# Sewage Sludge Quality and Management for Circular Economy Opportunities in Lombardy
## 1 Introduction
The Directive is currently obsolete and does not consider the most recent technologies and alternative sludge recovery opportunities. The review of the Directive was started by the European Union (EU) in 1999, but a revision of the law is still absent. Since then, beyond scientific progress and technological developments, the policy framework has changed following the Circular economy action plans, the Bioeconomy Strategy, the new Fertilizing Products Regulation, the Farm to Fork Strategy, and the EU Biodiversity Strategy for 2030 [27]. Besides the regulatory framework, the \"ideal\" strategy for the reuse/disposal of sludge has not been identified yet, though numerous efforts are ongoing additionally through international projects and research [28]. The produced amount of sewage sludge in Europe (EU27) can be estimated as approximately 10 million tonnes, dry solids [29]. In 2021, approximately 48% was spread on land for agricultural use, and incineration stood at about 27% [30]. In 2016, the EU produced 16.1 Mtoe (Million tonnes of oil equivalent) of biogas, with sewage sludge feedstock contributing with 1.4 Mtoe of biogas (8.7%) [21]. Significant differences between the Member States in sewage sludge management are reported: while the reuse of nutrients in agriculture (land spreading or composting) is the most common practice in Spain, Ireland, Finland, Hungary, and Cyprus, incineration is mainly applied in the Netherlands, Belgium, Germany, and Austria [31]. The main aspects influencing the choice for sludge recovery/ disposal are population density and the availability of agricultural lands. Moreover, the low level of acceptance by farmers and the public could represent another significant restriction to biosolid land spreading [32]. In Italy, the production of sewage sludge (European Waste Code EWC 190805) was 3.4 million tonnes in 2020, out of which about 44% was recovered, with reuse in agriculture being one of the possible options [33]. Agricultural reuse is the most prevalent route in the regions of northern Italy, with Lombardy leading this trend [32; 33]. In Lombardy, the production of sewage sludge was around 468,800 t in 2020 (13.8% of Italian production) [33]. In Italy, the European regulation 86/278/EEC has been implemented with the Legislative Decree 99/1992 [34], then integrated in 2018 (Law n. 130, article 41 [35]), which deputes the regions to establish further limits and conditions for the reuse of biosolids in agriculture in relation to the characteristics of the soils, crops, and sludge. At the regional level, Lombardy implemented D.G.R. X/2031/2014 [36], integrated in September 2017 by the D.G.R. X/7076/2017 [37] and by Executive Decree D.D. 6665/2019 [38]. Regional regulations introduced requirements for the acceptability of sludge entering the sludge treatment plants (STPs--authorized for the treatment on behalf of third parties); provided two quality classes for biosolids reused in agriculture (\"high-quality\" and \"suitable for spreading\") with different limit values; and defined the characteristics of agricultural soils receiving the biosolids and spreading methods [32], and set limit values for additional parameters [38]. In 2016, the production of biogas in Italy was about 8259 GWh (3.8% in Lombardy), of which about 129 GWh was produced from sludge [39]. The production of biomethane is recently gaining more attention and the first plants have been realized and tested in the region in the last year, in parallel with the planning and design of full-scale plants. In short, possibilities of nutrients or energy recovery of sewage sludge are potentially virtuous solutions and promising perspectives for the circular economy, even though regulations and costs have an impact favoring or preventing this process. While there are no ready-made solutions for sewage sludge management, possible options need to be assessed case by case.