WATER DRAINAGE SYSTEM FOR DRAINING WATER INTO A GROUNDWATER CONDITIONER

Abstract

The invention relates to a water drainage system for discharging water, such as field runoff water, into an aquifer, wherein the water drainage system has the following features: a water inlet configured to receive water to be discharged; a water filter device in fluid communication with the water inlet to receive water to be discharged from the water inlet and configured to filter water received from the water inlet; and a discharge device in fluid communication with the water filter device and configured to receive water from the water filter device and discharge the filtered water into the aquifer, wherein the water filter device comprises in series a sand filter stage and a biologically activated filter stage configured to filter impurities from the water to be discharged.

Description

BACKGROUND

[0001] The invention relates to a water drainage system for draining water into an aquifer. Furthermore, the invention relates to a method for draining water into an aquifer.

[0002] Such a water drainage system is known from the prior art, comprising, for example, a porous PVC plastic pipe or a flexible plastic pipe laid below the ground surface. Drainage water is collected in the pipe and directed to a collection pit, from which an electric pump can pump the water into an aquifer. SUMMARY OF THE INVENTION

[0003] The known water drainage system, as described, can be used, among other things, to drain field runoff water. Field runoff water typically contains pesticides, nutrients, plant pathogens, or a combination thereof. Therefore, a disadvantage of the known water drainage system is that materials such as pesticides, nutrients, plant pathogens, or a combination thereof are discharged into the aquifer, causing all kinds of adverse environmental impacts.

[0004] An object of the present invention is to improve or eliminate one or more disadvantages of the known prior art, to provide an improved water drainage system or at least to provide an alternative water drainage system.

[0005] According to a first aspect, the invention provides a water drainage system for draining water, such as field drainage water, into an aquifer, the water drainage system having the following features: a water inlet configured to receive water to be drained; a water filter device in fluid communication with the water inlet for receiving water to be discharged from the water inlet and configured to filter water received from the water inlet; and a discharge device in fluid communication with the water filter device and configured to receive water from the water filter device and discharge the filtered water into the aquifer, wherein the water filter device comprises in series a sand filter stage and a biologically activated filter stage configured to filter contaminants from the water to be discharged.

[0006] During use of the drainage system according to the invention, water, such as field drainage water, flows into the drainage system via the water inlet. After entering the drainage system, the field drainage water flows into and through the water filtration device, passing in series through the sand filter stage and the biologically activated filter stage. The inventors have surprisingly found that the drainage system according to the invention is efficient in removing contaminants, including pesticides, including reducing nutrients such as nitrate and phosphate, from the field drainage water. This is advantageous because the drainage system achieves the desired subsurface infiltration water quality in terms of nutrients, total suspended solids (TSS), and pesticide concentration.The water drainage system according to the invention thus advantageously prevents pesticides, nutrients, plant pathogens or a combination thereof from being discharged into the aquifer.

[0007] Additionally, the water drainage system can meet the needs of potential users, such as farmers, in terms of being an affordable and sustainable system that requires little monitoring and maintenance.

[0008] In the context of the present patent application, field drainage may be understood as a form of agricultural, sports field, golf course, etc. drainage system for removing excess subsurface water from one or more fields so as to, among other things, provide sufficient air space within the soil of the one or more fields.

[0009] In one embodiment, the sand filter stage is a biologically active sand filter stage and / or a slow sand filter.

[0010] In one embodiment, the water filter device comprises a filter housing and a filter chamber defined therein, wherein the sand filter stage and the biologically activated filter stage are arranged in the filter chamber.

[0011] In one embodiment, the sand filter stage is formed by a layer of sand, and the biologically activated filter stage is formed by a layer of biologically activated material. In one embodiment, the sand layer is arranged on the layer of biologically activated material.

[0012] In one embodiment, the water filtration device comprises a further sand filtration stage arranged downstream of the biologically activated filtration stage so that water can flow from the biologically activated filtration stage into the further sand filtration stage. In one embodiment thereof, the further sand filtration stage is formed by a further layer of sand. In yet another embodiment thereof, the layer of biologically activated material is arranged on the further layer of sand. The further layer of sand advantageously provides a physical barrier to the penetration of particles of the biologically activated filtration stage and provides an environment for the biodegradation of less soluble organic substances in a nutrient-limited environment.

[0013] Preferably, the further sand filter stage is arranged in the filter chamber.

[0014] In one embodiment, the water filter device comprises a sub-drainage layer located downstream of the biologically activated filter stage. In one embodiment, the sub-drainage layer is formed by a gravel layer located beneath the further sand layer, allowing water to flow from the further sand layer into the gravel layer.

[0015] In one embodiment, when the water filter device comprises a filter housing and a filter chamber defined therein, wherein the sand filter stage and the biologically activated filter stage are arranged in the filter chamber, the filter chamber has an upstream water space defined therein for retaining upstream water, wherein the upstream water space is arranged upstream of the sand filter stage. An advantage of the upstream water space is that the upstream water retained therein provides sufficient hydrostatic pressure to drive the water to be filtered through the sand filter stage and the biologically activated filter stage.

[0016] In one embodiment, the water filter device comprises a filter housing and a filter chamber defined therein, wherein the sand filter stage and the biologically activated filter stage are arranged in the filter chamber, wherein the filter chamber is provided with a filter inlet for allowing water to enter the filter chamber and a filter outlet for allowing water to exit the filter chamber. In one embodiment thereof, the filter inlet opens into the upstream water space, and the filter outlet opens into the sub-drainage layer. An advantage of this embodiment is that, due to the sub-drainage layer, filtered water can be easily collected and transported out of the water filter device.

[0017] In one embodiment, the sand filter stage and the biologically activated filter stage are spaced apart from each other. In one embodiment, the sand filter stage comprises a first filter tank having a first filter space defined therein, a sand layer and optionally a gravel layer disposed in the first filter space, and a first headwater portion disposed above the sand layer, the first headwater portion being configured to retain overlying water. wherein the biologically activated filter stage comprises a second filter tank in fluid communication with the first filter tank and having a second filter space defined therein, a layer of biologically activated material disposed in the second filter space, and a second headwater portion above the layer of biologically activated material, the second headwater portion being configured to retain supernatant water, and wherein water from the first filter tank enters the second filter tank via the second headwater part or the second filter chamber.

[0018] In one embodiment, the further sand filter stage is arranged downstream of the biologically activated filter stage and is spaced apart from the biologically activated filter stage. In one embodiment thereof, the further sand filter stage comprises a third filter tank in fluid communication with the second filter tank and with a third filter space defined therein, a sand layer arranged in the third filter space, and a third headwater portion arranged above the sand layer, the third headwater portion being configured to retain overlying water.

[0019] In one embodiment, the water drainage system includes an aeration and / or settling stage located upstream of and in fluid communication with the sand filter stage and configured to inject air into the water and allow particles to settle from the water under the influence of gravity to remove suspended particles in the water. Alternatively or additionally, the water drainage system includes a further aeration adjustment stage located downstream of and in fluid communication with the sand filter stage and configured to inject air into the water. An advantage of this embodiment may be that iron present in the aquifer can react with the air in the water, thereby preventing iron from settling in fluid lines of the water drainage system.

[0020] In one embodiment, the aeration and settling stage includes one or more selector valves configured to select whether or not water in the aeration and settling stage is allowed to flow into the sand filter stage. In one embodiment thereof, the aeration and settling stage includes one or more sensors for sensing one or more properties of the water therein, wherein the one or more properties are selected from the group consisting of dissolved organic carbon (DOC) concentration, nitrate (NO3), electrical conductivity of the water, turbidity, and flow rate.Preferably, one of the one or more sensors is configured to detect the electrical conductivity of the water and / or the one or more selector valves are configured to allow water to flow into the sand filter stage when a detected property, such as the electrical conductivity value, of the water is below or above a predetermined threshold. The water drainage system according to this embodiment and according to the invention can be used in an environment where brackish water may be present. By measuring the electrical conductivity of, for example, the field drainage water, its salinity can be determined. According to this embodiment, the field drainage water can advantageously be filtered when the salinity is below a predetermined threshold. This is advantageous because it prevents brackish water from seeping into an aquifer.

[0021] In one embodiment, a safety filter is provided between and in fluid communication with the sand filter stage and the biologically activated filter stage, and / or downstream of and in fluid communication with the biologically activated filter stage. In one embodiment thereof, the safety filter is provided with one or more sensors for sensing one or more properties of the water therein, wherein the one or more properties are selected from a group including water temperature and O2 concentration.

[0022] In one embodiment, the water drainage system comprises a sampling stage provided downstream of and in fluid communication with the water filtration device and upstream of and in fluid communication with the drainage device, wherein the sampling stage is provided with one or more sensors for detecting one or more properties of the water therein, wherein the one or more properties are selected from the group comprising the concentration of dissolved organic carbon (DOC), nitrate (NO3), electrical conductivity of the water and the flow rate.

[0023] In one embodiment, the sand filter stage and / or the biologically activated filter stage is provided with one or more sensors for detecting one or more properties of the water therein, wherein the one or more properties are selected from a group comprising the temperature of the water and the O2 concentration.

[0024] In one embodiment, the water drainage system comprises a reclaimer disposed downstream of the reclaimer and configured to reclaim water from the aquifer into which the reclaimer discharges water. In one embodiment thereof, the reclaimer comprises a further sampling stage configured to receive water reclaimed from the aquifer by the reclaimer, wherein the further sampling stage comprises one or more sensors for detecting one or more properties of the reclaimed water, wherein the one or more properties are selected from the group consisting of electrical conductivity and flow rate of the reclaimed water.In yet another embodiment thereof, the further sampling stage is provided with a first filtered water outlet intended for exporting water from the water drainage system and a second filtered water outlet having a first outlet branch in fluid communication with the biologically activated filter stage and a second outlet branch in fluid communication with the sand filter stage. According to this embodiment, filtered water can be provided to the sand filter stage and / or the biologically activated filter stage during use. This can be done, for example, when the amount of field drainage water to be filtered is relatively low, for example, during a dry period.By providing filtered water to the sand filter stage and / or the biologically activated filter stage, the biological activity within the respective stage(s) is advantageously maintained during a dry period.

[0025] In one embodiment, the biologically activated filter stage comprises a filter material selected from the group consisting of biologically activated carbon (BAC), granular activated carbon (GAC), and / or biochar. The inventors have surprisingly discovered that BAC and / or biochar can function as a non-backwashed adsorbed material that can advantageously operate undisturbed for several years. In addition, the material can advantageously provide a more selective environment for the microbiological degradation of micropollutants after the readily biodegradable material has been removed in the sand filter stage.

[0026] In one embodiment, the sand filter stage comprises a sand layer and a dirt blanket formed on a side of the sand layer facing the water inlet of the water drainage system. A dirt blanket is a layer that develops on top of the sand layer and consists of microorganisms that feed on and degrade organic material trapped on the surface of the sand layer. As the organic material degrades, it adds mass to the dirt blanket, advantageously enhancing the adsorption mechanism in the sand layer below. Furthermore, due to biological growth in the dirt blanket, most of the filtration process occurs in the dirt blanket. This is advantageous because it prevents coagulation, which is necessary for the water filtration device to operate.

[0027] In one embodiment, the sand filter stage is formed by a sand layer comprising fine sand with substantially similar grain sizes. The inventors have surprisingly discovered that, due to the relatively small particle size, the sand layer provides a relatively large surface area for filtration and for the formation of a biofilm on the outer surface of the sand particles. This is advantageous because the sand layer forms a biological slow sand filter that biologically reduces the TOC load, thereby enabling maximum adsorption of micropollutants and non-biodegradable TOC (total organic carbon) on the biologically activated filter stage. An advantage of this embodiment may be that the pesticide content is kept sufficiently high to maintain the biological activity of the biologically activated filter stage.

[0028] In one embodiment, a water pump is provided upstream of the sand filter stage and / or downstream of the biologically activated filter stage, wherein the water pump is configured to transport water through the water drainage system. The water pump can be used to help provide sufficient hydrostatic pressure to force the drainage water to be filtered through the sand filter stage and the biologically activated filter stage.

[0029] In one embodiment, the water drainage system includes a recirculation device configured to recirculate water from the aquifer to the water filtration device. An advantage of this embodiment is that the recirculating water from the aquifer can be used to maintain the biological activity of, among other things, the biologically activated filtration stage.

[0030] In one embodiment, the water drainage system includes a pre-filter device located upstream of and in fluid communication with the water filter device and configured to receive pre-filtered water from the water inlet. In one embodiment, the pre-filter device includes one or more of the following features: - a gravel roughening filter stage; - a carbon or biochar filter stage configured to capture TOC; - a phosphorus pre-filter stage, such as a wood chip stage, configured to capture phosphorus compounds; and - a nitrogen pre-filter stage, such as an iron-coated sand stage or steel by-product stage, configured to capture nitrogen compounds.

[0031] In one embodiment, the water filter device comprises an iron-coated sand filter stage, preferably upstream of the sand filter stage, configured to capture phosphorus compounds.

[0032] In one embodiment, the water filter device comprises two or more sand filter stages and two or more biologically activated filter stages, wherein the two or more sand filter stages and the two or more biologically activated filter stages are arranged alternately.

[0033] In one embodiment, the water drainage system includes a flow diffuser disposed within the sand filter stage and / or the biologically activated filter stage. An advantage of providing a flow diffuser may be that the velocity of the water entering the sand filter stage and / or the biologically activated filter stage is reduced and that the static pressure of the water entering the sand filter stage and / or the biologically activated filter stage is increased.

[0034] According to a second aspect, the invention provides a method for draining water, such as field drainage water, into an aquifer by means of a water drainage system according to the first aspect of the invention, the method comprising the following steps: - Collecting water to be discharged at the water inlet of the water drainage system; - Filtering the collected water through the water filter device; and - Draining the water filtered by the water filtration device into an aquifer.

[0035] The method according to the second aspect of the invention has at least the same technical advantages as described with respect to the water drainage system according to the first aspect of the invention.

[0036] In one embodiment, when the sand filter stage comprises a sand layer, the method further comprises the step of growing a dirt blanket on a side of the sand layer facing the water inlet of the water drainage system.

[0037] The various aspects and features described and shown in the description may, where possible, be applied individually. These individual aspects, in particular the aspects and features described in the appended dependent claims, may be the subject of divisional applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The invention is explained using an exemplary embodiment shown in the attached drawings. They show: Fig. 1 a schematic overview of a water drainage system with a water filter device according to an embodiment of the invention; Fig. 2 a schematic overview of a water drainage system according to another embodiment of the invention; Fig. 3 a detailed schematic view of a sand filter stage of the water drainage system of Fig. 2; Fig. 4 a schematic overview of a water drainage system according to another embodiment of the invention; Fig. 5 an alternative embodiment of the water filter device of Fig. 1; and Fig. 6A and Fig. 6B alternative embodiments of the water drainage system according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0039] A schematic overview of a water drainage system 1 according to an embodiment is shown in Fig. 1, wherein the water drainage system 1 may be configured to drain excess water from one or more fields. Draining excess water from one or more fields may be done to provide sufficient air space within the soil of the one or more fields to allow proper cultivation and / or to allow access by heavy machinery, for example, for harvesting.

[0040] The water drainage system 1, as in Fig. 1, comprises a water inlet 2, which may be surface water, for receiving water to be drained away. A water filter device 3 is provided downstream of the water inlet 2, the water filter device 3 comprising a housing 8 with a filter inlet 4, a filter outlet 5, and a filter chamber 6 defined between the filter inlet 4 and the filter outlet 5. The filter inlet 4 is fluidly connected to the water inlet 2, allowing water received at the water inlet 2 to flow towards the water filter device 3 and into the filter chamber 6. As shown in Fig. As shown in Figure 1, the filter inlet 4 is located at a first level, and the filter outlet 5 is located at a second level below the first level. As a result, water that has entered the filter chamber 6 via the filter inlet 4 can flow toward and out of the filter outlet 5 under the influence of gravity.

[0041] Downstream of the water filter device 3, a discharge device 7 is provided in fluid communication with the water filter device 3, in particular the filter outlet 5 thereof. The discharge device 7 is configured to discharge filtered water into an aquifer or to reclaim stored water from the aquifer. Thus, the discharge device 7 receives water from the water filter device 3 for further processing into the filtered water. In the exemplary embodiment of Fig. 1, the discharge device 7 is a so-called MAR infiltration well (MAR = Managed Aquifer Recharge) or a pump for pumping the filtered water to surface water.

[0042] As in Fig. As indicated in Figure 1, the drainage device 7 can also reclaim water from the aquifer, and the reclaimed water can be supplied to the water filtration device 3. In this embodiment, the drainage device 7 also functions as a recirculation device.

[0043] The water filter device 3 is configured to filter, for example, nutrients, pesticides, and plant pathogens from the water taken in from the water inlet 2. To do this, the water filter device 3 is provided in series and in the filter chamber 6 with an upstream water space 10 for holding upstream water, also referred to as supernatant water, and a sand filter stage 11 formed by a layer of sand below the upstream water space 10. The sand layer can, for example, consist of fine sand with more or less similar grain sizes. A biologically activated filter stage 12 is arranged below the sand filter stage 11, wherein the biologically activated filter stage 12 is formed by a layer of biologically activated carbon (BAC), granular activated carbon (GAC), or biochar.A further sand filter stage 13 is arranged below the biologically activated filter stage 12, whereby the further sand filter stage 13 can also be formed by a layer of sand. The further sand filter stage 13 is arranged on a sub-drainage layer 14, which can be formed by a layer of gravel. It should be noted that the filter outlet 5 opens into the sub-drainage layer 14, so that water can exit the water filter device 3 via the sub-drainage layer 14.

[0044] It is noted that in an alternative embodiment, the biologically activated filter 12 may be formed by a biochar layer.

[0045] During use, water enters the water filter device 3 via the filter inlet 4, thereby entering the headwater chamber 6. The water in the headwater chamber 6 forms a supernatant layer, which is the water column being filtered. The water volume in the headwater chamber 6, or the fill level therein, is kept substantially constant during use. The supernatant layer is provided to provide sufficient hydrostatic pressure to drive the water to be filtered through the underlying layers.

[0046] A dirt blanket 15 is formed on top of the sand filter stage 11. The dirt blanket 15 is a layer composed of microorganisms that feed on and degrade organic material trapped on the upper surface of the sand filter stage 11. During the degradation of the organic material, mass is added to the dirt blanket 15, thereby increasing the screening effect of the water filter device 3. In addition, the dirt blanket 15 can improve the adsorption mechanism in the water filter device 3. The inventors have surprisingly discovered that the biological growth of the dirt blanket 15 causes most of the filtration to occur therein, thus preventing coagulation, which is necessary for the water filter device 3 to function.

[0047] After passing through the dirt blanket 15, the water flows into the sand filter stage 11. Due to the small particle size of the sand used to form the sand filter stage 11, this sand layer provides a relatively large surface area for filtration, as well as for a biofilm that can form around the sand particles. The sand filter stage 11 is configured to remove particles from the water flowing through it. The presence of a biological slow sand filter formed by the dirt blanket 15 and the sand filter stage 11 can (biologically) reduce the TOC (total organic carbon) load, thereby enabling optimal adsorption of micropollutants and non-biodegradable TOC on the biologically activated layer 12 formed by the BAC layer.

[0048] Following the sand filter stage 11, the water enters the biologically activated layer 12, formed by the BAC layer. The BAC layer functions as a non-backwashed adsorbent that can operate undisturbed for several years. Due to the sand filter stage 11 located on top of it and its relatively long operating time, the BAC layer can provide an optimal environment for the microbiological degradation of micropollutants after the readily biodegradable material has been filtered out by the sand filter stage 11.

[0049] The further sand filter stage 12, formed by a further layer of sand, is arranged to provide a physical barrier to the penetration of carbon fines and biofilms and an environment for the biological degradation of heavy soluble organic substances in a nutrient-limited environment.

[0050] The sub-drainage layer 14 is configured to collect water and transport it to the filter outlet 5.

[0051] Although this is the case in the exemplary embodiment of Fig. 1 is not shown, a pump may be arranged upstream and / or downstream of the water filter device 3 for pumping water into the water filter device 3 and / or to the drainage device 7. Additionally or alternatively, the water filter device 3 may be provided with a partition wall (not shown) which divides the filter chamber 6 into two separate chamber sections.

[0052] A water drainage system 101 according to a further embodiment of the invention is shown schematically in Fig. 2 shown.

[0053] The water drainage system 101 has a water inlet 102, which may be a collecting ditch or a drainage pipe located below the surface of the ground.

[0054] The water inlet 102 is configured to receive drainage water, such as field drainage water. As shown in Fig. 2, the water inlet 102 has a fresh water channel 120 for transporting fresh water to a water filter device 103 located downstream of the water inlet 102, and a brackish water channel 121 for removing brackish water from the water drainage system 101.

[0055] Downstream of the water inlet 102 and in fluid communication with the fresh water channel 120 is an aeration and settling stage 130. The aeration and settling stage 130 is formed by an aeration and settling tank 131 configured to receive fresh water from the fresh water channel 120 of the water inlet 102. In the aeration and settling tank 131, air is injected into the fresh water, and suspended particles in the fresh water are removed therefrom by allowing the particles to settle out of the fresh water under the influence of gravity.

[0056] A water filter device 103 is arranged downstream of and in fluid communication with the aeration and settling stage 130. According to this exemplary embodiment, the water filter device 103 comprises, in series, a sand filter stage 111, a biologically activated filter stage 112, and a further sand filter stage 113. The sand filter stage 111 comprises a first filter tank 135 with a first filter chamber 136 defined therein. A sand layer 137, which may consist of fine sand with more or less similar grain sizes, is arranged in the first filter tank 135, in particular at the bottom thereof. A first headwater part 138 is arranged above the sand layer 137, wherein the first headwater part 138 is configured to hold supernatant water.

[0057] Although in Fig. 2, a layer of dirt may be formed on the sand layer 137 during use of the water filter device 103. Additionally or alternatively, a layer of gravel may be disposed beneath the sand layer 137.

[0058] A detailed schematic view of an optional embodiment of the sand filter stage 111 is shown in Fig. 3. The sand filter stage 111 comprises the first filter tank 135 with the first filter chamber 136 defined therein, wherein the sand layer 137 is arranged in the first filter tank 135, in particular at its bottom. As shown, the first upstream part 138 is arranged above the sand layer 137. Additionally or alternatively, a gravel layer 139 is arranged below the sand layer 137. The gravel layer 139 can comprise two or more partial layers of gravel, wherein each partial layer of gravel has a different particle size of the gravel particles.

[0059] Furthermore, a flow diffuser 160 is arranged in the first upstream part 138. The flow diffuser 160 has a substantially U-shaped insert 161 arranged on the top of the first filter tank 135. The insert 161 has a lower part 162 and two legs 163 that protrude upright from the lower part 162, so that the lower part 162 is spaced from the top of the first filter tank 135. The lower part 162 has a plurality of openings 164 to allow water to pass through them. Due to the flow diffuser 160, a static water layer 165 is present on the debris cover 115.

[0060] Downstream of and in fluid communication with the sand filter stage 111 is a biologically activated filter stage 112. The biologically activated filter stage 112 comprises a second filter tank 140 with a second filter chamber 141 defined therein. A layer of biologically activated material 142, which may be made of BAC, GAC, or biochar, is disposed in the second filter tank 140, particularly at its bottom. A second headwater portion 143 is disposed above the layer of biologically activated material 142, wherein the second headwater portion 143 is configured to retain supernatant water.

[0061] It is schematically indicated that the sand filter stage 111 is in fluid communication with the biologically activated filter stage 112. In view of this, it should be noted that the water from the sand filter stage 111 can enter the second filter tank 140 via the second upstream part 143 or via the layer of biologically activated material 142.

[0062] Although in Fig. 2, a layer of gravel may be disposed beneath the layer of biologically activated material 142.

[0063] Downstream of and in fluid communication with the biologically activated filter stage 112 is a further sand filter stage 113. The further sand filter stage 113 has a third filter tank 150 with a third filter chamber 151 defined therein. A sand layer 152, which may correspond to the sand of the sand filter stage 111, is arranged in the third filter tank 150, in particular at its bottom. A third headwater part 153 is arranged above the sand layer 152, wherein the third headwater part 153 is configured to hold supernatant water.

[0064] Although in Fig. 2, a layer of gravel may be arranged under the sand layer 152.

[0065] After it has left the further sand filter stage 113, the filtered water is allowed to flow to the drainage device, not shown, of the water drainage system 101.

[0066] A water drainage system 201 according to a further embodiment of the invention is shown schematically in Fig. 4 shown.

[0067] The water drainage system 201 according to this exemplary embodiment is also provided with a water inlet 202, which may be formed by field drains (not shown) and a manifold. The water drainage system 201 has, in series, an aeration and settling stage 230, which corresponds to the aeration and settling stage 130 of the exemplary embodiment of Fig. 2, a sand filter stage 211, which corresponds to the sand filter stage 111 of the exemplary embodiment of Fig. 2, and a biologically activated filter stage 212 which corresponds to the biologically activated filter stage 112 of the exemplary embodiment of Fig. 2 can correspond.

[0068] In addition to the above, the aeration and settling stage 230 is also configured to allow samples to be taken to check the field discharge water. Furthermore, the aeration and settling stage 230 is provided with selector valves (not shown) for selecting whether water in the aeration and settling stage 230 is transported to the sand filter stage 211 or removed from the aeration and settling stage 230. The selector valves are controlled by an electrical conductivity sensor configured to detect the electrical conductivity of the water in the aeration and settling stage 230. If the detected electrical conductivity value is too high, this can be understood to mean that the salinity of the water is too high and that the water in the aeration and settling stage 230 is brackish water. In this case, water can be removed from the aeration and settling stage 230.If the detected electrical conductivity value is below a predetermined value, for example below 2 mS cm. -1 , it can be determined that fresh water is present in the aeration and settling stage 230, which can be transported to the sand filter stage 211. In the context of this exemplary embodiment, it is noted that the sand filter stage 211 and / or the biologically activated filter stage 212 can be provided with one or more sensors for monitoring the temperature of the water therein and / or the O2 concentration.

[0069] Additionally or alternatively, the aeration and settling stage 230 may be provided with one or more sensors (not shown) for monitoring the concentration of dissolved organic carbon (DOC), nitrate (NO3) and / or the flow rate.

[0070] As in Fig. As shown in Figure 4, a safety filter stage 261, 262 is arranged between the sand filter stage 211 and the biologically activated filter stage 212 and downstream of the biologically activated filter stage 212. In each of the safety filter stages 261, 262, the O2 concentration and / or the water temperature can be monitored.

[0071] Downstream of the safety filter stage 262, after the biologically activated filter stage 212, a sampling stage 260 is provided, which is in fluid communication with the safety filter stage 262 for receiving water therefrom. The sampling stage 260 may be provided with one or more sensors for detecting one or more of the DOC concentration, NO3 concentration, electrical conductivity of the water, and / or the flow rate. After passing through the sampling stage 262, the water is transported to a discharge device 207 for infiltration of the filtered water into the ground, in particular an aquifer thereof.

[0072] The water drainage system 201 is further provided with a recovery device (not shown) having a further sampling stage 270 configured to receive water recovered from the aquifer. The further sampling stage 270 includes one or more sensors for detecting one or more of the electrical conductivity and the flow rate of the recovered water. As shown in Fig. As shown in Figure 4, the further sampling stage 270 is provided with a first filtered water outlet 271, which is intended for transporting water to one or more fields, and a second filtered water outlet 272. The second filtered water outlet 272 has a first outlet branch 273, which is in fluid communication with the biologically activated filter stage 212, and a second outlet branch 274, which is in fluid communication with the sand filter stage 211. The second filtered water outlet 272 is intended to provide water to the biologically activated filter stage 212 and the sand filter stage 211, so that the biological activity in each of the stages 211, 212 can be maintained.

[0073] An alternative embodiment of the water filter device 3 of Fig. 1 is in Fig. 5. The water filter device 303 of Fig. 5 has essentially the same features as the water filter device 3 of Fig. 1. In order to avoid reintroducing features, similar or corresponding features are indicated with the same reference numerals increased by 300.

[0074] Additionally, the water filter device 303 includes a layer of iron-coated sand 316 disposed between the dirt blanket 315 and the sand layer 311. The layer of iron-coated sand 316 is configured to capture phosphorus compounds from the water flowing therethrough.

[0075] Another alternative embodiment of the water drainage system 401 is shown in Fig. 6A. The water drainage system 401 comprises a water inlet 402, a water filter device 403, which may correspond to the water filter device 3, 103, 203, 303 of a previous figure, and a drainage device 407, which may also correspond to one of the previously described drainage devices.

[0076] Disposed between the water inlet 402 and the water filter device 403 is a pre-filter device 480 in fluid communication with the water filter device 403 and the water inlet 402. The pre-filter device 480 is configured to pre-filter the water before it enters the water filter device 403. As shown, the pre-filter device 480 includes a pre-filter stage 481, which may be a gravel roughening filter stage; a carbon or biochar filter stage configured to capture TOC; a phosphorus pre-filter stage, such as a wood chip stage, configured to capture phosphorus compounds; or a nitrogen pre-filter stage, such as an iron-coated sand stage or steel byproduct stage, configured to capture nitrogen compounds.

[0077] Another alternative embodiment of the water drainage system 401, in particular the pre-filter device 480 thereof, is shown in Fig. 6B. In this embodiment, the pre-filter device 480 includes a second pre-filter stage 482 in addition to the first pre-filter stage 481. The second pre-filter stage 482 is different from the first pre-filter stage 481 and may also be a gravel roughening filter stage; a carbon or biochar filter stage configured to capture TOC; a phosphorus pre-filter stage, such as a wood chip stage, configured to capture phosphorus compounds; or a nitrogen pre-filter stage, such as an iron-coated sand stage or steel byproduct stage configured to capture nitrogen compounds.

[0078] As shown schematically in Fig. 6A and Fig.6B, each of the first and second pre-filter stages 481, 482 may be formed by a pre-filter tank 490 having one or more layers of pre-filter material 491 disposed therein and a pre-filter headwater portion 492 above the one or more layers of pre-filter material 491. It is schematically indicated that the first pre-filter stage 481 is in fluid communication with the second pre-filter stage 482. In view of this, it should be noted that the water from the first pre-filter stage 481 may enter the pre-filter tank 490 of the second pre-filter stage 482 via the pre-filter headwater portion 492 or via the one or more layers of pre-filter material 491.

[0079] It should be understood that the foregoing description is included to illustrate the operation of the preferred embodiments and is not intended to limit the scope of the invention. From the foregoing discussion, many variations will be apparent to those skilled in the art that are still encompassed by the scope of the present invention.

Claims

[1] A water drainage system for draining water, such as field drainage water, into an aquifer, the water drainage system having the following features: a water inlet configured to receive water to be drained; a water filter device in fluid communication with the water inlet for receiving water to be discharged from the water inlet and configured to filter water received from the water inlet; and a discharge device in fluid communication with the water filter device and configured to receive water from the water filter device and discharge the filtered water into the aquifer, wherein the water filter device comprises in series a sand filter stage and a biologically activated filter stage configured to filter contaminants from the water to be discharged. [2] Water drainage system according to claim 1, wherein the sand filter stage is a biologically activated sand filter stage and / or a slow sand filter. [3] A water drainage system according to claim 1 or 2, wherein the water filter device comprises a filter housing and a filter chamber defined therein, wherein the sand filter stage and the biologically activated filter stage are arranged in the filter chamber. [4] A water drainage system according to claim 1, 2 or 3, wherein the sand filter stage is formed by a layer of sand, and the biologically activated filter stage is formed by a layer of biologically activated material. [5] A water drainage system according to claim 4, wherein the sand layer is arranged on the layer of biologically activated material. [6] A water drainage system according to any one of the preceding claims, wherein the water filter device comprises a further sand filter stage arranged downstream of the biologically activated filter stage so that water can flow from the biologically activated filter stage into the further sand filter stage. [7] Water drainage system according to claim 6, wherein the further sand filter stage is formed by a further layer of sand. [8] Water drainage system according to claims 4 and 7, wherein the layer of biologically activated material is arranged on the further sand layer. [9] Water drainage system according to claim 3 and claim 6 or 7, wherein the further sand filter stage is arranged in the filter chamber. [10] A water drainage system according to any one of the preceding claims, wherein the water filter device comprises an under-drainage layer located downstream of the biologically activated filter stage. [11] Water drainage system according to claim 8 or 9 and 10, wherein the sub-drainage layer is formed by a gravel layer arranged under the further sand layer so that water can flow from the further sand layer into the gravel layer. [12] A water drainage system according to any one of the preceding claims when dependent on claim 3, wherein the filter chamber has an upstream water space defined therein for holding upstream water, the upstream water space being located upstream of the sand filter stage. [13] A water drainage system according to any one of the preceding claims when dependent on claim 3, wherein the filter chamber is provided with a filter inlet for allowing water to enter the filter chamber and a filter outlet for allowing water to exit the filter chamber. [14] Water drainage system according to claims 11, 12 and 13, wherein the filter inlet opens into the upstream water space and the filter outlet opens into the sub-drainage layer. [15] A water drainage system according to claim 1, wherein the sand filter stage and the biologically activated filter stage are spaced apart from each other. [16] Water drainage system according to claim 15, wherein the sand filter stage comprises a first filter tank with a first filter space defined therein, a sand layer and optionally a gravel layer arranged in the first filter space, and a first headwater part arranged above the sand layer, the first headwater part being configured to hold overlying water, wherein the biologically activated filter stage comprises a second filter tank in fluid communication with the first filter tank and having a second filter space defined therein, a layer of biologically activated material disposed in the second filter space, and a second headwater portion above the layer of biologically activated material, the second headwater portion being configured to retain supernatant water, and wherein water from the first filter tank enters the second filter tank via the second headwater part or the second filter chamber. [17] A water drainage system according to claim 6 and claim 15 or 16, wherein the further sand filter stage is arranged downstream of the biologically activated filter stage and is spaced with respect to the biologically activated filter stage. [18] A water drainage system according to claim 17, wherein the further sand filter stage comprises a third filter tank in fluid communication with the second filter tank and having a third filter space defined therein, a sand layer disposed in the third filter space, and a third headwater portion disposed above the sand layer, the third headwater portion being configured to hold overlying water. [19] A water drainage system according to any one of the preceding claims, comprising an aeration and settling stage arranged upstream of and in fluid communication with the sand filter stage and configured to inject air into the water and allow particles to settle out of the water under the influence of gravity to remove suspended particles in the water, and / or a further aeration adjustment stage arranged downstream of and in fluid communication with the sand filter stage and configured to inject air into the water. [20] The water drainage system of claim 19, wherein the aeration and settling stage comprises one or more selector valves configured to select whether or not water in the aeration and settling stage is allowed to flow into the sand filter stage. [21] A water drainage system according to claim 19 or 20, wherein the aeration and settling stage comprises one or more sensors for detecting one or more properties of the water therein, the one or more properties being selected from the group comprising dissolved organic carbon (DOC) concentration, nitrate (NO3), electrical conductivity of the water, turbidity, and flow rate. [22] A water drainage system according to claim 20 and 21, wherein one of the one or more sensors is configured to detect the electrical conductivity of the water and / or wherein the one or more selector valves are configured to allow water to flow into the sand filter stage when a detected property, such as the electrical conductivity value, of the water is below or above a predetermined threshold value. [23] A water drainage system according to any one of the preceding claims, wherein a safety filter is provided between and in fluid communication with the sand filter stage and the biologically activated filter stage and / or downstream of and in fluid communication with the biologically activated filter stage. [24] A water drainage system according to claim 23, wherein the safety filter is provided with one or more sensors for detecting one or more properties of the water therein, the one or more properties being selected from a group comprising the temperature of the water and the O2 concentration. [25] A water drainage system according to any one of the preceding claims, comprising a sampling stage provided downstream of and in fluid communication with the water filtration device and upstream of and in fluid communication with the drainage device, the sampling stage being provided with one or more sensors for detecting one or more properties of the water therein, the one or more properties being selected from the group comprising the concentration of dissolved organic carbon (DOC), nitrate (NO3), electrical conductivity of the water and the flow rate. [26] A water drainage system according to any one of the preceding claims, wherein the sand filter stage and / or the biologically activated filter stage is provided with one or more sensors for detecting one or more properties of the water therein, the one or more properties being selected from a group comprising the temperature of the water and the O2 concentration. [27] A water drainage system according to any preceding claim, comprising a recovery device located downstream of the drainage device and configured to recover water from the aquifer into which the drainage device discharges water. [28] The water drainage system of claim 27, wherein the reclaimer comprises a further sampling stage configured to receive water reclaimed from the aquifer by the reclaimer, the further sampling stage comprising one or more sensors for detecting one or more properties of the reclaimed water, the one or more properties being selected from the group comprising electrical conductivity and flow rate of the reclaimed water. [29] A water drainage system according to claim 28, wherein the further sampling stage is provided with a first filtered water outlet arranged to export water from the water drainage system and a second filtered water outlet having a first outlet branch in fluid communication with the biologically activated filter stage and a second outlet branch in fluid communication with the sand filter stage. [30] A water drainage system according to any one of the preceding claims, wherein the biologically activated filter stage comprises a filter material selected from the group comprising biologically activated carbon (BAC), granular activated carbon (GAC) and / or biochar. [31] A water drainage system according to any one of the preceding claims, wherein the sand filter stage comprises a sand layer and a dirt blanket formed on a side of the sand layer facing the water inlet of the water drainage system. [32] Water drainage system according to one of the preceding claims, wherein the sand filter stage is formed by a sand layer comprising fine sand with substantially similar grain sizes. [33] A water drainage system according to any one of the preceding claims, wherein a water pump is provided upstream of the sand filter stage and / or downstream of the biologically activated filter stage, the water pump being configured to transport water through the water drainage system. [34] A water drainage system according to any preceding claim, comprising a recirculation device configured to recirculate water from the aquifer to the water filtration device. [35] A water drainage system according to any preceding claim, comprising a pre-filter device disposed upstream of and in fluid communication with the water filter device and configured to receive pre-filtered water from the water inlet. [36] Water drainage system according to claim 35, wherein the pre-filter device has one or more of the following features: - a gravel roughening filter stage; - a carbon or biochar filter stage configured to capture TOC; - a phosphorus pre-filter stage, such as a wood chip stage, configured to capture phosphorus compounds; and - a nitrogen pre-filter stage, such as an iron-coated sand stage or steel by-product stage, configured to capture nitrogen compounds. [37] A water drainage system according to any one of the preceding claims, wherein the water filter device comprises an iron-coated sand filter stage, preferably upstream of the sand filter stage, configured to capture phosphorus compounds. [38] A water drainage system according to any one of the preceding claims, wherein the water filter device comprises two or more sand filter stages and two or more biologically activated filter stages, wherein the two or more sand filter stages and the two or more biologically activated filter stages are arranged alternately. [39] A water drainage system according to any one of the preceding claims, comprising a flow diffuser arranged within the sand filter stage and / or the biologically activated filter stage. [40] A method of draining water, such as field drainage water, into an aquifer by means of a water drainage system according to any one of the preceding claims, the method comprising the steps of: - Collecting water to be discharged at the water inlet of the water drainage system; - Filtering the collected water through the water filter device; and - Draining the water filtered by the water filtration device into an aquifer. [41] A method according to claim 40, wherein the sand filter stage comprises a sand layer, the method further comprising the step of growing a blanket of dirt on a side of the sand layer facing the water inlet of the water drainage system.

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