Faculteit Bio-ingenieurswetenschappen Academiejaar 2005 - 2006 PERFORMANCE OF CONSTRUCTED TREATMENT WETLANDS: MODEL-BASED EVALUATION AND IMPACT OF OPERATION AND MAINTENANCE WERKING VAN AANGELEGDE ZUIVERINGSMOERASSEN: MODELGEBASEERDE EVALUATIE EN IMPACT VAN BEDRIJFSVOERING EN ONDERHOUD door: ir. Diederik Rousseau Thesis submitted in fulfillment of the requirements for the degree of Doctor (Ph.D) in Applied Biological Sciences: Environmental Technology Proefschrift voorgedragen tot het bekomen van de graad van Doctor in de Toegepaste Biologische Wetenschappen: Milieutechnologie op gezag van Rector: Prof. dr. P. Van Cauwenberge Decaan: Promotoren: Prof. dr. ir. H. VAN LANGENHOVE Prof. dr. N. DE PAUW Prof. dr. ir. P. VANROLLEGHEM Water is H2O, hydrogen two parts, oxygen one, but there is also a third thing, that makes it water and nobody knows what that is. D. H. Lawrence (1885—1930), British novelist. If there is magic on this planet, it is contained in water. L. Eisely, The Immense Journey, 1957. Promoters: Prof. dr. Niels De Pauw Department of Applied Ecology and Environmental Biology Ghent University Prof. dr. ir. Peter Vanrolleghem Department of Applied Mathematics, Biometrics and Process Control Ghent University Dean: Prof. dr. ir. Herman Van Langenhove Rector: Prof. dr. Paul Van Cauwenberge DIEDERIK ROUSSEAU PERFORMANCE OF CONSTRUCTED TREATMENT WETLANDS: MODEL-BASED EVALUATION AND IMPACT OF OPERATION AND MAINTENANCE Thesis submitted in fulfillment of the requirements for the degree of Doctor (PhD) in Applied Biological Sciences: Environmental Technology Dutch translation of the title: Werking van aangelegde zuiveringsmoerassen: modelgebaseerde evaluatie en impact van bedrijfsvoering en onderhoud Cover illustrations: Front: subsurface-flow constructed wetland at Butlers Marston (UK) Back: free-water-surface constructed wetland at Põltsamaa (Estonia) Please refer to this work as follows: Rousseau D. (2005). Performance of constructed treatment wetlands: model-based evaluation and impact of operation and maintenance. PhD thesis, Ghent University, Ghent, Belgium, pp. 300. ISBN 90-5989-092-2 The author and the promotor give the authorisation to consult and to copy parts of this work for personal use only. Every other use is subject to the copyright laws. Permission to reproduce any material contained in this work should be obtained from the author. ACKNOWLEDGEMENTS Six years of PhD work to be summarised in a 40 minute presentation, six years of interacting and enjoying life with so many people to be summarised in just a couple of pages. The hardest part truly comes with the finish in sight. Reaching the finish certainly has been a ride with many unexpected turns. Had the original subject I chose for my MSc thesis not been cancelled, I probably would have ended up doing research on algae. Had I not attended that specific New Year reception, I probably would have dropped out of university. And had I not been so fortunate to have the support and friendship of my promoters, family, colleagues and friends, this ride would have been a very short one! I firstly would like to acknowledge both my promoters, Prof. dr. Niels De Pauw and Prof. dr. ir. Peter Vanrolleghem. It was a pleasure to learn from and cooperate with two experts in their respective fields although I have to admit that it was sometimes also a burden to reconcile both worlds. But that is probably what interdisciplinary research is all about. I especially appreciate their trust in me by giving me a large degree of freedom to define and carry out my research. I am also most grateful to Prof. De Pauw for the many opportunities he gave me to visit foreign countries, to establish contacts with researchers from abroad and to experience the cultural diversity in the world. I would further like to acknowledge the support I got from the countless colleagues of AECO, ECOTOX, CMS, BIOMATH, ANAFYS, the Lab of Plant Ecology and the Bio- engineering Faculty for both my research and teaching activities. One person in particular deserves the proverbial flowers: Anke, thank you for taking over so many of my duties and for your patience in coping with my sometimes chaotic way of working. Without your help, I never would have finished this PhD in time! Also Gisèle, thank you for your perfect preparations of and support during the practicals, it was a pleasure to work together with you. Mark and Guido, thank you for lending a hand from time to time to this clumsy engineer. Martine, thank you for your administrative support and the in-between talks. I also feel very fortunate to have been part of an expanding group of enthousiastic people doing research on constructed wetlands: Annelies, Dieter, Els, Erik and Gijs, thanks for sharing ideas and be willing to work interdepartmental, and I will certainly ii never forget our WETPOL adventure. I sincerely hope we will find each other again for new editions. When I was a first year Bio-engineering student, one particular phrase during the speech of the Dean got my attention: “... studying at our Bio-engineering Faculty is 50% hard work, and 50% social life”. Although I am not sure I always managed to keep the balance, in essence he was right. AECO walks, laboratory Christmas parties, BIOMATH springwalks, BIOMATH parties, BIOMATH cocktails, BIOMATH weekends, ANAFYS bowling night, Academic Club barbeque and so many other activities certainly gave an extra dimension to the word colleague. Without money no research, especially as a non-funded assistant, so I would like to express my gratitude to Aquafin for financially supporting part of this research and for their generosity in sharing data and know-how. I am also indebted to Severn Trent Water Ltd for accommodating me during a two-months research stay, it was a priceless experience. And finally my appreciation goes towards the Scientific Research Funds Flanders (FWO) for funding my research stays in the UK and Bulgaria and for several conference grants. I found it very motivating to meet and share ideas with other wetland scientists. Which brings me seamless to my colleagues from abroad whom I met among others through NecoV and the IWA Wetlands Specialist Group. It was a real pleasure to meet the persons behind the author names and if anything encouraged me to keep going with this PhD, it were those international, intercultural nights during the conferences! I especially want to acknowledge dr. Joan García from the Technical University Barcelona for his contribution to the model part of this thesis and for the inspiring scientific and other discussions we had during his stay in Ghent. Finally also a word of appreciation for my new colleagues at UNESCO-IHE for their warm welcome and for giving me some much needed time to finish this thesis. Many students and trainees have also contributed to this PhD and therefore deserve a special word of thanks: Wouter, Saskia, Jeroen, Bernard, Dierik, Annemie, An, Jan, iii Natalie, Joachim, Anke, Bram, Kevin, Abby, Isabelle and Melanie, it was a pleasure to work with you and I hope it has been a fruitful experience. I also would like to thank my friends for making me sometimes forget about my PhD. An, Anne, Bernard, Bram, Bruno, Carine, Eline, Els, Emmy, Isabelle, Joeri, Karen, Katrien, Klaas, Koen, Kris, Leen, Miguel, Nathalie, Susana and Yves: our weekend and other trips, parties, bar nights, diners and all the other things we did together were a perfect counterbalance. I missed a lot of these activities during these last quite stressful months but I hope we can now resume the old pace! And last, but as always certainly not least, a special word of thanks to my parents for their love and support. I now know that being a supporter is much harder and far more stressful than being a player. This adventure ends here, new adventures can begin, or quoting from one of my favourite movies: second star to the right, and straight on till the morning ... Diederik, 12 November 2005 iv 1 TABLE OF CONTENTS Chapter 1 An introduction to constructed wetlands technology 3 Chapter 2 Constructed wetlands in Flanders: a performance analysis 21 Chapter 3 Subsurface-flow constructed wetlands: processes and 47 influencing factors Chapter 4 Short and long-term dynamics in subsurface-flow constructed 61 wetlands: a pilot-scale study Chapter 5 Model-based design of horizontal subsurface-flow constructed 95 wetlands: a review Chapter 6 Model study of short-term dynamics of secondary treatment 117 reed beds at Saxby (Leicestershire, UK) Chapter 7 A conceptual model framework for interpreting carbon and 133 nitrogen cycles in horizontal subsurface-flow constructed wetlands Chapter 8 Carbon, nitrogen and sulphur cycles in horizontal subsurface- 185 flow constructed wetlands: a model-based evaluation Chapter 9 Operation and maintenance of constructed wetlands 217 Chapter 10 Impact of operational maintenance on the asset life of storm 229 reed beds Chapter 11 General discussion, conclusions and perspectives 241 References 251 List of abbreviations 277 Summary 279 Samenvatting 283 Curriculum vitae 287 2 3 Chapter 1 An introduction to constructed wetlands technology 4 1.1. HISTORY AND APPLICATIONS OF CONSTRUCTED WETLANDS Although wastewater treatment is a relatively young technology, avoiding septic conditions by evacuating wastewater from human settlements has a considerable history. Angelakis et al. (2005) for instance describe the advanced sewer system at Knossos (Crete), dating from the second millenium B.C. Bertrand-Krajewski (2002) elaborates on the ‘Cloaca Maxima’ in ancient Rome and on early sewer systems in London and Paris, while Poulussen (1987) strikingly depicts the development of water sanitation in Antwerp (Belgium). Once outside the city boundaries, the wastewater was often conveyed to nearby natural wetlands which at that time were considered as useless lands (Vymazal, 1998a; Kadlec et al., 2000a). From the fifties and sixties of the past century on, however, ecologists started to realise the value of these wetlands and initiated many studies on this topic.