Sludge Treatment Reed Beds Research Articles

Bacterial community composition and diversity under increasing loading rates in reed wetland for sludge treatment

Efficient and sustainable sludge management is a significant environmental and health challenge. Sludge-treatment reed beds (STRBs) are widely recognized as a cost-effective, highly efficient, and environmentally friendly solution for sludge treatment and dewatering. This study investigated the bacterial community composition and diversity in pilot-scale STRBs operating at different sludge loading rates (75, 100, and 125 ​kg ​m2 year−1). 16S rRNA V4 DNA sequencing was used to assess the diversity of the bacterial communities within the sludge samples. The relative abundance of prokaryotic taxa was affected by all treatments. As the sludge loads increased, the Shannon entropy and evenness diversity also increased for the STRBs and unplanted beds. Interestingly, the presence of reeds resulted in significantly lower Shannon and evenness indices than unplanted beds, regardless of the sludge. Additionally, the correlation network analysis revealed distinct microbial clusters with distinct responses to reeds and sludge loads. Principal component analysis evidenced an association between cluster 5 and organic matter decomposition, primarily at higher sludge doses, while clusters 4 and 6 were related to sludge decomposition at lower doses. Additionally, cluster 4 was associated with nutrient removal. The formation of distinct microbial niches was linked to sludge stabilization and nutrient removal and was influenced by both sludge loading rates and the presence of reeds. Future research can leverage these findings to innovate pollutant removal and ecosystem services for sludge treatment, thus advancing sustainable sludge management and environmental preservation.

Modelling sludge dewatering in treatment reed bed considering sludge deposit formation

AbstractThe accumulation of sludge deposits is a crucial factor in the dewatering efficiency of sludge treatment reed bed (STRB). This paper presents an improved one-dimensional process-based mathematical model to simulate the dewatering mechanism in STRBs, in which the compressible cake filtration (CCF) theory was implemented to simulate the sludge deposits accumulation on the surface of the reed bed, while the varying sludge deposit thickness was accounted for using the moving mesh method. The proposed model also included the dual porosity variably saturated flow model and the Penman–Monteith equation to describe the dewatering through gravity drainage and evapotranspiration, respectively. The results from the model were validated with experimental data from laboratory-scale STRBs treating septage. The simulation results showed that considering the sludge deposit layer as a specific flow resistance effectively avoids the overprediction of water infiltration rate in the reed bed. The predicted results showed excellent agreement with the actual data, where only five cases of the root mean square error were above 10% compared to the average effluent flux. Further, the effect of evapotranspiration was found to be insignificant within a short-term simulation. The consideration of the influence of sludge deposit formation on drainage dewatering using the CCF model and moving mesh model has delivered a more robust simulation for sludge dewatering in STRBs, and the proposed model is capable of facilitating the understanding of the interactions between the sludge dewatering in STRB with respect to the bed characteristics, hydraulic load, and solid load.

Mapping the causality of interacting perceptions for nature-based solution and sludge treatment reed bed: A causal loop diagram in Iceland

To ensure the successful implementation of Nature-Based Solutions (NBS), it is essential to assess the perception of key stakeholders. To visualize the perception of NBS key stakeholders and to identify potential opportunities and eventual conflicting interests, five groups of stakeholders were identified: (i) academics, (ii) governments, (iii) NGOs, (iv) water companies, and (v) local communities. Semi-structured interviews with the representatives of these five groups were conducted across Iceland. The interviews were transcribed using Vivo coding, an open-coded method. 170 variables were found within codes and classified into Independent, Dependent, and Intervening Groups of variables (InDGs, DGs, and IGs, respectively). These variables were mapped using the Vensim model to visualize the causality of each variable with one another. The Vensim model identified 85 InDGs, 43 DGs, and 42 IGs. The InDGs and DGs were classified into themes to visualize the effect of variables on 13 topical groups in Causal Diagrams (CDs) focusing on NBS and Sludge Treatment Reed Bed (STRB) technology. A causal loop between biodiversity, sustainability, and seawater quality was identified in the aggregated CD. This study sheds light on the reforms needed in the Icelandic system to facilitate resource recovery from sewage sludge in Iceland using NBS and STRB. Hence, our findings provide policy and decision-makers with intra-community information to identify factors influencing STRB application.

Modelling of Hydraulic Dynamics in Sludge Treatment Reed Beds with Moving Boundary Condition

The conventional method of simulation using fixed mesh method (FMM) of discretization is a well-known and trusted procedure in modelling hydraulic dynamics. However, new ideas of innovation in modelling should be advanced. The moving mesh method (MMM) has been considered as a novel approach in modelling hydraulic dynamics after depending on the existing simulation model for decades. The MMM is capable of describing the moving boundary condition of an actual wetland system due to water ponding. An idealized model should be able to simulate the actual hydraulic flows through the system with the corresponding porosity. Hence, a combination of MMM and FMM (MM-FMM) of discretization for hydraulic dynamics is studied in this project to model the flux with respect to water ponding scenario in a sludge treatment reed bed and unsaturated transient flow within the bed. Such method has evidently proved to simulate the actual hydraulic flows in contrast to conventional method. The application of MMM limits the maximum flux to keep within its saturated conductivity, thus reduces the effect of flow overprediction. Subsequently, the simulated results for hydraulic head and moisture content can be predicted for actual condition of different cases according to their respective fluxes.

Dewatering, Stabilization, and Final Disposal of Waste Activated Sludge in Constructed Wetlands

Objective: This research aimed to assay the dehydration and stabilization of surplus biosolids from a wastewater activated sludge treatment plant, with sludge-treatment wetlands, at the Iguazú National Park (Misiones, Argentina). Materials and Methods: A 12-cell sludge-treatment reed beds (STRB) system was built and operated for four years. Afterwards, the accumulated sediments were analyzed for total solids (TS) concentration, volatile solids (VS) reduction, specific oxygen-uptake rate (SOUR), and heavy metals and pathogens concentrations. Results and Discussion: TS concentration increased from 0.55 % to 14.3 %, VS were reduced by 33.3 %, and SOUR lowered to 1.09 mg O2gTS-1 h-1. These figures and the final concentrations of heavy metals and pathogenic microorganisms (102 MPN E.coli.gTS-1) indicated a degree of stabilization and sanitation that allowed classifying these biosolids as Class A, according to the Argentine guidelines, National Resolution 410/18, and enabled their reuse for soil amendment in landscapes and other agronomic purposes. Conclusion: The technology tested showed good results applied under a tropical climate, with annual temperatures between 17 and 27 °C, rainfall of 1870 mm y-1, and planted with autochthonous vegetation. Furthermore, it allowed the reuse of 221 t (144 m3) of a harmless product in an environmentally sustainable way.

Assessment of diversity and composition of bacterial community in sludge treatment reed bed systems

Due to their low emission of odours and lack of the need to apply additional chemical agents, sludge treatment reed beds (STRBs) constitute an economically feasible and eco-friendly approach to sewage sludge management. Correctly designed and operated STRBs ensure effective reduction of the dry matter content coupled with the mineralisation of organic compounds. Successful operation of STRBs relies on complex interactions between the plants and microorganisms responsible for the decomposition of organic matter and nutrient cycling. While the biocenoses of wetland systems dedicated to wastewater treatment have been intensively investigated, in the case of sludge treatment applications, there is a deficit of available microbial data. The aim of this study was to explore the diversity and spatial distribution of the bacteria in three distinct STRBs which differ in maturation and feeding patterns. Analyses of the dry mass and organic matter content showed the general trend of the sludge stabilisation processes advancing through the bed depth, with the best performance in the Matured Continuous Feed (MCF) bed being noted. Samples from the MCF bed showed the statistically greatest biodiversity in relation to the other beds. Moreover, increased biodiversity of microorganisms was observed on the surface of the STRBs and the bottom zone of the MCF equipped with a passive aeration system, which proves the application of such solutions in order to enhance the performance of the process. The results of 16S rRNA gene sequencing revealed that Bacteroidetes, Proteobacteria and Firmicutes contributed approximately 80% of all identified sequences read. Network analysis revealed dominant role of Bacteroidetes in the formation of interspecies co-existence patterns. Nitrospira was the most abundant organism responsible for nitrogen metabolism in the STRBs.

Sustainable Dewatering of Industrial Sludges in Sludge Treatment Reed Beds: Experiences from Pilot and Full-Scale Studies under Different Climates

Sludge treatment reed beds (STRBs) are an established sludge treatment technology with multiple environmental and economic advantages in dewatering sludge generated during domestic wastewater treatment. However, little is reported regarding their appropriateness and efficiency for the treatment of sludge produced during industrial wastewater treatment and from water works. These sludge types may have significantly different quality characteristics than typical domestic sludge and may contain constituents that could affect their dewaterability. Therefore, the dewatering of these industrial sludge types is usually tested in small-scale pilot STRBs before the construction of full-scale systems. This paper presents and summarizes the state-of-the-art experience from existing pilot and full-scale STRB systems from various countries and climates treating sludge from various industrial sources, evaluates the suitability and the advantages of this sustainable treatment technology, and proposes the required dimensioning for efficient full-scale STRB operation and performance.

Can additional air supply enhance decomposition processes in sludge treatment reed beds?

This work was designed to investigate the influence of artificial aeration on the sludge decomposition process in mesocosm sludge treatment reed beds (STRBs). In addition to the typical STRB design, where ventilation is mainly provided by a drainage pipe, passive aeration via a "chimney" and active aeration via a blower were introduced. During the entire observation period of 1.5 years, O2 concentrations in the upper part of the filter were significantly higher in the artificially aerated beds. To determine decomposition rates, a study with decomposition bags, measurements of CO2 emissions from the STRB and isotopic partitioning of CO2 emissions were performed. The results indicate an accelerated sludge degradation process in both active and passive beds. However, this effect was limited to part of the season and could not be demonstrated by episodic measurements of CO2 efflux. The CO2 efflux showed a seasonal pattern. Average CO2 efflux was below 3.0 μmol m−2 s−1 in the winter months and reached 43 μmol m−2 s−1 in the warmer months. The low sludge load and drought period in summer 2018 resulted in an extremely low CO2 efflux in August 2018. Isotopic analyses revealed changes in decomposition dynamics for certain parts of the season, differences in contributions of sludge and plant derived CO2 to total CO2 emissions from differently aerated beds. Overall, passive aeration proved to be similarly efficient as active aeration and could therefore be considered for application in a full-scale system.

Spatial distribution of pharmaceuticals in conventional wastewater treatment plant with Sludge Treatment Reed Beds technology

Pharmaceutical residues are an emerging environmental problem. It is strongly confirmed that pharmaceuticals are present in soils and environmental waters (surface, marine and even groundwater), and that wastewater treatment plant (WWTP) effluents are the main source of pharmaceuticals in the watershed. The aim of this study was to recognize the spatial distribution and seasonal changes of selected pharmaceuticals in conventional WWTP with Sludge Treatment Reed Beds (STRBs) technology used for dewatering and stabilization of sewage sludge, because these systems have never been studied in terms of pharmaceuticals distribution or removal potential.The research was conducted in conventional WWTP in Gniewino, where raw wastewater was treated using mechanical, biological and chemical removal of the organic matter and nutrients, and sewage sludge was treated with STRB. Determinations of pharmaceuticals (non-steroidal anti-inflammatory drugs - ibuprofen, paracetamol, flurbiprofen, naproxen, diclofenac and its metabolites) and basic parameters were carried out in samples of influent and effluent from WWTP and in the liquid phase of surplus activated sludge (SAS) as well as reject water from STRB.The potential of removal varied among target pharmaceuticals. Ibuprofen and naproxen were completely removed by the standard applied technology of the Gniewino WWTP. Diclofenac and its metabolites were the chemicals with the lowest removal potential in wastewater and the highest detection frequency. These pharmaceuticals were also detected in the liquid phase of SAS as well as in reject water. However, removal potential when using STRB was higher than 94% (mostly higher than 99%), independent of the season. Indeed, the STRB technology is not only efficient in sludge dewatering and nutrient removal (primary purpose), but also elimination of polar pollutants. Nevertheless, removal in STRB did not mean that pharmaceuticals were totally eliminated because these compounds could be “trapped and stored” in beds (by the process of sorption) or transformed into other products. This study is a starting point for further exploration of STRB technology for elimination of emerging pollutants.

Polish experience in operation of sludge treatment reed beds

Sludge Treatment Reed Beds (STRBs) is the technology of sludge treatment, which is based on natural processes occurring in the environment, in specially designed and operated facilities to achieve benefits for the environment. Integrated dewatering and stabilization occur in reed systems. For economic and environmental reasons it is an attractive solution, especially in rural areas where there are no appropriate facilities.In the recent years many European countries like Denmark, France or Germany have applied this technology for sewage sludge management. Poland has also some experience in dewatering and stabilization of sewage sludge in STRB systems.The objective of the paper is to present the current experience and lessons learned from the operation and to assess the quality of sewage sludge from STRBs in Poland.The analyzed sewage sludge was treated in STRBs located in five wastewater treatment plants: Darżlubie, Swarzewo, Zambrów, Nadole and Gniewino, Poland. Two from the analyzed systems (Darżlubie and Swarzewo) worked only in a pilot scale and three of them (Darżlubie, Swarzewo and Nadole) did not work any longer. In the collected samples of sludge the evaluation of dewatering and stabilization processes, fertilizer properties, as well as heavy metals concentrations were determined.The average dry matter content in sludge treated in Polish STRBs was from 11.2 to even 53.7%. The degree of mineralization in analyzed systems was from 31.4 to 68.6%. The average nutrient contents was for nitrogen from 1.0 to 10% DM and for phosphorus from 0.2 to 1.0% DM.The conducted research confirms that sludge treated in STRBs is dewatered and stabilized, thus it could be used as a fertilizer in agriculture.

Septage unit treatment by sludge treatment reed beds for easy management and reuse: performance and design considerations.

Sustainable treatment and management of fecal sludge in rural areas require adapted solutions. Rustic and simple operating processes such as sludge treatment reed beds (STRB) have been increasingly considered for this purpose. The biggest full scale (2,600 m2 of STRB) septage treatment unit in France had been built in Nègrepelisse with the final objectives of reusing treated sludge and leachates for agriculture spreading and tree irrigation, respectively. The aim of this investigation was to validate the treatment chain of this installation. The obtained field data showed firstly that the overall removal efficiencies of STRB were satisfactory and stable. Removal rates higher than 98% for chemical oxygen demand and suspended solids and a 95% for Kjeldahl nitrogen represented so far a beneficial septage treatment by STRB. The highlighted necessity of a suitable complementary leachate treatment (before tree irrigation) justified the presence of the second stage of vertical flow constructed wetland. The sludge deposit drying and mineralization efficiencies were on the right track. According to hydrotextural diagram analysis, surface deposit was however found to have high deformability probably due to the youth of the installation. An in-depth understanding of STRB system needs continuous long-term studies.

Sewage sludge and waterworks sludge stabilization in sludge treatment reed bed systems.

In this study, results about sludge stabilization in sludge treatment reed bed (STRB) systems in two different systems, Hanningfield STRB 1 (England), treating waterworks sludge, and Stenlille STRB 2 (Denmark), treating surplus activated sludge, are presented. The study mainly focused on the effectiveness of the STRBs systems in stabilizing sludge organic matter; in fact, parameters correlated to biochemical and chemico-structural properties of organic sludge matter were determined. Dewatering and sludge stabilization were effective in both STRBs, as highlighted by total and volatile dry solids trend. β-glucosidase, phosphatase, arylsulphatase, leucine amino-peptidase and butyrate esterase activities, enzymes related to C, P, S, N and overall microbial activity, respectively, significantly declined along the profile in both STRBs. The determination of humic carbon highlighted the formation of a stable nucleus of humified organic matter in both STRBs in the deepest layers, thus meaning the successful stabilization of sludge organic matter for both kind of sludges. Similar conclusions can be drawn from pyrolysis gas chromatography analysis (Py-GC), which enables the characterization of soil organic matter quality from a chemical-structural point of view. The pyrolytic indices of mineralization and humification showed that in both STRBs the sludge organic matter is well stabilized.

Sludge Dewatering and Mineralization in Sludge Treatment Reed Beds

Sludge Treatment Reed Beds (STRBs) are widely used in Northern Europe to dewater and mineralize surplus sludge from activated sludge systems used to treat urban domestic sewage. STRBs are low-technology, energy-efficient, and do not require addition of chemicals. They dewater and stabilize the sludge and produce a final product that can be safely used as a fertilizer for agricultural crops. Long-term sludge reduction takes place in the reed beds due to dewatering and mineralization of the organic matter in the sludge. Although, in theory, a simple technique relying largely on natural processes, experience has shown that it is very important to understand and respect the basic design and operation requirements of STRBs. This paper describes the basic design and operation requirements of STRBs, with special focus on pivotal requirements to respect in order to secure proper functioning. Also, the paper summarizes performance experience concerning final dry matter content, degree of mineralization, emission of greenhouse gases, and degradation of micro-pollutants in STRBs. There are still a number of outstanding issues that are not fully understood, particularly in relation to the importance of the sludge quality for the dewatering in an STRB. Therefore, extreme care should be taken when attempting to extrapolate the use of STRBs to applications and regions outside of their ‘normal’ and documented area of application.

Integrated dewatering and stabilization system as an environmentally friendly technology in sewage sludge management in Poland

Sludge treatment reed beds (STRBs) are an environmentally friendly technology which provides integrated dewatering and stabilization of sewage sludge. STRBs do not require the use of chemicals to improve the dewatering process. STRB is both, a low-emission and a low-energy-consuming method. After the stabilization process, sludge is characterized by the chemical composition similar to that of humus. The aim of the paper is to present the comprehensive data from Waste Water Treatment Plant (WWTP) in Gniewino (Poland) where the sewage sludge is dewatered and stabilized in a STRB.Research and literature reports indicate that sewage sludge treated in STRB is dewatered, which results in an increase in the dry matter (dm) (from 1.1% to 15.5%) and stabilization due to the decrease in the content of the organic matter (from 71.2% of the dm to 52.4% of the dm). Likewise, thanks to the high concentration of nutrients (TKN concentration − 3.64% of the dm and P concentration − 3.54% of the dm) and the low concentration of heavy metals (below permissible values for the agricultural use) after the time of stabilization, safe and valuable product can be recycled to the environment. Reject water (RW) generated during this process has relatively stable and much better properties in comparison to these which are generated in high technologies for sludge treatment. Thus, recycling the RW from the slugde dewatering in STRB represents a very low internal pollution and should not alert the treatment proceses of wastewater.

Operational strategy, economic and environmental performance of sludge treatment reed bed systems - based on 28 years of experience.

Sludge treatment reed bed (STRB) systems have been used for dewatering and mineralisation of sludge in Europe since 1988. STRB systems provide substantial environmental, economic, and operational benefits compared to mechanical sludge dewatering solutions such as belt presses and centrifuges. They require less energy, no chemicals, reduce the sludge volume and produce bio solids with dry solid contents up to 20-40% under Danish climate conditions, depending on the sludge quality. Experience has shown that sludge treated in STRBs represents a high quality product with a low content of pathogens and hazardous organic compounds, qualities that make it suitable for recycling on agricultural land. The upfront capital cost for STRBs are often higher compared to mechanical dewatering devices. However, the operational expenses (OPEX) (including energy, chemicals, bio solid handling) are significantly lower compared to conventional mechanical dewatering devices, delivering an economic break-even of about 3-5 years. This paper provides an overview of the operation and maintenance costs and environmental benefits of a typical STRB based on the experiences gained from the operation of a large number of STRBs with yearly treatment capacities between 100 and 3,000 tonnes of dry solid up to approximately 250,000 PE in Denmark and Europe.

Emissions of CO2 and CH4 from sludge treatment reed beds depend on system management and sludge loading

Sludge treatment reed beds (STRB) are considered as eco-friendly and sustainable alternatives to conventional sludge treatment methods, although little is known about greenhouse gas emissions from such systems. We measured CO2 and CH4 emissions and substrate characteristics in a STRB, an occasionally loaded sludge depot (SD) and a natural reed wetland (NW). The aim was to compare (i) emissions among the sites in relation to substrate characteristics and (ii) emissions before and after sludge loading in the STRB. The STRB emitted twice as much CO2 (1200 mg m−2 h−1) as the SD, whereas the SD emitted four times more CH4 (2 mg m−2 h−1) than the STRB. The NW had the lowest emissions of both gases. The differences in gas emissions among the sites were primarily explained by differences in the availability of oxygen in the substrate. As a consequence of overloading and poor management, the SD had no vegetation and a poor dewatering capacity, which resulted in anaerobic conditions favoring CH4 emission. In contrast, the well-managed STRB had more aerobic conditions in the sludge residue resulting in low CH4 emission rates. We conclude that well-designed and well-managed STRBs have a low climate impact relative to conventional treatment alternatives, but that overloading and poor sludge management enhances the emissions of CH4.

Short-term performance analysis of sludge treatment reed beds

Sludge treatment reed beds (STRBs) represent an established technology for managing sludge produced by wastewater treatment plants (WWTPs). In this study, an analysis conducted on sludge stratigraphy in a STRB serving the municipal WWTPs of Helsinge (42,000 person equivalent, Denmark) is presented. The STRB has been in operation since 1996. The analysis was conducted for four months including two consecutive loadings of one of the 10 basins. The amount of dewatering during the short initial phase was significant, and the rehydration of deeper layers was negligible. A clear reduction trend was observed for volatile solids and labile organic matter, which is the first step towards organic matter humification. This hypothesis was also confirmed by water soluble carbon, which decreased with the increasing depth and the time of resting. About the N cycle, ammonification and nitrification showed a reciprocal balancing effect, so as to cause an equilibrium between the stable trends of NH(4)(+) and NO(3)(-) which were similar along the depth and the time of monitoring. The highest values of both parameters were found at the surface, where the combined effect of plant action, direct diffusive oxygen transfer from the atmosphere and high nutrient contents of the freshly loaded sludge was likely more intense.

Potential fertilizing properties of sewage sludge treated in the sludge treatment reed beds (STRB)

In previous research the fertilizer value of sludge from reed beds was evaluated based on the sampling sludge on different depths from four Danish sludge treatment reed beds (STRB) after long periods of stabilization. The dewatering efficiency of sewage sludge in the STRB is comparable to mechanical dewatering. The long-term stabilization of sewage sludge progressively decreases the concentration of organic matter due to the process of humification. The aim of the work was to determine the changes of organic matter concentration, nutrients concentrations as well as speciation of selected heavy metals (Cd, Pb, Ni, Cr, Cu and Zn) in vertical profile of the sewage sludge stabilized in the STRB for 7-15 years. The analyzed sewage sludge was collected from the STRB treating sludge from four municipal wastewater treatment plants located in Denmark serving from 9,000 to 40,000 person equivalent. Analyzed heavy metals (except for Zn) were mostly bound with the most stable - residual - fraction. The most stable metals were Pb and Cr, where the share of the residual fraction exceeded 80.0%. The most mobile metal was Zn, where the share of the mobile fractions (calculated as the sum of I, II and III fractions) exceeded 85.0%. The high concentration of nitrogen and phosphorus is the decisive factor in the high valuation of sludge stabilized in the STRB as fertilizer.

Carbon footprint of sludge treatment reed beds

Sludge treatment reed beds (STRBs) performance has become a popular solution to dewater and stabilize surplus sludge from wastewater treatment systems because of the low investment, operational and maintenance costs of the systems. The environmental impact associated with this technology has, however, to be assessed in order to evaluate the appropriateness of the technology. The goal of this study is to determine the carbon footprint of STRBs. To this end, a Life Cycle Assessment was performed using methane and nitrous oxide emissions quantified in two full-scale STRBs located in Northern and Southern Europe (Denmark and Spain). Methane emissions ranged between 1000 and 3700mg CH4/m2d, while nitrous oxides ranged between 200 and 750mg N2O/m2d. Thus, greenhouse gas emissions correspond to 0.09 and 0.25kg CO2eq/m2d for the Danish and Spanish system, respectively. The treatment of 1 ton of sludge (wet weigh) in the Spanish system corresponds to 2.1kg CO2eq, while in the Danish system it corresponds to 1.0kg CO2eq. The contribution of greenhouse gas emissions in the carbon footprint is insignificant in comparison with raw materials and energy consumption. However, the results put forward the relevance of STRB design in the environmental impact of the technology. Thus, the excavation of basins or the use of recycled concrete are recommended to guarantee a low carbon footprint of this technology.

Musk fragrances, DEHP and heavy metals in a 20 years old sludge treatment reed bed system

The Sludge Treatment Reed Bed (STRB) technology is a cost-efficient and environmentally friendly technology to dewater and mineralize surplus sludge from conventional wastewater treatment systems. Primary and secondary liquid sludge is loaded onto the surface of the bed over several years, where it is dewatered, mineralized and turned into a biosolid with a high dry matter content for use as an organic fertilizer on agricultural land. We analysed the concentrations of five organic micropollutants (galaxolide, tonalide, cashmeran, celestolide and DEHP) and six heavy metals (Pb, Ni, Cu, Cd, Zn and Cr) in the accumulated sludge in a 20-year old STRB in Denmark in order to assess the degradation and fate of these contaminants in a STRB and the relation to sludge composition. The results showed that the deposited sludge was dewatered to reach a dry matter content of 29%, and that up to a third of the organic content of the sludge was mineralized. The concentrations of heavy metals generally increased with depth in the vertical sludge profile due to the dewatering and mineralization of organic matter, but in all cases the concentrations were below the European Union legal limits for agricultural land disposal. The concentrations of fragrances and DEHP ranged from 10 to 9000 ng g−1 dry mass. The attenuation of hydrophobic micropollutants from the top to the bottom layer of the reed bed ranged from 40 to 98%, except for tonalide which increased significantly with sludge depth, and consequently showed an unusual depth distribution of the galaxolide/tonalide ratio. This unexpected pattern may reflect changes imposed by a long storage time and/or different composition of the fresh sludge in the past. The lack of a significant decreasing DEHP concentration with sludge age might indicate that this compound is very persistent in STRBs. In conclusion the STRB was a feasible technology for sludge treatment before its land disposal.