WO2020027715A1

WO2020027715A1 - System intended for purification of contaminated water by phytoremediation

Info

Publication number: WO2020027715A1
Application number: PCT/SE2019/050716
Authority: WO
Inventors: Dahn ROSENQUIST
Original assignee: Laqua Treatment Ab
Priority date: 2018-08-02
Filing date: 2019-07-31
Publication date: 2020-02-06
Also published as: EP3830039A1; EP3830039A4

Abstract

The present invention describes a system intended for purification of contaminated water, said system comprising - a filter unit; - a filter substrate; - a plant growth environment with access to a water source intended to be purified via phytoremediation; wherein the filter unit is a horizontal filter unit, and wherein the system comprises a recirculation loop.

Description

SYSTEM INTENDED FOR PURIFICATION OF CONTAMINATED WATER

BY PHYTOREMEDIATION

Field of the invention

The present invention relates to a system intended for purification of contaminated water by phytoremediation.

Technical Background

Phytoremediation is a known concept. It is the direct use of plants for the removal, degradation, or containment of contaminants in soils, sludges, sediments, surface water and groundwater Furthermore, it is also known to use filters in phytoremediation systems. For instance, in US7718063 there is disclosed a method of depollution by phytoremediation intended for treating wastewater, polluted air or soil comprising a first step of introducing the pollutants in solid, liquid or gaseous form in a planted filter bed, and where the method also comprises a step of irrigation of the planted filter bed so as to define aerobic or anaerobic periods. The document also discloses a device for carrying out that method. Moreover, also in the document

WO2012/026947 there is disclosed a filter system arrangement which may be used in the context of phytoremediation.

The present invention is directed to providing an improved system intended for phytoremediation, which system has several advantages when being compared to what is used or known today.

Summary of the invention

The stated purpose above is achieved by a system intended for purification of contaminated water, said system comprising

- a filter unit;

- a filter substrate;

- a plant growth environment with access to a water source intended to be purified via phytoremediation;

wherein the filter unit is a horizontal filter unit,

and wherein the system comprises a recirculation loop.

The horizontal filter unit according to the present invention provides several advantages. First of all, it is an optimal nitrogen reducing source for use in wetlands or the like. The horizontal filter unit provides a stable solution in a phytoremediation solution and it also has the ability to provide a comparatively high contact time for the water intended to be purified, which in turn enables a high uptake of nitrogen and other substances in the plants in the plant growth environment. To mention some other advantages it should be said that a system according to the present invention is much easier and inexpensive to construct and arrange than typical wetland arrangement used today. There is not any need for large influences on nature and to restore the site after a temporal arrangement is comparatively easy. Moreover, the start- up time for a system according to the present invention is very low when being compared to typical wetland arrangements used today. Furthermore, another possible technical advantage is that the system according to the present invention provides high evaporation of water compared to used arrangements today, which in turn implies that a comparatively lower amount of water needs to be pumped further to another place.

The plants are arranged in the plant growth environment in the filter substrate. Moreover, the filter substrate is in turn provided as an arrangement within the filter unit, which filter unit is the bottom section of the system.

Furthermore, in relation to the expression“horizontal”, this should be interpreted relating to such type of filter unit and not the exact orientation during use of the filter unit. This also implies that the system according to the present invention of course may be used in a declined hill or the like. Then the horizontal filter unit follows the natural declination of the surroundings. Flowever, in such a case it is important to consider which short side that should have the water inflow and which should have the water outflow, so that a high contact time is maintained. These parameters are further discussed below in relation to the present invention.

Moreover, the system according to the present invention comprises a recirculation loop. The recirculation provides an increased contact time overall, which is very important to provide an effective system. Without the recirculation the flow through the system would have been too low.

To provide some additional prior art documents it may be mentioned that e.g. in US2012/0024780 there is disclosed a waste water treatment system which includes a basin for holding water; nitrifying and denitrifying bacteria; macroalgae; and a bio-bed having at least one layer and being constructed of materials selected to provide sufficient level of pH for enabling bacterial growth.

Furthermore, in WO2011/114290 there is disclosed a biotechnical phytodepuration system which comprises a filtering bed constituted by inert porous materials and vegetable species planted on the filtering bed, where the filtering bed is inoculated with a consortium of microorganisms.

Both US2012/0024780 and WO2011/114290 relate to what may be seen as regular purification by use of ground plant growth. To give some examples of important differences in relation to the present invention it may be said that the present invention uses carbon as the first absorbing source for organic contaminants in the filter substrate. The plants of plant growth environment are then used as a second absorbing source so that the contaminants are transferred from the filter substrate to the plants growing so that the shelf life of the filter is prolonged. This is very different when comparing to the systems in US2012/0024780 and WO2011/114290, where it is only the growing plants that are intended as the absorbing source.

The arrangement according to the present invention provides an effective system which does not have to be replaced with a new system as often as in the case of when using ground plant growth systems, e.g. as the ones disclosed in US2012/0024780 and WO2011/114290.

Furthermore, according to the present invention, the system comprises a recirculation loop, which is not comprises in the systems disclosed in US2012/0024780 and WO2011/114290.

Moreover, all differences mentioned below are also differences which are true when comparing the present invention with US7718063.

Specific embodiments of the invention

Below specific embodiments of the present invention are discussed. According to one specific embodiment of the present invention, the filter unit has a depth in the range of 0.2 - 1.0 meter. This is a suitable range of depth to ensure a flexibility in water flow and residence time, and which still enables a comparatively large conversion volume. Moreover, the depth range also enables to keep an enough large filter substrate within the filter unit bed.

Moreover, according to yet another specific embodiment, a relationship between the length (L) of the filter unit and the width (W) of the filter unit is in the range of L = W x (3-6) and wherein an inflow side of the filter unit and an outflow side of the filter unit are arranged on the opposite shortest sides. The rectangular shape or a larger L versus W has several advantages. The oblong design enables a large contact time for the water flow when this is flown from an inflow arranged on one short side towards an outflow arranged on the opposite short side. Moreover, the oblong design of the filter unit also enables the water flow to come in contact with much of the roots of the plants to ensure a high phytoremediation level. The roots only extend about 20 - 40 cm vertically so it is important to consider the flow arrangement to ensure a high contact time. Moreover, and in line with what has been mentioned above, according to yet another specific embodiment of the present invention, the filter unit is arranged to ensure a flow from an inflow side of the filter unit to an outflow side of the filter unit which has a flow length larger than the shortest distance between the inflow side and the outflow side of the filter unit. This type of flow pattern ensure that the water flow does not go from the inflow point directly to the outflow point, but in fact goes through the filter bed unit to increase the contact time and contact time with the roots.

Moreover, according to another embodiment of the present invention, the filter unit is arranged with a flow system counteracting crossflow in the filter unit. So, even if a high contact time is of interest by leading the flow back and forth through the filter unit, one flow should not cross another flow so there is an interconnected flow grid. Furthermore, according to yet another specific embodiment of the present invention, the flow inside of the filter unit is collected in a mutual point before the outflow. This feature is of interest to control the outflow of the water after having flown through the filter unit.

Furthermore, according to yet another specific embodiment of the present invention, the filter unit comprises individual sections to drive a water flow with increased contact time from the inflow side of the filter unit to the outflow side of the filter unit. Such section has inner walls controlling the flow direction. Moreover, the sections may provide different types of flow pattern from one side of the filter unit to the other, e.g. a zigzag pattern.

Moreover, the filter unit bed is suitably sealed with a sealing

membrane. Therefore, according to one embodiment, the filter unit comprises a sealing membrane, e.g. comprising HDPE.

Furthermore, the concept according to the present invention also involves an improved filter substrate to use in a filter unit such as according to the present invention and in a phytoremediation application. According to one specific embodiment of the present invention, the filter substrate comprises peat, ash and light expanded day aggregate (LECA) or pumice stone. As may be understood a light-weight material like light expanded clay aggregate (LECA) or pumice stone should be used in the filter substrate to enable porosity between aggregates thereof. Moreover, also other components may be incorporated, such as sand or lime. For instance, according to one embodiment, the relationship between the components except for light expanded clay aggregate (LECA) or pumice stone may be 50-90%, preferably 60-80%, peat, 5-30%, preferably, 10-25%, ash, 2-25%, preferably 5-20%, sand and 2-25%, preferably 5-20%, lime. It should be noted that then the light-weight component is not counted. Furthermore, according to yet another specific embodiment of the present invention, the filter substrate comprises 10-90 vol% light expanded clay aggregate (LECA) or pumice stone.

It may be mentioned that by using LECA according to the present invention an insulation is obtained, which also enables operation around the year also in colder geographies. Furthermore, LECA provides structure to the filter unit and surface and structure for microorganisms to grow on.

It should be noted that there are alternatives to LECA which may be used according to the present invention. One such example is recycled crushed building material (bricks), which is not as effective however an inexpensive alternative.

The light-weight component has several features. First of ail, by- adjusting the amount of light-weight material, the permeability may be adjusted. This and the water level may be important parameters to control the entire system and its contact time etc. Secondly, the light-weight component also works as an insulating material, which is of special interest during the winter. This is for instance not possible when using a regular muddy wetland.

Furthermore, according to yet another specific embodiment of the present invention the filter substrate is arranged in sections in the filter unit, and wherein the sections comprise a certain filter substrate material.

By incorporating these sections there is obtained a pressure

equalization between the sections. This enables a stronger flow through the entire filter substrate and filter unit. Moreover, the flow is horizontally equalized so that possible channelization is minimized.

Moreover, according to yet another embodiment of the present invention, some sections comprise light expanded clay aggregate (LECA) and other sections comprise light expanded clay aggregate (LECA) together with peat and/or ash, preferably wherein the two end sections of the filter substrate comprise only light expanded clay aggregate (LECA). As mentioned above, LECA may be used to provide structure and good flow through properties of the filter substrate and thus filter unit. Where only LECA is provided, there water may flow freely in the that plane. This provides better flow through properties and also pressure equalization towards sections with a mixture of peat and/or ash and LECA Without these sections and different type of sections there is a risk of water not flowing through parts of the entire filter unit. By using the sections according to the present invention, the filter unit ensures to lead the water flow through the filter unit in a planned way.

To give one example according to the present invention, the width of the filter unit is in the range of 2-6 metres and a depth of 0.3 - 0.6 metres.

The length, as well as the set width, depend on the intended capacity.

The filter unit may also be arranged to provide for an adjustable water level in the system according to the present invention in relation to the ground water. This may be provided to enable to optimize the properties in relation to the root system of the crops grown and their needs.

Moreover, the system comprises a recirculation loop. As said, the recirculation provides an increased contact time overall. Furthermore, according to yet another embodiment, the system comprises a connection with one or more a wind or sun energy generation units, which one or more generation units drive water recirculation from an outflow side of the filter unit to an inflow side of the filter unit. The recirculation is driven by a pump. This pump may get power from a connection with a wind or sun energy generation unit.

Moreover, the outflow in the first part of the filter unit may be arranged to enable to ventilate the water. This may be of interest if the contaminated water has a high level of BOD. The design may be provided with a sprinkler or ventilation stairs. Another possibility is a tower or cylinder of a net with LECA bails through which the wind may blow at the same time as water is fed to the top and may flow along the LECA balls.

Moreover, according to one specific embodiment of the present invention, a system according to the present invention comprises several filter units. These type of system may then comprises a series of filter units where different plants may be grown in the different filter units. These are then optimised to handle different types of contaminants. Moreover, certain steps may be provided in parallel to enable some to be in operation while others are resting or being harvested. This decreases the risk if certain difficult contaminants enter the system. Otherwise there is a risk for very difficult contaminants creating a stop of an entire system. Therefore, according to one embodiment of the present invention, the system comprises several connected filter units.

The present invention is also directed to a method. According to one specific embodiment of the present invention there is provided a method for purification of contaminated water, said method comprising flowing a water flow intended to be purified from an inflow side of the filter unit of a system according to the present invention and regulating said flow from that side of the filter unit towards the outflow side of the filter unit and out from that side of the filter unit.

According to yet another embodiment of the present invention, the filter substrate is maintained at least 0.05 m above the water level. Furthermore, according to another specific embodiment, the water level is regulated to adjust for the permeability of the light expanded clay aggregate (LECA) or pumice stone of the filter substrate. The light expanded clay aggregate (LECA) or pumice stone is light-weight structures and float and as such, hole spaces expand and the permeability increases. Therefore, it may also be of interest to maintain the filter substrate and its light expanded clay aggregate (LECA) or pumice stone above the water level. Therefore, the water level may be used to adjust the permeability of the filter substrate.

Furthermore, according to yet another specific embodiment of the present invention, the water flow is recirculated from an outflow side of the filter unit to an inflow side of the filter unit. Moreover, according to one specific embodiment, the water flow is recirculated or converted from an outflow of the filter unit to an inflow of the filter unit in a range of 2-24 times / 24 hours.

Furthermore, the water flow, recirculation and as such contact time may be regulated, for instance by use of PLC regulation. Furthermore, the system may also be scheduled to be drained now and then to guarantee a strong oxygenation.

Moreover, the plants to use in the system according to the present invention are also important, and fast growing crops are preferred as this increases the potential of uptake of substances, especially substances which otherwise are difficult to degrade in nature. Such substances are e.g. heavy metals and organic contaminants, inter alia hydrocarbon contaminants. Such substances are effective to incorporate in the plants during growth in a system according to the present invention.

Moreover, plant nutrients like nitrogen och phosphorous are

substances that are strongly incorporated in the plants during growth according to the present invention. Furthermore, other substances possible to take care of are the so called perfluoroalkyl substances (PFAS). Moreover, another relevant example is perfluorooctane sulphonate (PFOS) substances, which are used as inter alia flame retardants. These are problematic and difficult to take care of in the nature. The present invention provides an effective solution to this problem.

As mentioned above, fast growing crops, such as willows, poplar, hybrid aspen or energy grass, are preferred to use according to the present invention. In line with this, according to one specific embodiment of the present invention, fast growing crops, such as, willows, poplar, hybrid aspen, energy grass or a combination thereof, is planted in the filter substrate to form the plant growth environment. In relation to the above it may be mentioned that already after 1 month of planting fast growing crops in a system

according to the present invention, one may see a positive effect of

purification of a contaminated water flow. After about 2-3 months a substantial positive effect may be noted. This may be compared to wetland arrangements or similar techniques used today where the standard recommendation is to wait at least 2 years until expecting a substantial effect.

Moreover, it may be mentioned that the type of plants or crops used may be set based on the type of contaminants in comparatively high concentration in that specific area.

It should also be mentioned that the system and method according to the present invention has no negative effect on the environment and provides only positive contributions by the uptake of substances important to remove from wetlands and the like.

Moreover, the system according to the present invention in

combination with recirculation of water increases the root development with 2- 10 times as much when compared to conventional growth. The plants are harvested yearly. According to one possible example, about 1/3 of the filter area is harvested by removing entire plants with their roots. This is to ensure maximal removal of all substances, e.g. heavy metals, which have been incorporated in the plants and their roots. The plants are burned in a typical and controlled combustion plant where most substances are burned and some, such as heavy metals, are removed and taken care of. Bioenergy is then also produced, and the bioenergy is a result of uptake of nutrients and sun energy in the plants, and this energy may be extracted by burning the plants. The area harvested is re-planted.

The system according to the present invention may also comprise specific regulation and measurement equipment, such as online

measurement and alarm functions etc. to ensure a purification level of the water which is enough.

The system according to the present invention finds use in many different applications One example is water purification/decontamination of leachate from landfills, mining and quarrying, by removing organic substances such as PFOS or the like, and e.g. medicine residues. Another example is water purification of process water, such as washing waters. Yet other examples are for the purification of waste waters and as a very effective alternative in traditional wetlands.

Description of the drawings

In fig. 1 and 2 there are shown one specific embodiment according to the present invention. As may be seen, the system comprises a filter unit which contains a filter substrate. In the filter substrate there are plants planted which constitute the plant growth environment with access to a water source intended to be purified via phytoremediation. As may be seen in fig. 2, the filter unit in the bottom provides the water access through the filter substrate to the plants. Moreover, there are inflow, outflow and tubing etc. provided in the filter unit to enable a suitable water flowing from the inflow side to the outflow side. Furthermore, the filter unit may also be provided with sections to enable a water flow that is driven across the filter unit from one side to the other and back again until it reaches the water flow outside.

In fig. 3 there is shown part of a system according to one specific embodiment of the present invention. In this case the filter unit is shown as the bottom part and then the filter substrate is arranged in sections. In this case the outermost end sections comprise light expanded clay aggregate (LECA) only. Such sections comprising light expanded day aggregate (LECA) are also provided as every other section with intermediate sections

comprising a mixture of light expanded clay aggregate (LECA) together with peat and ash.

Trials

Different trials have been performed. Below two trials are presented where a water volume of 21 litres was flown through a system according to the present invention. The used filter area in the trials was 0.17 m²and the water flow out from the filter was recirculated over the system during 10 days. The same contaminated starting water (see day 0 below) was used in both trials. Below you will see the content of nitric substances measured as N tot, the content of ammonium presented as NH4-N and the phosphorous content presented as P tot.

Trial 1

Trial 2

As is clearly notable from above, already after one day the content levels of N tot, NH4-N and P tot have been reduced substantially. After yet another day, the content if further reduced, which is also the case up until around day 5. After that the content levels are more or less constant. As should be evident from above, a system according to the present invention is very effective for purification of contaminated water, such as contaminated water flows in wetlands. The purification and thus uptake by the plants are made both quickly and to a high purification level.

It should be noted the present invention enables the roots of the plants to take up contaminants and thus remove them when the plants are harvested. This also implies that the according to the present invention it may be of interest to harvest at least some of the plants from the roots and not only above the ground. Therefore, according to one embodiment of the present invention there is provided a method involving using a system intended for purification of contaminated water, and then harvesting grown plants, wherein at least some are harvested also partly from the roots.

This direction of the present invention implies that it is of interest to provide an environment which is effective for root development. Possible features are using a substrate which is effective for root development, the possibility of providing oxygen so that the roots are not inhibited by anaerobic conditions.

Claims

1. System intended for purification of contaminated water, said system comprising

- a filter unit;

- a filter substrate;

wherein the filter unit is a horizontal filter unit,

and wherein the system comprises a recirculation loop.

2. System according to claim 1 , wherein the filter unit has a depth in the range of 0.2 - 1.0 meter.

3. System according to claim 1 or 2, wherein a relationship between the length (L) of the filter unit and the width (W) of the filter unit is in the range of L = W x (3-6) and wherein an inflow side of the filter unit and an outflow side of the filter unit are arranged on the opposite shortest sides.

4. System according to any of claims 1 -3, wherein the filter unit is arranged to ensure a flow from an inflow side of the filter unit to an outflow side of the filter unit which has a flow length larger than the shortest distance between the inflow side and the outflow side of the filter unit.

5. System according to claim 3 or 4, wherein the filter unit is arranged with a flow system counteracting crossflow in the filter unit.

6. System according to any of claims 3-5, wherein the flow inside of the filter unit is collected in a mutual point before the outflow.

7. System according to any of claims 3-6, wherein the filter unit comprises individual sections to drive a water flow with increased contact time from the inflow side of the filter unit to the outflow side of the filter unit.

8. System according to any of claims 1 -7, wherein the filter unit comprises a sealing membrane.

9. System according to any of claims 1 -8, wherein the filter substrate comprises peat, ash and light expanded clay aggregate (LECA) or pumice stone.

10. System according to claim 9, wherein the filter substrate comprises 10-90 vol% light expanded clay aggregate (LECA) or pumice stone.

11. System according to any of claims 1-10, wherein the filter substrate is arranged in sections in the filter unit, and wherein the sections comprise a certain filter substrate material.

12. System according to claim 11 , wherein some sections comprise light expanded clay aggregate (LECA) and other sections comprise light expanded clay aggregate (LECA) together with peat and/or ash, preferably wherein the two end sections of the filter substrate comprise only light expanded clay- aggregate (LECA).

13. System according to any of the preceding claims, wherein the system comprises a connection with one or more wind or sun energy generation units, which one or more generation units drive water recirculation from an outflow side of the filter unit to an inflow side of the filter unit.

14. Method for purification of contaminated water, said method comprising flowing a water flow intended to be purified from an inflow side of the filter unit of a system according to any of claims 1 -13 and regulating said flow from that side of the filter unit towards the outflow side of the filter unit and out from that side of the filter unit.

15. Method according to claim 14, wherein the filter substrate is maintained at least 0.05 m above the water level.

16. Method according to claim 14 or 15, wherein the water level is regulated to adjust for the permeability of the light expanded day aggregate (LECA) or pumice stone of the filter substrate.

17. Method according to any of claims 14-16, wherein the water flow is recirculated from an outflow side of the filter unit to an inflow side of the filter unit.

18. Method according to any of claims 14-17, wherein the water flow is recirculated or converted from an outflow of the filter unit to an inflow of the filter unit in a range of 2-24 times / 24 hours.

19. Method according to any of claims 14-18, wherein fast growing crops, such as, willows, poplar, hybrid aspen, energy grass or a combination thereof, is planted in the filter substrate to form the plant growth environment.