therefore immobilize the contaminants.

Question 23

26. Explain how the hydraulic gradient influences contaminant transport in soil. What happens to the contaminant spread when the hydraulic gradient is equal to 0?

Answer 23

The hydraulic gradient says how much flow there is. If it is equal to 0 there is no water the transport is not through flow but rather diffusion of the contaminants. The velocity of the water is zero.

Question 24

27. Explain why landfill top covers are often made of material with very low permeability.
    How does it affect the waste degradation in the landfill?
    Discuss the sustainability of such covers for landfill management in a long-term perspective.

Answer 24

To prevent gas from leaking and water from infiltrating.
It makes the waste degradation of the landfill take much longer time. Therefore, you should not cap the landfill too soon.
The liner has low permeability – no water comes in. There will be a mumification which can cause the liner to break -> the processes start again even though there is no control of the landfill anymore.
When you extract LFG you also take out all the existing water from the landfill which contributes to the mumification.

Question 25

28. Why do you need a highly permeable drainage layer?

Answer 25

To drain the cover layer. However, you want some water to prevent desiccation of the liner. If you have a higher permeable drainage layer you don’t need a more dense liner. You don’t want a high hydraulic load on the liner. The distance between the pipes and the slope also impacts how much water goes through the liner. You don’t want air in the drainage layer to prevent plant roots from forming. The drainage layer reduces leachate generation by up to 75%.

Question 26

29. Name three different barrier materials that can be used for sealing of bottom and/or the surface of a landfill. Describe advantages and disadvantages of the chosen materials.

Answer 26

Bentonite/textile liners – low permeability, low weight. Disadvantage that cracks form during drying. Settlements can deform the liner. The overlap between sheets is a weak spot. Clay minerals – good to use to reduce permeability. It has plasticity which helps during landfill settling. However, it needs to be easily accessible and homogenous – could be a problem. There can be CEC which decreases the permeability of the clay. Concentrated organic compounds also decreases the permeability. Disadvantage is that cracks can form during freezing or drying. Geomembranes – can be completely impermeable. Weaknesses and disadvantages are risk of puncture, the durability and the quality of the seams, resistance to chemicals and general durability (ageing problems)

Question 27

30. How would you design a cover construction for a municipal landfill? Describe the different layers and their function.

Answer 27

Vegetation layer – visual improvement. Erosion control. Increase evaporation. Protection layer – water storage. Protection from roots and animals. Protect underlaying layers from desiccation and freezing. Drainage layer – drain cover layer. Prevent desiccation of liner. Reduce leachate generation. Barrier layer/liner – prevent gas leakage and water infiltration. Gas drainage/foundation layer – foundation for cover. Gas drainage. Shapes the landfill.

Question 28

31. How would you design a bottom construction for a municipal landfill? Describe the different layers and their function.

Answer 28

Drainage layer – thicker than 0.5 m. To get rid of leachate. Artificial sealing liner – required in all landfill classes. Can be geomembrane for example. For hazardous landfills you double the sealing and liner system. Usually surrounded by sand and geotextile. Geological barrier – natural or artificial. Thickness and permeability of the layer depends on if its natural or artificial and the landfill class. To keep waste and leachate inside the landfill and to keep out groundwater etc.

Question 29

32. What is landfill aftercare?

Answer 29

The time between landfill operation and a restored site where certain monitoring and treatments need to be done. The time period under which aftercare is done is unclear, it is up to the operators.

Question 30

33. What is meant by performance-based aftercare?

Answer 30

Through monitoring you see how much aftercare is needed, which will change over time until you reach a stable environment. You will go from active aftercare to passive aftercare and then hand the custodial care over to the government. If you seal the waste too soon the degrading processes will stop and the aftercare cannot decrease. There is no specific timescale for this process – it is site specific.

Question 31

34. Discuss sustainability with regard to landfill aftercare.

Answer 31

Operators give away responsibility to the government after some time – otherwise no one would ever want a landfill. Come countries only do aftercare for 30 years while others do it for 100 years. The definition of sustainability is that future generations shouldn’t be affected by our actions. In a strict interpretation, no aftercare would then be done after 30-50 years. However at this point there are often still environmental impacts, LFG for example is produced for a long time. If you want no environmental impacts at that time – a lot of money has to be spent on cleaning the waste.

Question 32

35. Name two landfill post-closure activities.

Answer 32

Old landfills can be used as parks or gold courses.

Question 33

36. How may landfills affect the global warming?

Answer 33

Emissions of landfill gas - especially methane emissions have an impact on the global warming. This happens on a badly driven landfill. If you have a good system, methane can be oxidised even in the surrounding air. You remover organic material from the cycle -> less global warming... Low air pressure -> more emissions