18 October 2022

Plastic, glass, metals: the “enemies” that dirty the compost

Il compost è un fertilizzante naturale estremamente utile in agricoltura, che riduce l'uso dei prodotti chimici e valorizza la frazione umida dei rifiuti urbani (la cosiddetta FORSU). FOTO: Matteo Berlenga

The alarm emerges from a series of video interviews with managers of composting plants carried out by the italian Biorepack consortium. Too high percentages of “foreign fractions” (up to 12%) make it more difficult and expensive to make compost. On the other hand, compostable, flexible and rigid bioplastics were promoted with flying colors: “very useful for increasing quantity and quality of the final product”

by Emanuele Isonio


To public opinion, the concept of “extraneous fractions” says little or nothing. For those who work every day in the world of waste, it is an obstacle and by no means secondary. Let’s take the case of organic waste, the most significant component of urban waste (about 40% of the total). Their enhancement is fundamental because they can be transformed into compost, a precious natural fertilizer that is twice as valuable: they are a valid substitute for synthetic chemicals and, in addition to increasing agricultural yields, they help to restore organic substance to agricultural land, which is increasingly at risk for desertification. To produce compost it is necessary that the starting raw material is as “clean” as possible. That is, it must be composed only of compostable materials. Unfortunately, this is not always the case. the non-compostable extraneous fractions reach up to 12% of the total waste sent to the composting plants.

The complaint emerges from a series of investigations in which the managers of composting and anaerobic digestion plants are given a voice. To make them, the national consortium for the organic recycling of biodegradable and compostable plastic packaging, Biorepack, which then transformed them into a series of video interviews. From North to South a journey through images to inform about the end of life of humid products: from Piedmont to Puglia passing through Veneto, Abruzzo and Sardinia.

Traditional plastics, glass and metals

The five plants visited by Biorepack are responsible, all together, for the management of over 800 thousand tons of organic fraction every year, both through composting-only plants and with integrated plants, which combine the anaerobic and aerobic digestion phase. It is significant that their analyzes coincide on the different points dealt with in the interviews. Starting, in fact, from the danger caused by extraneous fractions. “Non-compostable materials (NCM) reach percentages between 8 and 12% of organic waste disposed” reveals for example Flaviano Fracaro, responsible for the FORSU Supply Chain of Iren Ambiente, the multi-utility that manages waste collection in the provinces of Parma, Piacenza, Reggio Emilia, La Spezia and Turin. “Most of them are made up of traditional plastics, despite the legislation that bans them is now more than 10 years old. But also from glass and metals “.

“The real challenge is to be able to completely eliminate these impurities that damage the composting process and the quality of the final product” adds Fabrizio Pilo, sole director of Verde Vita, which manages waste in 15 municipalities in the north-west of Sardinia. According to Pilo, the synergy between all the players in the supply chain is essential to achieve the goal. “They must be put into the system and made responsible to help create a virtuous path. Our experience, for example, has shown that building a rigorous door-to-door collection greatly reduces the rate of non-compostable materials ”.

In fact, the case of the Sardinian plant shows that, by organizing the collection of wet waste in a methodical way, the advantages can really be for everyone: for citizens who see the cost of the waste tariff decrease on average, for Municipalities that have lower management costs and for local farmers. The compost produced by the Verde Vita plant, for example, is entirely distributed on farms within a radius of 40 kilometers. 

Bioplastics passed with flying colors: “Like an apple or a piece of wood”

Another aspect on which the replies of the installers coincide to the letter is on products made of compostable bioplastic. Bags for the collection of wet waste, shopping bags or fruit and vegetables bags, plates, glasses, cutlery and coffee pods. Packaging of this type is growing significantly, since the EU SUP directive banned the use of traditional plastic disposables. Since January 1st, Italian law has established that compostable bioplastics must be thrown away with organic waste. Precisely because their peculiarity is to be able to degrade together with the latter. But there is still a lot of misinformation on the subject.

A clear green light comes from the plant managers: compostable bioplastics do not create any kind of problem for composting, even if this occurs within plants that, at the head of the cycle, have the anaerobic digestion phase.

“Due to their characteristics, compostable bioplastics adapt perfectly to our production system and are transformed into compost like the FORSU” explains for example Alberto Torelli, CEO of ACIAM, which manages the largest composting plant in Abruzzo.

“They behave like other materials of plant origin” confirms Mario Mongelli, technical director of PROGEVA. “Flexible bioplastics, such as compostable bags, are comparable to an apple or an orange peel in terms of degradation times. Rigid packaging, which in any case represent more or less 1% of the MSW treated, are comparable to a piece of wood. If at the end of a first composting process they are not yet completely degraded, they are separated at the end of the cycle to be put back in the head”. A virtuous process from all points of view: environmental, agronomic, social and economic. “The compost made – Pilo emphasizes – can be marketed and distributed from farms in the same territory, thus building a short chain of organic waste that brings benefits for all”.

Clear labels and fight against those who bypass the rules

“Our problem is traditional plastic” clearly says Werner Zanardi, SESA SpA technician. “Plastic has nothing to do with bioplastic. They are different materials, with different behaviors and which must follow different recovery flows ”. Hence the need to take action in two directions: to counter the illegal trade in bags and dishes made of conventional plastic. And to help citizens understand clearly how to distinguish bioplastic packaging.

“On sale there are traditional plastic plates classified as ‘reusable‘” complains Lella Miccolis, managing director of the Apulian PROGEVA. One way to exploit a controversial regulatory gap and get around the marketing ban. “The problem for us composters is that these products are difficult to recognize for the citizen. Not knowing how to distinguish them, he throws them in the waste collection together with the compostable dishes. The question of having clear and unique labeling is crucial. It is necessary to understand very well, right from the packaging and eco-design, which compostable waste is to be disposed of in the workforce and which ones must be thrown elsewhere “.