Advanced oxidation and managed aquifer recharge: A synergistic hybrid for organic micropollutant removal

AdvAnced oxidAtion And

mAnAged Aquifer rechArge

A synergistic hybrid for orgAnic micropollutAnt removAl

Proefschrift

ter verkrijging van de graad van doctor aan de Technische Universiteit Delft,

op gezag van de Rector Magnificus prof.ir. K.C.A.M. Luyben, voorzitter van het College voor Promoties,

in het openbaar te verdedigen op 14 november 2012 om 12:30 uur

door

Karin LEKKERKERKER-TEUNISSEN civiel ingenieur

Dit proefschrift is goedgekeurd door de promotoren: Prof. ir. J.C. van Dijk

Prof. dr. G.L. Amy

Samenstelling promotiecommissie:

Rector Magnificus, Voorzitter

Prof. ir. J.C. van Dijk Technische Universiteit Delft, promotor

Prof. dr. G.L. Amy King Abdullah University of Saoudi Arabia, promotor Dr. ir. J.Q.J.C. Verberk Technische Universiteit Delft

Prof. dr. ing. M. Jekel Technische Universität Berlin Prof. dr. ir. B. van der Bruggen Katholieke Universiteit Leuven

Dr. J.C. Kruithof Wetsus

Prof. dr. ir. J.P. van der Hoek Technische Universiteit Delft

Prof. dr. ir. L.C. Rietveld Technische Universiteit Delft, reservelid

Advanced oxidation and managed aquifer recharge a synergistic hybrid for organic micropollutant removal Author: K. Lekkerkerker-Teunissen

Lay-ouyt: Akimoto

Printed by: Klomp Grafische communicatie Photography: page 37 & 204, Noclichés/Beeldzaak Copyright © K. Lekkerkerker-Teunissen

All rights reserved. No part of this thesis may be reproduced or transmitted in any form or by any means without permission of the author.

This research was supported by Dunea drinking water company, the Netherlands. Additional finan-cial support was provided by the NWO, Netherlands Organisation for Scientific Research.

voor JAco en boAz

chapter 1 introduction

6

chapter 2 uv - Aop

30

chapter 3 trAnsformAtion products

62

chapter 4 seriAl - Aop

90

chapter 5 omps And mAr

110

chapter 6 Aop And mAr

154

chapter 7 conclusions And AdditionAl remArKs

178

chapter 8 summAry, sAmenvAtting, dAnKwoord

190

curriculum vitAe & list of publicAtions

tAble of contents

chApter 1:

introduction

multiple bArrier ApproAch for

surfAce wAter treAtment

In the Netherlands, drinking water is prefer-ably produced from groundwater. Groundwater is a reliable source since it is protected by the surrounding soil and the influences of human activities are minor. The usual long residence times of groundwater in the subsurface ensure a microbiological stable and reliable source for drinking water. In general, after local abstraction by wells, the subsequent treatment is relatively simple and the water is distributed to a relatively small supply area.

When reliable groundwater is not available an-other source for drinking water should be found, as is the case in the Western part of the Nether-lands. The North Sea along the Western Coast results in saline or brackish groundwater by sea water intrusion. Surface water is often used as the alternative fresh water source. In the Neth-erlands surface water is almost always abun-dantly available and relatively easy to abstract. A drawback of surface water as a source for drinking water is the strong variation in quantity

and quality over the year. This problem requires storage of source water, for example in reservoirs or in subsurface aquifers. Another drawback is the high impact of human activities on the water quality. Usually, rivers are used, which are fed by rainwater and melting snow and ice from mountains. They have large catchment areas with intensive human activities. Especially in the downstream countries the river water has passed many waste water treatment plants, industrial and agricultural areas, hospitals and the influ-ence of human activities can therefore be meas-ured with modern analytical instruments. Surface water treatment plants are character-ized by extensive infrastructures and multiple barrier treatment process trains. The water can be abstracted many kilometers away from the treatment plant, resulting in long transportation pipelines. The scale of surface water treatment plants is usually larger compared to groundwater treatment plants.

The treatment of surface water has changed in the past decades by increasing water consump-tion and quality requirements. Surface water treatment began with the so-called conventional treatment process train, consisting of floccula-tion, sedimentafloccula-tion, rapid sand filtration and (optionally) slow sand filtration. Bacteriological quality was guaranteed by chlorination of the drinking water as a final step. When the produc-tion capacity increased, slow sand filtraproduc-tion was

problem definition

sometimes replaced by chemical disinfection. In 1974, Rook discovered harmful disinfecting by-products (trihalomethanes (THM), mainly chloroform) from the chlorination process. The VEWIN recommended a maximum concen-tration of 0.55 mmol/L THM and 70 µg/L for chloroform. The first standard was set at 100 µg/L THM, with 25 µg/L per component. From 2008 this standard is 25 µg/L for THM, with 10 µg/L per component. These standards could not be met when chlorination was applied. In 1987 the insecticide bentazon was found to pass through most traditional treatment processes, even through aquifer recharge in the dunes. Granular activated carbon filtration or powdered activated carbon dosing was added to most con-ventional treatment plants. Finally, in 1993 it was found that Cryptosporidium and Giardia were resistant to chlorination, and higher chlorine doses and longer contact times were not effec-tive and not possible because of higher THM formation. Other disinfection techniques were found in chlorine dioxide dosage or ozonation. Nowadays surface water treatment plants usually consist of multiple disinfection steps, such as ozone for primary disinfection and chlorination for secondary disinfection. This concept with subsequent treatment steps to ensure

bacterio-for primary and secondary disinfection, in the Netherlands. The multiple barrier treatment ap-proach together with the well maintained distri-bution system are key factors for the success of the Dutch drinking water sector. We drink water from the tap without the taste of chlorine!

mAnAged Aquifer rechArge

A good alternative for direct surface water treat-ment is indirect treattreat-ment after infiltration. Infil-tration of surface water has three major functions: treatment, storage and leveling. Treatment results in the removal and/or inactivation of pathogenic microorganisms, the water is disinfected and becomes biologically stable. The water is infiltrated in the subsurface, where it is stored. This stored water stock can be utilized when surface water is temporary not available, for example as a result of an industrial spill into the river. Leveling of quality is attained by long residence time and residence time distribution. The river water itself varies strongly in quality over the year, the quality of re-covered water is much more stable, which is better for the subsequent treatment processes and a more constant drinking water quality is distributed to the customers. Due to these three major functions of subsurface infiltration, this process is an important step in the multiple barrier approach, ensuring bacteriologically safe and biologically stable water without the use of chlorine. In the Western parts of

the Netherlands the coastal dune area is used for managed aquifer recharge (i.e., dune (in)filtration). This has its origin in the abstraction of the fresh water lens which was created by rainwater float-ing on top of the brackish/saline seawater. This fresh water lens was found to be a good source for drinking water in 1853 (Amsterdam) and 1874 (The Hague). The water was abstracted and distributed to the customers. In the beginning of the 20th century the water consumption increased and the amount of rain water replenishing the dune area was no longer sufficient. In 1954 Dunea started the infiltration of surface water as an alternative source for rain water to restore and maintain the fresh water lens under the dune area. The surface water is transported towards the dune area, infiltrated by infiltration ponds and abstracted by (preferably) wells or open canals. Before the surface water is suitable for infiltration, it needs to be pre-treated. The main function of the pre-treatment is to remove suspended solids and, in case of open infiltration, high concentrations of nutrients (e.g., phosphate). Therefore the pre-treatment consists of a flocculation/sedimentation step and a rapid sand filtration step. The quality standards for infiltration water also require that no contaminants foreign to the infiltration environment accumulate in the subsurface. This includes organic micropol-lutants, which are not removed with conventional pre-treatment. Changes in the pre-treatment are required, for example the addition of granular acti-vated carbon filtration or advanced oxidation.

orgAnic micropollutAnts

Although the Dutch current water supply is very reliable and most consumers drink water from the tap, there are several issues that threaten this high drinking water quality in the near future. One of these issues is the occurrence of organic micropoll-utants (OMPs) in the sources and, though in lower numbers and even lower concentrations, in the drinking water itself.

OMPs, such as pesticides, pharmaceutically ac-tive compounds (PhACs), endocrine disrupting compounds (EDCs), X-ray contrast media and personal care products (PCPs), have been found at ng/L to low µg/L concentrations in surface waters throughout the world (Kolpin et al., 2002; Jurgens et al., 2002; Stolker et al., 2004; Kasprzyk-Hordem et al., 2008; Gros et al., 2009, and reviewed by Houtman, 2010). Large quantities of OMPs are used in Western societies. They may enter, in

of OMPs in the water is not new; river water has been under the influence of human activities for centuries. However, since the recent development in analytical tools and monitoring programs, more and more compounds are being detected and the detection levels are still decreasing. In the past the problem was not recognized, since all compounds were found to be below the detection limit, and the water was assumed to be clear of OMPs. Nowadays hundreds of compounds are found on a regular basis above detection limits and questions arise about their effects on the environment and on human health.

OMPs with biological activity, such as PhACs and pesticides, are of concern to drinking water utilities (Ray et al., 2002), because of their possible long-term effects, the possibility of mixture activity and the sensitivity to customer perception. Customer trust should be considered seriously. Imagine the impact on the environment when more and more people are drinking bottled water instead of tap water, because of rumors about hormones in their tap water.

Although the effect on human health for a single compound in the low concentrations present is judged negligible (Schriks et al., 2010), these com-pounds do not belong in drinking water. As long as there is no evidence that there is no impact at all

duneA

Dunea uses the Meuse River as its source for drinking water. The Meuse River is a rain-fed river with high discharge in winter (up to 400 m3_{/s) and low discharge in summer (100 m}3_/s).

The catchment area includes large parts of France, Belgium and the Netherlands. Dunea abstracts water (2.5 m3_{/s) from the}

dammed Meuse, a dead-end tributary from the Meuse River. This tributary acts like a natural reservoir through its low current and long residence time of several weeks. There is also an influence of the discharge of adjacent polder water on this tributary.

The treatment applied by dune water company Dunea is a typical multiple barrier treatment, characterized by an extensive infrastructure and subsequent treatment steps. The water is first collected in a dead end side stream of the Meuse River, acting as a process reservoir. In the beginning of this side stream, coagula-tion, flocculation and sedimentation take place

through dosing of ferrous sulphate (FeSO₄) in combination with aeration. At the water intake, the water is treated by microsieves (sieve width 35 µm) and transported for 27 km to Bergam-bacht where the water is filtered by dual media rapid filters and transported by twotransport pipelines to the dune area, with a length of 46 and 57 km, respectively. In the dune area, mainly open infiltration takes place. There is also a deep well infiltration facility which is used incidentally. After a residence time in the dunes of at least 21 days, but on average 120 days, the water is abstracted and post-treated at three different locations. Post-treatment con-sists of softening, dosing powdered activated carbon, cascade aeration, rapid sand filtration and finally slow sand filtration. The water is distributed without post-disinfection. Dunea considers an OMP to be a priority substance if its presence, its toxicity and/or its low removal by current treatment are reasons to take precautions or measures to remove this compound with additional treatment. The present barriers against OMPs in Dunea’s treatment are the managed aquifer recharge (MAR) by dune passage and the combination of powdered activated carbon (PAC) dosing on the rapid sand filtration (RSF) in the post-treatment.

A MAR system can remove a range of OMPs present in (the background water matrix of) the

water. The dune system of Dunea also levels off peaks of incidentally high concentrations in the water. Although this natural system has a lot of advantages and a large potential to remove OMPs (to a certain extent), it is not an adequate process to remove all OMPs from the water, and thus additional measures are required. For the PAC and RSF step it was found that compounds such as MTBE, NDMA and 1,4-dioxane were removed by less than 20%. The compounds carbendazim, carbamazepine, bisphenol-S and metropolol were removed above 80%, but only in the first half of the filter run time. 15 out of 25 compounds were removed below 60%.

The removal of OMPs by the current treatment is not adequate, and since Dunea argues that these compounds do not belong in drinking water, measures are required.

treAtment philosophy duneA

When Dunea is facing a threat towards water quality, the preferred approach is: prevention – removal – oxidation, in this order. When this treatment philosophy is used for the challenge of OMPs, the following considerations can be made:

prevention. The problem of OMPs in the source for drinking water exists because these compounds enter the source. The ultimate so-lution to this problem lies therefore in prevent-ing these compounds from enterprevent-ing the source. Solutions can be found in a lower use of pesti-cides in agriculture or a different dosing system reducing leaching of the OMPs to the surface water. The amount of pharmaceuticals in the water can be reduced by producing pharmaceu-ticals that are better biodegraded in the

envi-the hospital of Delft). The number of industrial compounds can be reduced by less application of these compounds, but this is hard to estab-lish and control. Many personal care products reach the surface water by passing through the waste water treatment plants. Using more advanced waste water treatment plants can also reduce the number and concentrations of OMPs in surface water.

All of these proposed measures will finally lead to lower emission levels compared to today’s concentrations. But other developments can cause the reverse effect. People are getting older and more and more pharmaceuticals are expected to be used and excreted in the coming decades. Climate change is expected to change the discharge of rivers in such a way that there is higher discharge in winter and less discharge in summer. When the emissions of OMPs into the river are assumed to stay the same, while the discharge of the river itself is decreasing in summer, the OMPs are less diluted by the river water and concentrations of OMPs will there-fore increase.

Dunea has some experience with preventive measurements in the agricultural area Bommel-erwaard. This area is located around the abstrac-tion point of Dunea and discharges polder water nearby the drinking water abstraction point. For example the compound atrazine was used frequently in this area. Efforts by the water

companies resulted in a legislation in the EU that banned this compound. A decrease in atra-zine concentration was measured in the Meuse River, but, after a few years, it became clear that the agricultural sector found an alternative for atrazine. First the concentration of diurone, and a few years later the concentration of glyphosate in the Meuse River increased (Figure 1). Un-fortunately, the latter compound is more polar and more difficult to remove from the water by conventional treatment and by GAC filtration. Although prevention is the ultimate and prefer-able solution, the last decades have proven that this is not an easy approach. Expensive and time intensive efforts of Dunea did not result in a measurable increase in water quality (con-cerning OMPs) of the source water. Although prevention and the public awareness resulting from these efforts are positive, preventive meas-urements only do not meet the duty of care that water supply companies have towards the dune area and the consumers.

removAl. If it cannot be prevented that organic micropollutants enter the surface water, they can be removed from the water before distribu-tion and preferably also before infiltradistribu-tion in the dunes. The state of the art technique that removes OMPs from drinking water is (biologi-cal) granular activated carbon ((B)GAC) filtra-tion, but polar compounds are not removed

by this technique. A more recent developed technique is membrane filtration. An advan-tage of this latter technique is the fact that the compounds are removed from the water phase without degradation. This prevents the forma-tion of degradaforma-tion products and possible by-products. By this technique the water is pressed through an extremely thin film with very small pores. In case of nanofiltration (NF) or reverse osmosis (RO) these pores are small enough to remove even most dissolved solutes like OMPs. But there is no removal of low molecular com-pounds. Another drawback of this small pore size is that a large filter surface area is required and a high pressure to press the water through, and the combined removal of other dissolved particles as salts and nutrients, which are (to some extent) required in drinking water. The effluent of NF/RO membranes is too clean to drink, which makes addition of salts or side stream treatment necessary. Another drawback of membrane filtration is the waste stream. Not only are the OMPs retained, but also part of the water itself, up to 20% for RO. This can cause

be treated separately or has to be disposed in receiving water bodies, maintaining the original problem.

The high energy consumption and the waste stream are major objections to the application of membrane filtration. But more specifically in the Dunea treatment the limited recovery of membrane filtration is indeed causing capacity problems. In addition the most suitable loca-tion to install RO is after MAR. The treatment of MAR effluent water ensures high quality drinking water for the customers, but does not protect the dune area against infiltration of anthropogenic compounds.

oxidAtion. If prevention and removal are both not able to solve the problem, oxidation can be the solution. The interest in oxidation tech-nologies is primarily based on their expected robustness and relatively low costs. However, a drawback may be the formation of transforma-tion products and by-products, when complete mineralization is not achieved.

Oxidation involves strong oxidants, such as

1990 1993 1996 1999 2002 2005 2008 0 0,1 0,2 0,3 0,4 _atrazine glyphosate diurone

Figuur 1: Atrazine, glyphosate and diurone in the Meuse River (in µg/l)

oxidation process (AOP) does not remove OMPs from the water, but transforms the par-ent compounds completely to carbon dioxide and water or, more likely, into transformation products. Also other water constituents pre-sent in the water matrix can potentially be oxi-dized (e.g., NOM and bromide), resulting in by-products (e.g., bromate). When considering implementing an AOP process, not only the conversion of parent compounds, but also the formation of transformation products and by-products need to be evaluated carefully. These products will influence subsequent treatment processes where they are ideally removed biologically. In the case of Dunea, this biologi-cal treatment step can be the managed aquifer recharge in the dune area. Therefore, Dunea considers to install AOP in the pre-treatment for three main reasons:

• This will result in a multiple barrier of two complementary processes, AOP and MAR. • MAR can biologically remove transformation

products and by-products.

• Dunea can fulfill the standards set for OMPs in the infiltration water.

A first reason to implement AOP before MAR is that advanced oxidation is a chemical process with a short residence time while dune passage is characterized as a biological process with a long residence time that also levels peak

concentra-tions. Oxidation will generally result in smaller molecules that are more easily biodegradable. The second aspect for using AOP in the pre-treatment is the formation of assimilable or-ganic carbon (AOC) during AOP. By UV/H2O2,

AOC is formed as a result of direct photolysis (UV dose ≥100 mJ/cm2_{) of dissolved organic}

carbon (DOC) or through a reaction of DOC with hydroxyl radicals (IJpelaar et al., 2005; Richardson et al., 1999; Huang et al., 2005). The organic by-products comprising AOC have been linked to increased bacterial regrowth in drinking water distribution systems (LeCheval-lier et al., 1992; van der Kooij, 1992). Biological filtration is used to remove these by-products, creating a biologically stable water prior to distribution (Huck et al., 1991; Krasner et al., 1993). A low AOC concentration in the finished drinking water is of major importance to Dunea because it (Dunea) distributes the water without post-disinfection. The current AOC levels in Dunea’s drinking water are low (3.5 – 7.5 µg/L), which should be maintained in the future. The third reason to implement AOP in the pre-treatment relates to legal standards for OMPs in pre-treated river water that is infiltrated in the dune area. Standards are set by provincial governments and are, for most compounds, similar to limits set for drinking water. The maximum allowed concentration for individual pesticides is 0.1 µg/L, and for the total concen-tration of all pesticides is 0.5 µg/L.

Implement-ing a barrier against OMPs before MAR will ensure that Dunea can maintain these, and future, standards. For other OMPs there are no standards, but they can be expected in the fu-ture. And removal of OMPs before infiltration does meet the duty of care water companies have to protect the dune area.

Implementing AOP in the pre-treatment also has a drawback, as the water quality of Meuse water is relatively poor compared to the quality of the water after the post-treatment. The pre-treated river water has a relatively high DOC concentration (3-5 mg/L) and low UV-transmis-sion (73-83% UV-T), rendering it a real chal-lenge to find an appropriate AOP process and, in case of UV/H2O2, the lamp technology that is

most energy efficient.

Since in the specific situation of Dunea AOP can be placed before MAR, both duty of care is-sues are addressed: the production of excellent quality of drinking water and avoiding OMPs accumulation in the dune area.

problem definition. Organic micropollutants are present in sources for drinking water and, although in lower numbers and concentrations, also in finished drinking water. Although there is still discussion about their effect on human health, water companies should be cautious. The current treatment of Dunea cannot ad-equately remove OMPs. When extension of the current treatment is considered, the application of AOP before MAR is proposed as the solution that fits best into the current treatment train. This chemical oxidation step is believed to en-hance the natural treatment by MAR, resulting in a synergistic hybrid system against organic micropollutants. This thesis focuses on the performance of an AOP process, implemented in the pre-treatment of Dunea, and its influence on the sequential dune filtration step.

AdvAnced oxidAtion processes

Advanced oxidation comprises a group of water treatment processes which involve the generation of hydroxyl radicals in sufficient quantity to effect water purification. Hydroxyl radicals can be generated by (a combination of) different agents, such as ozone, hydrogen peroxide and ultraviolet radiation. The gener-ated hydroxyl radicals attack most organic compounds by abstracting a hydrogen atom from water or by adding itself to unsaturated sites of the molecule or to aromatic structures. Several methods are available for generating OH radicals:

• Ozonation at elevated pH (>8.5) • Ozone + hydrogen peroxide (O₃/H2O2)

• Ozone + catalyst (O₃/CAT) • Fenton system (H2O2/Fe2+)

• O₃/UV • H2O2/UV

• O₃/ H2O2/UV

• Photo-Fenton/Fenton-like systems • Photocatalytic oxidation (UV/TiO₂)

Although these processes have mechanistically much in common, there are enough differ-ences to make one or the other more practical depending on the water quality and water treat-ment goals (Glaze et al., 1987).

In this study, the aim was to select a combina-tion of oxidative processes for a non-selective degradation of organic micropollutants with a restricted by-product formation. Most applied techniques are a selection between ozona-tion, UV photolysis, and ozone and UV based advanced oxidation.

The reaction rate constants for the reaction of pesticides and ozone vary between < 0.04 M-1_s-1

(for lindane) and 4.4 x 104 _{(for aldicarb).}

There-fore ozonation is a selective oxidation process. The reaction with lindane is infinitely slow, the reaction with atrazine takes many hours, while aldicarb reacts within a few seconds. The degradation by UV photolysis is depending on the absorption of UV-photons and the quantum yield. Therefore, as ozonation, UV photolysis is a selective process. Pesticides like metaldehyde do not absorb UV light and are not degraded at all, while atrazine with a high molar absorption coefficient (3683 M-1_cm-1_{) and a high quantum}

yield (0.033 M/Einstein) shows a high conver-sion. The reaction rate constants for hydroxyl radicals produce by O₃/H₂O₂ and UV/H₂O₂ are in the range of 106 – 109 M-1_s-1_{. For example}

the reaction rate constant for atrazine is 2.7 x 109 M-1_s-1_{. Therefore reaction takes place within}

bAcKground And

microseconds after the hydroxyl radicals are produced from H₂O₂ by O₃ or UV. Therefore molecular ozone and UV-light will give a sig-nificant, but selective, contribution to organic micropollutant control. For a more non selec-tive degradation an advanced oxidation process based on hydroxyl radical reaction is needed. Therefore, the agents used in this study are 1) ozone/hydrogen peroxide (O₃(/H₂O₂)2) ul-traviolet radiation/hydrogen peroxide UV/H₂O₂ and 3) a serial combination of ozone/hydrogen peroxide and UV (O₃/H2O2/UV). The basics of

these three AOP processes are described and discussed in the next few paragraphs.

o3/h2o2. Ozone has been used for water treat-ment for decades and was shown to be success-ful for enhancing taste, aiding coagulation and filtration processes and as a first barrier against micro-organisms. Ozone is also known to be a powerful oxidant. In theory ozone should be able to oxidize inorganic substances and organic compounds (the latter ideally to carbon dioxide and water), but in practice ozone is quite selective in its oxidation reactions. Ozone is most useful for cleavage of multiple bonds and disrupting aromatic systems. (Glaze et al., 1987). The combination of microbial

disinfec-hydrogen peroxide enhanced the efficiency of oxidation of several organic substances and increased the rate of ozone transfer. Hydrogen peroxide can initiate the ozone decomposition cycle, resulting in the formation of hydroxyl radicals (Hoigne, 1982).

O₃/H₂O₂ can cost effectively degrade most OMPs, although there are some persistent com-pounds such as NDMA and amidotrizoic acid (Lekkerkerker et al., 2009). Acero et al., (2001) concluded that O₃/H₂O₂ is not very effective for MTBE degradation at oxidant doses typically applied in drinking water treatment.

During the application of O₃(/H₂O₂) in drink-ing water treatment, the formation of organic (e.g., Assimilable organic carbon (AOC), alde-hydes, carboxylic acids and ketons) and inor-ganic (e.g., bromate) by-products has been well documented (Richardson et al., 1999; Huang et al., 2005).

When bromide is present in the source water, bromate formation should be an issue to con-sider, because bromate is a suspected carcino-gen (Kurokawa et al., 1990).

Hydrogen peroxide is the main source to produce OH radicals, but also acts as a radical scavenger. Also water matrix components act

dosing of ozone not only results in the forma-tion of OH radicals, but also limits bromate for-mation (Lekkerkerker et al., 2009, Scheideler et al., 2011). A disadvantage of this combination is that less ozone reacts with the DOC in the water and less ozone is available for disinfec-tion. Duguet et al., (1985) found that best per-formance was achieved when H₂O₂ was added after the oxidation of highly reactive substances with ozone alone. Choices to be made really depend on local circumstances such as water quality and treatment goals.

uv/h2o2. When using the combination of UV radiation and hydrogen peroxide, the direct photolysis of hydrogen peroxide leads to the formation of OH radicals. For water treatment purposes, the energy input to produce these radicals highly depends on the background absorbance of the water to be treated.

Besides the radical oxidation mechanism, the UV radiation itself can also degrade compounds by the process of direct photolysis. The effec-tiveness of this process depends on the output spectrum of the UV lamp used and the absorp-tion spectra of the water to be treated and the absorption spectra of the target compounds. The UV/H₂O₂ process has been successfully used for the destruction of chlorinated com-pounds (Hirvonen et al., 1996). Hormones are already highly degraded at relatively low UV fluence (300 mJ/cm2_{) for UV/H}

2O2 applications

(IJpelaar et al., 2010; Rosenfeldt and Linden, 2004). Although the cleavage of triazine rings is difficult, also triazines such as atrazine can be converted by this process (IJpelaar et al., 2010; Kruithof et al., 2007; Watanabe et al., 2005). Full scale applications have been in-stalled at several locations (Kruithof et al., 2007 and Swaim et al., 2008).

different lAmp technologies for uv/h2o2. For the UV/H₂O₂ process, different lamp tech-nologies are applied. The most applied lamps are medium pressure (MP) mercury vapor lamps and low pressure (LP) mercury vapor lamps. In this study also a prototype of a mer-cury free lamp is used, the dielectrical barrier discharge (DBD) lamp from Philips.

Medium pressure lamps emit a broad spectrum of light, between 200-800 nm, of which the range between 235 – 300 nm is relevant for UV/H₂O₂. This range of wavelengths corre-sponds with the absorbance spectrum of many compounds, hydrogen peroxide and that of natural water. This results in a high photolytic capacity, but also in a lower efficiency and a higher by-product formation potential. Low pressure lamps emit UV-light at just one single wavelength (253.7 nm). Consequently, they can only photolyze compounds with an absorbance around 254 nm. The absorbance of hydrogen peroxide shows a maximum between 200-235 nm (~179 M-1_cm-1 _{at 200 nm), and thus}

exhib-its a lower absorbance at 254 nm (~19 M-1_cm-1_).

But due to the low background absorbance, the OH radical formation potential in natural waters can be higher at 254 nm than at the wavelength between 200-235 nm, caused by the absorption of water itself. IJpelaar et al., (2010) demonstrated in a study including tests with Dunea water that LP mercury lamps can be suc-cessfully applied for the production

of hydroxyl radicals from H₂O₂.

A disadvantage of the LP-UV/H₂O₂ process is the low installed power of a single LP lamp. More and bigger reactors are required, resulting in a larger footprint. However, there is also less absorbance by other interfering natural water components, resulting in a higher efficiency and less by-product formation by LP lamps (IJpelaar et al., 2010).

When a choice between lamps has to be made, aspects that need to be considered are energy consumption, footprint, investments costs and maintenance costs. Depending of which aspect is most important is a specific situation will influence the choice of lamp technology. MP and LP UV lamps are both mercury lamps. Because of environmental concerns when disposing of mercury-containing lamps, there

is a significant interest in mercury-free lamps. In cooperation with Philips Research, the KWR Watercycle Research Institute, AwwaRF, and the Greater Cincinnati Water Works, a newly developed mercury-free lamp was tested in the pilot installation at Dunea. This lamp, the dielectrical barrier discharge (DBD) lamp, emits wavelengths around 240 nm.

h2o2 / o3 / uv. O₃/H₂O₂ can cost effectively degradate most OMPs, though there are some persistent compounds such as NDMA and amidotrizoic acid (Lekkerkerker et al., 2009). When bromide is present in the source wa-ter, bromate formation should be an issue to consider, because bromate is a suspected carcinogenic (Kurokawa et al., 1990). UV/H₂O₂ is a more energy consuming AOP technology, but encompasses a broad barrier against most OMPs. Common practice is to install O₃/H₂O₂ or UV/H₂O₂, depending on treatment demands and water quality. Other considerations for

se-lection of the desired AOP also involve existing infrastructure, such as pre- and post-treatment and available footprint. Dunea considers install-ing a combination of the two AOP technolo-gies: O₃/H₂O₂+LP-UV. A minor ozone dose can provide an efficient and cost effective first degradation and bromate formation can be lim-ited. Depending on the desired treatment goals further degradation can be achieved by UV and UV/H₂O₂, as the residual H₂O₂ from the ozone step is still present.

An expected advantage of this combination is that part of the ozone will react with the DOC in the water. This will increase the UV-trans-mission and enhance the UV/H₂O₂ process in terms of energy use and by-product formation.

What are the synergistic effects of serial O3/H2O2 and UV/H2O2? What are the design parameters for both processes at Dunea’s treatment at which the bromate formation is limited, but the OMPs degradation successful?

O3 UV

h2O2

•

• the intake and an infiltration pond of Dunea

mAr And omp removAl

Because of the biological and chemical pro-cesses occurring, MAR has the potential to (sustainably) remove OMPs. Howard (2000) found seven different structural properties that determine the biodegradability of a solute. By the combination of microbial activity and compound properties, MAR is, in addition to the removals of bacteria, viruses and suspended solids, also able to remove (many) OMPs. A study by Segers and Stuyfzand (2007) investi-gated the contribution of MAR to the removal of OMPs at the Dunea treatment plant. Re-moval efficiency during MAR depended on the influent concentrations, residence time, media sorption characteristics, water temperature and redox conditions. For 61% of the OMPs, the concentration after MAR appeared to have decreased to below the detection limit. X-ray

contrast media, except iopamidol, were well removed under oxic conditions. Amidotrizoic acid, another X-ray contrast medium, and the pesticide carbendazim were well removed under anoxic conditions. However, other sub-stances were barely removed, either during oxic or anoxic MAR conditions. These substances were usually poorly biodegradable and had poor sorption characteristics. Examples included MTBE, diglyme, bentazone and 1,4-dioxane. Although it is known that MAR is not an ab-solute barrier against all OMPs, it is a natural barrier. Dunea has mentioned in the company strategy that it prefers to use natural treat-ment processes when possible. Since MAR is already implemented and has shown to be a robust and natural process, it should be used by Dunea to remove OMPs to the extent possible. Therefore the mechanism and limits of this process should be better understood. If ad-ditional treatment is necessary, the interaction between this additional treatment and MAR is of importance.

If Dunea wants to rely on MAR for OMP removal, more insight is necessary into the mechanisms and limits of this treatment step. This will also provide the basics for understand-ing the combination of AOP and MAR.

Which compounds can be removed by MAR under which circumstances and which cannot? What are the most important removal mechanisms playing a role during OMPs

Aop And mAr: A synergistic hybrid

An oxidative treatment step is preferably fol-lowed by a biological treatment step. In this specific case, AOP and MAR have diverse properties so the two processes are considered complementary. They will affect various com-pound structures by different removal mecha-nisms and the transformation products and by-products can be removed by the biological treatment step.

But these two processes are not only expected to be complementary, but also synergistic. Transformation products are, because they are usually smaller, expected to be removed more easily by the biological step than the parent compound itself. So it is expected to find a synergistic effect in the pre-oxidation of the compound that is removed biologically. In addition not only the OMPs, but the complete

water matrix, will be oxidized. This will create more biodegradable dissolved organic carbon (BDOC), which is expected to enhance the overall biodegradation. So it is also expected to find a synergistic effect in the pre-oxidation of the water matrix, especially the NOM.

outline thesis

Individual research questions addressed above in the introduction are addressed in several chapters of this thesis. The final chapter, Chapter 7, will provide an overall conclusion and some additional remarks where the results of individual chapters will come together.

uv-Aop. Which compounds can be removed by AOP? What is the best UV lamp technology for the application of UV/H₂O₂ in the pre-treatment of Dunea, concerning degradation of organic micropollutants, energy consumption and the formation of by-products?

trAnsformAtion products. What is the best UV lamp technology for the application of UV/ H₂O₂ concerning the formation of transforma-tion products?

seriAl-Aop. What are the synergistic effects of serial O₃/H₂O₂ and UV/H₂O₂? What are the de-sign parameters for both processes at Dunea’s treatment at which the bromate formation is limited, but the OMPs degradation successful?

chApter 2 will present the results of a one year data set from pilot plant experiments, where three different types of UV lamps were com-pared for the UV/H₂O₂ application in Bergam-bacht.

chApter 3 involves a detailed and fundamental study on transformation products in DI water that can occur during the degradation of parent compounds with LP and MP UV/H₂O₂.

chApter 4 provides the basic design criteria for serial O₃/H₂O₂ and UV/H₂O₂ and shows the synergistic effects of serial-AOP.

chApter 7 represents an overall discussion on the topic and the results found in the studies. This omps And mAr. Which compounds can be

removed by MAR under which circumstances and which cannot? What are the most impor-tant removal mechanisms playing a role during OMPs removal by MAR?

Aop And mAr. What are the removal ranges and removal mechanisms at the MAR site of Dunea? What is the complementary effect of AOP and MAR? And what is the synergistic effect of pre-oxidation of the parent compounds and the water matrix on the removal of OMPs during MAR?

chApter 5 is a literature study focusing on the potential of MAR systems to remove OMPs.

chApter 6 shows the results of lab scale batch experiments assessing the potential of the Dunea MAR system to remove OMPs, and ad-dresses the synergistic effect of AOP and MAR.

references

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Duguet, J. P., Brodard, E., Dussert, B. & Mallevialle, J. Improvement in the effectiveness of ozonation of drinking water through the use of hydrogen peroxide. Ozone: Sci. Eng., 7, 241–258. (1985)

Glaze, W. H., Kang, J. W. & Chapin, D. H. The chemistry of water treat-ment processes involving ozone, hydrogen peroxide and UV-radiation. Ozone: Sci. Eng., 9, 335–352. (1987)

Gros, M., M. Petrovic and D. Barcelo. “Tracing Pharmaceutocal residues of different therapeutic classes in environmental waters by using liquid chromatography/ quadrupole-linear ion trap mass spectrometry and automated library searching” Analytical Chemistry 81 (3):898-912. (2009)

Hoigne, J. Mechanisms, rates and selectivities of oxidations of organic compounds initiated by ozonation of water. In Handbook of Ozone Tech-nology and Applications. Ann Arbor Science Publ., Ann Arbor, MI, (1982)

Houtman CJ., “Emerging contami-nants in surface waters and their

relevance for the production of drinking water in Europe” Journal of Integrative Environmental Sciences 7: 271-295. (2010)

Howard, P. H. Biodegradation. Hand-book of property estimation methods for chemicals and health sciences. CRC Press LLC, Boca Raton. (2000)

Huang, W.-J., Fang, G.-C., Wang, C.-C., . The determination and fate of disinfection by-products from ozona-tion of polluted raw water. Sci. Total Environ. 345, 261–272. (2005)

Huck, P.M., Fedorak, P.M., Ander-son, W.B., Formation and removal of assimilable organic carbon during biological treatment. J. Am. Water Works Assoc. 83 (12), 69–80. (1991)

IJpelaar, G. F., D. J. H. Harmsen, et al., “Comparison of low pressure and medium pressure UV lamps for UV/ H2O2 treatment of natural waters containing micro pollutants.” Ozone: Science and Engineering 32(5): 329-337. (2010)

IJpelaar, G., van der Veer, A., Me-dema, G.-J., & Kruithof, J. “By-product formation during ultraviolet disinfec-tion of a pre-treated surface water”. Environmental Engineering and Science , 4, S51-S56. (2005)

Jurgens M.D., K.I.E. Holthaus, A.C. Johnson, J.J.L. Smith, M. Hetheridge, R.J. Williams. “The potential for estra-diol and ethinylestraestra-diol degradation in English rivers”. Environ Toxicol Chem 21(3):480-8 (2002)

Kasprzyk-Hordern, B., R.M. Dinsdale, A.J. Guwy. “The occurrence of phar-maceuticals, personal care products, endocrine disruptors and illicit drugs in surface water in South Wales, UK” Water Research. 42, 3498-3518. (2008)

Kolpin D.W., E.T. Furlong, M.T. Meyer, E.M. Thurman, S.D. Zaugg, L.B. Barber, H.T. Buxton “Phar-maceuticals, Hormones, and Other Organic Wastewater Contaminants in U.S. Streams, 1999-2000: A National Reconnaissance”. Environmental Science & Technology. 36 (6) p 1202-1211. (2002)

Krasner, S.W., Sclimenti, M.J., Coffey, B.M., Testing biologically active filters from removing aldehydes formed dur-ing ozonation. J. Am. Water Works Assoc. 85 (5), 62–71. (1993)

Kruithof, J. C., P. C. Kamp, and B. J. Martijn. UV/H2O2 Treatment: A Practical Solution for Organic Contaminant Control and Primary Disinfection. Ozone: Science and Engineering, 29: 273–280 (2007)

Kurokawa, Y., A. Maekawa, M. Takahashi and Y. Hayashi, Toxicity and carcinogenicity of potassium bromate—a new renal carcinogen, Environmental Health Perspectives 87, 309–335 (1990)

LeChevallier, M.W., Becker, W.C., Schorr, P., Lee, R.G., Evaluating the performance of biologically active rapid filters. J. Am. Water Works As-soc. 84 (4), 1 36–140. (1992)

Lekkerkerker-, K., J. Scheideler, A.H. Knol, A. Ried, K., Verberk, J., Amy, G., & van Dijk, J. “Advanced oxidation and artificial recharge: a synergistic hybrid system for removal of organic micropollutants”. Water Science and Technology – Wa-ter supply 9(6): 643-651. (2009)

Ray, C., T.W Soong, Y.Q. Lian, G.S. Roadcap. “Effect of flood-induced chemical load on filtrate quality at bank filtration sites”. J. Hydrol. 266, 235-258. (2002)

Richardson, S.D., Thruston Jr., A.D., Caughran, T.V., Chen, P.H., Collette, T.W., Floyd, T.L., Schenck, K.M., Lykins Jr., B.W., Identification of new ozone disinfection byproducts in drinking water. Environ. Sci. Technol.

ing chemicals bisphenol a, ethinyl estradiol, and estradiol during UV photolysis and advanced oxidation processes. Environ. Sci. Technol. 38, 5476-5483. (2004)

Scheideler, J., K. Lekkerkerker-Teunissen, T. Knol, A. Ried, J. Verberk and H. van Dijk, Combination of O3/H2O2 and UV for multiple barrier micropollutant treatment and bromate formation control – an economic attractive option, Water Practise and Technology, 6, 1-8 (2011)

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Segers, W.C.J., and P.J. Stuyfzand, Appereance and behaviour of emerg-ing substances duremerg-ing dune filtration (in Dutch). M.Sc. thesis, VU Univer-sity Amsterdam., The Netherlands, (2007)

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Swaim, P., A. Royce, T. Schmith, T. Maloney, D. Ehlen and B. Carter. Ef-fectiveness of UV advanced oxidation for destruction of micro-pollutants. Ozone-Science & Engineering 30, pp 34-42. (2008)

Van der Kooij, D. “Assimilable organic carbon as an indicator of bacterial regrowth.” Journal / American Water Works Association 84(2): 57-65. (1992)

Watanabe, N., S. Horikoshi, et al., “On the recalcitrant nature of the triazinic ring species, cyanuric acid, to degradation in Fenton solutions and in UV-illuminated TiO2 (naked) and fluorinated TiO2 aqueous disper-sions.” Journal of Photochemistry and Photobiology A: Chemistry 174(3): 229-238. (2005)

chApter 2: uv - Aop

pilot plAnt results

with three different

types of uv lAmps

for AdvAnced

oxidAtion

Accepted for publication by Ozone

Science and Engineering (2013)

Authors: K. Lekkerkerker-Teunissen,

A.H. Knol, J.G. Derks, M.B. Heringa,

C.J. Houtman, C.H.M. Hofman-Caris,

E.F. Beerendonk, A. Reus,

• Low pressure UV-reactor (Xylem)

AbstrAct

Three different types of ultraviolet lamps were tested for the advanced oxidation process application on pre-treated surface water in a pilot plant. The pilot set-up consisted of three parallel reactors with either medium pressure, low pressure or dielectrical barrier discharge UV-lamps. Four model compounds (atrazine, bromacil, ibuprofen and N-nitroso-dimethyl-amine (ndma)) and 0, 5 or 10 ppm hydrogen peroxide were dosed. Low pressure lamps were shown to have the lowest energy demand, cal-culated as electrical energy per order, followed by dielectrical barrier discharge lamps and then medium pressure lamps. Medium pressure lamps gave the highest formation of genotoxic activity and nitrite formation, whereas no formation of genotoxic activity was observed for

introduction

Organic micropollutants (OMPs), such as pesticides, pharmaceutically active compounds (PhAC), endocrine disrupting compounds, X-ray contrast media and personal care products, have been found at ng/L to low µg/L concentra-tions in surface waters throughout the world (Kolpin et al., 2002; Jurgens et al., 2002; Stolker et al., 2004; Kasprzyk-Hordem et al., 2008; Gros et al., 2009, and reviewed by Hout-man, 2010). Large quantities of OMPs are used in Western society. They may enter, in metabo-lized or unmetabometabo-lized form, into the environ-ment (e.g., through municipal sewage discharg-es, hospital effluents, sewage sludge, landfill leachates, and industrial discharges). OMPs with biological activity, such as PhACs and pesticides, are of concern to drinking water

uv - Aop

contaminants detected structurally in the Dutch Meuse River (Houtman, 2010). This river is used by Dunea, a water supply company in the West of the Netherlands, as a source for drink-ing water. While the effect on human health for a single compound in the low concentrations present is judged negligible by Schriks et al., (2010), according to Dunea these compounds do not belong in drinking water. The preferred approach therefore is (1) to protect the sources and (2) to remove those undesired compounds. Dunea considers an OMP to be a priority substance if its presence, its toxicity and/or its low removal by current treatment are reasons to take precautions or measures to remove this compound with additional treatment. The present barriers against OmPs in Dunea’s treat-ment are dune passage by Managed Aquifer Re-charge (MAR) and powdered activated carbon dosing in the post-treatment.

A study by Segers and Stuyfzand (2007) investi-gated the contribution of ARR to the removal of OMPs at the Dunea treatment plant. Removal efficiency during ARR depended on the influent concentrations, residence time, media sorption characteristics, water temperature and redox conditions. For 61% of the OMPs, the concen-tration after ARR appeared to have decreased to below the detection limit. X-ray contrast media, except iopamidol, were well removed under oxic conditions. Amidotrizoic acid, another X-ray contrast medium, and the pesticide

carbendazim were well removed under anoxic conditions. However, other substances were barely removed, neither during oxic nor anoxic MAR conditions. These substances were usu-ally poorly biodegradable and had poor sorp-tion characteristics. Examples included MTBE, diglyme, bentazone and 1,4-dioxane (Segers and Stuyfzand, 2007).

To assess the degradation of OMPs and the water quality change by an additional treatment step, Dunea is conducting research to extend the current multiple barrier treatment with advanced oxidation processes (AOP) via ultra-violet (uv) light and hydrogen peroxide, situated at the pre-treatment location Bergambacht. Implementing AOP before MAR, resulting in two complementary processes in series, makes the combination a promising multiple barrier approach (Lekkerkerker et al., 2009).

Advanced oxidation is a chemical process with a short residence time while dune passage is characterized as a biological process with a long residence time that levels peak concentra-tions. Oxidation will generally result in smaller molecules that are more easily biodegradable. Another important aspect for placing the AOP in the pre-treatment is the formation of assim-ilable organic carbon (AOC) during AOP. AOC is formed as a result of direct photolysis (≥100 mJ/cm2_{) of dissolved organic carbon (DOC)}

or through a reaction of DOC with hydroxyl radicals (IJpelaar et al., 2005). Increased AOC

concentrations, a readily available food source for microorganisms, are found to decrease the biological stability of drinking water during distribution (van der Kooij, 1992). AOC is of major importance for Dunea because it distrib-utes the water without post-disinfection. The current AOC levels in Dunea’s drinking water are low (3.5 – 7.5 µg/L), which should be main-tained in the future. MAR is a robust barrier against AOC. The second barrier against AOC is the slow sand filtration step, implemented at the post-treatment locations. A third reason to implement AOP in the pre-treatment relates to legal standards for OMPs in pre-treated river water that is infiltrated in the dune area. Standards are set by provincial governments and are, for most compounds, similar with limits set for drinking water. The maximum allowed concentration for individual pesticides is 0.1 µg/L, and for the total concentration of all pesticides is not to exceed 0.5 µg/L. Imple-menting a barrier against OMPs before MAR will ensure that Dunea can maintain these standards in the future.

Implementing AOP in the pre-treatment also has a drawback, as the water quality of Meuse water is relatively poor compared to the quality of the water after the post-treatment. The

pre-energy efficient. Therefore, Dunea compared three different lamp technologies on site in a pilot installation.

different lAmp technologies for uv/h2o2.

Me-dium pressure (MP) mercury vapor ultraviolet lamps emit a broad spectrum of light, between 200-800 nm (Stefan, 2004). This range of wavelengths corresponds with the absorbance spectrum of many substances and that of natu-ral water. This results in a high photolytic ca-pacity, but also in low efficiency and a high by-product formation potential. Low pressure (LP) mercury vapor ultraviolet lamps emit ultraviolet light at just one single wavelength (253.7 nm). Consequently, they can only photolyze com-pounds with an absorbance around 254 nm. The absorbance of hydrogen peroxide shows a maximum between 200-235 nm, and thus exhibits a lower absorbance at 254 nm. The emittance of MP lamps between 200-235 nm, however, is rather low, while the adsorption by the water matrix is much lower at 254 nm than at 200-235 nm. As a result, LP lamps are more effective in radical formation than MP lamps. In addition, because the installed power of a single LP lamp is low, more and bigger reac-tors are required, resulting in a larger footprint.

MP and LP UV lamps are both mercury lamps. Because of environmental concerns when disposing of mercury-containing lamps, there is a large interest in mercury-free lamps. In cooperation with Philips Research, the KWR Watercycle Research Institute, AwwaRF, and the Greater Cincinnati Water Works, a newly developed mercury-free lamp was included in the pilot installation at Dunea. This lamp, the dielectrical barrier discharge (DBD) lamp, emits a couple of wavelengths around 240 nm. These three lamp technologies were first compared in a pilot reactor by Hofman-Caris et al., (2011). All three lamps were subsequently tested in one reactor to ensure comparable hydraulic conditions. Conclusions from that research were that all three lamps can produce OH radicals from hydrogen peroxide. The MP lamp had the highest photo-degradation capacity, the highest degradation achieved in the set-up and the highest energy consumption. The LP lamp and DBD lamp both showed less photo-degradation of the tested OMPs, but were good alternatives for OH radical formation and OMPs degradation. The treatment with MP lamps was found to lead to formation of genotoxic activity, probably from the formation of one or more genotoxic by-products (Heringa et al., 2011) and to a higher nitrite formation compared to the LP and DBD lamp (Hofman-Caris et al., 2011).

The objective of this study was to compare the performance of the three lamps in three parallel reactors in terms of degradation of OMPs, en-ergy consumption and the possible formation of genotoxic activity and nitrite on a pilot scale. The efficiency and by-product formation of AOP depend on the quality of the water matrix of the influent water. Because Dunea would implement AOP in the pre-treatment, the influ-ent water has river water characteristics and the quality varies over the year.

mAteriAls And

methods

mAteriAls

reActors. A pilot-scale installation was built with a design flow of 5 m3_{/h per reactor. Three reactors}

were installed, one for each lamp technology. The LP reactor (LBX 10) was obtained from ITT Wedeco (Herford, Germany) and was equipped with four 330 W lamps with an automatic wiping system, thus rendering a total installed power of 1.32 kW. The MP reactor (B 2020) was obtained from Berson UV Technology (Nuenen, the Netherlands) and was equipped with two 2200 W lamps with an automatic wiping system, thus ren-dering a total installed power of 4.4 kW. The DBD reactor was specially designed by KWR Watercycle Research Institute and constructed by Melamo (Helmond, the Netherlands), equipped with four 300 W lamps and no wiping system. As the DBD lamp is still in the developmental phase, prototype lamps were used.

uv dose. The degradation by photolysis and radi-cal oxidation is a result of the UV-dose applied to the water. The UV-dose to the water in turn is a

result of the flow through the reactor, the installed UV-power and the transmitted UV-dose, which depends on the UV-transmittance of the water and light blocking by particles. Because in this research pre-treated river water is used, there is a variation in UV-T between 73 and 83%. For these two values the actual UV dose to the water was calculated by using a commercially available finite-element package, COMSOL v3.5a, with a standard k-e model (Wols et al., 2010). The calcu-lated UV doses are displayed in Table 1.

As can be seen from the modeling results, the UV dose in the DBD reactor strongly varies by the ap-plied flow. Although the 5 m3_{/h flow has not been}

modeled for the DBD reactor, a low UV dose is expected, based on the other two values (1179 and 329 for 1 m3_{/h and 3 m}3_{/h, respectively).}

model compounds. The influent water of the reactors is pre-treated (by coagulation, flocculation and sedimentation in a natural reservoir,

micro-Table 1: Results from the UV dose calculation

Lamp Set-ting Flow Power (UV-C) UVT UV-dose % m3_{/h W % mJ/cm}2 MP 100 5 834 75 875 MP 100 5 834 82 1150 LP 100 5 600 75 741 LP 100 5 600 82 927 DBD 100 1 145 78 1179 DBD 100 3 145 78 329

straining and dual layer rapid sand filtration) Meuse River water. Four model compounds were spiked at a concentration of 10 µg/L for atrazine (ATZ), bromacil (BRO) and N-Nitrosodimeth-ylamine (NDMA), and 20 µg/L for ibuprofen (IBU). The higher concentration of IBU was chosen because of the higher limit of detection for this compound. Spike solutions were obtained from the Water Laboratory (Haarlem, the Neth-erlands) and delivered in two containers, one 10 L Milli-Q aqueous solution containing 100 mg of ATZ, BRO and NDMA and one 10 L Milli-Q aque-ous solution containing 200 mg of IBU. Both solutions were dosed into a 300-liter container and 180 liters of regular tap water was added. This model compound solution was dosed in a flow of 100 or 150 L/h into the influent water, which had a flow of 10 or 15 m3_{/h, depending on the number}

of reactors in use. The dosing was performed in such a way that the influent water of the reactors contained a model compound concentration of 10 (ATZ, BRO, NDMA) or 20 (IBU) µg/L, respec-tively.

Atrazine degrades by photo-degradation under monochromatic and polychromatic radiations and via OH radical oxidation (Stefan, 2004) making it a good indicator for the overall per-formance of the AOP. Because radical oxidation

only by photo-degradation: oxidation effects are negligible (Stefan and Bolton, 2002; Jobb and Hunsinger, 1994).

spiKe compounds. Once during the test period of one year, not only the four model compounds, but a set of 15 compounds was spiked and removal was measured. The concentrated spike solution was prepared by the Water Laboratory and diluted on site with local drinking water and spiked the same day into the pilot installation using a procedure comparable to the one described above for the four model compounds. The fol-lowing compounds were spiked simultaneously: 1,1,1-trichloorethane, 2,4-chloorfenoxy acetic acid (2,4-D), atrazine, bentazone, bromacil, bromo-chloromethane, carbendazim, chlorobromurone, clofibrinic acid, diclofenac, diuron, ibuprofen, iso-proturone, 2-methyl-4-chloro-phenoxy acetic acid (MCPA), meta-chloro phenyl piperazin (MCPP, mecoprop), methyl-tertiary-butylether (MTBE), metolachlor and tertiary-amyl-methylether (TAME) at concentrations between 5 and 10 µg/L. peroxide. Hydrogen peroxide (H2O2; 10% w/v)

was purchased from Quaron (Wormerveer, the Netherlands) and dosed by a constant dosing pump into the influent water. An inline static

experiments

stAndArd experiments. Every other week a standard experiment was performed. A stand-ard experiment existed of nine settings: three peroxide concentrations (0, 5 and 10 ppm) and three UV ballast settings (60, 80 and 100%). As for the DBD reactor, the ballast percentage could not be changed; the flow through the reactor was varied (5, 3 and 1 m3_{/h) to achieve}

different UV-doses to the water.

Rapid sand filtrate (for water quality see Table 2) was tapped directly from the full-scale plant, in a flow of 10 or 15 m3_{/h, depending on the}

number of UV reactors in operation (two or

three, respectively). The solution with model compounds was dosed first with a flow of 90 L/h or 135 L/h, aiming at 10-20 µg/L for the model compounds. A static mixer was installed after the dosing point.

One meter after the model compound dosing point, the peroxide was dosed inline. Perox-ide concentrations were set automatically by a control panel and the flow of the pump was adjusted based on the water flow. The perox-ide dosing point was also followed by a static mixer. After the two dosing points the water was divided into three pipelines, each supplying one of the three reactors. Sample points were located before dosing, after dosing of model compounds, after dosing of peroxide, at the influent of the LP reactor and at the effluent of all three reactors. The LP influent sample point was used as the influent sample point for all three reactors.

A residence time distribution experiment showed that stable conditions at the last sample point were achieved after 4 minutes. Six

min-T pH Turb. DOC UVT NH4 NO3 NO2 HCO3 CO3 Mn Fe

°C - FTU mg/L C % at 254 mg/L NH4 mg/L NO4 mg/L NO2 mg/L HCO3 mg/L CO3 mg/L Mn mg/L Fe avg* 14.2 8.01 0.19 3.8 78.7 0.02 14.9 0.009 170 0.0 <0.01 0.03 min 2.5 7.79 <0.03 3.1 73.2 <0.02 11.5 <0.007 134 0.0 <0.01 <0.05 max 24.5 8.46 0.89 4.6 83.0 0.12 17.8 0.070 192 0.0 <0.01 0.09

Table 2: Water quality of pilot influent water between July 2009 and June 2010

utes after every setting adjustment, samples were taken. One liter samples were taken to ensure a well-mixed sample. Of this, 40 mL was sent to the laboratory in brown vials for analyses of model compounds.

The data used for the MP and LP lamps were obtained from July 2009 to June 2010, a total of 24 experiments. Since the DBD lamp was only in operation between November and February, this lamp data could only be obtained during these period (6 experiments).

spiKing experiment And genotoxicity study. In February 2010, two additional experiments were performed: an experiment investigating the possible formation of genotoxic activity during AOP and a spiking experiment using a larger set of test compounds to obtain a more detailed view of the degradation of relevant OMPs. For both experiments the same pilot installation was used as during standard experi-ments. The spiking experiment was performed with a worst-case water quality: UV-transmis-sion at 254 nm was 72.5% and DOC concentra-tion was 4.7 mg/L, nitrate concentraconcentra-tion was 3.64 mg N/L or 16.1 mg NO₃ /L. During the spiking experiment four settings were used; peroxide concentrations were varied at 5 and

During the genotoxicity experiment only one setting was used: peroxide concentration was 10 mg/L and the UV ballast setting was 100%. For the DBD reactor the flow through the reactor was set at 3 m3_{/h. No compounds were spiked.}

Per sample location three liters were collected, from the rapid sand filtrate (pilot influent) and from the 3 UV reactor effluent sample points. Directly after sampling, 300 mg sodium sul-phite per L was added to the samples.

AnAlyticAl methods

chemicAl AnAlyses. Analysis of the model compounds was performed using an Ultra Performance Liquid Chromatograph (UPLC, Waters Acquity) equipped with a quaternary pump, combined with a Quattro Xevo triple quadrupole Mass Selective Detector (Waters Mi-cromass). A sample of 15 µL was injected on a UPLC BEH C18 column (5 cm, particle size 1.7 µm, internal diameter 2.1 mm, Waters Acquity) with a flow rate of 0.45 ml/min.

Limits of detection were determined by analy-sis of nine drinking water samples spiked with 0.05 µg/L atrazine and bromacil and 5 µg/L ibuprofen. Recoveries were 0.063±0.003 µg/L atrazine, 0.058±0.004 µg/L bromacil, 4.0±0,6 µg/L ibuprofen. The limit of detection of NDMA was determined using an unspiked process water sample containing about 1.5 µg/L NDMA. Limits of detection, determined as 3*standard deviations from these results, were calculated to be 0.008 µg/L for atrazine,

0.013 µg/L for bromacil, 0.61 µg/L for NDMA and 1.8 µg/L for ibuprofen.

Bicarbonate concentrations were determined via titration of hypochloric acid (0.1 N incre-ments) using methyl orange as the indica-tor. Nitrate concentrations were determined with continuous flow analysis (Skalar San++). Concentrations of ammonium and nitrite were determined with an automated discrete photo-metric analyzer (Aquakem). Dissolved organic carbon (DOC) concentrations were determined with a Non-Purgeable Organic Carbon Analysis (Shimadzu TOC-VCPH). A sample was acidi-fied to a pH of 2-3 with hypochloric acid, and the inorganic carbon was subsequently elimi-nated with purging gas (O₂). The remaining total carbon C was measured and the result is reported as TOC (total organic carbon). genotoxicity tests. Possible formation of geno-toxic activity was investigated using the comet assay and the Ames II test. These tests detect different types of genotoxic substances. The comet test detects compounds causing strand breaks in the DNA and incomplete repair sites, while the Ames II test detects compounds causing mutations in the bases of the DNA, changing the genetic code. Detailed procedures can be found in the Annex. In brief, within 24 hours after collection three replicates of one liter of every sample were extracted by solid phase extraction (SPE) with 200-mg Oasis®

HLB cartridges (Waters Corporation, Milford, USA) at pH 2.3. Mineral water samples (Evian from glass bottles) were included as procedure controls. The eluates were evaporated and taken up in 50 µL of dimethylsulfoxide (DMSO) yielding 20,000-fold concentrated extracts. All extracts were stored at -18°C until analysis. The comet assay was performed as described by Singh et al., (1988), with minor modifica-tions as fully described in the Annex. In brief, HepG2 cells were treated for 3 hours and for 24 hours with Hank’s balanced salt solution (HBSS) medium containing aliquots of water extract at a concentration of 1% (v/v) in dupli-cate (exposure to a 200-fold concentration of the water samples). DNA damage was evaluated by calculation of the mean percent tail DNA for a total of 200 cells per water sample (2 slides per culture, 50 cells per slide). The water ex-tracts were considered positive for genotoxicity when a more than three-fold increase in tail in-tensity over the negative control was observed. The Ames II test was performed with TA98 and TAMix bacterial strains, with and without an ex-ogenous metabolic activation system (S9). The water extracts were diluted to 100 µL (1:1) with DMSO and the bacteria were finally exposed to

control for genotoxicity and a triplicate positive control for cytotoxicity. A custom cytotoxicity test was performed with subsamples of the exposed cultures in a medium with histidine, to check for possible artifacts due to the effects on cell survival and growth. Finally, the number of yellow wells per 48 wells of one sample was counted manually as a measure of genotoxic-ity. A sample was considered genotoxic if the response of the sample was different from the response of the negative control with a certainty of 99%, based on a binomial distribution (see Annex of this chapter).