Annex 11 Complementary information to source category 1c Medical Waste Incineration
Overview of recent revisions
No revisions were made to emission factors in this source category. Additional guidance has been introduced on classifying sources within this category, estimating activity rates, and on data quality aspects.
Derivation of emission factors
Default emission factors are based on the assumption that the medical waste burned leads to about 3% of fly ash and the PCDD/PCDF release associated with the disposal of bottom ash is uncertain. A bottom ash generation rate of ~10% has been reported (Alvim-Ferraz and Alfonso 2003, Grochowalski 1998) with an average concentration of 19.3 µg TEQ/kg (Grochowalski 1998). Also, the removal efficiency of particulate matter increases with the quality of the plant.
Class 1 should be chosen for very small and simple, small box type incinerators operated intermittently (in which a load of waste is ignited and left) with no secondary combustion chamber, no temperature controls and no pollution control equipment.
Class 2 applies to all medical waste incinerators with controlled combustion and equipped with an afterburner, which, how-ever, are still operated in a batch type mode.
Class 3 should be applied for controlled batch-type plants, which have good APC systems in place, e.g., ESPs or preferably baghouse filters.
Class 4 should only be used for highly sophisticated medical waste incineration plants, e.g., if a limit value equivalent to 0.1 ng TEQ/Nm³ (at 11% O2) is strictly enforced, and the facility can be assumed to be in compliance. In this latter case the question of continuous versus batch type operation will become irrelevant, since these facilities are usually preheated with oil or natural gas extensively. Only after the intended furnace operating temperature of usually well above 900°C is reached, medical waste is introduced into the furnace.
The vast majority of medical waste incineration plants can be assumed to fall into class 2. Larger, centralized plants may be grouped into class 3.
Release to Air
The default emission factor for class 1 was derived from a specific flue gas volume flow rate of about 20,000 Nm³/t medical wastes burned and a concentration of about 2,000 ng TEQ/Nm³ (at 11% O2).
Class 2 assumes a reduction in the specific flue gas volume flow rate to 15,000 Nm³/t medical wastes due to better combustion controls and lower excess air. The PCDD/PCDF concentration drops to 200 ng TEQ/Nm³ (at 11% O2) in this case.
Class 3 is based on European data where a concentration of 35 ng TEQ/Nm³ (at 11% O2) with 15,000 Nm³/t has been determined.
Class 4 represents the current state-of-the-art in medical waste incineration and good APC technology. In these cases, only 10,000 Nm³/t of medical waste was generated and a concentration of less than 0.1 ng TEQ/Nm³ (at 11% O2) was measured (LUA 1997, IFEU 1998, Environment Canada 1999).
PCDD/PCDF concentrations emitted via the stack to air from a medical waste incinerator in Thailand – adjusted to 11% O2 – were between 21.8 and 43 ng TEQ/Nm³ for line A and between 10.7 and 45.0 ng TEQ/Nm³ for line B; the averages were 33.8 and 28.6 ng TEQ/Nm³, respectively. These emissions resulted in an emission factor of approximately 1,200 µg TEQ/t of waste burned, which is between the class 2 (3,000 µg TEQ/t) and class 3 (525 µg TEQ/t) emission factors.
Release to Water
Releases to water occur when wet scrubbers are employed for the removal of particulate matter and quench water is used to cool ashes. Measured concentrations of PCDD/PCDF in scrubber water after medical waste incinerators are not available. Where wet scrubbers and quenching of ashes are identified, the water treatment should be noted.
Release to Land
No release to land is expected unless untreated residue is directly placed onto or mixed with soil. The concentration released in such cases will be covered under “Release in Residues”.
Release in Products
The process has no product, thus no release to product occurs.
Release in Residues
PCDD/PCDF concentrations in fly ash are substantial. Default emission factors provided in the residue category only relate to PCDD/PCDF releases via fly ash. A study of 18 medical waste incinerators reported PCDD/PCDF concentrations in bottom ash ranging from 8-45 µg TEQ/kg, with an average of 19.3 µg TEQ/kg (Grochowalski 1998). PCDD/PCDF concentrations in the residues can be especially high, when combustion is poor (e.g., in a simple batch-type incinerator). Classes 1 and 2 medical waste incinerators will not generate fly ash due to the lack of dust removal equipment. In these cases, all residues will consist of the residue left in the combustion chamber. The class 1 emission factor is based on the assumption that the 200 kg of residue per ton of medical waste burned is left in the combustion chamber with a concentration of 1,000 ng TEQ/kg. For class 2, combustion is improved, so the bottom ash residue should contain only 100 ng TEQ/kg; resulting in an emission factor of 20 µg TEQ/t of waste.
For classes 3 and 4, the amount of fly ash typically is around 3%. Class 3 assumes 30,000 ng TEQ/kg in the fly ash and 100 ng TEQ/kg in the grate ash (same as class 2). Class 4 incinerators have high combustion efficiency, resulting in an organic carbon content of about 1% of unburned carbon but also a very high collection efficiency of the small fly ash particles. Fly ash is collected (30 kg/t of waste) with a concentration of 5,000 ng TEQ/kg fly ash and 10 ng TEQ/kg of grate ash is chosen. These small particles supply a large adsorption surface for PCDD/PCDF and therefore the overall concentration does not decrease any further.
The results from a medical waste incinerator in Thailand were extremely high due to the poor combustion conditions in the primary chamber and the operation on-site, where the bottom ashes were left overnight in the chamber to slowly cool down. Such conditions create high concentrations of PCDD/PCDF. We found bottom ash concentrations of 1,390 and 1,980 ng TEQ/kg of bottom ash, which is about 20 times higher than was expected for a class 2 bottom ash (UNEP 2001, Fiedler et al. 2002).