https://www.mdu.se/

Background Soil-based on-site wastewater treatment systems (OWSs) are suspected to contribute to eutrophication of surface waters, due to the discharge of phosphorus (P). However, along the flow path between the facilities and surface waters, different processes contribute to delay the transport of phosphorus through the ground. This may reduce the unwanted impact on receiving water bodies. However, the strength and significance of this so-called soil retention remains unclear. In Sweden, there are nearly one million OWSs. To protect surface waters, a high P removal rate (up to 90%) is often required by the local municipalities. However, since these requirements may have costly consequences to property owners, it is debated as to whether they are too strict. In this debate, it is often claimed that the retention of P occurring in natural environments may be underestimated by authorities. Accordingly, there is a need for a scrutiny of the available evidence related to soil retention of phosphorus from OWSs. This is the objective of the planned systematic map. Focus will be on boreal and temperate climate zones. Methods Searches will be made for peer-reviewed articles and grey literature using bibliographic databases, search engines, specialist websites and stakeholder contacts. The references will be screened for relevance according to a predefined set of eligibility criteria. At stage one, after testing and clarifying the eligibility criteria, the references will be single-screened based on title and abstract. At stage two, potentially relevant references will be screened in full-text independently by two reviewers. We will compile a detailed database of the relevant studies. Moreover, a narrative report will be produced, describing the research landscape in general terms. This will be carried out with a conceptual model, describing the processes involved in P retention in natural environments, as a foundation. It will be discussed where the respective studies/study types fit into the conceptual model, and also evaluated how each study/study type can be related to the overarching question of eutrophication. Moreover, we will describe identified knowledge gaps that warrant further primary research effort, as well as identified knowledge clusters that could be suitable for systematic reviews.

Background: In Sweden there are nearly one million soil-based on-site wastewater treatment systems (OWTSs). OWTSs may contribute to eutrophication of surface waters, due to the discharge of phosphorus (P). Hence, in certain cases, a high P removal rate (up to 90%) of OWTSs is required by Swedish authorities. Since these requirements may have costly consequences to property owners, it is debated whether they are too strict. In this debate, it is often claimed that the soil retention of P occurring in the natural environments may be underestimated by authorities. Soil retention is the inhibition of the transport of P through the ground, due to different chemical, physical and biological processes occurring there. These processes make the P transport slower, which may reduce the unwanted impact on receiving water bodies. However, the efficiency of soil retention of P remains unclear. The objective of this systematic map was to collect, code, organise and elucidate the relevant evidence related to the topic, to be able to guide stakeholders through the evidence base, and to support future research synthesising, commissioning, and funding. The systematic map was carried out in response to needs declared by the Swedish Agency for Marine and Water Management but the conclusions should be valid for a wider range of countries across boreo-temperate regions.

Methods: Searches were made for peer-reviewed and grey literature using bibliographic databases, search engines, specialist websites, and stakeholder contacts. The references were screened for relevance according to a predefined set of eligibility criteria. A detailed database of the relevant studies was compiled. Data and metadata that enable evaluation and discussion of the character and quality of the evidence base were extracted and coded. Special focus was placed on assessing if existing evidence could contribute to policy and practice decision making. Descriptive information about the evidence base was presented in tables and figures. An interactive evidence atlas and a choropleth were created, displaying the locations of all studies.

Review findings: 234 articles out of 10,797 screened records fulfilled the eligibility criteria. These articles contain 256 studies, performed in the field or in the laboratory. Six different study types were identified, based on where the measurements were conducted. Most studies, including laboratory studies, lack replicates. Most field studies are observational case studies.

Conclusions: It is not possible to derive valid generic measures of the efficiency of soil retention of P occurring in the natural soil environment from available research. Neither does the evidence base allow for answering the question of the magnitude of the potential impact of OWTSs on the P concentration in recipients on a general basis, or under what conditions OWTSs generally have such an impact. A compilation of groundwater studies may provide examples of how far the P may reach in x years, but the number of groundwater studies is insufficient to draw any general conclusions, given the complexity and variability of the systems. Future research should strive for replicated study designs, more elaborate reporting, and the establishment of a reporting standard.

The adsorption of Ni2+, Cd2+, PO4 3- and NO3 - by carbonated hydroxyapatite (CHA) modified microfibrillated cellulose (MFC) was studied in the aqueous solution. The modified adsorbent was characterized using elemental analysis, FTIR, SEM and EDAX analysis. The adsorption studies were conducted in batch mode. The effects of pH, contact time, the concentration of metals and the regeneration efficiency were studied. The removal of Ni2+, Cd2+, PO4 3- and NO3 - was not pH dependent. The maximum removal capacities of the CHA/MFC adsorbent for Ni2+, Cd2+, PO4 3- and NO3 - were 2.021, 1.224, 0.843 and 0.209mmol/g, respectively. The Langmuir and Sips models were representative to simulate adsorption isotherms. The results of adsorption kinetic indicate that adsorption was very fast for all studied compounds.

Filter substrates that efficiently remove phosphorus (P) from wastewater can be used to optimise the nutrient removal by on-site wastewater treatment systems. A number of filter substrates have been investigated and the industrial by-product blast furnace slag has attracted attention as a promising substrate. To further evaluate the sorption and attenuation of PO(4)(3-), a column experiment was carried out under conditions of intermittent P loading. Two types of slag were used; crystalline slag (CS) and amorphous slag (AS). The slags were available in two particle sizes; 0-0.125 mm and 0.25-4 mm, respectively. The slags were mixed with inert sand to improve the hydraulic conductivity. In addition to the column experiment, a P fractionation experiment was conducted. The sorption experiment indicated that the removal of P by the CS (0.25-4 mm), the AS (0.25-4 mm) and the AS (0-0.125 mm) columns at the end of the experiment exceeded 95%. In the other columns, the P sorption had decreased remarkably indicating a beginning saturation of the substrates. The P fractionation experiment showed that the P sorption was largest in the uppermost layers. Clear gradients of the P sorption in the downward direction could also be observed. It was concluded that the P sorption by the coarser slags was high at the end of the experiment indicating that saturation had not been achieved.

The efficiency of phosphorus (P) removal in ecologically-engineered wastewater treatment facilities, such as artificial wetlands and sand filters, can be improved by using a reactive sorbent. The sorbent must therefore have a high P-sorption capacity and an adequate hydraulic conductivity. Several filter materials have been tested here in regard to their P-sorption capacity. In this study, three natural materials - opoka (a bedrock found in south-eastern Poland) limestone and the B horizon of a forest soil, plus two artificial materials - blast furnace slag (crystalline and amorphous, in two particle sizes (0-0.125 mm and 0.25-4 mm), and fly ash were investigated. Phosphate sorption and isotherm studies were performed. In addition, physical and chemical properties of the materials were also investigated. The P-sorption experiment showed that all materials were capable of sorbing P to various extents. The coarse crystalline slag had the highest P-sorption capacity followed in order by the fine crystalline slag, the fine amorphous slag, the B horizon, the limestone, the coarse amorphous slag, the ash and the opoka. The isotherm studies showed that the B horizon was the most efficient P retainer, followed in order by the coarse crystalline slag, the fine crystalline slag, the fine amorphous slag and the coarse amorphous slag, with opoka and limestone showing the poorest retention. It was concluded that the crystalline slags had the highest P-sorption capacities, and that coarse crystalline slag possessed the highest hydraulic conductivity, suggesting that this material is the most suitable for use in ecological wastewater treatment systems.

Increasing attention is being focused on the phosphorus retention capacity of wetlands. Several attempts have been made to improve the reduction of phosphorus in wastewater by the use of constructed wetlands. One way of improving the phosphorus reduction capacity is to use efficient filter materials in the wetland. Leca(R) (Light Expanded Clay Aggregates) has been tested in Norway, where laboratory and field investigations gave promising results. To further study the chemical removal mechanism of Leca, an experiment utilising five columns was performed. A phosphate solution was applied to the columns intermittently and samples were taken twice a week. Parallel to this study, a P-fractionation experiment was conducted to find out how the phosphate was sorbed to various components of the material. Both experiments showed that only a small amount of the applied phosphate was sorbed by the Leca. The amount sorbed was primarily attached to Al-complexes. In a second column experiment Opoka, a reactive medium rich in CaCO3, was added to Leca and sand to investigate the P-sorption capacity. The results from this investigation showed a higher P-uptake than in the previous column experiment. The lime additive clearly increased the P-sorption and, in this study, Leca in its pure form could be considered as chemically non-reactive. 

The abiotic sorption efficiency of on-site wastewater treatment systems can be improved by using a strongly sorbing filter material that, if it retains phosphorus (P) in a plant available way, can be used as fertiliser when P saturation is achieved. Two materials, blast furnace slag and the siliceous sedimentary rock opoka, have shown a high P sorption capacity and were included in a set of experiments to investigate the P retention mechanisms from model P-solution. Experiments focusing on the P sorption, capacity and calcium (Ca) and PO4 determination were carried out. The pH was also measured. The P sorption experiment showed that some slags were efficient P retainers, while the opoka was the least efficient P retainer. The pH decreased in all samples as a function of P addition. In the slag samples, the Ca concentration also decreased as a function of P addition, suggesting Ca-P precipitation as the major P removal mechanism for the slag. The Ca and PO4 speciation data ruled out the formation of amorphous calcium phosphates and/or octacalcium phosphate as the major P removal mechanism. However, the calculated ion activity products displayed clear evidence that hydroxyapatite had precipitated above a certain critical supersaturation limit. This would explain the poor P retention efficiency of the opoka samples in this study as the ion activity products were too low. The finding that direct hydroxyapatite formation is the predominant P removal mechanism might have important implications for their possible use as fertiliser due to the poor solubility of hydroxyapatite.

Aquatic mosses Cinclidotus nigricans and freshwater mussels Dreissena polymorpha were transferred at eight monitoring sites along the rivers Meurthe and Plaine (northeastern France) for a biological assessment of the trace metal contamination. Autochthonous Fontinalis antipyretica mosses were collected at the end of the experiment. The major contaminants detected in the organisms were Cr, Ni, Pb and Zn. A comparison between the native and the introduced bryophytes showed that the transfer technique was preferable to assess the recent pollution situation. In the case of the transplanted mosses, high initial levels of strongly bound Pb and Zn prevented an accurate assessment of the contamination with these two metals, since only little depuration occurred at unpolluted sites. A good qualitative agreement was observed between the indications obtained from the mosses and those obtained from the mussels, suggesting that both are suitable indicators for monitoring purposes. The observed quantitative disparities were attributed to inherent differences in the accumulation strategies of each sentinel organism. Due to specific uptake and depuration kinetics, mosses and mussels appeared to be complementary in the detection of various types of pollution.

A large number of substrates potential for removal of phosphorus (P) in wastewater has been reviewed. The substrates consist of natural materials, industrial by-products and man-made products. Most substrates have been investigated in batch and column studies in the laboratory; others have also been tested in field trials. The results from these investigations vary, but a few substrates, e.g. wollastonite, slag material and, to some extent, light weight aggregate products, have demonstrated promising properties with regard to P-sorption capacity and hydraulics. The problems of normalisation of data are discussed, as well as the substrates potential benefits for on-site wastewater treatment.

 Research on Phosphorus (P) removal capacity by blast furnace slags (BFS) has been undertaken in Sweden for the last decade. Both laboratory experiments and field trials have been carried out. While laboratory investigations revealed that BFS has a high P-sorption capacity (95–100%), P removal in field trials was much lower, ranging from 40 to 53%. In addition, a number of problems have been observed in BFS field testing including clogging, sulfuric odor and environmental (regulatory) concerns about possible leaching of heavy metals from the slag. In spite of these problems, and questioning by the environmental regulatory authorities, research continues to provide evidence that BFS can be regarded as a suitable filter media, and attempts have also been undertaken in order to further improve the P-removal capacity of this adsorbing material.

Filter technology has proved to be successful with regard to removal of pollutants from varying wastewater streams. A large number of filter materials have been investigated with promising results, among them several steel and iron slag materials. However, despite significant scientific evidence over the past 15 years on the efficiency of steel slag in P removal in particular from a variety of wastewaters around the world, currently there are very few full-scale steel slag filters in operation. In this paper we will present research efforts and experiences in using blast furnace slag in Sweden and electric arc furnace steel slag in Vermont, USA and hindrances faced in obtaining regulatory approvals for this innovative technology.

A large number of filter materials, organic and inorganic, for removal of heavy metals in mine drainage have been reviewed. Bark, chitin, chitosan, commercial ion exchangers, dairy manure compost, lignite, peat, rice husks, vegetal compost, and yeast are examples of organic materials, while bio-carbons, calcareous shale, dolomite, fly ash, limestone, olivine, steel slag materials and zeolites are examples of inorganic materials. The majority of these filter materials have been investigated in laboratory studies, based on various experimental set-ups (batch and/or column tests) and different conditions. A few materials, for instance steel slag materials, have also been subjects to field investigations under real-life conditions. The results from these investigations show that steel slag materials have the potential to remove heavy metals under different conditions. Ion exchange has been suggested as the major metal removal mechanisms not only for steel slag but also for lignite. Other suggested removal mechanisms have also been identified. Adsorption has been suggested important for activated carbon, precipitation for chitosan and sulphate reduction for olivine. General findings indicate that the results with regard to metal removal vary due to experimental set ups, composition of mine drainage and properties of filter materials and the discrepancies between studies renders normalisation of data difficult. However, the literature reveals that Fe, Zn, Pb, Hg and Al are removed to a large extent. Further investigations, especially under real-life conditions, are however necessary in order to find suitable filter materials for treatment of mine drainage. 

The surface properties of pine bark before and after the treatment with urea solution and the adsorption of Cu(II), Ni(II) and Zn(II) from aqueous solutions at different pH values have been studied. Types of active sorption sites, their surface concentration and change after the bark treatment with urea solution were determined. The results of potentiometric titration were processed by using ProtoFit and FITEQL software programs. The data obtained make it possible to conclude that in the extraction mechanism of heavy metals from water the share of ion exchange decreases and the share of complexation increases. The impact of alkaline and alkaline earth metals in the range of their concentrations up to 3000 mg/dm3 on Cu(II) extraction from model aqueous solutions was also investigated. 

Treatment of landfill leachate using blast furnace slag and pine bark as reactive sorbents was studied in an in situ column experiment at the Lilla Nyby landfill site in Eskilstuna, Sweden. The columns were filled with approximately 10 1 of each sorbent and leachate was supplied at three different flow rates during a period of 4 months. Samples of inflow and outflow were collected three times a week and were analyzed for physical and chemical parameters, including concentrations of some metals, and toxicity. It was found that pine bark removed metals more efficiently than did the blast furnace slags; that Zn was most efficiently retained in the filters and that both retention time and initial concentration played an important role in the sorption process. It was also observed that the pine bark column did not release COD. No toxicity of the untreated or the treated leachate was found with the test organisms and test responses used.  

The organic matter released from septic tanks can disturb the subsequent step in on-site wastewater treatment such as the innovative filters for phosphorus removal. This study investigated the effect of organic load on phosphorus (P) and bacteria removal by reactive filter materials under real-life treatment conditions. Two long-term column experiments were conducted at very short hydraulic residence times (average ~5.5h), using wastewater with high (mean ~120mgL^-1) and low (mean ~20mgL^-1) BOD₇ values. Two alkaline filter materials, the calcium-silicate material Polonite and blast furnace slag (BFS), were tested for the removal capacity of total P, total organic carbon (TOC) and Enterococci. Both experiments showed that Polonite removed P significantly (p<0.01) better than BFS. An increase in P removal efficiency of 29.3% was observed for the Polonite filter at the lower concentration of BOD₇ (p<0.05). Polonite was also better than BFS with regard to removal of TOC, but there were no significant differences between the two filter materials with regard to removal of Enterococci. The reduction in Enterococci was greater in the experiment using wastewater with high BOD₇, an effect attributable to the higher concentration of bacteria in that wastewater. Overall, the results demonstrate the importance of extensive pre-treatment of wastewater to achieve good phosphorus removal in reactive bed filters and prolonged filter life.

Industrial byproduct, steel slag was used as a low-cost sorbent for the removal of Co(II), Ni(II), Cd(II), and Pb(II) from aqueous solutions containing chelating agents; EDTA, citrate, and oxalate. Equilibrium and kinetic studies were conducted. Clear dependency between speciation of metals and their sorption behavior was observed. Precipitation and adsorption were suggested as main mechanisms. Diffusion played an important role in the kinetics of metal removal. Notable leaching of elements was observed when steel slag was in contact with the solutions under study. Modification with chitosan was successfully used to prevent leaching and improve the sorption capacity of steel slag.

Cadmium (Cd) is a highly toxic metal, occurring in municipal wastewater and stormwater as well as in wastewater from various industries. Char derived from the pyrolysis of municipal sewage sludge has the potential to be a low-cost sorption media for the removal of Cd. However, the balance between possible local char production and demand has not been assessed previously. In this study, the Cd sorption capacities of chars derived from primary (PSC) and secondary sludge (DSC), as well as the feasibility of char production for Cd sorbent purposes, and the pyrolysis energy balance were evaluated. Results showed that the sorption capacity of PSC (9.1 mg/g; 800 degrees C, 70 min) was superior to that of DSC (6.0 mg/g; 800 degrees C, 70 min), and increased with a higher pyrolysis temperature. Pyrolysis of primary sludge had a more favourable energy balance compared with the pyrolysis of digested sludge, however, when accounting for loss of biogas production the energy balance of primary sludge pyrolysis was negative. Assessment of the regional demand (V & auml;ster & aring;s, Sweden) indicated that PSC or DSC may cover the local Cd sorbent demand. However, it was estimated that large char volumes would be required, thus making the use of DSC/PSC less feasible.

Municipal wastewater management causes metal exposure to humans and the environment. Targeted metal removal is suggested to reduce metal loads during sludge reuse and release of effluent to receiving waters. Biochar is considered a low-cost sorbent with high sorption capacity for heavy metals. In this study, heavy metal sorption to sludge-derived biochar (SDBC) was investigated through batch experiments and modeling and compared to that of wood-derived biochar (WDBC) and activated carbon (AC). The aim was to investigate the sorption efficiency at metal concentrations comparable to those in municipal wastewater (&lt;1 mg/L), for which experimental data are lacking and isotherm models have not been verified in previous works. Pb2+ removal of up to 83% was demonstrated at concentrations comparable to those in municipal wastewater, at pH 2. SDBC showed superior Pb2+ sorption capacity (maximum ~2 mg/g at pH 2) compared to WDBC and AC (&lt;0 and (3.5 ± 0.4) × 10−3 mg/g, respectively); however, at the lowest concentration investigated (0.005 mg/L), SDBC released Pb2+. The potential risk of release of other heavy metals (i.e., Ni, Cd, Cu, and Zn) needs to be further examined. The sorption capacity of SDBC over a metal concentration span of 0.005–150 mg Pb2+/L could be predicted with the Redlich– Peterson model. It was shown that experimental data at concentrations comparable to those in municipal wastewater are necessary to accurately model and predict the sorption capacity of SDBC at these concentrations. 

Storm water treatment and management will be more important in the future due to climate changes, e.g., more frequent, and intense rain events that might cause flooding. To meet these challenges, low impact development (LID) technologies such as paved surfaces, green roofs and various bioretention systems have been suggested in urban areas. Various filter media, natural and engineered materials, have been used to amend the LID solutions in field experiments enhancing the removal of different contaminants present in storm water of different kinds. Researchers suggest locally available low-cost media having high capacity to remove pollutants. Other parameters to take into consideration when selecting filter media are clogging, hydraulic parameters. Climatic conditions in different regions, e.g., temperate, or cold climatic zones, do not seem to have a large impact on performance on LID solutions.

A large number of substrates potential for removal of phosphor-us (P) in wastewater has been reviewed. The substrates consist of natural materials, industrial by-products and man-made products. Most substrates have been investigated in batch and column studies in the laboratory; others have also been tested in field trials. The results from these investigations vary, but a few substrates, e.g. wollastonite, slag material and, to some extent, light weight aggregate products, have demonstrated promising properties with regard to P-sorption capacity and hydraulics. The problems of normalisation of data are discussed, as well as the substrates potential benefits for on-site wastewater treatment.

I den här rapporten presenteras en deskriptiv och kartläggande undersökning som kan betraktas som en förstudie till ett framtida mera djuplodande projekt.

Syftet är att genom litteraturstudier, kommunernas policydokument och intervjuer undersöka hur några kommuner i Mellansverige arbetar med klimatanpassningsåtgärder för sina VA-anläggningar. Den övergripande frågan gäller vilka drivkrafter och utmaningar som aktörerna har identifierat. Vi fokuserar på möjligheter och hinder för klimatanpassning av avloppssystemet inkluderande ledningar, pumpstationer och avloppsreningsverk i fyra kommuner i Mälardalsregionen.

Med hjälp av litteraturen och kommunernas policydokument (som till exempel vattentjänstplaner) beskriver vi det politiska, lagstiftningsmässiga och klimatrelaterade sammanhang som VA-organisationerna måste ta hänsyn till i arbetet med att klimatsäkra sina avloppssystem.

Resultaten visar att såväl kommunerna, i sin övergripande planering, och VA-organisationerna tar klimatfaran på allvar och arbetar med åtgärder för klimatanpassning av VA-sektorn, inklusive byggnader, och annan infrastruktur samt avloppsystemen. Generellt kan man säga att man inte hunnit särskilt långt med att implementera klimatåtgärderna. Planer och medvetenhet finns, men än så länge är man bara i början av det konkreta arbetet att klimatsäkra.

Åtgärderna består av flera olika aktiviteter som dels sker i samband med planering av nybebyggelse, dels i redan existerande områden inklusive den befintliga VA-infrastruktur som där finns. I områden som planeras att bebyggas kan dessa skyfallssäkras, till exempel genom att införa en klimatfaktor vid dimensionering av ledningssystem eller genom att ombesörja att det finns möjlighet att bygga någon form av anläggning för lokalt omhändertagande av dagvatten, så kallad LOD. I befintliga områden försöker man att identifiera områden som riskerar att drabbas av översvämningar vid skyfall eller långvarig nederbörd, i avrinningsområdena kan anläggningar för omhändertagande av ovidkommande vatten eventuellt byggas. Renovering av ledningar och brunnar samt installation av backventiler för att förhindra att avloppsvatten pressas bakåt i systemet vid skyfall eller långvarig nederbörd är relativt enkla åtgärder som nämns av de VA-organisationerna. En annan viktig åtgärd som nämns är att försöka skapa samarbete med andra berörda aktörer, det kan handla om ökat samarbete mellan olika förvaltningar i en kommun, samarbete mellan den kommunala VA-organisationen och förvaltningarna eller andra aktörer, exempelvis privata fastighetsägare.

I det avslutande kapitlet presenterar vi några övergripande slutsatser – främst vad gäller behovet av samarbete mellan olika organisationer inom sektorn – och pekar ut ett intressant område för framtida forskning.

There has been an increased interest in the production of sustainable biochar in the past years, as biochar shows versatile physicochemical properties and, can have a wide applicability in diverse fields. Comprehensive studies have been made to characterize biochar produced from various biomass materials, using different production technologies and under different process conditions. However, research is still lacking in correlating biochar properties needed for certain applications with (i) feedstock, (ii) biochar production processes and conditions and (iii) biochar upgrading and modification strategies. To produce biochar with desired properties, there is a great need to establish and clarify such correlations, which can guide the selection of feedstock, tuning and optimization of the production process and more efficient utilization of biochar. On the other hand, further elucidation of these correlations is also important for biochar-stakeholder and end-users for predicting physiochemical properties of biochar from certain feedstock and production conditions, assessing potential effects of biochar utilization and clearly address needs towards biochar critical properties. This review summarizes a wide range of literature on the impact of feedstocks and production processes and reactions conditions on the biochar properties and the most important biochar properties required for the different potential applications. Based on collected data, recommendations are provided for mapping out biochar production for different biochar applications. Knowledge gaps and perspectives for future research have also been identified regarding the characterization and production of biochar.