Friday, 12nd march 2021 | Environment
Marco Arezio - Consulente materie plastiche - Non-recyclable Plastic in Cemente Ovens: are we Safe?

If the Thermovalorizers are created to use the End of Waste correctly, the cements leave many doubts.

From a circular economy perspective, the waste of plastic recycling products, which by its chemical composition cannot be used, has a thermal value as fuel. But if the End of Waste cannot be recycled it is because it is composed of a mix of plastic waste that, if burned in the ovens, result in the emission of toxic substances that should not be fed into the atmosphere. That’s why the thermovalorizers were born.

The heat-tray systems are designed, built and intended for the combustion of the End of Waste, taking into account the chemical process of processing the various plastics under the effect of heat. 

This process involves the production of fumes in which substances that are dangerous to humans and the environment are contained, which, a plant born for this work, manages correctly, with the aim of reducing harmful substances.

It is a common practice, however, to allocate part of the End of Waste also to cement production plants, which uses it as a combustible for their ovens at low prices, but through plants that have not been designed specifically for waste disposal.

But what is the End of Waste?

In the correct urban waste management policies there are two categories of waste that are collected and treated differently and with different purposes: 

  • Organic waste, which we produce daily in the household, which is delivered in differentiated waste collection centres. These products are treated for the production of biogas, fertilizer, carbon dioxide for food and electricity use. 
  • Urban waste,in the form of mixed plastics, which are selected by type of plastic and started for recycling turning them into scales, densified and polymers. 

In the context of the selection of plastic fractions, some families emerge, the characteristics of which do not lend themselves to a mechanical selection such as, for example, the paired poles, plastics formed by families of polymers different and incompatible.

When a plastic, at the end of its cycle  is not recoverable mechanically, it can assume an important thermal value by creating a combustible material, of decidedly appreciable caloric characteristics, which helps, through its use, to continue the path of the circular economy. 

In fact, in addition to not dumping this fraction of mixed plastics, which in terms of annual volume is very important, we can save the use of natural resources derived from oil.

The End of Waste 

now mainly powers power plants and cement plants. The use of this waste in power plants has also reduced dependence on coal, a fossil fuel with a very high level of pollution and responsible for health problems of citizens living near power plants.

The production of electricity, through the End of Waste

has allowed to calibrate the design of the plants with respect to the product that serves as fuel, creating a high ecological efficiency compared to other systems.

In northern Europe, the production of energy through the burning of non-recyclable plastic waste is a good compromise between technical and environmental results.

The second area of fuel use derived from the End of Waste concerns the use in cements, which use it to power the furnaces for the production of clinkers.

According to a study done  Augustine of Ciaula , the plants for the production of clinker/cement would not be adequate, from the health point, to use this type of plastic waste. 

According to this research, the use of the End of Waste in cement mills, in place of variable percentages of fossil fuels, causes the production and emission of heavy metals, which are toxic to the environment and harmful to human health.

These substances, when emitted into the environment, are able to determine an increase in health risk for residents due to their non-biodegradability (persistence in the environment), the ability to move with the food chain and to accumulate progressively in biological tissues (plant, animal, human).

It has been shown that,  for some heavy metals (especially those with increased volatility), the transfer factor of these substances from waste fuel to plant emissions is far greater in the case of cement mills when compared with classical incinerators. 

This value is significantly higher than that detectable as a result of the use of End of Waste in plants designed for this purpose (Thermovalorizers) and, in the same cement plants, to a greater extent than the use of fossil fuels alone.

This use can increase emissions into the environment of  dioxins, PCBs and other persistent chlorinated toxic compounds with negative consequences on human health. 

Significantly higher transfer factors for cement mills are also evident in the case of  cadmium, a substance recognised as a certain carcinogen (percentage emissions 3.7 times higher in the case of cement mills) and lead (percentage transfer factor 203 times higher in the case of cement mills). 

Despite the technological measures to limit emissions taken by cement plants, given the high volume of fumes emitted by these plants, the total amount of Hg that will reach the environment will, however, significantly increase the health risk of residents in neighbouring territories. 

Limiting the analysis to mercury alone,

it has been calculated that more than two million children with mercury levels are born in Europe each year above the limit considered “safe” by the WHO.

While ignoring the increased health risk from the emission of heavy carcinogenic metals present in the End of Waste (arsenic, cadmium, chromium, nickel), equally significant problems arise from the presence, granted in the waste itself, of significant amounts of lead

The lead transfer factor, from the End of Waste to emissions, is about 203 times greater in cement mills than in traditional incinerators, and emissive values are made, in the case of cement mills, even more problematic by an average volume of fumes emitted, about five times greater in conventional cements than in classical incinerators. 

Even for lead, as for other heavy metals, compliance with legal limits is not able to adequately protect the paediatric age.

Exposure to lead, in fact, like that of mercury, begins during fetal life (in utero) and involves a progressive and irreversible accumulation in the body.

In order to limit lead intake through  drinking water, according to the World Health Organization, water intake with lead concentrations of only 5g/L results in a total lead intake ranging from 3.8g per day in paediatric age to 10g/day for an adult. 

Another problem encountered is dioxin emissions,

wherees where the number of chlorogens and other toxic chlorinated compounds is still considered to be at high risk for the formation and consequent emission into the atmosphere of dioxins (of which chlorine is a precursor) and other chlorinated toxic compounds by cement plants that use end-of-waste co-combustion to replace fossil fuels.

The high temperatures present in some places in the production cycle of these plants facilitate the dioxeation.

However, scientific evidence clearly shows that, although  dioxin molecules have a breaking point of their bond at temperatures above 850 degrees Celsius, during cooling phases, (at the end of the production cycle the temperature drops to about 300 degrees Celsius) they regroup and reform, 

appearing accordingly in emissions.

SINTEF reports and international scientific publications document the production  of polychlorinated dioxins and moths 

by cement plants with co-combustion practices and, a recent study, demonstrated considerable amounts of dioxins in the household dust of homes located in neighboring territories to cements with co-combustion of waste.

The Stockholm Convention 

calls for the implementation of all possible measures to reduce or eliminate the release of chlorinated organic compounds

(POPs) into the environment and, co-combustion cement plants, waste are explicitly mentioned in it. 

In addition, even when dioxin emissions are quantitatively low, the use of fuel derived from plastic waste can generate the production and emission of large amounts of PCBs (thousands of times higher concentrations), compounds similar to dioxins in terms of environmental and health hazard. 

Dioxins are non-biodegradable compounds, persistent in the environment with a long half-life (which for some congeners reaches the century), transmissible with the food chain and, above all, bio-accumulatible. 

The U.S. Environmental Protection Agency (EPA) recently recalculated the daily level of dioxin exposure considered not at risk to the human body, which is 0.7pg (0.0007ng) of dioxins per kg of body weight.

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