Waste characterization

Question 1

Why is waste characterization important in landfill technology?

Answer 1

Because the properties of the waste will determine how it can be handled and what
measures must be taken to prevent emissions (should be developed by a number of
concretizations)

Question 2

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

Answer 2

• the pH increases
• the pe decreases and sulphide complexes may be formed
• organic complexing agents are degraded

Question 3

There are different goals for the characterization of waste. What is the general goal for
waste characterization? Name and explain three goals from the perspective of a landfill
operator

Answer 3

The general aim of waste characterisation is to understand and be able to predict the behaviour of a waste.
A landfill operator may need to identify wastes as being the same as declared by the classification. The characterisation is then made in order to avoid erroneous placement
of wastes and to charge the correct fee for disposal or treatment.

Question 4

The L/S ratio is the liquid to solids ratio that a waste has been exposed to. Estimated insitu L/S ratios from real landfills can be used to develop bench-scale leaching tests for
simulating landfill leaching processes over time. Sometimes the L/S is translated into a time
scale by the use of infiltration rates and predictions regarding future changes of the leachate
quality are made.
Explain why there is a risk for such leaching tests giving misleading results and give
examples for over/underestimations of concentrations and/or time frames. Take into account
your knowledge about (a) the factors controlling leaching as well as (b) in-situ waste
conversion processes.

Answer 4

The L/S ratio is just one out of many possible factors that can affect leaching, e g pH,
redox potential, complexing agents and more. The effect of the L/S ratio is often linear (e.g.
for solubility controlled leaching) while the impact of factors such as redox potential and pH
may be even logarithmic, i.e. much more pronounced. Also, the way how the water moves
through the landfill affects the leaching.
Factors affecting leaching can be assorted into 1. Surface accessibility (Surface enrichment,
Particle size), and 2. Surface solubility (Surface speciation (oxides, carbonates, sulfides,
adsorption, complex-bound etc.) and leaching conditions (L/S, pH, pe, temperature, ionic
strength etc.). Describe how these factors can affect concentrations and estimated time frames
…
For highly soluble components such as some salts (sodium, potassium and chloride ions), the L/S ratio has a minor impact on the leaching as already small amounts of water are sufficient to cause a complete dissolution. Therefore, the L/S-ratio can be used to roughly predict the
leaching of such conservative substances.

b) In-situ waste conversion processes include e.g. changes in the waste mineralogy. The
latter may increase as well as decrease leaching.