Circular Economy: does the Refusal of Refusal go “to Ash”?

Nothing is thrown away in modern waste-to-energy plants. After the production of electricity and heat for heating, ash also has its place

The ash that is produced through the incineration of waste in waste-to-energy plants, can have a place in the circular economy, based on how the refusal of the ovens is identified and on the basis of the national environmental legislation in force and the reuse of the material.

The waste-to-energy treatment of non-recyclable waste is never to be seen as an option to the waste separation and recycling system, but rather an additional system to mechanical recycling that intercepts and manages that part of the waste that is no longer reusable.

The incineration of this waste normally generates electricity and heat for the heating of our homes, as well as being engaged in other industrial areas as an alternative fuel to fossil sources.

What are defined as ” Bottom Ashes ” in the international arena, concern the residual ash of the waste combustion process, which is represented by the unburnt waste of the masses placed in the ovens.

The composition of the unburnt ash includes residues of glass, minerals, ferrous and non-ferrous metals and ceramics , in the measure of 20-25% for each ton placed in the oven, according to the indications of the ISWA (International Solid Waste Organization) which deals with to promote and develop sustainable and professional waste management worldwide.

The residual ashes are extracted from the ovens through a process in which water is used to cool them and to prevent the creation of potentially harmful dusts , therefore their removal from the plants takes place in the form of wet and compact agglomerates.

Until a few years ago, generally, the extracted ashes did not have a different location from that of the landfill, but with the advent of the circular economy processes, consideration was given to the possibility of reusing them.

Considering that the chemical compounds contained in the ashes are on average composed of Sodium, Aluminum, Potassium, Magnesium, Iron, Calcium and Silicon , we can say that the prevalence of the components is normally constituted by silicon, calcium and iron.

With regard to the average chemical analyzes that each plant provides, many countries have adopted legislation to classify these ashes and have recommended their treatments and uses.

Let’s see what indications come from some countries:

•  In Italy , according to the decree n ° 22 of 5 February 1997, the ashes coming from the incineration plants can be reused, if they do not contain harmful substances, such as inert cement, but only after having been properly treated. In reality, their use in the country still remains limited compared to production.

•  The Netherlands regulates the management of the ashes within the national waste management plan (LAP) which includes, among others, some indications regarding the use of the waste material where it is widely used as part of the embankments.

•  In Denmark , already in 1987, the government had allowed the use of ash produced by incineration plants as an inert material for the construction of roads, with the aim of finding employment for at least 85% of the waste produced. Furthermore, it also allowed its use in residential civil construction only following the environmental opinion of the Environmental Protecion Act.

•  France has decided to classify the residual ash through analyzes that can identify three distinct categories: V, M and S, attributing to these three categories the percentage of ash (50%, 30% and 20%) admitted within the compounds usable.

•  In Spain most of the ashes are still sent to landfills even if an inert use for road construction is being promoted.

•  In Finland, the use of incinerators is not a priority for the government which prefers to follow the path of waste disposal through gasifiers, therefore, it directs the low quantities of ash produced in landfills.

•  Since 2006, Germany has allowed the use of ash in road construction, provided that chemical analyzes do not identify elements that are potentially harmful to the environment. Together with Holland, Denmark and France, Germany is the country that most reuses this waste.

The use of the ashes coming from the waste incineration plants, where possible, constitutes the full circularity of the raw materials, fully utilizing every part of the waste through the processes of recycling, energy production and reuse of the final waste.

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