Search

A simple theory to predict groundwater quality upon contamination from diffuse sources was developed. It appeared that an analogy exists between the predominant transport phenomena and the reaction of a reservoir, in which perfect mixing takes place. Such an analogy enables a simple incorporation of physico-chemical processes (decomposition, adsorption), as was shown by an illustrative response of the quality of groundwater to an input of a radio-active decaying solute (and its decay components) in its recharge area.Before solute migration in the saturated zone occurs, transport takes place in the unsaturated zone. The above mentioned analogy allows the derivation of analytical expressions for the response of a coupled unsaturatedsaturated transport system. The unsaturated soil is then represented by a series of "perfectly mixed" reservoirs. Each reservoir can be defined in terms of its thickness, water content, inand outflow rate, decomposition rate or retardation factor. Moreover, the process of bypass flow can be accounted for in a simple way.To study the practical application of the presented theory, a field experiment was carried out. An amount of tracer was applied to the catchment area of a drain, followed by soil sampling and monitoring of tracer concentrations in the drainage water. From both soil and drainage water sampling it appeared, that transport velocities in the subsoil could impossibly correspond with the observed water content profiles. Therefore it was concluded that preferential flow paths in the subsoil caused this accelerated breakthrough, and transport was confined to these zones only.To visualize these zones of preferential flow, we used a coloring technique that was developed during this study. This method was applied to ten plots in the same experimental field, where the tracer had been applied before. Preferential flow paths were shown to occur at some plots, but the variation of penetration depth of the solute front could be adequately described by the convection-dispersion equation, using dispersivities of the order of centimetres. The accelerated breakthrough that was measured in our former experiment, could not be explained.At the same experimental field, a study of the spatial variability of soil physical parameters had been completed recently. From the measured variability, expressed in the distribution of the scaling parameter, the solute breakthrough curve was predicted, and compared with our measured curve. The variation of travel times, based on the soil variability, was estimated too large. It is concluded that this large variation of travel times might have been present under different experimental conditions, such as ponded infiltration.

Bij de bescherming van grond- en oppervlaktewater tegen verontreiniging neemt in Nederland nitraat een belangrijke plaats in vanwege de risico's voor de volksgezondheid en voor de kwaliteit van het natuurlijke milieu. Voor het voeren van een beschermingsbeleid is kennis nodig van de optredende processen, zodat de maatregelen kunnen worden afgestemd op maximaal toelaatbare belasting van grond- en oppervlaktewater in het beschouwde gebied.

Ongeveer 70% (circa 2 miljoen ha) van het grondoppervlak in Nederland is in gebruik voor de landbouw, zodat de landbouwkundige aktiviteiten voor grote gebieden van invloed kunnen zijn voor de chemische samenstelling van het water. Het water dat landbouwgebieden verlaat via grond- en oppervlaktewaterstroming heeft veelal weer een andere gebruiksbestemming zoals: natuurbeheer, drinkwatervoorziening, recreatie etc.

This thesis deals with the development of a new process for nitrate removal from ground water. High nitrate concentrations in ground water are a result of fertilization in agriculture. According to a directive of the European Community the maximum admissible concentration of nitrate in drinking water is 11.3 mg NO 3--N/l and the guide level is 5.6 mg NO 3--N/l. To supply water that meets this standard several water supply companies will have to remove nitrate from ground water. Two existing techniques, viz ion exchange and biological denitrification, have serious disadvantages when used separately. Therefore, a new process has been developed that consists of a combination of ion exchange and biological denitrification. In this process nitrate is removed from the ground water by ion exchange. The ion exchange resins are regenerated in a closed circuit through an upflow sludge blanket (USB) denitrification reactor. In this reactor denitrifying bacteria remove nitrate from the regenerant, so that it can be used again and has not to be disposed of. As compared with conventional regeneration of anion exchange resins regeneration salt requirement and brine production are minimized. Further, in contrast with traditional single denitrification procedures, there is no direct contact between ground water and denitrifying bacteria.The first part of this thesis deals with the effect of high salt concentrations, as present in the closed regeneration system, on biological denitrification. Concentrations up to 30 g NaHCO 3 /l or 30 g NaCl/l have only little effect on the activity of denitrifying sludge. With high NaHCO 3 concentrations the sludge yield coefficient decreases and nitrite accumulation is suppressed. High sulfate concentrations (5.5 9 SO 42-/l) do not result in sulfide production in an USB denitrification reactor fed with methanol, when methanol is added in an appropriate ratio to the amount of nitrate to be denitrified.The second part of this thesis deals with the ion exchange part of the combined process. Regeneration of anion exchange resins can be achieved with a solution containing 30 g NaHCO 3 /l provided that a larger flow rate and a longer regeneration time are used as compared with conventional regeneration procedures. With nitrate selective resins it is possible to remove nitrate from ground water that contains high sulfate concentrations, while the nitrate capacity of these resins is not affected by high sulfate concentrations in the regenerant. To safeguard the bacteriological drinking water quality the resins have to be disinfected after each regeneration cycle by rinsing with 0.075% peracetic acid for 15 minutes or by rinsing with 0.20% hydrogen peroxide for 45 minutes. Since the first possibility results in an important loss of resin capacity on the long term, only the latter can be applied in practice.The third part of this thesis deals with the operation of a lab-scale pilot plant. The most important process variables studied were the regenerant composition (NaCl or NaHCO 3 ), the ion exchange resin type (sulfate selective or nitrate selective) and the ground water composition (low sulfate concentration or high sulfate concentration). To explain some phenomena that were observed during this research a computer model has been developed. With this model the regeneration of anion exchange resins in a closed circuit can be optimized.

De bestudering van de kwaliteit van het diepe grondwater in het Zuidelijk Peelgebied, werd in 1981 gestart met het uitvoeren van een bemonsteringsronde. Op dat moment was over de situatie tav. de grondwaterkwaliteit in het gebied nog betrekkelijk weinig bekend.

This thesis deals with the development of a new process for nitrate removal from ground water. High nitrate concentrations in ground water are a result of fertilization in agriculture. According to a directive of the European Community the maximum admissible concentration of nitrate in drinking water is 11.3 mg NO 3--N/l and the guide level is 5.6 mg NO 3--N/l. To supply water that meets this standard several water supply companies will have to remove nitrate from ground water. Two existing techniques, viz ion exchange and biological denitrification, have serious disadvantages when used separately. Therefore, a new process has been developed that consists of a combination of ion exchange and biological denitrification. In this process nitrate is removed from the ground water by ion exchange. The ion exchange resins are regenerated in a closed circuit through an upflow sludge blanket (USB) denitrification reactor. In this reactor denitrifying bacteria remove nitrate from the regenerant, so that it can be used again and has not to be disposed of. As compared with conventional regeneration of anion exchange resins regeneration salt requirement and brine production are minimized. Further, in contrast with traditional single denitrification procedures, there is no direct contact between ground water and denitrifying bacteria.The first part of this thesis deals with the effect of high salt concentrations, as present in the closed regeneration system, on biological denitrification. Concentrations up to 30 g NaHCO 3 /l or 30 g NaCl/l have only little effect on the activity of denitrifying sludge. With high NaHCO 3 concentrations the sludge yield coefficient decreases and nitrite accumulation is suppressed. High sulfate concentrations (5.5 9 SO 42-/l) do not result in sulfide production in an USB denitrification reactor fed with methanol, when methanol is added in an appropriate ratio to the amount of nitrate to be denitrified.The second part of this thesis deals with the ion exchange part of the combined process. Regeneration of anion exchange resins can be achieved with a solution containing 30 g NaHCO 3 /l provided that a larger flow rate and a longer regeneration time are used as compared with conventional regeneration procedures. With nitrate selective resins it is possible to remove nitrate from ground water that contains high sulfate concentrations, while the nitrate capacity of these resins is not affected by high sulfate concentrations in the regenerant. To safeguard the bacteriological drinking water quality the resins have to be disinfected after each regeneration cycle by rinsing with 0.075% peracetic acid for 15 minutes or by rinsing with 0.20% hydrogen peroxide for 45 minutes. Since the first possibility results in an important loss of resin capacity on the long term, only the latter can be applied in practice.The third part of this thesis deals with the operation of a lab-scale pilot plant. The most important process variables studied were the regenerant composition (NaCl or NaHCO 3 ), the ion exchange resin type (sulfate selective or nitrate selective) and the ground water composition (low sulfate concentration or high sulfate concentration). To explain some phenomena that were observed during this research a computer model has been developed. With this model the regeneration of anion exchange resins in a closed circuit can be optimized.

Een bestudering van het verloop van het nitraatgehalte van het ondiepe grondwater en bepaling van de menselijke invloed op de samenstelling van het ondiepe grondwater door het chloridegehalte hiervan te vergelijken met het nitraatgehalte; dit in verband met de eutrofiering van het grond- en oppervlaktewater door bemestingsgiten (in een gedeelte van de Gelderse Vallei)

In een kolomproef en via literatuuronderzoek is het effect van verschillende gehalten aan EDTA (Ethyl-Diamine-Tetra-Azijnzuur) in het afvalwater op de gehalten van metaalionen in het drainwater onderzocht.

Onderzoek om een methodiek te ontwikkelen om bufferzones rondom beekdalen met natuurwetenschappelijke waarden aan te wijzen en te begrenzen. Deze nota is geschreven als aanvulling op het verschenen rapport naar aanleiding van het uitgevoerde onderzoek over de bufferzones (Adriaanse en Kemmers, 1988)

A simple theory to predict groundwater quality upon contamination from diffuse sources was developed. It appeared that an analogy exists between the predominant transport phenomena and the reaction of a reservoir, in which perfect mixing takes place. Such an analogy enables a simple incorporation of physico-chemical processes (decomposition, adsorption), as was shown by an illustrative response of the quality of groundwater to an input of a radio-active decaying solute (and its decay components) in its recharge area.Before solute migration in the saturated zone occurs, transport takes place in the unsaturated zone. The above mentioned analogy allows the derivation of analytical expressions for the response of a coupled unsaturatedsaturated transport system. The unsaturated soil is then represented by a series of "perfectly mixed" reservoirs. Each reservoir can be defined in terms of its thickness, water content, inand outflow rate, decomposition rate or retardation factor. Moreover, the process of bypass flow can be accounted for in a simple way.To study the practical application of the presented theory, a field experiment was carried out. An amount of tracer was applied to the catchment area of a drain, followed by soil sampling and monitoring of tracer concentrations in the drainage water. From both soil and drainage water sampling it appeared, that transport velocities in the subsoil could impossibly correspond with the observed water content profiles. Therefore it was concluded that preferential flow paths in the subsoil caused this accelerated breakthrough, and transport was confined to these zones only.To visualize these zones of preferential flow, we used a coloring technique that was developed during this study. This method was applied to ten plots in the same experimental field, where the tracer had been applied before. Preferential flow paths were shown to occur at some plots, but the variation of penetration depth of the solute front could be adequately described by the convection-dispersion equation, using dispersivities of the order of centimetres. The accelerated breakthrough that was measured in our former experiment, could not be explained.At the same experimental field, a study of the spatial variability of soil physical parameters had been completed recently. From the measured variability, expressed in the distribution of the scaling parameter, the solute breakthrough curve was predicted, and compared with our measured curve. The variation of travel times, based on the soil variability, was estimated too large. It is concluded that this large variation of travel times might have been present under different experimental conditions, such as ponded infiltration.

Deze nota is geschreven ten behoeve van de PAO-cursus 'Waterkwaliteit Landelijk gebied; aspecten van waterkwaliteitsbeheer'

Een bestudering van het verloop van het nitraatgehalte van het ondiepe grondwater en bepaling van de menselijke invloed op de samenstelling van het ondiepe grondwater door het chloridegehalte hiervan te vergelijken met het nitraatgehalte; dit in verband met de eutrofiering van het grond- en oppervlaktewater door bemestingsgiten (in een gedeelte van de Gelderse Vallei)

The groundwater quality model ANIMO describes the nitrogen and carbon cycle and its interrelation. With as main purpose the prediction of nitrate leaching to ground and surface water

Transport van grondwater: stroomlijnen en verblijftijd, transport van opgeloste stoffen, koppeling van grondwaterstroming en stoftransport. Voorbeelden van toepassing van grondwaterkwaliteitsmodellen

Weergave van 3 proeven met haver, zomergerst afgewisseld met aardappelen in met olie verontreinigde grond, waarbij het drain- en percolatiewater werden geanalyseerd, en tenslotte werd de invloed op de kwaliteit van het grondwater onderzocht

Deze nota is geschreven ten behoeve van de Post Hoger Landbouwonderwijs (PHLO) cursus 'Waterkwaliteit Landelijk Gebied; aspecten van kwaliteitsbeheer'.

Analyse van de waterkwaliteit van het ruwwater en de bestaande observatiebuizen van de drinkwaterwingebieden 't Klooster en Eerbeek in de provincie Gelderland

Voor de Commissie Waterhuishouding Gelderland is voor de Achterhoek een studie gemaakt naar de omvang van de mestproduktie - te beschouwen als mestoverschot - van de zogenaamde intensieve veehouderijbedrijven, en de fosfaat- en stikstofbelasting die deze mestoverschotten betekenen voor het grond- en oppervlaktewater bij een aantal verschillende afzetwijzen binnen de landbouw. Zowel voor 1972 als 1980.

Transport processes governing soil and groundwater contamination by a diffuse (non-point) source were studied by means of a field tracer experiment in the Hupselse Beek catchment area in The Netherlands. A bromide tracer was applied to the intake area (11m × 260m) of a drain, and subsequently monitored in the unsaturated zone, as well as in the drain effluent. Data from the unsaturated zone were analyzed using both the classical convection-dispersion solute transport equation (CDE) and a regional stochastic model (RSM) which assumes lognormal distributions of the pore water velocity and the dispersion coefficient across the field. Both models described the data equally well, with the CDE model giving a somewhat better mass balance of the recovered bromide. Calculated solute fluxes leaving the unsaturated were used as input into a mixing cell type model for transport in the saturated zone. Drain effluent concentrations predicted with the coupled unsaturated-saturated transport model were compared with the observed breakthrough curve; results indicate the presence of preferential flow in the unsaturated zone.