Incineration of Oxo-biodegradable Plastics with Energy Recovery

Calorific Value

The calorific energy recoverable by incineration of hydrocarbon-based plastics, whether oxo
-biodegradable or conventional, is almost identical to that of the fossil resources from which
they were originally made (1). This must therefore be included as a benefit in Life-Cycle
Assessments. In normal combustion of such plastics the effluent may contain toxic
combustion-products and modern waste to energy incinerators are designed to remove                                                                                                          these from the exit gases so that they do not escape into the environment (2).

Vegetable-based plastics have a much lower calorific value than hydrocarbon based
plastics and they normally contain absorbed water, so they are not as suitable for
incineration with energy-recovery.

Oxo-biodegradable Plastics

These materials are currently and for the foreseeable future hydrocarbon-based plastics.
They are designed to biodegrade like nature’s wastes at the end of their useful life and
this is achieved by incorporating during manufacture very small quantities of metal
compounds (e.g. iron, cobalt or manganese – but not “heavy metals” i.e. lead,
cadmium, mercury or hexavalent chromium) that are converted to the
corresponding oxides during incineration of the plastics.

These end-products do not escape into the environment from a modern incinerator, but even
if they did they are normally found at appreciable concentrations in most agricultural soils
from which they are extracted into plants and into the water supplies. In a risk-assessment
the UK Food Standards Agency has shown (3) that they are non-toxic and are absorbed
by plants used for food by animals (including humans), thus providing them with
essential trace-elements. Cobalamine and manganese peroxidase are
particularly important in cases of vitamin deficiency.

Consequently, even in the event of an accidental escape of these
materials into the environment, they would present no possible
hazard to animals or humans.

 

1 A. Bousted and G.F. Hancock, Energy and Packaging, Ellis Horwood, 1981
2 G. Scott, Polymers and the Environment, Royal Society of Chemistry, 1999, p. 87-91
3 Expert Group on Vitamins and Minerals, UK Food Standards Agency, Trace Elements,
Risk Assessment, 2002, Part 3