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de Vet W.W.J.M.,Oasen Drinking Water Company | de Vet W.W.J.M.,Technical University of Delft | Dinkla I.J.T.,Bioclear BV | Abbas B.A.,Technical University of Delft | And 2 more authors.
Biotechnology and Bioengineering | Year: 2012

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. © 2011 Wiley Periodicals, Inc.

Van der Laan H.,Technical University of Delft | Van der Laan H.,Oasen Drinking Water Company | van Halem D.,Technical University of Delft | Smeets P.W.M.H.,KWR Watercycle Research Institute | And 7 more authors.
Water Research | Year: 2014

In 2012 more than 4 million people used a ceramic pot filter (CPF) as household water treatment system for their daily drinking water needs. In the normal production protocol most low cost filters are impregnated with a silver solution to enhance the microbial removal efficiency. The aim of this study was to determine the role of silver during the filtration and subsequent storage. Twenty-two CPFs with three different silver applications (non, only outside and both sides) were compared in a long-term loading experiment with Escherichia coli (K12 and WR1) and MS2 bacteriophages in natural challenge water under highly controlled laboratory circumstances. No significant difference in Log Removal Values were found between the filters with different silver applications. The results show that the storage time in the receptacle is the dominant parameter to reach E. coli inactivation by silver, and not the contact time during the filtration phase. The hypothesis that the absence of silver would enhance the virus removal, due to biofilm formation on the ceramic filter element, could not be confirmed. The removal effectiveness for viruses is still of major concern for the CPF. This study suggests that the ceramic pot filter characteristics, such as burnt material content, do not determine E. coli removal efficacies, but rather the contact time with silver during storage is the dominant parameter to reach E. coli inactivation. © 2013 Elsevier Ltd.

Van Halem D.,Technical University of Delft | de Vet W.,Technical University of Delft | de Vet W.,Oasen Drinking Water Company | Verberk J.,Technical University of Delft | And 3 more authors.
Applied Geochemistry | Year: 2011

The principle of subsurface iron removal for drinking water supply is that aerated water is periodically injected into the aquifer through a tube well. On its way into the aquifer, the injected O2-rich water oxidizes adsorbed Fe 2+, creating a subsurface oxidation zone. When groundwater abstraction is resumed, the soluble Fe 2+ is adsorbed and water with reduced Fe concentrations is abstracted for multiple volumes of the injection water. In this article, Fe accumulation deposits in the aquifer near subsurface treatment wells were identified and characterized to assess the sustainability of subsurface iron removal regarding clogging of the aquifer and the potential co-accumulation of other groundwater constituents, such as As. Chemical extraction of soil samples, with Acid-Oxalate and HNO3, showed that Fe had accumulated at specific depths near subsurface iron removal wells after 12 years of operation. Whether it was due to preferred flow paths or geochemical mineralogy conditions; subsurface iron removal clearly favoured certain soil layers. The total Fe content increased between 11.5 and 390.8 mmol/kg ds in the affected soil layers, and the accumulated Fe was found to be 56-100% crystalline. These results suggest that precipitated amorphous Fe hydroxides have transformed to Fe hydroxides of higher crystallinity. These crystalline, compact Fe hydroxides have not noticeably clogged the investigated well and/or aquifer between 1996 and 2008. The subsurface iron removal wells even need less frequent rehabilitation, as drawdown increases more slowly than in normal production wells. Other groundwater constituents, such as Mn, As and Sr were found to co-accumulate with Fe. Acid extraction and ESEM-EDX showed that Ca occurred together with Fe and by X-ray Powder Diffraction it was identified as calcite. © 2010 Elsevier Ltd. All rights reserved.

de Vet W.W.J.M.,Oasen Drinking Water Company | de Vet W.W.J.M.,Technical University of Delft | Dinkla I.J.T.,Bioclear bv. Rozenburglaan 13 | Rietveld L.C.,Technical University of Delft | And 2 more authors.
Water Research | Year: 2011

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. © 2011 Elsevier Ltd.

De Vet W.W.J.M.,Technical University of Delft | De Vet W.W.J.M.,Oasen Drinking Water Company | Van Genuchten C.C.A.,Oasen Drinking Water Company | Van Loosdrecht M.C.M.,Technical University of Delft | Van Dijk J.C.,Technical University of Delft
Drinking Water Engineering and Science | Year: 2010

In drinking water production, river bank filtration has the advantages of dampening peak concentrations of many dissolved components, substantially removing many micropollutants and removing, virtually completely, the pathogens and suspended solids. The production aquifer is not only fed by the river bank infiltrate but also by water percolating through covering layers. In the polder areas, these top layers consist of peat and deposits from river sediments and sea intrusions. This paper discusses the origin and fate of macro components in river bank filtrate, based on extensive full-scale measurements in well fields and treatment systems of the Drinking Water Company Oasen in the Netherlands. First, it clarifies and illustrates redox reactions and the mixing of river bank filtrate and PW as the dominant processes determining the raw water quality for drinking water production. Next, full-scale results are elaborated on to evaluate trickling filtration as an efficient and proven one-step process to remove methane, iron, ammonium and manganese. The interaction of methane and manganese removal with nitrification in these systems is further analyzed. Methane is mostly stripped during trickling filtration and its removal hardly interferes with nitrification. Under specific conditions, microbial manganese removal may play a dominant role. © Author(s) 2010.

van Halem D.,Technical University of Delft | Olivero S.,Technical University of Delft | de Vet W.W.J.M.,Technical University of Delft | de Vet W.W.J.M.,Oasen Drinking Water Company | And 3 more authors.
Water Research | Year: 2010

Subsurface iron and arsenic removal has the potential to be a cost-effective technology to provide safe drinking water in rural decentralized applications, using existing shallow tube wells. A community-scale test facility in Bangladesh was constructed for injection of aerated water (∼1m3) into an anoxic aquifer with elevated iron (0.27mmolL-1) and arsenic (0.27μmolL-1) concentrations. The injection (oxidation) and abstraction (adsorption) cycles were monitored at the test facility and simultaneously simulated in the laboratory with anoxic column experiments.Dimensionless retardation factors (R) were determined to represent the delayed arrival of iron or arsenic in the well compared to the original groundwater. At the test facility the iron removal efficacies increased after every injection-abstraction cycle, with retardation factors (RFe) up to 17. These high removal efficacies could not be explained by the theory of adsorptive-catalytic oxidation, and therefore other ((a)biotic or transport) processes have contributed to the system's efficacy. This finding was confirmed in the anoxic column experiments, since the mechanism of adsorptive-catalytic oxidation dominated in the columns and iron removal efficacies did not increase with every cycle (stable at RFe=∼8). RAs did not increase after multiple cycles, it remained stable around 2, illustrating that the process which is responsible for the effective iron removal did not promote the co-removal of arsenic. The columns showed that subsurface arsenic removal was an adsorptive process and only the freshly oxidized adsorbed iron was available for the co-adsorption of arsenic. This indicates that arsenic adsorption during subsurface treatment is controlled by the amount of adsorbed iron that is oxidized, and not by the amount of removed iron. For operational purposes this is an important finding, since apparently the oxygen concentration of the injection water does not control the subsurface arsenic removal, but rather the injection volume. Additionally, no relation has been observed in this study between the amount of removed arsenic at different molar Fe:As ratios (28, 63, and 103) of the groundwater. It is proposed that the removal of arsenic was limited by the presence of other anions, such as phosphate, competing for the same adsorption sites. © 2010 Elsevier Ltd.

De Vet W.W.J.M.,Oasen Drinking Water Company | De Vet W.W.J.M.,Technical University of Delft | Knibbe W.J.,Oasen Drinking Water Company | Rietveld L.C.,Technical University of Delft | Van Loosdrecht M.C.M.,Technical University of Delft
Water Science and Technology: Water Supply | Year: 2013

In the Netherlands, biological trickling filters without chemical pre-oxidation are generally applied to treat anaerobic groundwater, containing methane, iron, ammonium and manganese. Previous research showed that all compounds can be removed in one filter step and that not only the ammonia oxidation (by nitrification), but also the iron oxidation is often a biological process, despite oxygen saturated conditions and neutral pH. However, the optimal conditions for each process differs. In this paper, we report the preliminary results of a demonstration plant (40 m3 h-1) with two consecutive trickling filtration steps. The first highly loaded filter removed 1-1.5 ppm of methane and 5-6 ppm of iron with filtration rates up to 30 m h-1. The second filter step removed 5-6 ppm of ammonium and 0.5-0.6 ppm of manganese virtually completely at 2 m h-1. Quantitative (real time) polymerase chain reaction (qPCR) indicated that the growth of methane-oxidizing bacteria was marginal, but biological iron oxidation by Gallionella bacteria accounted for a quarter to over half of the total iron conversion. Copyright © IWA Publishing 2013.

De Vet W.W.J.M.,Oasen Drinking Water Company | De Vet W.W.J.M.,Technical University of Delft | Van Loosdrecht M.C.M.,Technical University of Delft | Rietveld L.C.,Technical University of Delft
Water Research | Year: 2012

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 etal. (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 100μg PO 4-PL -1. The nitrification and microbial growth rates were limited at under 100μg PO 4-PL -1 and virtually stopped at under 10μg PO 4-PL -1. In the range between 10 and 50μg PO 4-PL -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 etal. (1999), biological growth was very slow for MAP concentrations less than 25μg PO 4-PL -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. © 2011 Elsevier Ltd.

de Vet W.W.J.M.,Oasen Drinking Water Company | de Vet W.W.J.M.,Technical University of Delft | Kleerebezem R.,Technical University of Delft | van der Wielen P.W.J.J.,KWR Watercycle Research Institute | And 3 more authors.
Water Research | Year: 2011

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. © 2011 Elsevier Ltd.

PubMed | Oasen Drinking Water Company, Carl von Ossietzky University and KWR Watercycle Research Institute
Type: | Journal: The Science of the total environment | Year: 2016

The fate of organic micropollutants during long-term/long-distance river bank filtration (RBF) at a temporal scale of several years was investigated along a row of monitoring wells perpendicular to the Lek River (the Netherlands). Out of 247 compounds, which were irregularly analyzed in the period 1999-2013, only 15 were detected in both the river and river bank observation wells. Out of these, 10 compounds (1,4-dioxan, 1,5-naphthalene disulfonate (1,5-NDS), 2-amino-1,5-NDS, 3-amino-1,5-NDS, AOX, carbamazepine, EDTA, MTBE, toluene and triphenylphosphine oxide) showed fully persistent behavior (showing no concentration decrease at all), even after 3.6 years transit time. The remaining 5 compounds (1,3,5-naphthalene trisulfonate (1,3,5-NTS), 1,3,6-NTS, diglyme, iopamidol, triglyme) were partially removed. Their reactive transport parameters (removal rate constants/half-lives, retardation coefficients) were inferred from numerical modeling. In addition, maximum half-lives for 14 of the fully removed compounds, for which the data availability was sufficient to deduce 100% removal during sub-surface passage, were approximated based on travel times to the nearest well. The study is one of very few reporting on the long-term field-scale behavior of organic micropollutants. It highlights the efficiency of RBF for water quality improvement as a pre-treatment step for drinking water production. However, it also shows the very persistent behavior of various compounds in groundwater.

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