IVL Swedish Environmental Research Institute

Stockholm’s wastewater treatment plant (WWTP) in is currently retrofitting from a conventional activated sludge process to a new membrane bioreactor (MBR) process. It also includes new treatment steps for sludge handling. Stockholm Vatten och Avfall (SVOA) and IVL have since 2014 conducted long-term MBR studies in pilot scale at the R&D facility Hammarby Sjöstadsverk. This report present results from the pilot operation during 2020. 

The MBR-pilot was continuously operated at a higher inflow than the design average flow. The average effluent concentration of nitrogen and phosphorus met the effluent requirements of the future WWTP also this year. A low consumption of phosphorus precipitation chemicals could be achieved mainly due to a high Bio-P activity. The pilot showed that glycerol can be a good temporary carbon source at Henriksdal WWTP during startup. 

Like previous years, the membranes in membrane tank 1 (MT1) was cleaned with oxalic acid and the membranes in MT2 with citric acid. Several tests to optimize the chemical consumption for membrane cleaning were performed. Recovery cleanings (RC) of the membranes were performed twice in 2020.

In the sludge pilot, a thermophilic and a mesophilic hydraulic retention time (HRT) crash test showed stable performance down to 4 days HRT. 

The overall resource consumption in the pilot showed that the optimization of phosphorus precipitation and membrane cleaning chemicals resulted in a significantly lower dosing than design values for the future Henriksdal WWTP. 

In this study, the performance of aeration diffusers from Swedish wastewater treatmentplants were tested for the first time. The results showed that fouling as well asageing of diffusers occur at Swedish treatment plants which leads to increased electricityusage for aeration. At the same time, there are opportunities with condition-basedmaintenance that can reduce unnecessary electricity use.With increasing CO2 emissions and electricity prices, energy efficiency has becomeimportant, not least to achieve the goal of a climate-neutral VA industry.

At the municipalwastewater treatment plants, aeration of the biological treatment basins typicallyaccounts for half of the treatment plant’s total electricity usage, and internationalstudies indicate that up to 40 % of this electricity is wastage due to fouling and ageingof membranes. But the Swedish experiences are limited. The limited knowledge islikely related to that it is not commonly known in the Swedish water sector how theperformance of aeration systems can best be monitored, how maintenance cleaningcan be done and how large the potential savings are.

In the project, membrane diffusersfrom six Swedish treatment plants were tested in a purposely built test facilitywith clean water and analysed with respect to oxygen transfer efficiency (SOTE) anddynamic wet pressure (DWP). Unlike previous studies, the effects of ageing of themembrane material and fouling of the membranes were assessed separately, whichis crucial to choose the right mitigation action.Two methods for diffuser condition monitoring were implemented at treatmentplants within the participating organisations. Although there were some practicalchallenges with implementation, the results show that it is feasible to monitor changesin SOTE and DWP, either with direct measurements or calculations based on availabledata.The results from the clean water tests showed that fouling primarily affected DWP(up to 40 mbar increase) which is therefore a suitable parameter to monitor, in orderto set the cleaning interval. Ageing, on the other hand, showed a greater impact onSOTE (up to 25 % decrease) compared to fouling (up to 10 % decrease).

Overall, themeasured effects are somewhat lower than what the literature indicates.However, the percentage values do not reflect the actual impact on electricity usage.Therefore, the combined effects of ageing and fouling were simulated in a model, withvarying maintenance intervals for cleaning and membrane replacement. The conclusionof the simulations was that it was both economically and climatically advantageouswith frequent maintenance (membrane replacement every five years in combinationwith two cleanings per year).The autors advice is therefore to facilitate membrane replacement so that it canbe carried out in a cost-effective manner. The performance of the diffusers should bemonitored using any of the suggested methods. It is furthermore important to actuallycarry out maintenance measures as often as economically justified, where localconditions affect the economic optimum.

Turbidity, which is the cloudiness or haziness of water caused by large numbers of individual particles, is a critical factor for drinking water producers. High turbidity can harbour harmful microorganisms and reduce the effectiveness of disinfection processes, making it essential to monitor and manage to ensure safe drinking water.This study was conducted at the Rökebo water production plant, which produces drinking water for Sandviken and nearby areas, serving around 29,000 people. The treatment process includes several steps, such as chemical precipitation, filtration, UV treatment, and chlorination, to ensure the water is safe to drink.

A new plant is being constructed to use only lake water and will include additional treatment steps to remove natural organic matter.Lake Öjaren is moderately sized, covering 21 square kilometres with an average depth of 4.66 meters, which means it is a shallow lake. The depth and shape of the lake influence how it responds to wind and weather, which can stir up sediments and affect water clarity. The catchment area of Lake Öjaren consists mainly of forest and moraine but has 5.5% clear-cuts, which contribute to higher turbidity levels in combination with heavy precipitation.

Climate change is expected to bring warmer temperatures and more rain to Sweden, affecting Lake Öjaren’s water quality and availability. Projections indicate that runoff to the lake will increase by about 15%, which is more than the average for the area. Less precipitation will fall as snow, leading to more water flowing into the lake during winter. These changes will likely increase the levels of nutrients and organic matter in the lake, increasing turbidity and calling for an adaptation strategy at the drinking water plant. We tested several machine learning models to predict water turbidity, including ElasticNet Regression, RandomForestRegressor, GradientBoostingRegressor, and XGBoost.

These models helped us understand which factors most affect turbidity. For example, the RandomForestRegressor model performed well, showing that air temperature, wind speed, and rainfall from the past few days were important predictors. The XGBoost model also provided valuable insights, particularly emphasising the impact of rainfall from four days prior. Despite using general meteorological data, our models successfully predicted local conditions in Lake Öjaren, demonstrating their robustness. However, capturing extreme turbidity events remains challenging. High-quality data and advanced techniques are crucial for improving predictive accuracy. Future work should focus on collecting more detailed data and refining models to support effective water management and mitigate climate change impacts on the drinking water production. This ongoing research is vital for ensuring a reliable drinking water supply, even under changing environmental conditions.

Dam monitoring is a large and important area for Swedish dam owners. It is a challenge to continuously monitor a dam construction with its sensors and be able to quickly react to changes that indicate a deviation in the dam. The report covers methods for computer-based detection of sensor and communication errors and the application of multivariate methods to detect and visualize anomalous states for a dam.The report is an account of the third of a series of research projects. The project has been run by IVL Swedish Environmental Research Institute AB during 2022–2023. All projects have been funded by Energiforsk and the SIVL foundation and with the aim to implement monitoring, detection, and visualization of sensor errors as well as overall condition monitoring of dams including warnings when the condition is moving towards a non-normal area.

One purposes of this project has been to deepen the knowledge of the methods through an additional case study which has a different character both regarding the dam and its monitoring sensors. A second purpose has been to increase knowledge and competence both in breadth and depth for the involved industry. A third purpose has been to find ways to improve the accessibility of the results that our methods provide.In the previous two projects in the series, it was reported how we developed and installed a general monitoring application that runs in real time at two of the dam owners with data transfer from and to their signal databases. We have developed methods for independent monitoring of individual signals, univariate monitoring and started the development of multivariate monitoring.In this project, the accumulated experience has been used to connect a third dam, Case Study III, and to continue the development of the methodology. A large part of the project has also been devoted to dissemination of results in the form of webinars, a deeper course for staff at the power companies on the methodology used and the underlying theory.The project series now has three case studies and through the plant owners the project has gained access to more than 5 years of historical data for each dam. These data form the basis for further development and evaluation of monitoring methods. Collecting, building a common understanding of and pre-processing this data requires a lot of time and good cooperation between data specialists and dam owners, a foundation that has now been laid.

This report is published both in Energiforsk's report series and in IVL's report series B.

This prefeasibility study assesses halocline ventilation as a solution to oxygenate hypoxic and anoxic bottom waters in the Baltic Proper. The method requires pumping 10,000 m³/s of water between stratified layers, demanding 600 GWh of energy annually, at an estimated cost of €50 million. While promising for mitigating eutrophication, technical barriers, including the lack of suitable submersible pumps, remain significant.

Powered by offshore wind, the method’s carbon footprint (10 kg CO₂eq/kg separated phosphorus) is lower than alternative strategies, with ecological benefits such as improved habitats, increased fish reproduction, and reduced harmful algal blooms. However, risks like halocline disruption and sediment mobilization require thorough evaluation.

The integration of wind energy and ecological restoration highlights the need for marine spatial planning and stakeholder dialogue to balance ecological, technical, and societal considerations. Further research and pilot studies are essential to validate its feasibility and long-term impact.

In urban environments, particularly areas under reconstruction, metals, organic pollutants (OP), and microplastics (MP), are released in large amounts due to heavy traffic. Road runoff, a major transport route for urban pollutants, contributes significantly to a deterioratedwater quality in receivingwaters. This studywas conducted in Gothenburg, Sweden, and is unique because it simultaneously investigates the occurrence of OP, metals, and MP on roads and in stormwater from an urban area under reconstruction. Correlations between the various pollutants were also explored.

The study was carried out by collecting washwater and sweepsand generated from street sweeping, road surface sampling, and flow-proportional stormwater sampling on several occasions. The liquid and solid samples were analyzed for metals, polycyclic aromatic hydrocarbons (PAH), oxyPAH, aliphatics, aromatics, phthalates, andMP. The occurrence ofOPwas also analyzedwith a non-target screening method of selected samples. Microplastics, i.e. plastic fragments/fibers, paint fragments, tire wear particles (TWP) and bitumen, were analyzed with a method based on density separation with sodium iodide and identificationwith a stereomicroscope, melt-tests, and tactile identification.MP concentrations amounted to 1500 particles/L in stormwater, 51,000 particles/L in washwater, and 2.6 × 106 particles/kg dw in sweepsand. In stormwater, washwater and sweepsand, MP ≥20 μmwere found to be dominated by TWP (38%, 83% and 78%, respectively). The results confirm traffic as an important source to MP, OP, andmetal emissions.

Concentrations exceeding water and sediment quality guidelines for metals (e.g. Cu and Zn), PAH, phthalates, and aliphatic hydrocarbons in the C16–C35 fraction were found inmost samples. The results show that the street sweeper collects large amounts of polluted materials and thereby prevents further spread of the pollutants to the receiving stormwater.

Microplastic particles in stormwater pose significant threats to the environment. This study investigated howeffective a stormwater treatment train was at removing rubber, bitumen and other microplastics (incl. fibers,fragments, and paint particles) in the 100–300 μm and >300 μm size fractions from highway runoff. The twotreatment trains comprise a gross pollutant trap (GPT) followed by either a vegetated bioretention cell or nonvegetatedsand filter. Flow-proportional composite samples were taken from the highway runoff, GPT outflowand the outflow from the two parallel filters during nine rain events to determine overall treatment performance,as well as the performance of individual system components.

The identified rubber, bitumen and other microplasticparticles mainly represented the 100–300 μm fraction and included high ratios of rubber (30%) andbitumen (60%). Overall, the treatment train efficiently removed rubber, bitumen and other microplastic particlesin the 100–300 μm size fraction from the stormwater. The filter cells accounted for a major share of this removal,as the GPT did not reduce microplastic particle concentrations. This observation is likely explained by the factthat the rubber, bitumen and other microplastic particles have a density close to the density of water and thusremoval by sedimentation is decreased. This identified an inherent weakness of the system; more specifically, thehigh microplastic concentrations in the surface water of the GPT means there can be a risk of microplastic releasethrough overflow pits when inflows surpass the system capacity. Despite some differences, both the vegetatedbioretention cell and the non-vegetated sand filter removed rubber, bitumen and other microplastic particles tosimilar extent.

Wastewater treatment plants are commonly dimensioned based on rules of thumb and expertknowledge without a clear specification of how uncertainties have been handled. The impact of thedifferent assumptions can be quantified with uncertainty and sensitivity analysis. Weaknesses with traditional design methodology can potentially be mitigated by an increased use of simulation.

Kungsbacka kommun behöver bygga ut Hammargårds avloppsreningsverk för att bibehålla den ekologiska statusen i Kungsbackafjorden, trots en ökade belastning från tillväxten i Kungsbacka med omnejd. Kommunen ser en möjlighet att dra nytta av digitala tekniker för att effektivisera både byggprocessen och de färdiga reningsverken.Processmodeller har använts som verktyg i de flesta faser i ett reningsverks livscykel, men det saknas praktiska exempel på hur det bör ske på ett handgripligt sätt i projekterings- och byggprocessen. Detta projekt initierades därför för att förstå hur processmodeller kan stödja processval och dimensionering inom partneringprojekt.

En digital tvilling i form av en dynamisk processmodell kan användas för flera syften under hela livscykeln av ett kommunalt eller industriellt reningsverk. Syftet med detta projekt var att (1) demonstrera möjligheter för och (2) identifiera behov och genomförbarhet med en digital tvilling hos de anläggningsägare som ingår i projektet.För att demonstrera möjligheter användes LEVA i Lysekils ombyggnadsprojekt för Långeviks reningsverk som fallstudie. Med dataunderlag från förstudien implementerades en processmodell av det framtida reningsverket i en kommersiellt tillgänglig mjukvara. Denna baseras på att den befintliga för- och efterbehandlingen behålls medan det biologiska reningssteget byggs om till en MBBR-process. Som indata till modellen (temperatur, flöde och koncentrationer på inkommande och försedimenterat vatten) beaktades de förutsättningar som angivits i det förfrågningsunderlag som LEVA tagit fram.

För att verifiera modellimplementeringen jämfördes modellresultaten med erfarenhetsbaserad kunskap om MBBR-processen. Resultaten visade att modellen i stort ger förväntade resultat vilket är viktigt för att verktyget skall få förtroende vid verklig tillämpning.Med den typ av digital tvilling som använts i projektet finns möjlighet att beskriva/modellera det inkommande avloppsvattnet med en högre detaljeringsgrad än vad som traditionellt görs vid ombyggnadsprojekt. För att demonstrera detta planerades och genomfördes en provtagningskampanj. Resultaten från denna var tyvärr inte tillförlitliga och därför användes i projektet standardvärden för inkommande vatten i projektet. Detta ökar osäkerheten i resultaten jämfört med om provtagningsresultaten hade funnits men förutsättningarna är fortfarande i enlighet med förfrågningsunderlaget.  

I projektet har det sedan visats att det är möjligt att kombinera den digitala tvillingen med LCA-data för att beräkna klimatpåverkan för olika processutföranden, styrstrategier, val av energikälla och insatsvaror. Detta presenteras som ett stöd för jämförelse av olika anbud vid upphandling även om det kräver mera förarbete av både beställare och entreprenörer. Ett exempel är att byta styrstrategi för dosering av kolkälla kan spara upp till 19 ton CO2-ekvivalenter på ett år. Den digitala tvillingen kan också användas av LEVA under hela den nya processlösningens livstid från design och upphandling till införande och justeringar av driftstrategier och slutligen som ett stöd vid kontinuerlig drift.Som påbyggnad till konventionell processmodellering demonstrerades slutligen möjligheten att köra simulering i realtid och med indata från en verklig process.

Implementeringen gjordes användarvänlig genom användning av mjukvaran Mediator som enkelt möjliggjorde sammankopplingen av signaler till/från ett styrsystem med kontaktpunkter definierade i simuleringsmjukvaran SIMBA#. Flera veckors stabil drift av systemet kunde visas. Tillämpningen anses dock för rudimentär för att kunna besvara frågor om krav på tidsupplösning, beräkningsprestanda och numerisk stabilitet. Under projektet genomfördes en behovs- och genomförbarhetsanalys genom informations- och kunskapsspridning vid ett flertal arbetsmöten och en avslutande workshop till vilken klustrets anläggningsägare bjöds in.

To reduce emissions of hazardous combustion gases to air, ship owners can switch to cleaner fuels or install so called “scrubbers”, onboard the ship. In a scrubber, combustions gases are sprayed with water and the dirty wash water, the scrubber water, is discharged to the sea. The number of ships with scrubbers and the volumes of discharged scrubber water have increased dramatically the past decade. When allowing the use of scrubbers, the focus was on improving the air quality, while the impact on the marine environment was not considered. We have here analysed polycyclic aromatic compounds (PACs), the most toxic fraction of oil, in scrubber water from ships, and reviewed recent ecotoxicological scientific literature on PAC toxicity to marine organisms. Our conclusion is that in areas with intense shipping there is a serious risk for negative effects on marine organisms. 

Landfill leachate is one of the major point sources of per- and polyfluoroalkyl substances (PFAS) pollution. In this study, powdered activated carbon (PAC), granular activated carbon (GAC), anion exchange resin (AIX), nanofiltration (NF), ozonation, and foam fractionation were tested for treatment of the same leachate.

These methods were compared in terms of PFAS removal efficiencies and treatment cost. More than 75% removal of long-chain PFAS (6-9 CF2) could be achieved with all the studied methods, though with high resource consumption. It was demonstrated that PFAS breakthrough was up to 27 times faster when the leachate was treated with GAC and AIX compared to groundwater treatment. Nanofiltration was the only method which could be practically applied for removal of PFAS with the shortest fluorinated carbon chain (3-4 CF2). Foam fractionation and AIX offered the most economical treatment, with an estimated cost of < 1 €/m3 for PFOS and PFOA reduction to ≥90%. The cost of treatment was shown to increase exponentially if the goal of > 60% ΣPFAS11 removal was applied. It was also discussed that composite parameters that include expected toxicity of different PFAS, such as ΣPFOAeq, should be used to obtain a cost-efficient reduction of PFAS-induced water toxicity.

Treatment of PFAS-contaminated leachate with ion exchange filters has been studied in several pilot studies and showed good results, especially in the case of requirements for the reduction of PFAS with longer carbon chains. The biggest challenge with using ion exchange mass for leachate treatment is that either a very advanced pre-treatment is required or that the filter needs to be backwashed frequently to avoid clogging. Backwashing of filters mixes the ion exchange mass, which causes the column action to be lost. 

The aim of the project was to test the design where leachate flows upstream of a filter bed with a sufficient flow to fluidize the bed. The report describes trials carried out on a larger pilot scale at the Sivik waste facility as well as trials on a smaller pilot scale at the Löt waste facility. At Sivik, a standard DynaSand filter has been filled with ion exchange resin and run for 9 months.

At Löt, comparative trials with downstream ion exchange filters and two upstream filters in series have been carried out. Trials at Sivik showed that it was crucial to mix the ion exchange mass in the filter by running the airlift pump to maintain good treatment results. However, it was challenging to find a balance between mixing the resin and the risk of media loss with flushing water. It was also discovered that the flow rate in the trials was too low for homogeneous suspension of the resin, which is believed to have created shortcuts of flow through the filter. This led to varying purification of the shorter PFAS. Despite the challenges, reduction of PFOS averaged 94% during the course of the trial where 14 300 bed volumes (BV) of water was treated.

Effluent PFOS concentrations were approximately 13 times lower than the respective effluent target value for the facility. Complementary lab-scale trials showed that the ion exchange resin had a lot of capacity left when the tests ended and reduced PFOS and other longer PFAS almost as good as new ion exchange resin. In tests at Löt, the 2-stage upstream filter showed similar treatment efficiency as a downstream filter, confirming that capacity utilization of ion exchange resin can be similar with the two process designs. Loss of mass was noted both with downstream ion exchangers (in trials on Löt during backwash) and upstream ion exchangers (due to poor design of a resin mixing system). Measures to reduce the risk of the resin loss as well as the importance of polishing removal of possible smaller amounts of resin are discussed in the report.

Syftet med projektet var att studera rening av PFAS-förorenat lakvatten med jonbytare med fokus på avskiljning av substanser med kort och medellång kolkedja. Dessa substanser avskiljs dåligt med de flesta tekniker. Tidigare studier har visat att jonbytarfilter avskiljer substanserna initialt när filtret tas i drift men reduktionsgraden minskar snabbt. För att behålla bra avskiljning av dessa substanser behöver jonbytarmassan därför bytas ofta, vilket medför en hög reningskostnad. Några studier har visat att jonbytarmassa kan regenereras från PFAS och användas flera upprepade gånger, vilket har potential att minska reningskostnaden och behålla bra reduktion av de kortare PFAS.

Regenerering av jonbytare har dock inte testats tidigare vid rening av lakvatten, bara vid rening av andra vattenströmmar. Dessutom behövde hantering av den förbrukade regenereringslösningen som innehåller höga PFAS halter studeras.I föreliggande studie gjordes litteraturgenomgång, försök i labb-, bänk-, och pilotskala samt processberäkningar och kostnadskalkyler för att studera hur regenerering av jonbytare och återvinning av regenereringslösningen kan tillämpas vid rening av PFAS-förorenat vatten. Försöken utfördes vid Ragn-Sells avfallsanläggning Högbytorp.Kortvariga labbförsök visade att det finns flera typer av jonbytare från de flesta stora leverantörer som fungerar bra vid rening av lakvatten från PFAS. De mest lovande av dessa testades avseende regenerering med två olika regenereringslösningar. En indikation från labbförsöken var att det är möjligt att regenerera jonbytarna och behålla liknande kapacitet i fler cykler av sorption-regenerering.

Pilotförsöken genomfördes i en anläggning bestående av förbehandling av lakvatten genom fällning, sedimentering, och ultrafiltrering följt av två jonbytarfilter som kördes i serie eller parallellt. Förbehandlingen fungerade för det mesta bra och producerade ett partikelfritt vatten, dock med en hög dos av en fällningskemikalie. Jonbytarfiltren renade det förbehandlade vattnet tills genombrott av medellånga PFAS observerades. Sedan regenererades ett av jonbytarfiltren och filtret togs i drift igen för att undersöka hur regenereringen påverkade kapaciteten för PFAS-reduktion.

Resultaten visade att det mesta av sorberade PFAS tvättades bort från massan och att den regenererade massan hade en kapacitet som liknande en ny.Den regenereringslösning som visade sig fungera bra i labb-, bänk-, och pilotskaleförsöken var 1% NH4Cl i 80%vol etanol. För regenerering av 1 m3 jonbytarmassa krävdes minst 13 m3 av lösningen. Att regenerera jonbytare och skicka lösningen på destruktion kostar  mer än att köpa ny jonbytarmassa. För att regenereringen ska vara ekonomiskt motiverad behöver den förbrukade regenereringslösningen återanvändas och/eller kemikalier från den behöver återvinnas. I projektet studerades två alternativ för återvinning av lösningen – destillering och nanofiltrering. Båda metoderna fungerade bra och separerade >98% av PFAS från regenereringslösningen. Koncentratet, som innehåller PFAS i halter 1 000 – 1 700 gånger högre än i inkommande lakvatten, kan då skickas på destruktion medan den renade regenereringslösningen återanvändas.

En grov kostnadsanalys visade att för de flöden och halter som förekommer i lakvatten på Högbytorp skulle regenerering och återvinning av regenereringslösningen med nanofiltrering vara ekonomiskt motiverad om en bra reduktion av medellånga PFAS eller väldigt höga reduktionsgrader (>95%) av de längre PFAS skulle krävas. Däremot, om 90% reduktionsgrad  eller lägre bedöms vara tillräckligt för ΣPFAS4 eller ΣPFOAekv så bedöms regenerering och återvinning av regenereringslösningen i en egen anläggning att inte vara ekonomiskt motiverat. Däremot finns en stor potential för en gemensam anläggning för regenerering av jonbytare från flera avfallsanläggningar eller andra verksamheter, liknande som det görs idag med reaktivering av aktivt kol.

The report describes established and new technologies for nitrogen recovery from wastewater and compares the nitrogen recovery methods with other ways of producing nitrogen fertilizer in terms of climate impact and costs. The report also includes a brief review of opportunities for potassium and sulfur recovery and a status update of phosphorus recovery methods.

Recycling of nutrients from sewage in Sweden today takes place almost exclusively by spreading of sewage sludge on arable land, but only about a third of all sludge is used in this way. Dewatered sludge contains only about 15 percent of the nitrogen present in incoming wastewater. This means that only a few percent of the nitrogen is recycled today. Increased nitrogen recovery therefore has great potential. There is a risk that even the minor nitrogen recycling with sludge today will be stopped if sludge use on arable land is to be banned at the same time as the requirement for phosphorus recycling is introduced. The most interesting methods of phosphorus recovery involves  sludge incineration and recovery from ashes, and this means that the nitrogen content is lost during the incineration.

Nitrogen is mainly removed with biological methods in the treatment plant's mainstream today. An alternative is to separate the nitrogen present in reject water, ie the highly concentrated water that remains when dewatering digested sludge. The amount of nitrogen in the reject water is about the same as the amount of nitrogen in the sludge itself. The nitrogen in reject water can be recycled into fertilizer products by various chemical-physical methods. If nitrogen is recycled, less nitrogen needs to be removed biologically, which saves energy and reduces greenhouse gas emissions, especially nitrous oxide. Nitrogen recovery processes are, however, energy and chemical intensive, resulting in indirect greenhouse gas emissions and relatively high cost.

A literature study showed that ammonia stripping and contact membranes are the techniques for nitrogen recovery from reject water that are applied in full scale and have similar and relatively high consumption of chemicals and energy. For wastewater streams similar to reject water, other methods have been tested, including thermal stripping of ammonia with further chemical reaction with gypsum or distillation to ammonia water. Evaporation and distillation are also developed techniques that have the potential for nitrogen recovery.

Conventional production of nitrogen fertilizer depends on natural gas to obtain energy. Several technologies are now being developed where renewable energy can be used for the production of ammonia. The project evaluated the climate impact and costs for different nitrogen recovery methods compared with the production of nitrogen fertilizer from fossil and renewable energy sources. There was a big variation of results for the different recovery methods, but some conclusions can be drawn. The operating cost of nitrogen recovery with the established technologies (ammonia stripping and contact membranes) is slightly higher than the cost of producing nitrogen fertilizer from fossil and renewable energy sources, even when the cost of biological treatment of reject water with the most cost-effective biological methods is deducted. On the other hand, the climate impact from nitrogen recycling is lower than the climate impact from nitrogen fertilizer production and biological nitrogen removal. Several new recycling techniques, such as thermal stripping of ammonia and struvite precipitation with further acid treatment, have the potential to provide both lower cost and lower climate impact.

An alternative for recovering as much nitrogen as possible is to introduce source sorting systems and separate treatment of toilet water or urine. Recovery from the low-concentration main stream of wastewater with an ion exchange process followed by recovery with stripping or contact membranes also has potential.

VA-kluster Mälardalen – ett högt värderat forsknings- och utbildningsklusterVA-kluster Mälardalen är ett viktigt och mycket uppskattat nätverk. Det vittnar våra medlemmar om. Som en del i arbetet med slutrapporteringen ställdes två frågor till alla medlemmar: ”Varför är ni medlemmar i VA-kluster Mälardalen?” och ”Vad betyder VA-kluster Mälardalen för er?”. Svaren visar att det våra medlemmar uppskattar mest är det nätverk som klustret utgör och den forskning vi bedriver tillsammans. Nätverket är kärnan i klustret, och tack vare det kan vi genomföra högklassig forskning med såväl akademisk höjd som praktiskt tillämpbara resultat. Den naturliga kontakten mellan de tretton VA-organisationerna och de sju forskande parterna gynnar VA-forskningen i Sverige och driver teknik- och kunskapsutvecklingen framåt.

Klustret ger VA-organisationerna en möjlighet att delta i projekt som genererar direkt nytta i verksamheten och som kan svara på frågor kopplat till de utmaningar de står inför – både på kort och lång sikt. De forskande parterna uppskattar att kunna arbeta med forskning som kommer till användning ”på riktigt”. Klustret ger också möjligheter för alla medlemmar att delta och driva projekt som de saknar kompetens eller ekonomiska förut-sättningar att driva ensamma. Den samlade projektvolymen inom VA-kluster Mälardalen har totalt uppgått till drygt 142 MSEK under programperioden 2019–2021. Det motsvarar en uppväxling av SVU- och SIVL-medlen med 17 gånger. Den faktiska projektfinansieringen speglar en del av nyttan med VA-kluster Mälardalen, men för att få en komplett bild bör det även beaktas att det totalt har genomförts närmare 100 forsknings- och utvecklingsprojekt under program-perioden, och att 17 av våra 20 medlemmar har varit direkt involverade i ett eller flera av dessa projekt. Många av projekten har dessutom genomförts i samarbete med andra VA-organisationer utanför klustret.

Resultaten från denna uppsjö av forsknings-projekt kan knappast sammanfattas på ett rättvist sätt i en slutrapport, än mindre i en sammanfattning som denna. Ett urval av de forskningsprojekt som helt eller delvis finansieras av SVU-medel genom VA-kluster Mälardalen redovisas i slutrapporten, men i övrigt hänvisar vi till vetenskapliga artiklar och andra rapporter enligt de referenslistor som finns både i slutrapporten och de verksamhetsberättelser som har publicerats årligen under programperioden (tillgängliga via klustrets hemsida www.va-malardalen.se). 

Diffuser maintenance such as cleaning and membrane replacement are key to energy-efficient aeration at water resource recovery facilities (WRRFs). In previous research, fouling and ageing effects on diffuser performance have been lumped together by only comparing new and used membranes. But meaningful diffuser maintenance requires that fouling (mitigated by cleaning) can be separately assessed from ageing (calling for membrane replacement).

Therefore, we analysed how the standard oxygen transfer efficiency (SOTE) and dynamic wet pressure (DWP) changed due to fouling, separately from the ageing effects, in six diffusers after 1.5 to 15 years in operation at different WRRFs. This required an elaborate cleaning procedure of the used membranes and additional measurements. The results showed that fouling increased DWP with up to 40 mbar, which is in line with previous findings and up to twice as much as new membranes. Ageing, on the other hand, surprisingly led to a reduced DWP in the order of 5–10 mbar.

The SOTE loss for the combined fouling and ageing effects (up to 28 %) were on par with previous research. However, fouling was only accountable for less than half of this performance loss (12 % SOTE loss and below), whereas ageing was attributed up to 25 % SOTE loss, which has not been seen before. The extent of performance loss as well as the relative contributions of fouling and ageing varied between WRRFs. Altogether, these new insights emphasize the need to monitor both ageing and fouling to facilitate effective maintenance and calls for more research on how ageing impacts diffuser membranes.

Oil spills, the most frequent environmental incidents in Sweden, have decreased in recent years but still pose risks to drinking water and aquatic ecosystems, with about 600 cases registered annually by the Swedish Fire Protection Association. Yet, detailed information about modern fuels and their environmental and human health impacts remains scarce. Hence, this study focuses on enhancing the understanding of the environmental impact of common fuels.This study collected thirty fuel samples of different types: petrol, diesel, fuel oil, and marine gas oil. A selected number of substances in the fuels and the water-soluble phase were analysed using GC-MS.

A crucial step in the analytical method in this project, since the focus was on the effect on sub-surface aquatic life and drinking water production, was to form a stable water-accommodated fraction (WAF) where non-dissolved fuel elements were separated from the water. Since odour properties were of interest, the mixing was extensive, with limited space allowed for gases, meaning that more volatile organic carbons (VOC:s) would be in solution. The chemical analysis focused on identifying and quantifying 50 substances, including aromatic hydrocarbons, aliphatic hydrocarbons, ethers, and esters, plus 17 polycyclic aromatic hydrocarbons (PAH:s) for eight of the samples. These substances were chosen for their significance in interpreting results related to odour and to illustrate the proportion of light and heavy substances in the fuels.Twelve of the thirty fuel samples were selected for odour threshold testing, where a dilution series from the WAF was used to evaluate the intensity of odours at different concentrations. Six samples were chosen for ecotoxicological assessments on crustaceans, algae, and bacteria, offering a comprehensive understanding of the ecotoxicity of the fuel-water mixtures. Four samples were used in tailor-made evaporation experiments to study how volatile fuel components evaporate from the water surface under different temperatures and ethanol concentrations.For odour, three fuels were notably distinguished, namely the fuels containing higher concentrations of ether: 98 Octane petrol and E85 fuel.

While there was significant variability in odour thresholds among different panel members, the concentration of MTBE (Methyl Tertiary-Butyl Ether) in the fuel-water mixtures was generally identified as a precise predictor of odour. Conversely, the lack of ether in diesel fuels made them significantly less prone to cause odour in the WAF.Generally, petrol-specific substances dissolve more readily in water than those in diesel, which only marginally ended up in the water-accommodated fraction. However, ethanol in petrol and RME (rapeseed methyl ester) in diesel favoured the dissolution of hydrocarbons into water. For ether, which is of utmost importance for odour, a strong correlation was observed between the concentration of ether in water and its content in the fuel. Therefore, it is possible to predict the ether concentration in the WAF solely from ether concentration in the fuel, meaning that ethanol did not significantly increase ether solubility.In the case of a fuel spill into surface water, volatile substances like ether or toluene evaporate into the air, reducing the water concentration. The experimental conditions in this study do not reflect actual real-world conditions. The evaporation experiments showed that the evaporation of ether can be predicted based on the WAF ether concentration, water temperature, and ethanol content. It was found that cold water (5 °C) conditions reduce the evaporation rate of ether to almost negligible levels.The ecotoxicological tests showed reproduction inhibitions in crustaceans across all fuel samples. However, the inhibiting effect from HVO (hydrogenated vegetable oil) was only marginally greater than that of the control. Fuel oil and some petrol fuels had detrimental effects on the algae growth, while diesel did not.

The decrease of luminescence of bacteria, an indicator of toxicity, exhibited a similar trend; petrol fuels inhibited luminescence more than diesel. None of the fuels disturbed activated sludge to the extent that respiration was inhibited at toxic levels. This shows that an active sludge is more robust than single organisms, probably due to the diverse bacteria flora.For a drinking water producer, fuels containing water-soluble ethers, such as E85 and 98 Octane petrol, are the most prominent risk. If a spill occurs in the drinking water supply, the production disturbance likelihood depends on the dilution prerequisites below the odour threshold of 1.5-4 µg/L. The study also shows that modern diesel has become an issue of marginal concern for surface water-based raw water sources due to very low solubility and regulations that have reduced the amounts of toxic substances in the products.For freshwater ecosystems, water-soluble petrol-associated substances and hydrophobic toxic substances in fuel oil or EU diesel have the most severe effects during a spill. However, MK1 and HVO diesel only marginally affected the test organisms compared to the control, which represents unaffected organisms.