DEVICE AND METHOD FOR EXTRACTING WATER FROM A SOIL SAMPLE

Abstract

A soil-water extraction device, with at least one matrix body (I), into which at least one channel (2) for receiving a soil-water sample is formed, a porous, hydrophilic ceramic (3), which likewise is introduced into the matrix body and which closes off the channel toward the soil side, flush with the matrix body (I), and a hose (4), which leads from the opposite side of the channel to a pump (5) driven by a motor driver (6), wherein: the motor driver (6) is controlled by means of a microcontroller (7); the microcontroller (7) is connected to at least one interface (8); and, by means of the interface (8), information about the moisture (9) is given to the microcontroller, said information being compared with stored target values (11) Also, a method for extracting soil water.

Claims

1. A soil water extraction device comprising at least one matrix body (1) into which at least one channel (2) for receiving a soil water sample is incorporated and a porous, hydrophilic ceramic (3) which is likewise incorporated into the matrix body and closes off the channel towards the soil side, flush with the matrix body (1) and a hose (4) which leads from the opposite side of the channel to a pump (5) which is driven by a motor driver (6), wherein the motor driver (6) is controlled by means of a microcontroller (7) and the microcontroller (7) is connected to at least one interface (8) and through the interface (8) information about the moisture (9) is given to the microcontroller during operation and are compared with stored target values (11).

2. The soil water extraction device according to claim 1, wherein the porous, hydrophilic ceramic (3) is made of aluminum oxide (Al.sub.2O.sub.3).

3. The soil water extraction device according to claim 1, wherein the power consumption is less than 1 W due to the dimensioning of the drive of the pump (5).

4. The soil water extraction device according to claim 1, wherein the matrix body (1) is attached to a substrate body (10).

5. The soil water extraction device according to claim 1, wherein the microcontroller (7) is also connected to a further interface (8).

6. The soil water extraction device according to claim 1, wherein the material for the matrix body (1) is selected from the group consisting of polydimethylsiloxane (PDMS), polyimide (PI), polystyrene (PS), polypropylene (PP), polycarbonate (PC), cycloolefin copolymer (COC) and polyetheretherketone (PEEK).

7. The soil water extraction device according to claim 1, wherein the channel (2) has a width from 10 ?m to 3 mm.

8. The soil water extraction device according to claim 1, wherein the average pore size of the porous hydrophilic ceramic (3) is from 500 nm to 5 ?m.

9. The soil water extraction device according to claim 1, wherein the volume of the pores in the total volume of the porous hydrophilic ceramic (3) is in the range from 20 to 60 percent of the volume.

10. A method for extracting of soil water comprising the following steps: i. transmitting information of the moisture (9) via an interface (8) to the microcontroller (7); ii. processing the information of the moisture (9) and comparison with stored target values (11) in the microcontroller (7); iii. actuating the motor driver (6) of the pump (5) by the microcontroller (7) on the basis of the basis of the result from step ii; iv. filling the channel and the hose with soil water by means of the ceramic and the pump (5) driven by the motor driver.

11. The soil water extraction device according to claim 1, wherein the power consumption is less than 500 mW due to the dimensioning of the drive of the pump (5).

12. The soil water extraction device according to claim 1, wherein the power consumption is less than 400 mW due to the dimensioning of the drive of the pump (5).

13. The soil water extraction device according to claim 1, wherein the volume of the pores in the total volume of the porous hydrophilic ceramic (3) is in the range from 30 to 50 percent of the volume.

14. The soil water extraction device according to claim 1, wherein the volume of the pores in the total volume of the porous hydrophilic ceramic (3) is in the range from 35 to 40 percent of the volume.

Description

[0041] FIG. 1 shows the schematic structure of the soil water extraction device according to the invention with a matrix body (1) in which at least one channel (2) for receiving a soil water sample is incorporated and a porous, hydrophilic ceramic (3) which is also incorporated in the matrix body and closes the channel flush with the matrix body on the soil side and a hose (4) which leads from the opposite side of the channel to a pump (5) which is driven by a motor driver (6), wherein the motor driver (6) is controlled via a microcontroller (7) and the microcontroller (7) is connected to at least one interface (8) and information about the moisture (9) is sent to the microcontroller via the interface (8) and compared with target values (11) stored there.

[0042] FIG. 2 shows a schematic representation of the application of the device according to the invention and the method in connection with the Internet of Underground Things (IoUT). The data is exchanged by radio via the gateway (14) between the sensor nodes (12) below the earth's surface (13) and the devices with the corresponding interface.

[0043] FIG. 3 shows a photograph of the matrix body with channel and glued-in ceramic attached to a substrate body measuring 2.5 cm?2.5 cm?0.1 cm.

[0044] FIG. 4 shows a sketch of the negative mold for molding the matrix body, the length of the channel is 12 mm, the volume of the channel is 12 ?l.

[0045] FIG. 5 shows the images of the hydrophilic ceramic used, taken using an atomic force microscope (AFM). Areas of 10 ?m?10 ?m (a, c) and 50 ?m?50 ?m (b and d) were examined. The height profiles (e and f) show a surface roughness between 2 ?m and 4.2 ?m.

[0046] Without limiting the overall scope of the invention, the application of the soil water extraction device according to the invention will be demonstrated in the following by way of example.

Exemplary Production of a Matrix Body with Channel and Ceramic

[0047] Based on the production drawing, the matrix body made of polydimethylsiloxane (PDMS) is molded using polytetrafluoroethylene (PTFE). For this purpose, the flowable PDMS prepolymer (SYLGARD? 184, Merck KGaA) is placed in the PTFE mold and cured at 90? C. within one hour. The cured fluidic body is then removed from the mold. A channel for the ceramic is then punched out so that it can be inserted flush into the fluidics and bonded.

[0048] The ceramic used is hydrophilic aluminum oxide (Al.sub.2O.sub.3). In this case, Keralpor 99, 99.5% Al.sub.2O.sub.3, Kerafol Keramische Folien GmbH & Co. KG, size 3 mm?2.5 mm?2 mm (length?width?height). The volume of the pores in the total volume of the porous, hydrophilic ceramic is between 36 and 38 percent by volume. The density of the hydrophilic ceramic is 2.56 g/cm.sub.3 and the average pore size is 1 ?m.

[0049] FIG. 5 shows the images of the hydrophilic ceramic used, taken using an atomic force microscope (AFM). Areas of 10 ?m?10 ?m (a, c) and 50 ?m?50 ?m (b and d) were examined. The height profiles (e and f) show a surface roughness between 2 ?m and 4.2 ?m.

[0050] The volume of the hydrophilic ceramic was determined by calculating the difference between the weight of the dehydrated hydrophilic ceramic (70.6 mg) and the water-saturated ceramic (84.3 mg) at 13.7 ?l.

[0051] The matrix body is glued to a glass substrate body measuring 2.5 cm?2.5 cm?0.1 cm, which has a through hole on the side of the channel opposite the hydrophilic ceramic.

[0052] On the side of the channel opposite the hydrophilic ceramic, the substrate body has a hole for guiding and attaching the hose.

[0053] The hose is plugged into the substrate body and connected to a peristaltic pump (RP-Q1.2N, Aquatech Co., Ltd.).

[0054] A Raspberry Pi 4 and a motor driver for the peristaltic pump type TB6612 (Adafruit Industries) are used as the microcontroller. The moisture information is provided by a sensor of the type SMT100, Truebner GmbH.

Determination of the Soil Moisture Required for Extraction (Target Values):

[0055] The required soil moisture for three different types of soil (sand, garden soil and silt) is determined. The volume of the soil samples placed in the sealed container is 2500 cm.sub.3.

[0056] Before starting the first measurement, the hydrophilic ceramic is moistened in order to have reproducible initial conditions. This is not necessary for continuous operation in the soil. The matrix body is then placed in the soil so that the ceramic is in direct contact with the soil. The sensor for recording the moisture in the soil is placed in the immediate vicinity of the matrix body.

[0057] In the experiment, the volume of extracted moisture in the channel is determined over time using a microscope. The soil moisture was varied by adding 100 ml of water at a time. The moisture was measured 15 minutes after adding the corresponding amount of water. The peristaltic pump was then operated for 30 minutes in each case.

[0058] Table 1 contains the measured moisture of the soil and the extracted volume for the different soils as a function of the added water.

[0059] An SMT 100 turbidity sensor was used for the experiments in Table 1. This has a specification range for the volumetric water content of the soil of 0 to 50% with an accuracy of +?3% with the factory calibration.

TABLE-US-00001 TABLE 1 Information of moisture and extracted volume for different soils Sand Garden soil Silt Ex- Ex- Ex- Added measured tracted Measured tracted Measured tracted water moisture volume moisture volume moisture volume [ml] [Vol.-%] [ml] [Vol.-%] [ml] [Vol.-%] [ml] 0 3 0 2 0 1 0 100 5 0 5 0 1 0 200 8 0.1 11 0.1 3 0 300 10 0.1 15 0.1 9 0 400 14 0.1 19 0.17 11 0 500 18 0.1 24 0.19 13 0.1 600 22 0.15 18 0.08 700 31 0.15 23 0.1 800 28 0.15 900 33 0.19

[0060] It is shown that extraction can start at a measured moisture of 8% by volume for sand, 11% by volume for garden soil and 13% by volume for silt.

[0061] Due to the different absorption capacity for water in the various soils, these values are achieved for garden soil and sand after the addition of 200 ml of water, whereas 500 ml must be added for silt in order to start extraction.

[0062] Depending on the required volume of the extracted sample and the nature of the soil, the target values can be rigidly set and stored in the microcontroller. This could be done by selecting the type of soil when it is added. Alternatively, a learning algorithm could be implemented that records the amount of water extracted at different pumping capacities and adjusts the target values based on this.

[0063] Further explanations on moisture are given below, which may be or are relevant for individual embodiments of the invention, but which are not necessarily limiting or must be limiting.

[0064] The moisture information is decisive for the invention in order to enable adaptive sampling, which is crucial for the low-energy operation of the sensor. Thus, if the soil is sufficiently moist, soil solution is extracted at a user-programmable minimum time interval. If the soil is drier than the minimum moisture value, the moisture information is evaluated regularly, e.g. every 5 minutes to every 6 hours. This can be transmitted to the sensor via weather data or read out with an associated soil moisture sensor.

[0065] The volumetric water content is the ratio between the water volume and the unit volume of the soil. The volumetric water content can be specified as a ratio, percentage or water depth per soil depth. Alternatively, a sensor that measures soil water tension can be used to determine soil moisture, e.g. from the reference Datta et al. (Datta et al., Understanding Soil Water Content and Thresholds for Irrigation Management, Oklahoma Cooperative Extension Service, BAE-1537, June 2017). Accordingly, moisture information can be stored, transmitted and processed as volumetric water content or soil water tension.

[0066] The maximum volumetric water content is reached when all the pores (voids between the rigidly bound soil components) are filled with water. This saturation value varies between 30% in sandy soils and 60% in clay soils (reference Datta et al.). Above a certain threshold, water flows out of larger pores by gravity. This is the maximum soil moisture for irrigation and is also strongly dependent on the soil type (reference Datta et al.). Most agricultural soils reach the threshold one to three days after irrigation or a rain event. This means that the moisture information must be evaluated within this period in order to benefit from the increased soil moisture. The permanent wilting point determines the moisture above which plants can no longer extract water from the respective soil type. Soils should typically be kept above this moisture level so as not to put plants at risk. This value is therefore the relevant minimum soil moisture for the sensor system and is also dependent on the soil type.

[0067] Due to the differences in the saturation values and the permanent wilting point for different soil types, a rigidly fixed threshold value should not simply be used for operation.

[0068] Table 1 demonstrates this difference and provides guidelines for the choice of threshold value. Soil solution extraction should be activated for sandy soils from 8%+?3% volumetric water content, for silt from 13%+?3% volumetric water content and for mixed soils in between.

[0069] In the first method of adaptive sampling, this threshold value is stored in the microprocessor together with the soil information. As soon as this threshold is exceeded, the soil solution is extracted. If the soil moisture information is transmitted via the interface from other sensors, the threshold values are programmed in advance.

[0070] In the second method of adaptive sampling, the change in soil moisture is observed instead of the absolute value. After irrigation, the water content in the soil suddenly increases by more than 50% (reference Datta et al.). Here, the soil moisture is recorded with a sensor with a time resolution of greater than 30 min (i.e. shorter time intervals) and the soil solution extraction is activated as soon as a jump in soil moisture of more than 50% is observed.

TABLE OF FIGURES

[0071] FIG. 1: Schematic representation of the soil water extraction device according to the invention

[0072] FIG. 2: FIG. 2 shows a schematic representation of the application of the device according to the invention and the method in connection with the Internet of Underground Things (IoUT)

[0073] FIG. 3: Photograph of the matrix body with channel and glued-in ceramic attached to a substrate body measuring 2.5 cm?2.5 cm?0.1 cm

[0074] FIG. 4: Sketch of the negative mold for the impression of the matrix body

[0075] FIG. 5: AFM image of the hydrophilic ceramic made of Al.sub.2O.sub.3

LIST OF REFERENCE SYMBOLS

[0076] 1 Matrix body [0077] 2 Channel [0078] 3 Ceramic [0079] 4 Hose [0080] 5 Pump [0081] 6 Motor driver [0082] 7 Microcontroller [0083] 8 Interface [0084] 9 Moisture information [0085] 10 Substrate body [0086] 11 Target values [0087] 12 Sensor node [0088] 13 Ground surface [0089] 14 Gateway