Study of Mercury-containing lamp waste management in Sub-Saharan Africa

34.1Mitigation potential

Mercury emissions in the different stages of the disposal chain are estimated for each MCL collection and treatment option presented above, and compared to the worst-case scenario. Seven scenarios are considered, each one being a combination of the collection, transport and treatment options, as summarized in the following table. If EoL lamps are collected through MSW collection, the extraction or recycling options cannot be chosen afterwards because separation of EoL lamps from the other waste after collection would not be possible.

Scenario	Description
A	Lamps are collected as part of the domestic waste collection scheme without a compression system. Disposal takes place in an uncontrolled landfill.
B	Lamps are collected as part of the domestic waste collection scheme with press container trucks. Disposal takes place in an uncontrolled landfill.
C	Lamps are collected as part of the domestic waste collection scheme without a compression system. The lamps are disposed of in an engineered landfill with LFG flaring and leachate evaporation systems and without activated carbon filtering.
D	Lamps are collected as part of the domestic waste collection scheme without a compression system. The lamps are disposed of in an engineered landfill with gas flaring and leachate evaporation and activated carbon filtering.
E	Lamps are collected as part of the domestic waste collection scheme without a compression system. The lamps are processed in a state-of-the-art incinerator equipped with filter technology using activated carbon injection.
F	Lamps are collected as part of the domestic waste collection scheme with press container trucks. The lamps are processed in a state-of-the-art incinerator equipped with filter technology using activated carbon injection.
G	Lamps are collected through a separate collection scheme for EoL lamps. The lamps are recycled and mercury is recovered either for recycling and sale, or for safe disposal in a hazardous waste landfill.
H	Lamps are collected as part of the domestic waste collection scheme without a compression system. The lamps are incinerated in an incinerator without proper filtering. This type of waste processing is quite common for medical waste in Sub-Saharan Africa so this scenario has been added for comparison with a treatment option already available.

The emission model developed is based on the following main parameters: temperature, breakage rate, and time of emissions, as detailed below. In this comparative exercise, the initial mercury content of the lamps does not influence the results.

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  The ambient temperature is 30° C.
  
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  In the domestic waste collection scheme, lamps stay in the waste bin for 168 hours before collection, and the breakage rate is 30% before collection. If a truck with a press container, which reduces the volume of the waste during collection (compression rates typically lie within a range of 1:2 to 1:5), is used, the remaining 70% lamps break during collection and transport resulting in a 100% breakage rate before the final destination. If the waste is not compressed, a significant number of lamps will reach the final destination (landfill or incinerator) unbroken, and an extra 10% breakage rate during collection and transport is assumed.
  
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  In a separate scheme for lamps, the average time until pickup is 336 hours, the breakage rate before collection is 15%, and the breakage rate during collection and transport is 10%.
  
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  The average time until processing is 48 hours in both domestic and separate collection, i.e. EoL lamps are treated (by recycling or disposal) 48 hours after collection.
  
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  In a controlled (engineered) landfill without open-air burning, 72 hours elapse before the waste lamps are sufficiently covered by other waste so that mercury emissions are mixed with the landfill gas.
  
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  The following emission factors (share of the amount of mercury entering that is emitted through evaporation) are used for the treatment options. The ‘state-of-the-art incineration’ emission factor refers to an incineration process in a plant using filter technology capable of mercury adsorption, i.e. activated carbon injection.
  

Treatment	Emission factor
Landfill (controlled)^67	0.6
State-of-the-art incineration^68	0.1
Incineration without filtering^47	0.8
Recycling^69	0.01

In the graph below, the scenarios are indexed to the scenario resulting in the highest mercury emissions, which has 100% emissions; all other scenario results are set in relation to this index, i.e. the resulting emissions are presented as a percentage of the maximum possible emissions. The scenario with the lowest total percentage has the highest mitigation potential.



Figure : Potential emissions of mitigation scenarios

The A and B scenarios, where final disposal is at an uncontrolled landfill, clearly cause the highest emissions and high pollution of soil and water around the landfill. As uncontrolled landfills do not have a liner protecting groundwater or soil, the mercury remaining in the waste lamps will be washed out by rainwater over time (elution), contaminating water and soil. The difference between these scenarios is only the point in time when the emission occurs. In scenario B, the waste is compressed during collection causing immediate breakage of all lamps collected. This leads to significantly higher mercury emissions during the collection stage, and less during treatment.

Scenario C involves an engineered landfill with advanced technologies (LFG flaring and leachate evaporation systems that divert water emissions to airborne emissions) that is not equipped with activated carbon filters. All mercury is emitted to the environment as in scenarios A and B, but there is no pollution of soil and water around the landfill. Engineered landfills are sealed against groundwater and soil, so no elution takes place in this scenario in the case of evaporation-based leachate treatment. However, post-treatment leachate released to the environment still contains airborne mercury emissions. Overall, the total impact on the environment will be lower (as explained in section 4.3).

In scenario D, involving an engineered landfill with advanced technologies (LFG flaring and leachate evaporation systems, equipped with activated carbon filters), emissions are much lower than in A, B, and C. When both systems are equipped with activated carbon filters, almost all post treatment airborne mercury emissions are captured. The remaining emissions that show up in the graph are due to breakage at the time of or shortly after disposal.

Scenarios E and F include state-of-the–art waste incineration. In these scenarios, the emissions during collection and transport are the highest within the scenario, reducing overall performance. In Scenario E, with a breakage rate of 100% before treatment, emissions are significantly higher than in scenario D.

Scenario G (recycling) produces the lowest overall emissions. These mainly happen during the logistics process (lamp breakage). Emissions from other lamp materials (glass, aluminum, etc.) are limited as mercury remaining in those materials is expected to be non-significant. If these other materials are recycled, precautions must be taken, for example to avoid the use of glass in the production of food containers.

In scenario H, where lamps are incinerated without proper filtering, mercury is released with the flue gases, and additional emissions after the incineration process are possible depending on the treatment of the residues.