The goal of Low Impact Development (LID) is to mimic the pre-development hydrologic regime of a catchment through infiltration, filtration, storage, evaporation, and detention of post-development runoff using small-scale hydrologic controls close to the source. A LID facility located in Northern Virginia was examined for pollutant removal and hydrologic performance. The treatment train included four in-line grass swales followed by a bioretention cell with a gravel base. The facility retained 85% of the rainfall. Influent and effluent pollutant loads were calculated using three common substitution methods for datasets censored by values below the analytical detection limit. The Summation of Loads (SOL) method was used to facilitate understanding of how data censoring affected performance results when substitution methods were used. The SOL analysis showed positive removal performance for most nutrient species, sediment, oxygen demanding substances, selected trace metals and total petroleum hydrocarbons. Negative performance was observed for oxidized nitrogen, total dissolved solids and oil & grease. LID facility influent and effluent loads were also compared using the Effluent Probability Method (EPM). The EPM analysis showed statistically significant (p d 0.05) pollutant load removal performance over the entire range of sampled events for total suspended solids, total phosphorus, total nitrogen, total Kjeldahl nitrogen, ammonia nitrogen, chemical oxygen demand, copper, zinc and alkalinity. EPM analysis did not show significant removals of oxidized nitrogen, total dissolved solids, orthophosphate phosphorus and hardness. / Master of Science

Multiple problems caused by urban runoff have emerged as a consequence to the continuing development of urban areas in recent decades. The increase of impervious land areas can significantly alter watershed hydrology and water quality. Typical impacts to downstream hydrologic regimes include higher peak flows and runoff volumes, shorter concentration times, and reduced infiltration. Urban runoff increases the transport of pollutants and nutrients and thus degrades water bodies adjacent to urban areas. One of the most frequently used practices to restore the hydrology and water quality of urban watersheds is bioretention (also known as a rain garden). Despite its wide applicability, an understanding of its multiple physiochemical and biological treatment processes remains an active research area. To provide a wide ability to evaluate the hydrologic input to bioretention systems, spatial and temporal distribution of storm events in Virginia were studied. Results generated from long-term frequency analysis of 60-year precipitation data demonstrate that the 90 percentile, or 10-year return period rainfall depth and dry duration in Virginia are between 22.9 – 35.6 mm and 15.3 – 25.8 days, respectively. Monte-Carlo simulations demonstrated that sampling programs applied in different regions would likely encounter more than 30% of precipitation events less than 2.54 mm, and 10% over 25.4 mm. Further experimental research was conducted to evaluate bioretention recipes for retaining stormwater nitrogen (N) and phosphorus (P). A mesocosm experiment was performed to simulate bioretention facilities with 3 different bioretention blends as media layers with underdrain pipes for leachate collection. A control group with 3 duplicates for each media was compared with a replicated vegetated group. Field measurement of dissolved oxygen (DO), oxidation-reduction potential (ORP), pH, and total dissolved solids (TDS) was combined with laboratory analyses of total suspended solids (TSS), nitrate (NO3), ammonium (NH4), phosphate (PO4), total Kjeldahl nitrogen (TKN) and total phosphorus (TP) to evaluate the nutrient removal efficacies of these blends. Physicochemical measurements for property parameters were performed to determine characteristics of blends. Isotherm experiments to examine P adsorption were also conducted to provide supplementary data for evaluation of bioretention media blends. The results show that the blend with water treatment residuals (WTR) removed >90% P from influent, and its effluent had the least TDS / TSS. Another blend with mulch-free compost retained the most (50 – 75%) total nitrogen (TN), and had the smallest DO / ORP values, which appears to promote denitrification under anaerobic conditions. Increase of hydraulic retention time (HRT) to 6 h could influence DO, ORP, TKN, and TN positively. Plant health should also be considered as part of a compromise mix that sustains vegetation. Two-way analysis of variance (ANOVA) found that single and interaction effects of HRT and plants existed, and could affect water quality parameters of mesocosm leachate. Based upon the understanding of the physiochemical and hydrologic conditions mentioned previously, a design model of a bioretention system became the next logical step. The computational model was developed within the Matlab® programming environment to describe the hydraulic performance and nutrient removal of a bioretention system. The model comprises a main function and multiple subroutines for hydraulics and treatment computations. Evapotranspiration (ET), inflow, infiltration, and outflow were calculated for hydrologic quantitation. Biomass accumulation, nitrogen cycle and phosphorus fate within bioretention systems were also computed on basis of the hydrologic outputs. The model was calibrated with the observed flow and water quality data from a field-scale bioretention in Blacksburg, VA. The calibrated model is capable of providing quantitative estimates on flow pattern and nutrient removal that agree with the observed data. Sensitivity analyses determined the major factors affecting discharge were: watershed width and roughness for inflow; pipe head and diameter for outflow. Nutrient concentrations in inflow are very influential to outflow quality. A long-term simulation demonstrates that the model can be used to estimate bioretention performance and evaluate its impact on the surrounding environment. This research advances the current understanding of bioretention systems in a systematic way, from hydrologic behavior, monitoring, design criteria, physiochemical performance, and computational modeling. The computational model, combined with the results from precipitation frequency analysis and evaluation of bioretention blends, can be used to improve the operation, maintenance, and design of bioretention facilities in practical applications. / Ph. D.

Impervious surfaces such as roads, sidewalks, and roofs increase the volume of runoff generated in a watershed. Traditional stormwater management techniques emphasize conveyance of runoff away from impervious surfaces in order to reduce flooding. Rain gardens are becoming popular as a different means to manage stormwater in such a way that runoff is captured and infiltrated onsite rather than conveyed offsite. A stormwater management system consisting of a rainwater harvest system, rain garden, and infiltration chamber was built at the Coca-Cola Refreshments USA, Inc. distribution center in Lexington, Kentucky during the fall of 2011. Precipitation, inflow, and water level were measured from May, 2012 to April, 2013 to evaluate the hydrologic performance of the rain garden. The rain garden had a high infiltrative capability and was able to capture and infiltrate 100% of the runoff generated during the study period. The results of the study were used to formulate recommendations for rain garden design and construction in central Kentucky.

The search for solutions in stormwater management has been a constant in human history. Being a well discussed topic nowadays, public agencies seek for quick solutions in order to minimize the catastrophes caused by floods in result to rapid and disorganized urbanization. Thus, the search for solutions in stormwater management is necessary for maintaining the quality of life, the environment and especially the preservation of the hydrological cycle. Furthermore, infiltration alternatives such as bioretention, trenches and swales have been shown as feasible and well accepted options because they minimize the negative effects of urbanization seeking to restore the natural water cycle. In Brazil, there are few studies focused on design criteria, operation and service-life of these structures, which are important data for the scale of a bioretention otherwise, would be leading to an oversized, costly and underused construction. The main purpose of this study is to analyze the sizing criteria for bioretention systems proposing suggestions for its implementation in the geomorphological conditions of the Santa Maria / RS region. The research evaluates the infiltration structure built in 2010 at the Universidade Federal de Santa Maria (UFSM). The performance of two sizing methodologies was analyzed and the dimensions were compared to the dimensions of the structure implemented at UFSM. The methodology consists of collecting infiltration data from infiltration tests recommended by NBR 13969/97, with some modifications in order to simulate a real event, data of monitoring bioretention at UFSM from 2011 to 2013, and data obtained in the stress test applied to the structure in December 2015. From these data, Horton infiltration curves for the average conditions were adjusted and inserted into the concept of unit infiltration rate (mm.h-1.m-2).The sizing was based on the analyzed methodologies (Curve-Envelope Method and LID method), after the results were compared to the actual behavior of the real structure suggesting adjustments. The results of this study indicate that the methodologies analyzes oversize the bioretention structure. From the analysis of the built bioretention behavior history it can be concluded that despite having smaller dimensions than those obtained through other methodologies sizing, it is effective to storage the drained volume. Therefore, it is clear that the lateral area and the hydrostatic pressure are important to the functioning of the structure, but also the soil-plant relationship, with the creation of preferential paths that end up improving infiltration over the service-life. Further studies are recommended in order to incorporate these items in sizing methodologies, and monitoring of similar structures in order to determine whether the behavior presented by the bioretention is default or an exception. / A procura por alternativas de manejo de águas pluviais sempre foi uma constante na história da Humanidade. Atualmente tem gerado muitos debates, agentes públicos procuram soluções rápidas no intuito de amenizar as constantes catástrofes em decorrências das enchentes e inundações, fruto de uma urbanização acelerada e desorganizada. A busca por inovações se faz necessária para a manutenção da qualidade de vida, do meio ambiente e principalmente pela preservação do ciclo hidrológico. Alternativas de infiltração como biorretenções, trincheiras e valas de infiltração tem se mostrado como opções viáveis e de aprovação geral porque amenizam os efeitos negativos da urbanização buscando restaurar o ciclo hidrológico natural. No Brasil, ainda são poucos os estudos voltados aos critérios de dimensionamento, funcionamento e vida útil das referidas estruturas, que são dados importantes para o profissional dimensionar uma biorretenção, caso contrário, estaria levando a construção de obras superdimensionadas, onerosas e subutilizadas. O objetivo deste trabalho é analisar os critérios de técnicas de dimensionamentos para sistemas de biorretenção e propor sugestões para sua aplicação nas condições geomorfológicas da região de Santa Maria/RS. A pesquisa teve como base a estrutura de infiltração construída, em 2010, na Universidade Federal de Santa Maria. E neste estudo, buscou-se analisar o desempenho de duas metodologias de dimensionamento comparando as dimensões com a estrutura implementada na UFSM. A metodologia utilizada consistiu na coleta de dados de infiltração a partir de: ensaios de infiltração recomendados pela NBR 13969/97, com algumas modificações visando simular um evento real; de dados coletados no monitoramento da biorretenção da UFSM no período de 2011 a 2013 e dados obtidos no Teste de estresse aplicado na estrutura em dezembro de 2015. A partir desses dados, ajustou-se as curvas de infiltração de Horton para as condições médias e inseriu-se o conceito de taxa de infiltração unitária (mm.h-1.m-2). Procedeu-se ao dimensionamento através das metodologias analisadas (Método da Curva-Envelope e Método do LID), após foram analisados os resultados dos dimensionamentos com o comportamento real da estrutura construída no campus Sede da UFSM sugerindo ajustes. Com base nos resultados obtidos neste estudo, os dimensionamentos apresentaram dimensões maiores do que o existente, porém, na análise do histórico da biorretenção construída indica que ela está funcionando perfeitamente no quesito armazenamento. Assim, consta-se a importância da área lateral e da pressão hidrostática no funcionamento da estrutura, como também, a relação solo-planta, com a criação de caminhos preferencias, que acabam melhorando a infiltração ao longo da vida útil. Sendo recomendados novos estudos com o objetivo de incorporar estes itens nas metodologias de dimensionamento, e monitoramento de estruturas semelhantes afim de verificar se o comportamento aqui encontrado é o padrão ou uma exceção.

Bioretention is increasingly being employed as a stormwater management tool in urban areas, with the intent of using infiltration to address both water quantity and quality concerns. However, bioretention soil media (BSM) has limited removal capacity for dissolved contaminants; hence, amendments may be justified to improve performance. In this study, the potential of five low-cost sorbents as BSM amendments – waste tire crumb rubber (WTCR), coconut coir fiber (CCF), blast furnace slag (BFS), biochar (BC) and iron coated biochar (FeBC) – were investigated for removing several classes of contaminants from simulated stormwater (SSW). The contaminated SSW contained a mixture of metals (Cr, Cd, Cu, Pb, Ni and Zn), nutrients (ammonium, nitrate, and phosphate) and PAHs (pyrene (PYR), phenanthrene (PHE), acenaphthylene (ACY) and naphthalene (NAP)). First, batch studies were used to investigate the sorption capacities, kinetics, and the effects of different water quality parameters on sorbents performance. Then, a long-term vegetated column study was conducted to investigate the performance of three amendments (CCF, WTCR, and BFS) under intermittent runoff condition considering different runoff intensities and antecedent dry periods (ADP). The long-term effects of amendments on plant health and infiltration rate of all media were also investigated. Finally, HYDRUS-1D and a cost model were used to investigate longevity and cost-effectiveness of all BSM. Batch test results revealed that among all sorbents, BC and FeBC were only effective for removing PAHs; CFF had high sorption capacity for both metals and PAHs; BFS was very effective for metals; and WTCR was effective for some of metals and PAHs. Metal removal by BFS occurred primarily via precipitation was due to the BFS mineral structure and high/alkaline pH. The effectiveness of CCF for removing both metals and PAHs was due to its lignocellulose structure and diverse functional groups. CCF could remove metals through several mechanisms including cation exchange, complexation, and electrostatic attraction, and remove PAHs through hydrophobic interaction. Biochar in this study had a highly aromatic structure with less O-containing functional groups, and PAHs were sorbed through hydrophobic pi-pi interactions. The selectivity orders of sorbents for the removal of different metals and PAHs were Cr~Cu~Pb > Ni > Cd > Zn and PYR > PHE > ACY > NAP. This selectivity was mainly caused by differences in properties of metal ions (e.g., ionic radius, hydrogen energy, etc.) and PAHs (e.g., hydrophobicity). Phosphate was removed by BFS due to its Al, Fe and Ca contents, but the other sorbents were ineffective for nutrient removal. Metals sorption capacity of sorbents was greater at higher pH, lower salinity and lower DOC; however, PAHs sorption capacity of sorbents was generally not sensitive to water quality parameters. Column experiments showed that almost all amended and non-amended BSM were able to remove > 99% of influent metals over the 7-month experiment period (except Zn in WTCR media). Cu and Cr effluent concentrations in all media (except BFS media) increased to ~ 10% of influent concentrations during heavy rainfall which was probably due to decomposition of Cu/Cr-organic matter complexes. All bioretention columns removed > 99% of PHE and PYR (higher molecular weight PAHs) regardless of rain intensity and ADP, while the performance of different media for removing the lower molecular weight PAHs (NAP and ACY) varied with the rain intensity, and removal decreased when larger storms were experimentally simulated. For nutrients, among all media, BFS-amended media had high phosphate removal capacity (> 90%). Nitrate removal in all columns was notably affected by changes in stormwater intensity and ADP, likely due to difference in degree of saturation and the potential that anoxic conditions were created, which are favorable for denitrification. All media were ineffective in ammonium removal, and ammonium production occurred throughout experiment which might be due to the lack of nitrifiers in the media. Hydraulic properties of all media were appropriate over the entire experiment. BFS-amended media had the greatest negative effect on plant health, while CCF-amended media was supportive for plants. The transport model results showed that the predicted metal breakthrough times (according to EPA criteria) for different media were 6 years for non-amended media, 7 years for WTCR media, 25 years for CCF media, and 70 years for BFS media. Modeling PAHs, nutrients and some metals (Cr and Cu) under intermittent flow conditions are complicated and other processes and models need to be investigated as future study. Finally, cost analysis results showed that among all bioretention media, CCF- and BFS-amended media with the lowest capital and maintenance costs were the most cost-effective BSM. This research will improve our understanding of BSM amendments that will improve water quality while simultaneously support bioretention system hydrologic function as well as estimating costs of bioretention systems for a long-term application. / Civil Engineering

Frågan kring hållbar dagvattenhantering har fått allt större uppmärksamhet i och med de pågående klimatförändringarna. Genom att implementera dagvattenlösningar i urbana miljöer som efterliknar naturens kretslopp kan kraftiga regn fördröjas vilket avlastar ledningsnätet. Detta främjar en hållbar stadsutveckling, som idag har blivit ett allt större krav. Studiens syfte avser att lyfta kunskapsläget kring användandet av växtbäddar avsedda för dagvattenhantering i det nordiska klimatet. Detta genom att undersöka vilka faktorer som bör beaktas vid utformning av växtbäddar för att de ska fungera optimalt, samt maximera livslängden med hänsyn till ett kallt klimat. Undersökningen tar även reda på vilka åtgärder som krävs för att underhålla en sådan anläggning samt vilka kostnader detta medför. Studiens frågeställningar besvaras genom intervjuer som riktades till beställare och projektörer av växtbäddar. Detta för att skapa en uppfattning kring hur utformningen sker samt vilka underhållsinsatser som vidtas. En enkätundersökning genomfördes som var riktad till kommuner för att undersöka hur väl de upplever att arbetet med växtbäddar fungerar inom deras organisation. Studien utfördes genom att först genomföra en litteraturstudie som lade grunden till rapportens teori, för att sedan kunna utforma intervju och enkätfrågor. För att skapa en uppfattning kring kostnaderna utfördes en dokumentinsamling från kommuner för att klargöra kostnadernas storlek. Studiens resultat påvisar att växtbäddar har bra förutsättningar i det nordiska klimatet samt att det anses finnas en god kunskapsnivå kring hur anläggningarna ska utformas och skötas. Detta gäller både projektörer och beställare av anläggningarna. De fel som uppstår i anläggningsskedet tycks främst grunda sig i den stora variationen av material som växtbäddarnas uppbyggnad består av. Därtill att entreprenören saknar kunskap i hur anläggningen senare ska fungera, då denna typ av anläggning skiljer sig från hur konventionella dagvattenanläggningar anläggs. I utformnings och driftskedet är utmaningarna kopplade till faktorer som ansvarsfördelning då det är ett flertal inblandade aktörer i både projekterings och driftskedet. Den faktor som främst styr kostnaden är kopplad till de material som används i uppbyggnaden av växtbädden. / The issue of sustainable stormwater management has received increasing attention with the ongoing climate change. By implementing stormwater solutions in urban environments that mimic nature heavy rainfall can be delayed, which relieves the conventional stormwater pipeline network. This promotes sustainable urban development, which today has become an increasing requirement. The purpose of the study is to raise the state of knowledge about the use of bioretention system intended for stormwater management in the Nordic climate. This is done by examining which factors should be taken into account when designing bioretention system in order to function optimally and maximize the lifespan with regard to a cold climate. The study also finds out what measures are required to maintain such a facility and what costs this entails. The study's questions are answered through interviews aimed at clients and designers of bioretention systems. The purpose is to create an understanding of how the design takes place and what maintenance efforts are taken. A survey was conducted which was aimed at municipalities to investigate how well they feel that the work with bioretention system works within their organization. The study was carried out by first conducting a literature study that laid the foundation for the report's theory, in order to then be able to design interview and survey questions. To create an understanding of the costs, a document collection from municipalities was carried out to clarify the size of the costs. The results of the study show that bioretention systems can sustain in the Nordic climate and that it is considered that there is a good level of knowledge about how the facilities should be designed and maintained. This applies to both designers and clients of the facilities. The errors that occur during the construction phase seem to be mainly based on the large variety of materials that make up the bioretention systems. In addition, the contractor lacks knowledge of how the facility will later function, as this type of facility differs from how conventional stormwater facilities are constructed. In the design and operational phase, the challenges are linked to factors such as the division of responsibilities as there are a number of actors involved in both the design and operational phases. The factor that primarily controls the cost is linked to the materials used in the construction. / <p>Examensarbetet är utfört vid Institutionen för teknik och naturvetenskap (ITN) vid Tekniska fakulteten, Linköpings universitet</p>

As the world’s population is migrating more into urban areas, landcover changes follow. Natural pervious areas are being converted to impervious areas, which when subjected to rain generates more stormwater runoff. Stormwater management is a problem that cities today are challenged with, infrastructure is getting older and precipitation patterns are changing due to climate change. Due to climate change extreme precipitation events are likely to increase and therefore increase the probability of urban flooding. Urban flooding can be caused by extreme precipitation events with a short duration, or so-called flash floods. These flash floods can overwhelm the drainage system in place which therefore can cause flooding. This problem has inspired engineers to rethink stormwater management, moving from traditional grey drainage systems to more green and sustainable drainage systems. Sustainable Urban Drainage System (SuDS) are drainage systems that aim to regain the properties of non-urbanised areas, retain the natural hydrological cycle, and have recreational values for the surrounding societies. This study investigated how different SuDS behave when subjected to flash floods. A model of a synthetic case study was built in the Storm Water Management Model (SWMM) and sustainable urban drainage systems implemented. The solutions investigated were bioretention cells, rain gardens, infiltration trenches, green roofs, and permeable pavements. Three different rain events were analysed, all with different precipitation depth but with the same duration of 1 hour. Results showed that bioretention cells could reduce runoff volumes to the highest extent while green roofs could reduce the peak runoff the most. Other results were analysed like efficiency and cost. Bioretention cell came out on top in efficiency but had the highest cost. Overall, all the solutions showed promise in reducing runoff during flash floods, but the reduction capacity goes down with increased precipitation. / När en större del av världens befolkning flyttar in till tätortsområden så medföljer en ändring av markytans beskaffenhet. Vanligtvis genomträngliga ytor omvandlas till hårdgjorda ytor vilket generar mer dagvattenavrinning när de utsätts för regn. Dagvattenhanteringen är en utmaning för många städer idag eftersom infrastrukturen blir äldre och nederbördsmönstren förändras på grund av klimatförändringar. Extrema nederbördshändelser väntas öka med anledning av dessa klimatförändringar och ökar därigenom sannolikheten för översvämningar i städer. Översvämningar i städer kan orsakas av korta nederbördshändelser med hög intensitet, så kallade Skyfall, vilket kan överbelasta dagvattensystemets kapacitet. Det har lett till att ingenjörer ändrat sitt tankesätt på hur dagvatten ska hanteras och börjat gå från konventionella till mer gröna och hållbara dräneringssystem. Hållbar dagvattenhantering är dräneringssystem som syftar till att använda egenskaperna hos naturliga områden, behålla det naturliga hydrologiska kretsloppet och skapa rekreationsvärden för de omkringliggande samhällena. Denna studie har undersökt hur olika hållbara dräneringssystem beter sig när de utsätts för översvämningar. En modell på en syntetisk fallstudie byggdes i Storm Water Management Model (SWMM) där hållbara dräneringssystem implementerades i en urban miljö. Lösningarna som undersöktes var biofilterbäddar, regnträdgårdar, infiltrationsbäddar, gröna tak och permeabla trottoarer. Tre olika nederbördshändelser analyserades, alla med olika nederbördsmängder men med samma varaktighet på en timme. Resultaten visade att biofilterbäddar kunde minska avrinningsvolymerna i största grad medan gröna tak minskade ytavrinningen mest. Effektivitet och kostnad analyserades också. Där visade biofilterbäddarna högst effektivitet men hade den högsta kostnaden. Sammantaget visade det sig att alla lösningar var lovande vad gäller minskning av avrinning under översvämningar, men reduktionskapaciteten minskar med ökad nederbörd.

Development of cities, new buildings and other impervious surfaces entails increased stormwater flows, volumes and pollutant loads. Heavy metals, nutrients, sediments and salt are common pollutants in stormwater. The conventional way to manage stormwater, which is by discharge to the receiving water body via a sewage network, will not be sufficient for mitigating high flows, flood risks and pollution export. Thus, Low Impact Development (LID) stormwater facilities, such as stormwater biofilters, are built in an increasing rate in Sweden and worldwide. The main function of a stormwater biofilter is water quality treatment, which is achieved when stormwater percolates through a vegetated filter media. Sometimes a pre-treatment facility is installed before the biofilter to reduce the sediment load on the biofilter and extend its life-length. However, there are knowledge gaps regarding pollutant removal in biofilters and the role of associated pre-treatment facilities. In this study the impact of a pre-treatment facility, calcium carbonate as amendment in the filter media and vegetation was investigated regarding treatment of heavy metals (Cd (cadmium), Cu (copper), Pb (lead) and Zn (zinc)), phosphorus and total suspended solids. To do this, influent and effluent stormwater samples from an existing biofilter in Sundsvall were analysed and evaluated regarding removal performance of the above-mentioned pollutants.  In general, the stormwater biofilter facility (including pre-treatment) removed total metals well while the removal of the dissolved fraction showed higher variations. Influent concentrations of TP were always higher than effluent concentrations. Leaching of phosphate repeatedly occurred from the filter sections. The mean removal of TSS was high (96.9%). CaCO3 as amendment in the filter material had a beneficial effect on the overall metal removal of the stormwater facility. Although leaching of phosphate occurred from all filter sections, the leaching was lowest from the section with CaCO3,indicating possible benefits of CaCO3 as amendment. CaCO3 did not seem to affect the mean total phosphorus removal significantly. Removal of total metals seemed to be improved by vegetation, but the removal of dissolved metals, total phosphorus and phosphate did not seem to be enhanced by vegetation. The filter section with vegetation and without CaCO3 amendment contributed with the highest effluent concentrations of total phosphorus and phosphate (leaching), considering that vegetation released more phosphate that it captured. The main treatment of the stormwater pollutants occurred within the biofilter and both positive and negative removal of all pollutants was observed by the pre-treatment facility. The result showed that the pre-treatment facility was most beneficial for removal of dissolved metals. / Utvecklingen av städer, nya byggnader och andra hårdgjorda ytor ökar både mängden dagvatten och föroreningshalterna. Vanligt förekommande föroreningar i dagvatten är tungmetaller, näringsämnen, sediment och salt. Det traditionella sättet att hantera dagvatten är genom avledning via avloppsnätet till närliggande recipient, men med den förändrade kvalitén och kvantitet på dagvatten blir kapaciteten i det befintliga ledningsnätet otillräckligt för de ökade flödena och föroreningsinnehållet. Därför byggs bland annat dagvattenbiofilter, som är en typ av Low Impact Development (LID), i en ökande takt i Sverige och globalt. Huvudsyftet med dagvattenbiofilter är dagvattenrening, vilket uppnås när dagvattnet filtreras genom en filterbädd med växter. För att minska (sediment)belastningen och förlänga livslängden på biofiltret kan ibland en förbehandlingsanläggning placeras i före biofiltret. Dock finns det fortfarande kunskapsluckor om reningspotentialen i biofilter och betydelsen av en förbehandlingsanläggning. I den här studien undersöktes betydelsen av en förbehandlingsanläggning, kalciumkarbonat som tillsats i filter materialet och växter på biofiltret för reningen av tungmetaller (Cd (kadmium), Cu (koppar), Pb (bly) och Zn (zink)), fosfor och totalt suspenderat material. För att undersöka detta analyserades och utvärderades dagvattenprover på inkommande och utgående vatten från ett biofilter i Sundsvall, med avseende på reningsprestation av ovan nämnda föroreningar. Resultatet visade att biofiltret (med förbehandlingsanläggningen inkluderad), renade totala metaller bra medan reningen av lösta metaller varierade mer. Inkommande koncentrationer av totalfosfor var alltid högre än utgående koncentrationer och fosfat lakades kontinuerligt ut från filtersektionerna. Den genomsnittliga reningen av TSS var hög (96,9%). CaCO3 som tillsats i filtermaterialet hade en positiv effekt på reningen av totala och lösta metaller i biofiltret. Fosfat lakades ut från alla filtersektioner, men urlakningen var lägst från filtersektionen med CaCO3, vilket tyder på möjliga positiva effekter det som tillsats i filtermaterialet. CaCO3 verkade inte öka genomsnittliga reningen av totalfosfor signifikant. Vegetationen verkade öka reningen av totala metaller men inte reningen av lösta metaller, totalfosfor eller fosfat. Filtersektionen med vegetation men utan CaCO3 genererade de högsta utgående koncentrationerna av totalfosfor och fosfat (urlakning), vilket tyder på att vegetation avgav mer fosfor än den tog upp. Den dominerande reningen av dagvattenföroreningarna skedde inuti biofiltret och både högre och lägre koncentrationer av samtliga föroreningar observerades efter förbehandlingsanläggningen. Resultatet visade att förbehandlingsanläggningen var mest effektiv för reningen av lösta metaller.

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