The European Directive 86/278/EEC implemented in 1986 was a means adopted by the European Union to improve use of the valuables in sewage sludge by applying treated sludge on agricultural soils. To prevent an accumulation of pollutants, the Directive provided suggestions limiting concentrations of toxic elements in sewage sludge and agricultural soil. The Directive was implemented diversely throughout EU member states, with current national legislations only partly reflecting the initial intentions of the EU Directive from 30 years ago. This study demonstrates how the European Directive was implemented in three countries currently at different stages of replacing the agricultural application of sewage sludge with incineration (Netherlands, Germany and Sweden). Additionally, recent changes in the legislation with regards to the re-use and final disposal of sewage sludge in the three chosen member states are analysed. The aim was to investigate how each member state has solved the conflict between improvement of nutrient recovery from sludge and limitation of pollutants in agricultural soil. Based on this review, limit values are not necessarily reflected in application rates of sewage sludge in agriculture. Following changes in current legislation, phosphorus recovery will become a priority task. The recovery of other valuables from sewage sludge is currently not regulated in the legislation of the three member states investigated.

This study uses a new approach for the recycling of plant nutrients by co-digesting sewage sludgewith fly ash from a wood combustion. Sewage sludge and fly ash both are enriched with nutrientsof the wastewater resp. wood, which makes these products an enhanced source for recycledfertilizers. The effects of the ash addition to the anaerobic digestion are studied in several labscale experiments including effects on the gas production and microbial activity. Following that,the fertilizing qualities of the digestate are evaluated by plant growth experiments. The resultsshow that the fertilizing qualities of the digested sludge were improved by the ash addition.Next to this, gas production results show that the methane production was not affected by theash addition, while the total gas release was reduced. The sulphur addition by the ashstimulated sulphate reducing bacteria. The sulphate reducing bacteria did not markedly inhibitthe methanogens.

Sewage sludge management is torn between a desire for pollution prevention and reuse of a valuable resource. Reconciling these interests in sustainable management is a challenge for researchers. This study focuses on how research on sewage sludge management practices has evolved and scrutinizes how this research is interlinked with concerns and societal issues such as contaminants, economic efficiency, and legislation. Based on published academic papers on sewage sludge management between 1971 and 2019, this study found four trends in research focused on sewage sludge management: a decreasing interest in disposal (landfilling and sea dumping), a dominant interest in land application, a growing interest in sewage sludge as product, and a stable interest in energy recovery. Research on disposal focuses on increasing sludge volumes, legislative changes, and economic challenges with an interest in waste co-treatment. Research on land application concerns nutrient use and contaminants, mainly heavy metals. Research on sewage sludge as a product focuses on the extraction of certain resources and less on use of sewage sludge specifically. Research on energy recovery of sewage sludge focuses on volume reduction rather than contaminants. Two-thirds of the papers are detailed studies aiming to improve single technologies and assessing single risks or benefits. As management of sewage sludge is multifaceted, the narrow focus resulting from detailed studies promotes some concerns while excluding others. Therefore, this study highlights potential gaps such as the combination of nutrient use and disposal and energy recovery and nutrient use. 

Usage pathways for sewage sludge are changing in Sweden but in contrast to other European countries Swedish legislation has no clear aim for phosphorus recovery from sewage sludge. Therefore, options like co-incineration and agricultural usage will become more important. Previous research identified hydrothermal carbonisation (HTC) as a potential treatment prior to incineration as it can help to dewater the sludge. Literature also discussed HTC as a pre-treatment for agricultural usage. This study investigates how HTC can be integrated into existing sewage sludge treatment systems using lifecycle assessments (LCA) of six archetype scenarios involving co incineration and agricultural usage of the solid product (hydrochar) of HTC. The results show that HTC can be advantageous as a pre-treatment to co incineration, especially when used before transporting the material to the incinerator. Utilizing the liquid product of HTC for biogas production reduces the climate change impacts but on the other hand increases ecotoxicity impacts. Utilizing hydrochar in agriculture as a soil amendment instead of incinerating it, does not show clear benefits over land application of sewage sludge, as hydrochar, in contrast to biochar from pyrolysis, decays in the soil within few years and is therefore not suitable for carbon sequestration.

Land application of sewage sludge has long been subject to concern. Among the reasons for these concerns are, for example, the occurrence of odours and the risk of spreading heavy metals and pathogens, but also a negative perception regarding the use of sludge. In this paper, we focus the actors' perceptions of sewage sludge use and investigate, through a series of interviews with key actors and stakeholders in the sewage sludge management chain, how technology, the regulatory framework or public perception may function as barriers for valuing sewage sludge as a resource. The uncertainty following outdated legislation and constantly changing policies are frequently mentioned as the main barriers to investment in new technologies, which, in the respondents' opinion, creates a deadlock within the sector with no clear path forward. Although all respondents act and argue with a focus on environment and circularity, their overall sludge management strategies, as well as the issues they focus on, differ. Our study indicate that Swedish sludge management is, to a large extent, siloed and there is a clear a need for a more holistic approach that can help actors to target common issues.