These days it's possible to measure most gaseous, vapour and particulate pollutant releases to atmosphere using continuous analysis equipment that requires practically no operator intervention. However, until recently it has not been possible to monitor some trace pollutants continuously, for example trace metals (with the exception of mercury) and some trace organic compounds, such as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (dioxins and furans).

Emissions of trace metals and trace organic pollutants are usually measured by extractive techniques. Common methods currently in use for the determination of dioxin concentrations are BS EN 1948 and US EPA Method 23. The period of dioxin sampling is typically 4 to 6 hours, during which time a gas sample volume of 4m3 to 6m3 (depending on the method used and the sample gas flow rate) is withdrawn isokinetically, and passed through a filter and a resin-filled 'trap'. The samples are then subsequently analysed in a laboratory by soxhlet extraction followed by high-resolution gas chromatography and high-resolution mass
spectrometry. At best, this assessment method can only produce a 'snap-shot' of the actual total dioxin release.

More dioxins and furans are present in the environment than can be accounted for by known sources. This phenomenon was reported on a World- wide scale , generally as a difference in the balance between levels in atmospheric depositions or soil samples, and the emissions inventory of known sources. Often 'missing sources' of dioxins are suspected with an emission that amounts to a multiple of the known sources. Cases of underestimation of dioxin emissions in municipal waste incinerators in Belgium have been reported. The size of this underestimation is of the same order of magnitude as the emissions sometimes attributed to the
missing sources.

In Belgium, studies have shown that the composition of waste supplied to incineration plant can vary tremendously. It was found that this can lead to dioxin release excursions in some plant. It is also known that the start-up and shut-down periods in the operation of some waste incinerators can produce high dioxin release rates. This is especially the case for plant where by-passing of the flue gas filtration plant is possible. Clearly in order to gain a complete picture of total dioxin releases to atmosphere a method for continuous monitoring is needed.

In 1998, following a period of intensive development, bm becker messtechnik of Germany launched an officially approved measuring system for continuously monitoring concentrations of dioxins and furans in releases to atmosphere. The Adsorption Method for Sampling of dioxins and Furans (AMESA) is capable of continuous sampling over periods of between 6 hours to 30 days.

The AMESA system extracts a sample from the gas stream continuously through a titanium probe, which is water-cooled to below 70°C. The sample flow rate is automatically controlled so that gases are withdrawn isokinetically. The water vapour laden sample is drawn through a cartridge filled with pre-spiked resin, typically XAD II, with quartz wool as a pre-filter. The water vapour is then condensed by cooling the sample to below 5°C. A sample of the condensate can be collected for
subsequent analysis if required.

The system measures flue gas velocity, the volume of sample gas, flue gas temperature and cartridge temperature as a half-hourly averages.
AMESA will also accept additional inputs from oxygen, pressure and RH analysers if required. All operating data is stored on a removable SRAM card. At the end of the monitoring period the resin cartridge and SRAM card are removed from the AMESA and sent to an accredited laboratory for analysis.

In January 2000 the Belgian Government introduced legislation which requires the continuous monitoring of dioxin and furan emissions from all refuse incineration plant in Flanders.

Other applications of the system include:

· Reduction of energy costs by lowering furnace temperature while demonstrating no increase in dioxin levels.
· Reduction of plant operating costs by minimisation of additives.
· Demonstrating a pollution-free stack.

AMESA is certified by TUV according to the German environmental regulation 17. BlmSchV, and complies with BS EN 1948.

For more information contact:
Paul Mudway
EMC Environment Engineering Ltd.
Stoke Orchard
Cheltenham
Glos. GL52 7RZ
Tel: 01242 673444
Fax: 01242 677258
Email: paul.mudway@emc-environment.com