The EUSDR Water Quality Priority Area (PA4) together with the International Commission for the Protection of the Danube River (ICPDR) and with the assistance of the Danube Strategy Point organized a Green Week Partner event: WASTEWATER AS A RESOURCE: REGIONAL WORKSHOP ON SEWAGE SLUDGE MANAGEMENT AND ENERGY EFFICIENCY on 20 June 2025, receiving more than 100 registrations.
The aim of the workshop was to provide an overview of sludge legislation and policies in the Danube Region, including an update on the current European Union policies, and a summary of the national situation in the Danube countries and further to showcase country experiences along with utility examples from both EU and Non-EU countries in relation to sewage sludge management.
In the keynote presentation Sylvie GRAJALES from the Directorate-General Environment of the European Commission provided an update on the recent European policy developments and referred to the upcoming Circular Economy Act that will be an omnibus regulation which can amend several pieces of legislation. It is expected to be adopted by the EU Commission by the end of 2026. In this regard, she pointed out to the upcoming public consultation starting in July 2025 and advising participants to provide input on sludge management in the Danube Region. Ms Grajales further stressed that the EU Sludge Directive will not be re-casted. Member State data on sludge, especially in relation to agriculture is not very precise, and the EC would like to have more precise data in that regard, also noting that sludge management is very dependent on local conditions.
Recognizing the significance of the issue of sewage sludge that has been steadily growing in the Danube Region, the EUSDR PA4, supported by the Hungarian Ministry of Foreign Affairs and Trade initiated the elaboration of a study on sewage sludge treatment and recovery in the Danube Region in 2024. The results of the study were presented by Attila Fürstand from the company Trenecon. He noted missing data on the use of the processed sludge products and reflected that countries differ greatly in the applied technologies; the historical development of sludge management is different in countries and stressed that 20% untreated sludge is used in agricultural land.
An overview both from an EU country (Hungary: Károly Kovács from the Hungarian Water Association ) and from a non-EU country (Bosnia and Hercegovina: Maja Čolović Daul from the company Dekonta) was presented with discussions on sludge defined as a waste and the need to have permit to deal with it in most cases. Sludge is very variable, similarly as the sewage systems and the technology; with occurring risks such heavy metals, microbes, pathogenic organisms. Financial investment seems very challenging in most places and most cities do not encounter it. Large debate was held among the participants on use of sludge in agriculture and its requirements needs, especially in relation to microplastics.
In the second session an overview was provided from 6 countries by utility experts. Whereas some countries have specific sludge management and recovery strategies, others manage sludge in line with the criteria set out in their water and wastewater management strategies. There are differences in the administrative backgrounds, the focus and the applied techniques, however similar aspects in management exist and common targets are derived from the EC legislation and strategies. Importantly, sludge can be considered an important resource and, at the same time, a risk for the environment in all EUSDR countries concerning soil and water quality as well as human and livestock health.
From Bosnia-Herzegovina: Alma Džubur from the University of Sarajevo presented the Central Sarajevo Sewerage System which serves about 90% of the population of Canton Sarajevo and covers the area of several municipalities (Stari Grad, Centar, Novi Grad, Novo Sarajevo, Ilidža and part of Vogošća, Hadžići and part of Trnovo and a part of Lukavica and Istočna Ilidža). The main technology is activated sludge process with suspended growth for carbon removal and nitrification, including primary sedimentation and anaerobic sludge digestion. Biogas is produced in digesters through alkaline, mesophilic digestion; the sludge retention time in digesters is approximately 25–30 days.
From Croatia: Wanda Plačko from the company Riko demonstrated the WWTP plant for the communal company ViO Jastrebarsko, the sludge treatment using a reed bed system at WWTP Jastrebarsko. Problems identified: estimation of sludge load, troubleshooting of drainage functionality, weeds and animals. Plans for future improvements might be achieved in 10 years, which might be a problem of management changes. The Croatian system is also using Nature-Based Solutions, and it was noted that overflow of the beds is not possible, as each bed includes space for sludge accumulation.
From Germany: Sven Vogt from the city of Augsburg provided an overview of the situation of the Augsburg WWTP. The WWTP is equipped with mechanical treatment (screens, grit chamber, primary clarification), biological treatment (upstream denitrification, nitrification, secondary clarification), coagulant dosing for phosphorus removal, sludge treatment (static pre-thickening of excess sludge, digestion, sludge dewatering using chamber filter presses, sludge utilization via sludge silo) and gas utilization/energy generation (gas purification, boiler, CHP) options. The efficient operation and the good energy management make the Augsburg WWTP one of the best plants in Europe in terms of both overall effectiveness and the degree of self-sufficiency.
From Romania: Monica Isacu from the company Aquatim presented that Romania promotes the use of sewage sludge as fertilizer in agriculture, under strict conditions. Sludge must be treated and stabilized (e.g. by anaerobic digestion). Further it was discussed whether it is waste or valuable resource and if it is a risk for environment and health. She pointed out that there is time limited storage on authorized and controlled sites e.g. specially designed platforms. Sludge thickening and dewatering solutions: mechanical thickening & dewatering and solar greenhouse drying.
From Slovakia: Lucia Šperňáková from the Liptovský Mikuláš WWTP presented a situation both from the country and from utility perspective and highlighted those pharmaceuticals on WWTP has ongoing research from 2013 with more than 1,500 samples, stressing that there is a wide range of removal efficiency, removal is by biodegradation. It was noted that 93 pharmaceuticals were analysed and 25 pharmaceuticals are present in every sewage sludge sample.
From Slovenia: Špela Železnikar from the University of Ljubljana provided an overview of the Ajdovščina WWTP experimental site, where they are actively performing experiments since 2019. The reconstructed WWTP operates as a conventional flow-through plant with pre-denitrification and anaerobic stabilisation of the sludge. Research is ongoing since 1989, with different projects and pilot scale experiments. The university established a demo centre for research, with practical solutions including evapotranspirative willow system, high-rate algae pond, test fields with lysimeters. Experience with tomatoes is growing: no differences between irrigation with different sources of treated wastewater can be found in metal concentrations at different parts of the plant.
The organisers, EUSDR PA4, Zsuzsanna Kocsis-Kupper and ICPDR, Ádám Kovács, summarised the key messages of the workshop and thanked all speakers and participants for their active contributions during the event. Discussions shall continue, stay tuned for the upcoming public stakeholder discussions on the Circular Economy Act. More wastewater-related events are planned in the future by EUSDR PA4 and ICPDR.
The video of the event can be viewed below:
The presentations are available below:
1. Sludge presentation EU Grajales
2. Sludge Study_Trenecon Fürstand
6. Sludge_WWTP Croatia Jastrebarsko_Wanda Plačko
8. Sludge_Romania Monica Isacu
10. WWTP Slovenia Ajdovscina_Zeleznikar
Key takeaways
- Sludge management is highly dependent on local conditions and requires country-specific approaches.
- Public consultation on the Circular Economy Act will begin in early July 2025 and input from the Danube Region is also expected.
- The EU Sludge Directive will not be recasted, but new rules will be applicable via the upcoming Circular Economy Act.
- In the future focus may be on updating contaminant lists and improving monitoring.
- Data management and monitoring of sludge usage remains a significant challenge.
- Microplastics and pharmaceuticals in sludge are emerging concerns.
- Financial investments continue to be a major barrier for implementing advanced sludge treatment.
