# Valorization of Agri-Food Waste into PHA and Bioplastics: From Waste Selection to Transformation
## 1 Introduction  
The generation of waste from the agri-food industry poses significant environmental, economic, and social challenges for Europe. According to the European Commission, around 20% of all food produced in the European Union is wasted annually, totaling over 88 million tons [1]. Of this waste, the agri-food sector (excluding household waste) is responsible for a substantial portion, distributed as follows:  
* Food processing: about 39% of the waste. * Primary production (agriculture and livestock): about 33%. Distribution and retail: about 5%. * Restaurants and catering: about 14%. The substantial volume of waste generation exerts a considerable environmental impact. However, if the recovery and transformation of agri-food waste were effectively managed, it could represent a significant economic market. Therefore, it is vital to adequately identify and manage by-products apart from non-valuable residues. In this sense, it is possible to gradually transform the current linear economy model into a circular one, where waste is introduced into the value chain. The circular economy model is based on minimizing waste and producing goods sustainably. Although European environmental policy is shifting toward a circular economy through various directives released by the European Parliament [2], there is still a long way to go. Large amounts of agri-food waste continue to be landfilled or incinated without any possibility of recovery. This not only represents poor economic management of available resources but also contributes to climate change through the release of methane (CH\({}_{4}\)), a greenhouse gas (GHG) produced in landfills. CH\({}_{4}\) traps around 120 times as much heat as CO\({}_{2}\) does. However, this does not mean that CH\({}_{4}\) is 120 times as potent a greenhouse gas as CO\({}_{2}\). Depending on how it is measured, CH\({}_{4}\) is usually counted as between 28 and 80 times as powerful a GHG as CO\({}_{2}\)[3]. This variation can be explained by the time span used to do the balance and the lifetime of CH\({}_{4}\) and CO\({}_{2}\) in the atmosphere. When CH\({}_{4}\) is released into the atmosphere, it immediately begins to trap heat--at least 100 times as much as CO\({}_{2}\). However, CH\({}_{4}\) starts to break down and disappear from the atmosphere relatively quickly compared to CO\({}_{2}\). As more time goes by, more CH\({}_{4}\) disappears, reducing its warming effect. Over 20 years, CH\({}_{4}\) would trap about 80 times as much heat as CO\({}_{2}\). Over 100 years, CH\({}_{4}\) would trap about 28 times as much heat as CO\({}_{2}\)[4]. In light of these challenges, the European Union (EU) has set its sights on achieving climate neutrality by 2050, a goal that encompasses all greenhouse gasses, including CH\({}_{4}\). Since 1990, emissions of this particular gas have declined by 36%, and experts project a further reduction of 44% by 2030. Despite the present difficulties posed by the energy crisis, there is an anticipated rise in ambition regarding both renewable and energy efficiency. Moreover, the European Commission is contemplating the incorporation of CH\({}_{4}\) as a regulated pollutant in the revision of the NEC Directive by 2025 [5]. The European Union initiated 135 new research projects in 2024 related to the circular economy model. These projects span a wide range of fields, including food and agriculture. Notably, 23 of these European projects apply different approaches to the reduction and valorization of agri-food waste. These 23 projects exemplify the ongoing commitment to the transition towards a circular bioeconomy [6]. Some of these projects are outlined below:  
* **LIFE Biogas. ** Focuses on the development of technologies for the production of biogas from organic waste. It also aims to improve the efficiency of converting waste into renewable energy and fertilizer [7]. * **RESURBIS (Resources from Urban Bio-Waste)**. Focuses on the conversion of urban organic waste into bioplastics, in particular, polyhydroxyalkanoates or PHA's.