ISSN: 1402-1544 ISBN 978-91-7439-XXX-X Se i listan och fyll i siffror där kryssen är DOCTORAL T H E SI S Department of Civil, Mining and Environmental Engineering Division of Architecture and Infrastructure Godecke-Tobias Blecken Biofiltration Technologies Treatment for Stormwater Quality Technologies Blecken Biofiltration Godecke-Tobias ISSN: 1402-1544 ISBN 978-91-7439-132-9 Biofiltration Technologies for Luleå University of Technology 2010 Stormwater Quality Treatment Godecke-Tobias Blecken Biofiltration Technologies for Stormwater Quality Treatment Godecke-Tobias Blecken Urban Water Division of Architecture and Infrastructure Department of Civil, Mining and Environmental Engineering Luleå University of Technology SE-971 87 LULEÅ SWEDEN Doctoral thesis Printed by Universitetstryckeriet, Luleå 2010 ISSN: 1402-1544 ISBN 978-91-7439-132-9 Luleå 2010 www.ltu.se ACKNOWLEDGEMENTS The experiments that were conducted at Luleå University of Technology were financially supported by Åke och Greta Lissheds stiftelse, J. Gust. Richert stiftelse and Luleå University of Technology. My participation in conferences and my research stay at Monash University in 2007 were supported by Seth M Kempes Stipendiefond, Wallenbergsstiftelsen - Jubileumsanslaget - and Stiftelsen Futura. Sincere thanks are extended for all that support. I also would like to thank the Peter Stahre stipendium committee for acknowledging the scientific value and practical applicability of this research. This work would not have been possible without the help of Monica Olofsson and Kerstin Nordqvist with the laboratory work. Huge thanks are also due to all other colleagues in the Urban Water group who contributed in one way or another to my doctoral efforts, by creating the stimulating work atmosphere at the research group at LTU, including discussions about work and private life during lots of coffee breaks. I would like to thank Tone Muthanna for providing insights regarding her own PhD studies and for being an inspiring co-author of several papers. Thanks also to my co- author Jiri Marsalek, for sharing his extraordinary experience which considerably improved this work. During 2007 I spent six months at Monash University in Melbourne, Australia. I would like to thank everyone there who helped to make my stay there a good experience. Yaron Zinger is especially acknowledged for conducting lots of experiments, sharing his data and always being a serious and competent discussion partner and co-author. I do not know which of my co-supervisors, Ana Deletic and Tim Fletcher, I should name first here, so I have put your names in alphabetical order. Both of you helped me greatly by enabling the productive collaboration with FAWB at Monash University. I am very grateful that you always willingly shared your experience, ideas, comments, data and (especially) your scarce time with me. I have learned a lot from you. Thank you! To my main supervisor Maria Viklander, many thanks for giving me the opportunity to undertake this doctoral research. Thank you for all your time, encouragement and guidance through all the obstacles on the way to presenting this thesis. I also would like to thank you for allowing me to take parental leave whenever I asked. Finally, I am grateful to have such a wonderful family. Thanks to all of you in Germany for regularly coming up to Luleå – or wheresoever we are. Henneke, Thies and Ehler, without you the last years would have been much less exciting. With your energy you three helped me to leave work behind every evening. Inga, thanks for taking me with you up to Luleå - otherwise there would not have been any thesis. Thanks for being my best friend. You are the perfect one for me. I am very much looking forward to spending more time with you again soon. ABSTRACT Due to high runoff volumes and peak flows, and significant contamination with (inter alia) sediment, metals, nutrients, polycyclic aromatic hydrocarbons and salt, urban stormwater is a major cause of degradation of urban water ways. Since current urban drainage systems, which heavily rely on piped sewer networks, may not be sustainable, attempts are being made to develop and refine sustainable urban drainage solutions, notably in Water Sensitive Urban Design (WSUD) and Low Impact Development (LID) concepts. Promising systems recommended for application in both WSUD and LID are stormwater biofilters (also known as bioretention systems or rain gardens) using vegetated filter media. Besides their capacity to attenuate flows and minimise runoff volumes, stormwater biofilters have proven efficacy for enhancing effluent water quality. Furthermore, they can be aesthetically pleasingly integrated even in dense urban environments. However, there are still gaps in our knowledge of the variability of biofilters’ pollutant removal performance, and the factors that affect their performance. In the studies this thesis is based upon, the effects of various ambient factors, stormwater characteristics and modifications of filter design on the removal of metals, nutrients and total suspended solids (TSS) in biofilters, and pollutant pathways through them, have been investigated. For these purposes, standard biofilters and variants equipped with a submerged zone, a carbon source and different filter materials were exposed to varying temperatures and dry periods, dosed with stormwater and snowmelt, and the inflow and outflow concentrations of the pollutants were measured. Although removal percentages were consistently high (>70%), demonstrating that biofilters can reliably treat stormwater, the results show that metal outflow concentrations may vary widely depending on the biofilter design and the ambient conditions. Prolonged drying especially impaired their removal efficiency, but variations in temperature and filter media variations had little effect on metal removal rates. The adverse effects of drying could be mitigated by using a submerged zone, and thus providing a more constant moisture regime in the filters between storm events. Combined with embedded organic matter, the submerged zone especially significantly enhances Cu removal, helping to meet outflow target concentrations. Similarly, installing a mulch layer on top of the filter provides additional sorption capacity, hence metals do not ingress far into the filter and are mainly trapped on/in the top layer by sorption processes and/or mechanical trapping associated with TSS. This leads to significant metal accumulation, which facilitates biofilter maintenance since scraping off the top layer removes high proportions of previously accumulated metals, thus delaying the need to replace the whole filter media. However, removal of accumulated pollutants from the filter media is crucial for successful long-term performance of the filters to ensure that no pollutant breakthrough occurs. Nitrogen removal was found to be more variable than metal removal, and to be adversely affected by temperature increases, leading to high nitrogen leaching in warm temperatures. Phosphorus removal rates were consistently high, since most phosphorus was particle-bound and thus trapped together with TSS. However, in initial stages phosphorus was washed out from the filter media, indicating that filter media that do not have high levels of labile phosphorus should be used to avoid high effluent concentrations. Given that most outflow concentrations were far lower than those in the stormwater, biofilters are appropriate stormwater treatment systems. Dependent on the ambient conditions, the target pollutants and the sensitivity of the recipient, adaptation of the filter design is recommended. Further work is required to investigate the winter performance and improve the reliability of nitrogen removal, which is highly variable. SAMMANFATTNING Dagvatten är en viktig orsak till ekologiska försämringar av urbana vattendrag p.g.a. stora avrinningsvolymer, och höga flöden samt en tillförsel av diverse föroreningar, t.ex. sediment, tungmetaller, näringsämnen, polycykliska aromatiska kolväten och salt. Dagvattenhanteringen har länge varit fokuserad enbart på att leda bort vattnet i rörledningar utan att hänsyn har tagits till retention av stora flöden eller till vattenkvalitén. På grund av dessa problem har utvecklingen av uthålliga dagvattensystem blivit allt viktigare och koncept som Lokalt Omhändertagande av Dagvatten (LOD), Water Sensitive Urban Design (WSUD) och Low Impact Development (LID) har utvecklats. En uthållig lösning inom dessa koncept är dagvattenbiofiltrering. Dagvattenbiofilter är infiltrationsbäddar med växter där dagvattnet infiltrerar och renas av växterna och filtermaterialet. De har en god förmåga att fördröja stora flöden samt att reducera föroreningar i dagvattnet innan det släpps ut till recipienten. Dessutom är det en estetisk och naturnära teknik som mycket väl kan integreras arkitektoniskt i både nya och befintliga stadsmiljöer. Dock saknas det fortfarande mycket kunskap om de processer som styr reningsförmågan samt hur de påverkas av varierande omgivningsförhållanden. I denna avhandling har därför effekterna av olika omgivningsfaktorer, dagvattenegenskaper och design av biofilter på reningen av metaller, näringsämnen och sediment undersökts. För att undersöka detta har biofilter, som delvis försetts med olika filtermaterial eller en vattenmättad zon, till dels kombinerad med en kolkälla, och utsatts för olika temperaturer och torra perioder. Biofiltren har bevattnats med dagvatten eller smältvatten. Prover har tagits på ingående och utgående vatten och föroreningskoncentrationerna