International Review of Waste Management Policy - Department of ...

These results suggest a significant variation in the relative performance of the
different AD and incineration options. A closer inspection of the pollution inventory
reveals that results against this assessment criterion are heavily influenced by heavy
metal emissions from the facility.
For example, whilst the treatment and recovery stage of the Generic AD facility is
indicated to result in 17.9 kg of 1,4 dichlorobenzene equivalent, the same stage
within the Arrowbio AD-based MBT plant results in 43.2 kg of 1,4 dichlorobenzene
equivalent. This impact is linked to a substantial differential in the emissions of
Chromium VI assumed to occur from the two facilities. Whilst the Generic AD process
assumes an annual emission of 2.3E-06 kg Chromium VI to air (per 60,000 tonnes of
waste to facility) the Arrowbio AD-based MBT plant assumes 0.42 kg Chromium VI is
emitted annually (from 70,000 tonnes treated at the plant).
An analysis of the emissions data embedded within WRATE indicates that the former
process derives its estimated Chromium VI emissions:
969
“from the waste gas figures and the efficiency of the purification system to
reach a clean gas emissions figure”.
An inspection of the same entry for the Arrowbio AD-based MBT process indicates
that the data has been extrapolated from similar AD technologies in Germany as
aerial emissions data is lacking. It is not clear which German technologies were
referenced when compiling the model for the Arrowbio process. It does demonstrate,
however, how the quest for complete inventories can bias results obtained.
There is even greater variation in the performance of the different incinerator options.
Here, results are heavily influenced by:
� Avoided emissions of barite to water; and
� Emissions of cadmium and thallium to air.
The mineral barite is used as a weighting agent in the petroleum drilling industry;
impacts here, therefore, relate the amount of energy generated by each option.
For incineration facilities, WRATE calculates emissions to air based on emissions data
supplied by plant operators. These are scaled up within the model to give an annual
emission figure for the facility. Heavy metal emissions are then weighted using an
estimate of the heavy metal content in the input waste (derived from waste
composition supplied by the user within each bespoke scenario), divided by heavy
metal content of what is termed the ‘typical waste’ composition. As an example, the
cadmium emission is calculated using the following allocation formula:
[Total cadmium in input waste] * [Emissions from process]
[Total cadmium in ‘typical waste’]
The worst performing incinerator with regard to its human toxicity potential is that
located at Dundee (a fluidised bed incinerator). The Dundee incinerator is assumed to
emit 0.75 kg cadmium per 120,000 tonnes of waste; by contrast the Chineham
facility emits 0.07 kg cadmium per 95,000 tonnes. Both figures relate to a series of
actual emissions measurements taken at each facility, and in both cases the upper
measurement was used from the series.
International Review of Waste Policy: Annexes