It is a sad, but a true fact, that waste is ubiquitous in the environment! So what should we do about it? The message is sound and clear and comes from both inside and outside of the European Union, via the proposed and now widely known “waste hierarchy” (shown underneath). The pyramid mainly ranks the processes based on their ability to protect the environment and human health, alongside resource value recovery, with the tip of the pyramid presenting the most favorable option, and from there downwards we have options ranked from the most favorable to the least favorable one.
The waste generated in the agricultural sector is mostly of organic nature. According to the waste hierarchy organic waste should be recycled via composting (aerobic decomposition of organic matter), but environmental impact assessments have shown that other alternatives such as anaerobic digestion (where microorganisms decompose the organic matter in the absence of oxygen into biogas) can offer more benefits compared to composting even though it ranks lower in the waste hierarchy. This offers a fundamental insight; the waste hierarchy should not be followed blindly but used as a blueprint to identifying the right option for the management of waste following a holistic analysis of the environmental, economic, social and technical impacts as shown in the Table below. You can find out more here.
This becomes more evident when we look into the other types of waste materials generated in the agricultural sector, specifically plastics. Plastics or plastic-based materials are used in many different processes in the agricultural sector, such as: plastic films in low tunnels regulating the temperature and controlling other climatic conditions; mulch cover to retain humidity; plastic irrigation pipes that restrict the unnecessary use of water and/or nutrients; plastic reservoirs that can collect rain water; and plastic films used for silage storage protecting crops, just to name a few. Other plastic articles used in the agricultural sector include the boxes and plastic crates for crop collection-handling-transport, other irrigation system components (e.g. fittings and spray cones), tapes for keeping elevated the upper parts of the greenhouse plants, nets to darken the interior of the greenhouses or minimise the effects of hail.
All those plastic components and products serve a useful purpose, but once they reach the of their service life they become waste. The best option to manage these wastes is to retrieve them from the fields, sort them into flexible and rigid type and having them collected by a waste collection company that takes them to specialized facilities for treatment. Rigid plastics can go to sorting and reprocessing facilities where here they are sorted to different types (e.g. PET, HDPE, LDPE, PP) before being grinded, washed, decontaminated and turned into pellets. The secondary plastic materials generated via this treatment process can then be used again as recycled content in the manufacturing of new products i.e. bags, plastic lumbers and sidewalk pavers, a process widely known as downcycling, or cascading recycling process. In the case of films that are heavily contaminated and cannot be cleaned sufficiently, or other flexible plastic articles that cannot be reprocessed mechanically, the energy recovery process (following in order the recycling in the waste hierarchy) is a valuable alternative, recovering the calorific value of plastics.
All this sounds great right? But does this happen in reality? With only ca. 10% of agricultural plastics being currently recycled globally, it is safe to suggest that we have a long way ahead of us in moving towards a circular plastics economy in the agricultural sector. Most importantly, we need to revisit the waste hierarchy and begin our efforts to tackle agricultural waste management from the tip of the pyramid and move downwards according to the context and types of wastes generated. To that end a system of systems approach can help us understand the multi-faceted challenges that currently hamper progress in promoting sustainable circularity in the agricultural sector, and help us identify which, and where changes are needed in the system to enable transformational change.
Dr. John N. Hahladakis
Chemical Engineer (M.Eng., double M.Sc., Ph.D.)
Center for Sustainable Development