La gestione dei rifiuti

There are many different aspects that must be considered in the correct planning of an integrated management system, and all these contribute to the choice of the most suited solution for disposal of the waste produced in the situation which is being examined. First of all, it is important to evaluate the qualitative and quantitative characteristics of waste, the aims of separate waste collection must be established, and also the transportation utilized, waste treatment and disposal plants that can receive the waste must be identified. Having evaluated these variables, the next step is the examination of the available operative instruments, with different possible options: separate waste collection, plants for pre-treatment of waste before disposal, plants for energy recovery, (such as incinerators, gasifiers, etc.) material recovery plants, and controlled dumps. When all the data has been collected, the appointed technicians and engineers and researchers will choose the best solution using a series of instruments such as: mass and energy flow, environmental impact assessment (EIA), economic assessments, life cycle analysis (LCA) and risk analysis.

Recycling

By the word recycling, we mean the set of operations, strategies and methods that are used in order to recover the materials and to reduce the quantity of waste sent to the dumps and incinerators. As pointed out before, man has always been used to recover his goods or to recycle his waste up to the industrial revolution. Starting from that time, the massive production of consumer goods and the great availability of resources did not make modern man feel the need to give his waste a second life.

Incineration

Incineration, with energy recovery (Waste to Energy systems), is another solution to dispose of waste and consists in the combustion of waste in order to:

• decrease the volume and weight of the material;
• to completely oxidize the waste into CO2 and H2O;
• recover the energy content of the waste;
• sterilize the residues.

The waste dump or landfill

In the controlled type of dump, waste is deposited in layers on the ground, in a suited and monitored manner, so as to minimize the negative effects on the environment and on human beings. Thus, pollution of surface and underground water is prevented and controlled, as also emissions of unpleasant or toxic substances, and all efforts are made to reduce the aesthetical impact.

With the Ronchi decree, separate waste collection was started in the Italian homes, and has now become part of our daily activities, and the small yet big contribution that we can give to the environment. Separate waste collection is the process in which domestic separation of waste is carried out with the aim of re-addressing, upstream, the various types of waste that are present in our homes and to optimize management of the same.

MSW materials that are collected separately often consist of the packaging of products we have purchased such as: paper, glass, plastic, aluminium, wood, humid or organic fraction, electronic waste (WEEE- waste electrical and electronic equipment) and bulky waste.

Paper

Paper is the material with the highest recycling rate in our country. Collection is extended to all types of paper, including drawing paper, paper for graphic use, for photocopies and for newspapers, cardboard and paper bags. However soiled paper (like the boxes used for pizza delivery) must not be put in the separate waste collection, as it might pollute and contaminate paper that can be recycled.

Glass

Glass is both fragile and eternal, and it is one of the most interesting materials from the point of view of recycling. Because of its physical and mechanical characteristics, it is a particularly interesting material that does not become degraded qualitatively during the recycling process and can be reutilized practically an infinite number of times. A bottle that is melted again in the furnace of a glass industry, will generate another bottle with the same qualities as the previous one, and this total recyclability enables a remarkable energy saving in the melting phase.

Plastic

If we look around, we will see that many of the objects that we use daily all around us are made of an extremely versatile, light and economical material, plastic. The toothbrush, the cover of the mobile phone, pens and felt pens, the computer, the television, all these objects and many others contain at least some plastic.

Wood

Wood is a rather uncommon material in our daily separate waste collection, however it is not less important than the others. Wood, like plastic, does not always have the same characteristics. In fact, there are many different kinds of wood, that are used in different ways depending on their nature. In any case recycling wood is very important for two reasons: firstly natural resources are preserved, since by recovering the material less trees are felled, and secondly, by avoiding sending wood to the dump there is a saving in emissions in the atmosphere of methane and carbon dioxide, which are gases that alter the climate.

Aluminium

Aluminium is light, versatile, durable and quite malleable. This metal has exceptional characteristics that make it particularly suited not only for the production of cans but also for car parts and for use in buildings. Recycling aluminium is very important because its production is a particularly costly one from the point of view of material and energy, in fact aluminium is obtained from bauxite which is a sedimentary rock, and 4t of bauxite and 14 MWh of electricity are required in order to obtain only one ton of aluminium.

Waste electrical and electronic equipment (WEEE)

In Italy, the acronym WEEE stands for waste electrical and electronic equipment. In this category, many types of waste that differ in composition, method of utilization and characteristics, but which are all afferent to electronic devices, are grouped - i.e. all the devices that use electric energy for their operation

Organic waste

What happens to a banana skin when we throw it away? If we want to try an experiment, and we leave it in a garden, we will notice that in a short period of time the skin will transform and disappear completely or almost completely, leaving a new organic substance in its place which is then absorbed by the ground. This happens because the banana is an organic waste and it is biodegradable like kitchen leftovers and garden cuttings, and therefore decomposes easily and is transformed by saprophytic bacteria.

In the context of the waste-to-energy strategy, we find the so-called refuse derived fuels (RDF) obtained from non-dangerous waste and used to recover energy in incineration plants (also known as Waste to Energy systems). The range of waste materials that are used is very large and includes the residues which have been excluded from the recycling processes, waste from the industries and the distribution networks, muds from water purification systems, dangerous industrial waste, discarded biomass materials, etc. ... These must be treated suitably in order to comply with the criteria, regulations and industrial specifications in order to reach a suitable heat producing potential. One of the least costly methods, which is most widespread, for the production of RDF, is mechanical biological pre-treatment, MBT. In a MBT plant, metals (which are recycled) and inert materials (e.g. glass), and organic fractions (that are sent to the composting plants, with or without an anaerobic digesting phase) are separated from the MSW, and fractions with a higher heat producing power for the production of RDF, are chosen. Other solutions, besides MBT, are bio-stabilization and bio-drying of materials from which metals and inert materials have been removed beforehand, in which the organic fraction is stabilized and loses a part of the humidity, thus obtaining a final fraction with a higher heat producing power, that is suited for combustion, and consisting of paper and cardboard, wood, plastic and textiles that can be burnt directly. The characteristics that are necessary for the product that is obtained with the treatments to be used as RDF are many, and include a heat producing power of at least 15 MJ and 25% humidity.

Which are the current uses of RDF? There are numerous possibilities, which include: Waste to Energy systems, cement plants, thermal energy plants for district heating, steel plants, coal thermo-electric power plants etc. and, depending on the plant, they are uses as the only fuel or as an auxiliary fuel.

Biogas

Apple peels, fish bones, leftover pasta and a handful of corn, no this is not some kind of strange secret recipe, but some of the elements that are necessary for the production of a very particular combustible, biogas. Biogas is a gas, but unlike methane that is extracted from the ground, it is produced from the decomposition of organic material (the organic waste of our waste), civil and zootechnical sewage, agricultural biomasses, etc. in anaerobic conditions, i.e. in absence of molecular oxygen (O2) or bound to other elements (as in the case of nitrates NO3).

Waste to Energy systems (WTE)

What to do with all the waste when none of the materials can be recovered? According to the hierarchic waste pyramid, the preferable option are the Waste to Energy systems, in other words incineration with energy and/or heat recovery, before disposal in the dump (where neither energy nor material can be recovered).

Gasification and pyrolysis

Combustion by means of incineration can be one of the solutions for recovering the energy content of waste, however it involves numerous difficulties, among which the emission of gas effluents that require a costly purification treatment and that have induced researchers and engineers to search for more solutions for the plants. Among these are gasification and pyrolysis, which are being experimented as a potential alternative to the Waste to Energy systems.