[show abstract][hide abstract] ABSTRACT: Disinfection in swimming pools is often performed by chlorination, However, anthropogenic pollutants from swimmers will react with chlorine and form disinfection by-products (DBPs). DBPs are unwanted from a health point of view, because some are irritating, while others might be carcinogenic. The reduction of anthropogenic pollutants will lead to a reduction in DBPs. This paper investigates the continual release of anthropogenic pollutants by means of controlled sweat experiments in a pool tank during laboratory time-series experiments (LTS experiments) and also during on-site experiments (OS experiments) in a swimming pool. The sweat released during the OS and LTS experiments was very similar. The sweat rate found was 0.1-0.2 L/m(2)/h at water temperatures below 29 °C and increased linearly with increasing water temperatures to 0.8 L/m(2)/h at 35 °C. The continual anthropogenic pollutant release (CAPR) not only consisted of sweat, particles (mainly skin fragments and hair) and micro-organisms, but also sebum (skin lipids) has to be considered. The release of most components can be explained by the composition of sweat. The average release during 30 min of exercise is 250 mg/bather non-purgeable organic carbon (NPOC), 77.3 mg/bather total nitrogen (TN), 37.1 mg/bather urea and 10.1 mg/bather ammonium. The release of NPOC cannot be explained by the composition of sweat and is most probably a result of sebum release. The average release of other components was 1.31 × 10(9) # particles/bather (2-50 μm), 5.2 μg/bather intracellular adenosine triphosphate (cATP) and 9.3 × 10(6) intact cell count/bather (iCC). The pool water temperature was the main parameter to restrain the CAPR. This study showed that a significant amount of the total anthropogenic pollutants release is due to unhygienic behaviour of bathers.
Water Research 01/2014; 53C:259-270. · 4.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: Organic carbon breaks down in boilers by hydrothermolysis, leading to the formation of organic acid anions, which are suspected to cause corrosion of steam–water cycle components. Prediction of the identity and quantity of these anions, based on feedwater organic carbon concentrations, has not been attempted, making it hard to establish a well-founded organic carbon guideline. By using a batch-reactor and flow reactor, the influence of temperature (276–352 °C), retention time (1–25 min), concentration (150–2400 ppb) and an oxygen scavenger (carbohydrazide) on organic acid anion formation from organic carbon was investigated. By comparing this to data gathered at a case-study site, the validity of setups was tested as well. The flow reactor provided results more representative for steam–water cycles than the batch reactor. It was found that lower heating rates give more organic acid anions as degradation products of organic carbon, both in quantity and species variety. The thermal stability of the organic acid anions is key. As boiler temperature increases, acetate becomes the dominant degradation product, due to its thermal stability. Shorter retention times lead to more variety and quantity of organic acid anions, due to a lack of time for the thermally less stable ones to degrade. Reducing conditions (or the absence of oxygen) increase the thermal stability of organic acid anions. As the feedwater organic carbon concentration decreases, there are relatively more organic acid anions formed.
[show abstract][hide abstract] ABSTRACT: Phosphate limitation has been reported as an effective approach to inhibit biofouling in reverse osmosis (RO) systems for water purification. The rejection of dissolved phosphate by negatively charged TiO2 tight ultrafiltration (UF) membranes (1 kDa and 3 kDa) was observed. These membranes can potentially be adopted as an effective process for RO pre-treatment in order to constrain biofouling by phosphate limitation. This paper focuses on electrostatic interactions during tight UF filtration. Despite the larger pore size, the 3 kDa ceramic membrane exhibited greater phosphate rejection than the 1 kDa membrane, because the 3 kDa membrane has a greater negative surface charge and thus greater electrostatic repulsion against phosphate. The increase of pH from 6 to 8.5 led to a substantial increase in phosphate rejection by both membranes due to increased electrostatic repulsion. At pH 8.5, the maximum phosphate rejections achieved by the 1 kDa and 3 kDa membrane were 75% and 86%, respectively. A Debye ratio (ratio of the Debye length to the pore radius) is introduced in order to evaluate double layer overlapping in tight UF membranes. Threshold Debye ratios were determined as 2 and 1 for the 1 kDa and 3 kDa membranes, respectively. A Debye ratio below the threshold Debye ratio leads to dramatically decreased phosphate rejection by tight UF membranes. The phosphate rejection by the tight UF, in combination with chemical phosphate removal by coagulation, might accomplish phosphate-limited conditions for biological growth and thus prevent biofouling in the RO systems.
Water Research 01/2014; 48(1):498-507. · 4.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: To address the water scarcity issue and advance the traditional drinking water treatment technique, a powdered activated carbon-amended membrane bioreactor (PAC-MBR) is proposed for micro-polluted surface water treatment. A pilot-scale study was carried out by initially dosing different amounts of PAC into the MBR. Comparative results showed that 2g/L performed the best among 0, 1, 2 and 3g/L PAC-MBR regarding organic matter and ammonia removal as well as membrane flux sustainability. 1g/L PAC-MBR exhibited a marginal improvement in pollutant removal compared to the non-PAC system. The accumulation of organic matter in the bulk mixture of 3g/L PAC-MBR led to poorer organic removal and severer membrane fouling. Molecular weight distribution of the bulk liquid in 2g/L PAC-MBR revealed the synergistic effects of PAC adsorption/biodegradation and membrane rejection on organic matter removal. Additionally, a lower amount of soluble extracellular polymer substances in the bulk can be secured in 21days operation.
[show abstract][hide abstract] ABSTRACT: The amount of pollutants brought into the swimming pool water by swimmers is called anthropogenic pollutant release. The continual pollutant release is the amount of pollutants which is released during the submerged swimming period. The actual level of the continual pollutant release has not been studied individually up till now. The objective of this study was to define and quantify the individual continual pollutant release both chemically and microbiologically at different swimming pool conditions and different levels of exercise.
The continual release was studied with a standardized exercise during time-series lab experiments. During these experiments, participants entered a preconditioned pool tank after having a pre-swim shower to remove the initial pollutant release. To prevent dilution of the continual release, participants were wearing a waterproof suit, filled with 50L non chlorinated tap water. The participants each had a 10 minute rest period subsequently followed by a 30 minute exercise on aqua-nordic-walker to simulate a swimming exercise, both submerged in the waterproof suite. During the experiment, the tap water inside the waterproof suite was circulated for good mixing and conditioning. Periodically samples were taken and analysed for total organic carbon (TOC) as well as total nitrogen (TN). Other parameters like urea, ammonium, nitrate, turbidity, UV254, particle count, total cell count and ATP concentration were also analysed. Sweat production was calculated by balancing the participant’s weight before and after each experiment. Assuming that the water temperature and the level of exercise are the most important factors influencing the continual release, the experiments were performed at different temperatures (25, 30 and 35°C) for each participant. First results show a low calculated sweat production by balancing of 70-100g per participant in 30 minutes, while the chemical results show an even lower sweat rate of 10-15g per participant in 30 minutes. Both results are lower than the up till now expected sweat release of 200-1000g/h. Possibly there is also some sweating from the unsubmerged skin, being the shoulders and the head. Also some weightloss can be explained by moist in the exhaled air. To confirm these new assumptions, more experiments will be done in October 2012
Fifth International Conference Swimming Pool & Spa, Rome; 04/2013
[show abstract][hide abstract] ABSTRACT: A bench-scale immersed microfiltration coupled with 50g/L PAC was developed to treat micro-polluted surface water (MPSW) under 10 and 20°C and the effects of temperatures on the performance and the membrane fouling were also investigated. The low temperature (10°C) delayed the time for the start-up by 9days and the complete nitrification by 10days. In the stable operation, two systems both had high NH3-N removal efficiency (above 90%) and better removal of organic matters (10% DOC, 5% UV254 and 4% SUVA) at 10°C. Polysaccharides (SMP) were the main membrane fouling matters at low temperature (10°C) and low temperature (10°C) didn't cause serious chemical irreversible membrane fouling.
[show abstract][hide abstract] ABSTRACT: In this study, different concentrations of PAC combined with MBR were carried out to treat slightly polluted surface water (SPSW) at low temperature (10°C). Effects of PAC on the efficiencies of operation, treatment, and the performance of the process were investigated. It was found that the effluent quality, performance efficiency, resistance of shock load were all enhanced and chemical irreversible membrane fouling was reduced with increasing dosage of PAC in MBR. Only when the concentration of PAC which acted as biological carriers was high enough (i.g., 50 g/L), nitrification without initial inoculation in the filtration tank could start within 19 days and be completed within 35 days at 10°C. Fifty grams per liter PAC was the optimal dosage in MBR for stable and extended operation. Under this condition, mean removal efficiencies of ammonia nitrogen (NH(3)-N), dissolved organic carbon (DOC) and UV(254) were 93%, 75%, and 85%, respectively.
[show abstract][hide abstract] ABSTRACT: The usefulness of a human-in-the-loop drinking-water-treatment-plant simulator was investigated for training and assessment. An in-simulator transfer of training experiment was conducted with three groups training with accelerated simulation, experienced operators (EO), inexperienced operators (IO), and laymen (L60x) and a group of laymen training at real-time speed (L1x). Participants learned how to improve water quality during training. Upon transfer, when confronted with a different process disturbance than during training, L60x performed significantly poorer than EO and IO combined. No difference was found between EO and IO, and during transfer, L60x outperformed L1x. These results indicate that learning to control slow and complex processes may improve by training with a realistic simulation running at accelerated speed.
Simulation Modelling Practice and Theory. 01/2012; 21:52-64.
[show abstract][hide abstract] ABSTRACT: Phosphorus limitation has been demonstrated for heterotrophic growth in groundwater, in drinking water production and distribution systems, and for nitrification of surface water treatment at low temperatures. In this study, phosphorus limitation was tested, in the Netherlands, for nitrification of anaerobic groundwater rich in iron, ammonium and orthophosphate. The bioassay method developed by Lehtola et al. (1999) was adapted to determine the microbially available phosphorus (MAP) for nitrification. In standardized batch experiments with an enriched mixed culture inoculum, the formation of nitrite and nitrate and ATP and the growth of ammonia-oxidizing bacteria (AOB; as indicated by qPCR targeting the amoA-coding gene) were determined for MAP concentrations between 0 and 100 μg PO4-P L(-1). The nitrification and microbial growth rates were limited at under 100 μg PO4-P L(-1) and virtually stopped at under 10 μg PO4-P L(-1). In the range between 10 and 50 μg PO4-P L(-1), a linear relationship was found between MAP and the maximum nitrification rate. AOB cell growth and ATP formation were proportional to the total ammonia oxidized. Contrary to Lehtola et al. (1999), biological growth was very slow for MAP concentrations less than 25 μg PO4-P L(-1). No full conversion nor maximum cell numbers were reached within 19 days. In full-scale groundwater filters, most of the orthophosphate was removed alongside with iron. The remaining orthophosphate appeared to have only limited availability for microbial growth and activity. In some groundwater filters, nitrification was almost totally prevented by limitation of MAP. In batch experiments with filtrate water from these filters, the nitrification process could be effectively stimulated by adding phosphoric acid.
Water Research 12/2011; 46(4):1061-9. · 4.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: The growth of iron-oxidizing bacteria, generally regarded as obligate microaerophilic at neutral pH conditions, has been reported in a wide range of environments, including engineered systems for drinking water production. This research focused on intensively aerated trickling filters treating deep anaerobic and subsurface aerated groundwater. The two systems, each comprising groundwater abstraction and trickling filtration, were monitored over a period of 9 months. Gallionella spp. were quantified by qPCR with specifically designed 16S rRNA primers and identified directly in the environmental samples using clone libraries with the same primers. In addition, enrichments in gradient tubes were evaluated after DGGE separation with general bacterial primers. No other iron-oxidizing bacteria than Gallionella spp. were found in the gradient tubes. qPCR provided an effective method to evaluate the growth of Gallionella spp. in these filter systems. The growth of Gallionella spp. was stimulated by subsurface aeration, but these bacteria hardly grew in the trickling filter. In the uninfluenced, natural anaerobic groundwater, Gallionella spp. were only present in low numbers, but they grew extensively in the trickling filter. Identification revealed that Gallionella spp., growing in the trickling filter were phylogenetically distinct from the species found growing during subsurface aeration, indicating that the different conditions in both systems selected for niche organisms, while inhibiting other groups. The results suggest a minor direct significance for inoculation of Gallionella spp. during filtration of subsurface aerated groundwater.
Biotechnology and Bioengineering 11/2011; 109(4):904-12. · 3.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Iron oxidation under neutral conditions (pH 6.5-8) may be a homo- or heterogeneous chemically- or a biologically-mediated process. The chemical oxidation is supposed to outpace the biological process under slightly alkaline conditions (pH 7-8). The iron oxidation kinetics and growth of Gallionella spp. - obligatory chemolithotrophic iron oxidizers - were assessed in natural, organic carbon-containing water, in continuous lab-scale reactors and full-scale groundwater trickling filters in the Netherlands. From Gallionella cell numbers determined by qPCR, balances were made for all systems. The homogeneous chemical iron oxidation occurred in accordance with the literature, but was retarded by a low water temperature (13 °C). The contribution of the heterogeneous chemical oxidation was, despite the presence of freshly formed iron oxyhydroxides, much lower than in previous studies in ultrapure water. This could be caused by the adsorption of natural organic matter (NOM) on the iron oxide surfaces. In the oxygen-saturated natural water with a pH ranging from 6.5 to 7.7, Gallionella spp. grew uninhibited and biological iron oxidation was an important, and probably the dominant, process. Gallionella growth was not even inhibited in a full-scale filter after plate aeration. From this we conclude that Gallionella spp. can grow under neutral pH and fully aerated conditions when the chemical iron oxidation is retarded by low water temperature and inhibition of the autocatalytic iron oxidation.
Water Research 07/2011; 45(17):5389-98. · 4.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: In groundwater treatment for drinking water production, the causes of nitrification problems and the effectiveness of process optimization in rapid sand filters are often not clear. To assess both issues, the performance of a full-scale groundwater filter with nitrification problems and another filter with complete nitrification and pretreatment by subsurface aeration was monitored over nine months. Quantitative real-time polymerase chain reaction (qPCR) targeting the amoA gene of bacteria and archaea and activity measurements of ammonia oxidation were used to regularly evaluate water and filter sand samples. Results demonstrated that subsurface aeration stimulated the growth of ammonia-oxidizing prokaryotes (AOP) in the aquifer. Cell balances, using qPCR counts of AOP for each filter, showed that the inoculated AOP numbers from the aquifer were marginal compared with AOP numbers detected in the filter. Excessive washout of AOP was not observed and did not cause the nitrification problems. Ammonia-oxidizing archaea grew in both filters, but only in low numbers compared to bacteria. The cell-specific nitrification rate in the sand and backwash water samples was high for the subsurface aerated filter, but systematically much lower for the filter with nitrification problems. From this, we conclude that incomplete nitrification was caused by nutrient limitation.
Water Research 07/2011; 45(13):4008-18. · 4.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: The implementation of wastewater reuse is becoming an increasingly important means of supplementing water supply needs and/or reducing costs. The present paper provides examples of possible uses of treated domestic effluent for the three sectors, i.e. public water supply, industrial and agricultural uses with the aim to address the feasibility of these applications. It is concluded that, although The Netherlands as a whole is considered to be a low water stressed country, regional fresh water scarcity and costs can result in the need for applications of domestic wastewater reuse.
Water Science & Technology 01/2011; 64(7):1540-6. · 1.10 Impact Factor
[show abstract][hide abstract] ABSTRACT: Natural organic matter (NOM) can influence pharmaceutical adsorption onto granular activated carbon (GAC) by direct adsorption competition and pore blocking. However, in the literature there is limited information on which of these mechanisms is more important and how this is related to NOM and pharmaceutical properties. Adsorption batch experiments were carried out in ultrapure, waste- and surface water and fresh and NOM preloaded GAC was used. Twenty-one pharmaceuticals were selected with varying hydrophobicity and with neutral, negative or positive charge. The influence of NOM competition and pore blocking could not be separated. However, while reduction in surface area was similar for both preloaded GACs, up to 50% lower pharmaceutical removal was observed on wastewater preloaded GAC. This was attributed to higher hydrophobicity of wastewater NOM, indicating that NOM competition may influence pharmaceutical removal more than pore blocking. Preloaded GAC was negatively charged, which influenced removal of charged pharmaceuticals significantly. At a GAC dose of 6.7 mg/L, negatively charged pharmaceuticals were removed for 0-58%, while removal of positively charged pharmaceuticals was between 32-98%. Charge effects were more pronounced in ultrapure water, as it contained no ions to shield the surface charge. Solutes with higher log D could compete better with NOM, resulting in higher removal.
Water Science & Technology 01/2011; 63(3):416-23. · 1.10 Impact Factor
[show abstract][hide abstract] ABSTRACT: Because of water scarcity in some regions of the Netherlands and new environmental concepts of water withdrawal, Dutch industrial water production has been shifting from surface water or scarce groundwater to wastewater in recent years. Because of this transformation, it is important to evaluate the advantages and disadvantages of using wastewater treatment plant (WWTP) effluent as a source to produce industrial water, and to gain knowledge about water recycling and treatment. Reverse osmosis (RO) treatment is mostly used to produce water for industry. Four selected Dutch RO plants producing industrial water are analysed in this paper. Demineralized Water Plant (DWP) DECO and DWP Sas van Gent are using WWTP effluent as source water; DWP Baanhoek and DWP Botlek are producing industrial water from surface water. The alternative water source alters pre-treatment needs and RO operations. Compared to surface water, WWTP effluent requires more pre-treatment to prevent UF and RO membranes from fouling. Detailed comparisons between both types of RO plants were made based on the following criteria: 1. Feed water qualities, including the seasonal changes for the surface water and quality fluctuation for WWTP effluent; 2. Pre-treatment methods in compliance with the feed water situation; 3. RO operational problems during both surface water and effluent water desalination; 4. Risk of effluent water quantity shortage and quality insufficiency and management. Finally, the practice and experiences of the RO plants are summarized.
Desalination and water treatment 01/2011; 34:408-415. · 0.85 Impact Factor
[show abstract][hide abstract] ABSTRACT: Computational Fluid Dynamics combined with a particle tracking technique provides valuable information concerning residence times and contact times in chemical reactors. In drinking water treatment, for example an accurate estimation of the disinfection is important to predict the microbial safety. Ozone contactors are widely used for disinfection, but the complex geometry of the system causes suboptimal hydraulics and requires optimizations of the flow. This results in a lower ozone dosage, which may reduce the formation of unwanted disinfection-by-products and the consumption of energy. To that end disinfection needs to be calculated precisely, accounting for the complex hydraulics. Several calculation methods estimating the disinfection performance of ozone contactors were evaluated using Computational Fluid Dynamics. For an accurate disinfection prediction, the full distribution of ozone exposures (CT values) is needed, only a mean CT value or residence time distribution provides insufficient information for an accurate disinfection prediction. Adjustments to the geometry of the ozone contactor that reduce the short-circuit flows resulted in an increase in disinfection capacity, whereas the mean CT value remained the same. A sensitivity analysis with respect to the kinetics was conducted. The gain in disinfection capacity obtained by optimizing the hydraulics was significant for typical values used in practice.
[show abstract][hide abstract] ABSTRACT: CFD modelling has proven to be a powerful tool for the design of UV reactors. However, the validation of the hydraulics predicted by the CFD model remains a point of attention. Using standard turbulence models such as the k–ɛ model, the CFD model often wrongly predicts local flow features around a UV lamp. Therefore, more advanced modelling approaches such as the LES model were considered. The modelling approaches were explored for a single cross-flow UV lamp. It is shown by means of comparison with experimental data that the LES model predicts the flow around a UV lamp more precisely than the k–ɛ model. The impact of differences in resolved velocity fields on the predicted disinfection was also investigated. Depending on the local geometry (presence and positioning of baffles) the disinfection results were completely different for the different modelling approaches.