Leachate, degradation phases Flashcards
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?
Aerobic phase: high degradation rate leads to compaction and high temperatures lead to
drought, thus some leachate will be pressed out of the material, but in small amounts with
high concentrations.
- Acidogenic phase → high organic content (BOD, COD; ratio BOD/COD > 0.4), low pH and
alkalinity, high concentration of most metals. Leachate volumes are reduced slightly by
hydrolysis but are much higher than during aerobic degradation.
- Methanogenic phase → low organic content (BOD, COD; ratio BOD/COD < 0.2),
immobilization of metals in the waste matrix, Water loss in gas yields similar leachate
volumes as during acidogenic degradation.
How will a biological treatment of biological degradable waste before landfilling affect
the leachate quality?
Lower concentrations of organic matter, nutrients in the leachate, direct start in the
methanogenic phase after landfilling, see methanogenic conditions above.
How will a grinding (particle size reduction) affect leachate quality?
Compaction of fresh organic rich waste → can delay the beginning of methanogenic
degradation (risk for longer acid phase)
How will leachate recycling (pumping back to the landfill) affect the leachate quality?
Intensification of whatever process is occurring in the waste (since all processes involves
water), homogenization of processes over the landfill body, including humidity, salt
concentration and temperature. All these factors can influence leachate quality differently
depending on conditions. E g a cold temperature may slow down degradation and promote a
different ecology than warm water.
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?
- Biological/chemical oxygen demand
- A value between 0.05-0.1 shows methanogenic degradation. Or basically hardly degradable organic matter, moderate-low metal content, etc
→ difficult with biological treatment, poor effects if co-treatment with municipal solid
waste water, etc whatever seems reasonable.
. Name four decisive factors for the amount of leachate that can be expected from a
landfill. Describe how each factor affects the leachate quantity.
When in the life-time of a landfill can you expect most leachate?
- Climate
- Landfill geometry
- Cover materials and design
- Waste properties (humidity, permeability)
- Degradation state
- Bottom liner & collection systems
Shortly after closure (saturation ↔ cover) has most leachate.
Name three important factors that affect the composition of landfill leachate (content and
concentration) and describe the influence of each factor.
- Waste type and composition
- Landfill environment
- Landfill operation/management
- Landfill age and leaching ratio
- Sampling
Basic considerations for the choice of leachate treatment:
Flexibility with regard to leachate quantity and quality
* Minimization of all rest products
▪ avoid to add extra substances like flocculants, precipitants
* Compliance with current and future regulations (e.g. discharge limits)
* Conformance and compatibility with secondary or extensive treatment steps
* Technical and economical feasibility
Co-treatment with municipal wastewater (MWW)
Effects often poor; treatment in the MWW plant is not designed for (methanogenic)
landfill leachate
* Variation in flow and quality (seasonal, precipitations & irrigation events). Can be
solved with equalisation basins
* Differences in quality
- Higher COD, AOX, N (NH4), metals (Fe, Mn) salts
- Lower P,
- Less particles
- Dependency on degradation phases (pH, conc., …)
