Technische Universität Dresden, Faculty of Environmental Sciences SWIMMING POOL WATER TREATMENT WITH CONVENTIONAL AND ALTERNATIVE WATER TREATMENT TECHNOLOGIES A thesis submitted to attain the degree of DOKTORINGENIEUR (Dr.-Ing.) presented by Bertram Skibinski Dipl.-Ing., Technische Universität Dresden born on Jan, 05th 1984 in Marienberg Reviewers: Prof. Dr. rer. nat. Eckhard Worch, Technische Universität Dresden Prof. Dr.-Ing. Wolfgang Uhl, Norwegian Institute for Water research Prof. Dr.-Ing. Martin Jekel, Technische Universität Berlin Day of oral defence: 22.02.2017 (Dresden) “Science is not finished until it is communicated” SIR MARK WALPORT 3 Table of contents 1  GENERAL INTRODUCTION ............................................................................................................... 6  2  THESIS OUTLINE ................................................................................................................................ 9  3  BACKGROUND ................................................................................................................................. 11  3.1  LOADING OF SWIMMING POOL WATER WITH PARTICULATE AND DISSOLVED SUBSTANCES ..................... 11  3.2  CHEMISTRY OF CHLORINE UNDER SPECIAL CONSIDERATION OF POOL WATER CONDITIONS .................. 18  3.3  DISINFECTION BY-PRODUCTS IN SWIMMING POOL WATER .................................................................. 21  3.4  SWIMMING POOL OPERATION AND REQUIREMENTS FOR POOL WATER QUALITY.................................... 31  3.5  WATER TREATMENT AND DBP MITIGATION STRATEGIES IN SWIMMING POOL SYSTEMS ........................ 35  4  COMPARING THE IMPACT OF DIFFERENT WATER TREATMENT PROCESSES ON THE CONCENTRATION OF DBPS AND DBP PRECURSORS IN SWIMMING POOL WATER. ........... 47  4.1  INTRODUCTION ............................................................................................................................... 48  4.2  MATERIALS AND METHODS ..............................................................................................................5 0  4.3  RESULTS AND DISCUSSION .............................................................................................................5 7  4.4  SUMMARY AND CONCLUSIONS ......................................................................................................... 70  5  REMOVAL OF INORGANIC CHLORAMINES WITH GAC FILTERS: IMPACT OF DIFFUSIONAL MASS TRANSPORT ON THE OVERALL REACTIVITY ..................................................................7 3  5.1  INTRODUCTION ............................................................................................................................... 74  5.2  MATERIALS AND METHODS ..............................................................................................................7 6  5.3  RESULTS AND DISCUSSION .............................................................................................................8 6  5.4  SUMMARY AND CONCLUSIONS ......................................................................................................... 97  6  IMPACT OF CHEMICAL CARBON PROPERTIES ON MONOCHLORAMINE REMOVAL WITH GAC FILTERS AND ITS RELEVANCE FOR SWIMMING POOL WATER QUALITY. .................... 99  6.1  INTRODUCTION .............................................................................................................................100  6.2  MATERIALS AND METHODS ............................................................................................................102  6.3  RESULTS AND DISCUSSION ...........................................................................................................111  6.4  SUMMARY AND CONCLUSIONS .......................................................................................................122  7  GENERAL CONCLUSIONS AND OUTLOOK ................................................................................123  8  SUPPORTING INFORMATION .......................................................................................................127  8.1  SUPPORTING INFORMATION FOR CHAPTER 4 ..................................................................................127  8.2  SUPPORTING INFORMATION FOR CHAPTER 6 ..................................................................................139  4 9  LIST OF ABBREVIATIONS, SYMBOLS AND GREEK SYMBOLS ............................................146  10  LIST OF FIGURES .......................................................................................................................152  11  LIST OF TABLES .........................................................................................................................156  12  REFERENCES .............................................................................................................................158  13  ACKNOWLEDGEMENTS ............................................................................................................187  5 1 General introduction Swimming is a popular year-round activity widely enjoyed for leisure, recreation and exercise by more than 250 - 300 million people in Germany per year [1, 2]. Comparable numbers of annual visitors have been reported for the United States (368 million people) [3]. A survey conducted in Germany in 2001 revealed that swimming is ranked on the second place of the most popular recreational activities placed only behind cycling [4]. These findings correlate with reported data from the United Kingdom [5] and the US [6]. The high level of acceptance of swimming among the population results in a high number of public and private pool facilities. The total number of public pools in Germany has been estimated in the year 2012 with 7.499 (excluding natural pools, counting combined indoor-outdoor pools twice) [7]. Comparable pool counts have been reported for Germany in the year 2002 [8, 9]. Including private pool facilities, the highest number of in-ground and above-ground pools in Europe has been reported for France (1.466.000), Spain (1.200.000) and Germany (862.000) [10]. A major drawback resulting from the simultaneous use of swimming pools by many people is the fact that serious diseases can be easily spread [11]. These waterborne infections are often associated with pathogens embracing viruses, bacteria and protozoa [11-21]. Previous studies showed that a high number of living cells and pathogens are introduced into pool water by shedding from the human skin [22, 23] or by fecal release [13, 14, 22, 24]. To assure the hygienic safety in pool systems, requirements for the quality of pool water have been set down in standards and regulations such as the German Protection Against Infection Act (IfSG Infektionsschutzgesetz) [25]. On the basis of the IfSG, the German swimming pool standard DIN 19643 sets specific microbiological and chemical quality parameters for swimming pools [26]. To guaranty the hygienic safety for bathers, swimming pools have a re-circulating water system that allows removing microorganisms and unwanted chemical substances from the water body by water treatment (Figure 1.1). The different treatment concepts, as they are allowed to be used in public pools in Germany are defined in DIN 19643 as well [26]. Therein, water treatment by filtration with upstream flocculation is described to be the first barrier against microorganisms followed by disinfection, which is the second barrier [26]. Chemicals used as disinfectant must be capable of inactivating microorganisms by 99.99% within 30 seconds (i.e. the indicator microorganism Pseudomonas aeruginosa). Only chlorine-based chemicals are permitted to be used for disinfection in Germany. Besides chlorine gas (Cl ), salts 2 6 of hyppochlorite are moost commmonly useed in laarge poolls [3]. CChlorine dispropportionatess in water forming cchloride and hypochhlorite ionss (OCl-). SSalts of hypochhlorite hydrolyze in aaqueous ssolutions fforming hyypochloritee ions as wwell. At neutral pH, as it is usual foor pool waater, the hyypochloritee ion protonnates formming the highly rreactive hyypochlorouus acid (HOOCl) [27, 228]. The suum of Cl , HOCl and OCl- is 2 denoted as free chlorine wwhile HOCCl comprisses the higghest disinnfection effficiency among the differrent speciees. Free cchlorine and in partticular HOCl does nnot only inactivaate microoorganisms at the doosing poinnt but commprises a depot effeect and assuress hygienicc safety in the baasin itselff. Due to this reaason, a cconstant concenntration of free chloorine has tto be estaablished inn the poool basin and free chlorinee concentrrations are subject too continuouus surveillaance [26]. Figure 1.1: SSimplified sscheme of a swimminng pool sysstem with rre-circulateed wwater flow, treatment section annd the polluutants remmoved by wwater trreatment aand DBP foormation from chlorine reactions. Besides its beneeficial effecct as disinffectant, HOOCl is knoown to reaact with dissolved and paarticulate oorganic maatter present in swimmming pool water forrming a vaariety of potentiaally harmfuul disinfecttion by-prooducts (DBPs) [3, 29--34]. Organnic matter present in poool water iss known to primariily originatte from thhe batherr and fromm fresh water [[35]. Givenn that somme of the fformed DBBPs are voolatile [30], bathers can not only taake them uup by dermal absorrption or oorally but aalso by innhalation oover the respiratory pathwway [1, 366]. Due to the limiteed air exchange in indoor swwimming pools, special cooncerns raaised in thhe past deecades witth regard to volatilee DBPs, which aare associated with adverse health effeccts such ass irritation of the resspiratory tract, eeyes or skkin [37-39] or develooping asthma [40-433]. Moreovver, epidemmiologic studiess showed tthat some of the DBBPs are suspected human carccinogens oor being consideered to be mutagenicc [33, 44-46]. 7 Thus, to guarantee optimal conditions for bathers, pool water treatment has to assure an efficient disinfection (i.e. low pathogenic risk) whilst having a minimal DBP formation. Zwiener et al. (2007) defined the following basic requirements for a suitable pool water treatment [3]: (i) removal of pathogens and particles, (ii) removal of dissolved organic matter and DBPs and (iii) sufficient disinfection with the lowest possible DBP formation. Recent research particularly emphasizes the importance of removing organic matter [24, 47, 48] and DBPs [49, 50] in the treatment train to lower concentration levels of DBPs in pool water. However, conventional pool water treatment (i.e. flocculation- sand filtration-chlorination) is suggested to insufficiently remove both, dissolved organic contaminants and DBPs [51, 52]. This leads to their accumulation in the swimming pool water cycle and increasing DBP concentrations over the operation time [53]. To prevent accumulation of substances, fresh water is often added to the pool water cycle for the purpose of dilution, which in turn increases the water and energy demand for operating a swimming pool system. To overcome the process of accumulation of DBPs and precursor substances in pool water while lowering the need for fresh water, alternative water treatment technologies have been introduced over the last decade [54]. Some of the most promising technologies which could accompany or partially replace conventional water treatment such as membrane filtration or oxidation processes [54, 55] have recently been integrated in the revised German pool standard DIN 19643 [56]. However, a detailed evaluation of their removal efficiencies for DBPs and DBP precursors under typical swimming pool operation is, in large parts, still subject to future research. 8 2 Thesis outline This thesis is intended to provide profound knowledge about the potential of various novel and conventional combinations of water treatment technologies to reduce hazardous impurities present in pool water. The pool water quality is primarily assessed by means of the emerging class of hazardous low molecular weight disinfection by-products (DBPs) and their organic or inorganic precursors. A special focus of this thesis will be on the removal of inorganic chloramines in granular activated carbon filters. Inorganic chloramines are of particular interest since they are often used as an indicator parameter in the surveillance of DBPs in pool water. Further, they are known precursors for the formation of highly carcinogenic DBPs (e.g. N-nitrosodimethylamine (NDMA)). It is therefore the aim of the research presented in this thesis to provide insights and clarifications with regard to the following questions: (i) To which extend do novel and conventional water treatment technologies contribute to the mitigation of DBPs and DBP precursors in swimming pool water? (ii) Which mechanisms and processes determine the removal of inorganic chloramines in granular activated carbon filtration? (iii) To which extend does granular activated carbon filtration contribute to the mitigation of inorganic chloramines and NDMA in pool water? Background information, results and conclusions of this thesis are given in Chapters 3 to 7. Chapter 3 provides a brief overview on the complex system of a modern swimming pool system and the chlorine chemistry within it. The current state of knowledge will be introduced in a causal order starting with an overview of sources for particulate and dissolved organic compounds in pool water followed by an explanation of reactions between the organic material and chlorine that lead to the formation of hazardous DBPs. Finally, the current state of art with regard to DBP mitigation by pool water treatment will be introduced. Chapter 4 provides a comprehensive assessment of the efficiency of different water treatment combinations towards the mitigation of dissolved organic precursors and DBPs in swimming pool water. A swimming pool model was engineered in the frame of this thesis to determine removal efficiencies for organic substances and DBPs under fully controlled and reproducible conditions. 9 Chapter 5 and Chapter 6 provide information on the removal of inorganic chloramines by granular activated carbon treatment. In Chapter 5, mechanisms are described that limit the overall reactivity for chloramine removal in a granular activated carbon filters. Further, the process of decreasing carbon reactivity for chloramine removal is investigated in detail. Chapter 6 gives information on the importance of surface chemical carbon properties with regard to the type of product formed when chloramines are transformed in a GAC filter. Simulations with a numerical model of a swimming pool system have been conducted to highlight the importance of the type of carbon used in a granular activated carbon filter operated in a swimming pool system. Depending on the type of carbon used, the concentration of carcinogenic NDMA, which is formed via reactions including chloramines, are calculated and compared. Chapter 7 contains the final conclusions about the use of conventional and novel processes for water treatment with regard to the mitigation of organic and inorganic precursors and DBPs in swimming pool water. 10