MICROPOLLUTANTS AND MICROORGANISMS FROM AQUEOUS MATRICES"

Technical field

This application relates to an electrochemical reactor for the removal of micropollutants and microorganisms from aqueous matrices by electrodegradation.

Background art

The upward trend in population size will make the availability of water in sufficient quantity and quality a challenge in Europe and all over the world. The number of areas and people affected by droughts have dramatically increased in number and intensity in the European Union (EU). At least 11% of the European population, and 17% of its territory, has been affected by water scarcity to date ¹ . Around the Mediterranean (Spain, Portugal, the Italian peninsula, Southern France, Cyprus, Greece and Malta) 20% of the population lives under constant water stress and in summer, over 50% of the population is affected by water stress ² . On the other hand, the volume of wastewater generated by domestic, industrial and commercial sources has been increasing along with population, urbanization, improved living conditions, and economic development ³ . In Europe, more than 40000 million m ³ of wastewater is produced every year, but only 964 million m ³ (2.5%) of this treated wastewater is reused. In Portugal, only 1.2% of wastewater is reused.

In order to avoid water scarcity and volatile prices, the European Commission (EC) is helping to create new business opportunities and promoting innovative, more efficient and sustainable ways of producing and consuming water ¹ . As part of an integrated water management approach, water reuse is encouraged by the EC, which has adopted measures to ensure safe reuse of treated water from urban wastewater treatment plants (WWTPs) for agricultural irrigation. The Directive 2013/39/EU (2013) updated the previous Water Framework Directive, highlighting the demand to develop new water treatment solutions. In 2018, May 28, the Regulation proposed by the EC aims to alleviating water scarcity across the EU. It will ensure that treated wastewater intended for agricultural irrigation is safe, protecting citizens and the environment .

WWTPs were designed in 1980' and mostly focused on specific parameters (N, P, CQO, CBO5, TSS, E. coli). The increase of human population and consumption created a broad range of active compounds entering in sewage system. WWTPs are not ready to remove compounds with so many different physic- chemical characteristics and sometimes in vestigial concentrations .

Water is divided in 4 categories (A-D) and the technology target varying from secondary treatment+filtration+disinfection (A) to secondary treatment + disinfection (B to D). In the wastewater management sector, health and environmental concerns about the effects of micropollutants in wastewater have been increasing. Public concern increases particularly in situations where wastewater effluents are released into the environment (e.g., streams and rivers) that are then used as a raw potable water source for communities located downstream ⁴ . This especially concerns countries in Europe, where recycled water is used, not only for agricultural purposes, but also for preparation of brackish water. Micropollutants have gained increasing attention due to the ineffective elimination of many of them in conventional water and wastewater treatment plants, and the consequent detection in the aquatic matrices ⁵ . Natural attenuation and conventional treatment processes are not capable of removing these micropollutants from wastewater, surface and drinking water ^6-8 .

Curiously, tertiary treatment is the less used in WWTPs but is the one with major alternatives for fine treatment. Tertiary treatment is mostly divided in: (1) sorption processes (ion adsorption, resins), (2) filtration processes, (3) membrane separation processes, (4) advanced oxidation processes and (5) biological processes such as constructed wetlands. From (1) to (3) regeneration costs or costs associated with the cleaning or disposal of the waste stream may be a limitation. In (4) Fenton, H2O2/O2, or O3 may be catalyzed by UV light but are also expensive and require additional reagents. In (6) UV light is known to damage DNA structure avoiding microorganisms multiplication but the effectiveness is limited by turbidity not being efficient for bacteria spores, virus and lime bacteria. In (5) constructed wetlands need higher residence time and space. According to REA APA, in 2016, Portugal (Mainland), had 8.1% of WWTPs with a treatment more advanced than the secondary one; 58% of the public WWTPs are equipped with secondary treatment ¹⁰ . It is assumed that advanced treatment is only needed if the receptor medium, or the further (re)use, requires specific consideration. This is the example of eutrophication process, recreational areas, agricultural use, human consumption, etc. Tertiary treatment is only needed in areas >10 000 p.e. and water discharged in sensitive areas ⁹ . Local governments are searching for strategies to minimize micropollutants release into surface waters and/or increase of removal from wastewater, in order to ensure the health of humans and their ecosystem; but so far, successful mitigation strategies have not yet been established. Thus, successful water reuse not only depends on availability, but appropriate treatment is also essential.

The present technology provides an alternative tertiary treatment step or an add-in step, avoiding ineffective or expensive techniques, providing a final product in accordance to specific legislative parameters in the framework of water reuse. The technology developed is fully in accordance with the 7th Environmental Action Programme and, at the global level, the United Nations' 2030 Agenda for sustainable development and the achievement of the sustainable development goal n°6 "Ensure access to water and sanitation for all".

This technology focus on the removal of micropollutants and microorganisms .

Existing methods for the removal of micropollutants have some limitations including cost and effectiveness. Currently available technologies include advanced oxidation processes (Fenton, ED, photocatalysis and ozonation), membrane separation processes (ultrafiltration, nanofiltration, etc.) and photodegradation.

The benefits of the present technology are: micropollutants and microorganisms removal providing a safer wastewater to be reused, for example, in irrigation, or discharge in the water bodies, avoiding contamination spread and deleterious effects to the ecosystem and food chain.

Summary

The present application relates to an advanced electrochemical reactor for the removal of micropollutants and microorganisms from aqueous matrices comprising: a reactor chamber (2); at least four electrodes (3), wherein: the electrodes (3) are placed in a parallel configuration across the reactor chamber (2);

- the electrodes (3) are placed with their polarization interchanged between anode and cathode;

- the electrodes (3) are a flexible ribbon material with circular mesh shape made of metal mixed oxide;

- the electrodes (3) are configured in shapes selected from a circular shape or helix spring shape or double helix shape; an inlet (4) at the top of the reactor and an outlet (5) at the bottom of the reactor; a power supply (6) connected to electrodes (3); valves (7) adapted to control the periodic flow prior inlet (4) and outlet (5).

In one embodiment the metal mixed oxide of the electrodes

(3) is IrOa and RuO2/Ti.

In another embodiment the reactor (1) operates in a continuous batch mode.

In yet another embodiment the reactor (1) operates for a minimum period of 2 hours/batch. In one embodiment the area occupied by each electrode is at least 105.80 cm ² .

In another embodiment each electrode (3) is at least 20 mm wide and 0.9 mm thick.

In yet another embodiment each electrode (3) is placed at least 5 cm apart from each other.

In one embodiment the inlet (4) is positioned at the top of the reactor chamber (2).

In another embodiment the outlet (5) is positioned at the bottom of the reactor chamber (2).

In one embodiment multiple reactors are assembled in series.

In another embodiment multiple reactors are assembled in a parallel assembly.

General description

The present application provides a reactor for the removal of micropollutants and microorganisms from aqueous matrices such as, but not limited to, wastewater. If applied to wastewaters, the present technology provides a safe discharge into the environment and possible reuse for various purposes.

The present technology consists in an electrochemical reactor with electrodes to remove micropollutants and microorganisms in short periods of time, with low energy consumption, low initial investment and maintenance, easy to operate, wherein the final product can be reused, providing a circular economy, and avoiding water scarcity.

The present technology provides:

• Removal of organic micropollutants by promoting direct and/or indirect oxidation and reduction reactions;

• Removal of microorganisms and related parameters; colony forming units (CFU) reduction; E. coli reduction, possibly including other pathogens such as Salmonella spp.

It was found that in the innovative reactor design, the electrode material and shape provide not only a competitive organic micropollutant removal but also of the microorganisms.

The present technology can be added to the already existent secondary settling tank in WWTP or be implemented as a separated unit tertiary treatment. This is an advantage for the implementation of this technology as it maximizes the use and applications according to a specific need.

In a first aspect, the present application provides a reactor to remove micropollutants and microorganisms from aqueous matrices comprising:

- An electrochemical reactor, which comprises:

- an inlet and outlet for the aqueous matrix;

- valves to control the periodic flow;

- electrodes with different shapes made of metal mixed oxide (IrO2 and RuO2/Ti);

- power supply to maintain a constant current; wherein the electrodes are placed interchangeably according with the polarity (anode and cathode).

The present reactor can be a stand-alone equipment or inserted into a pipeline of reactors for removal of different contaminants from aqueous matrices. Besides the reactor, electrodes, power supply, some mechanical material such as inlets/outlets and valves, no more features (e.g. pumps) are required as the reactor takes advantage of the gravity for the matrices to get in and out of the reactor.

In the present reactor, the contaminants are not transferred to another environmental compartment, but instead, an electrochemical process degrades them.

• This technology is able to remove a broad range of micropollutants (up to 98%) and microorganisms (>4-Logio reduction), in a short period (range of hours).

Brief description of drawings

For easier understanding of this application, figures are attached in the annex that represent the preferred forms of implementation which nevertheless are not intended to limit the technique disclosed herein.

Figure 1 illustrates one embodiment of the reactor of the present application with circular shaped electrodes, wherein the reference numbers refers to: reactor (1), reactor chamber (2), electrodes (3), inlet (4), outlet (5), power supply (6), valve (7).

Figure 2 illustrates one embodiment of the reactor of the present application with electrodes of helix spring shape, wherein the reference numbers refers to: reactor (1), reactor chamber (2), electrodes (3), inlet (4), outlet (5), power supply (6), valve (7).

Figure 3 illustrates one embodiment of the reactor of the present application with helix spring shape, wherein the reference numbers refers to: reactor (1), reactor chamber (2), electrodes (3), inlet (4), outlet (5), power supply (6), valve (7).

Description of embodiments

Now, preferred embodiments of the present application will be described in detail with reference to the annexed drawings. However, they are not intended to limit the scope of this application.

The present application relates to an electrochemical reactor for micropollutants and microorganism ⁷ s removal from aqueous matrices such as, but not limited to, wastewater. In general terms, the process of treatment of contaminated aqueous matrices consists in the application of direct electric current in the contaminated matrix promoting the contaminants removal by electrodegradation and generation of strong oxidizing agents, such as hydrogen peroxide. The reactor works in a continuous batch mode 24 h per day and it does not require the addition of reagents or the control of parameters e.g. temperature.

Due to the WWTPs inefficiency, organic micropollutants are not completely removed from aqueous matrices, which typically comprise compounds such as pharmaceuticals and personal care products. Legislated microbiological parameters can be decreased. The reactor herein described is optimized in terms of cost- benefit for microorganisms and organic micropollutants comprising a broad range of physicochemical characteristics such as, octanol-water partition coefficient, solubility, etc.

Table 1 shows nine compounds which can be removed with the reactor herein described.

Micropollutants include a broad range of compounds such as pharmaceuticals and personal care products, hormone active pills, surfactants, industrial chemicals and pesticides.

The reactor also works for microbiological parameters such as removal of microorganisms and related parameters: colony forming units (CFU) reduction; E. coli reduction, possibly including other pathogens such as Salmonella spp.

The findings will increase the possibility of having a resource of quality, to be discharged or to be reused e.g. for irrigation purposes.

Table 1 - Chemical structure and properties of the micropollutants

Technical characteristics:

According to Figure 1, the reactor (1) comprises a chamber (2) comprising:

- an inlet (4) and an outlet (5) for the aqueous matrix;

- valves (7) to control the periodic flow prior inlet (4) and outlet (5);

- electrodes (3) placed interchangeably according with the polarity (anode and cathode);

- power supply (6) connected to the electrodes (3).

Reactor (1)

The reactor (1) operates for 24h per day in a continuous batch mode. In one embodiment, the reactor operates for a minimum period of 2 hours/batch, depending on the matrix characteristics. In another embodiment, the reactor operates for a period of 2 to 8 hours/batch.

This technology does not need the addition of any reagents or chemicals and the electrons naturally produced due to oxidation/reduction reactions through the electrodes are considered 'green' agents to remove the organic micropollutants and microorganisms from the aqueous matrices. The direct contact between the electrodes (anode and cathode) and the aqueous matrix promotes the removal of different pollutants thus ensuring that regulations are met for discharge or water reuse of the treated matrix.

Compartment :

The reactor chamber (2) is adapted to receive the aqueous matrices to be treated and allows the matrices to be in contact with the electrodes (3).

Electrodes:

The electrodes (3) are placed in a parallel configuration across the reactor chamber (2), and their polarization interchanges between anode and cathode, as shown in Figures 1, 2 and 3. During the removal of micropollutants and microorganisms, the electrodes (3) are in permanent contact with the aqueous matrix.

In one embodiment the reactor (1) comprises at least four electrodes (3).

The quantity of electrodes (3) varies with the reactor (1) capacity.

The electrodes (3) are made of metal mixed oxide. In one embodiment, the metal mixed oxide is IrO2 and RuO2/Ti.

The electrochemical reactor relies on several interacting mechanisms but, when using inert electrodes, the dominant and most important electron transfer reactions that occur is the electrolysis of water. As a result of the induced electric potential, electrolysis of water occurs at the electrodes, involving reduction at the cathode (reaction Rl) and oxidation at the anode (reaction R2) ¹⁰ :

Cathode: 4H ₂ 0 + 4e- 2H ₂ + 40H- (Rl) Anode: 2H ₂ O O2 + 4H ⁺ + 4e- (R2)

The organic micropollutants suffer degradation by the action of oxidizing agents, such as -OH radicals and hydrogen peroxide, produced at the electrodes. The hydroxyl radical can react with organic matter as reaction (1) indicates.

RH + -OH R· + H2O (1)

Therefore, one of the main advantages of using the electrochemical treatment is to produce this hydroxyl radical, which will react with the micropollutants present in the matrix. Other oxidizing/reducing agents can be formed in the course of the reaction, depending on the matrix characteristics and/or the adjuvants added to accelerate the process if needed.

Electrodes are a flexible ribbon material with circular mesh shape.

The electrodes (3) are configured in at least three different shapes in order to provide a suitable ratio between area covered by the electrodes and the capacity of the reactor. Thus, the electrodes (3) shapes are selected from: circular shape, helix spring shape, or double helix shape.

In one embodiment, the electrodes (3) are configured in a circular shape placed interchangeably (anode and cathode), as shown in Figure 1. In another embodiment, as shown in Figure 2, the shape of the electrodes (3) is a helix spring, also placed interchangeably. In yet another embodiment, the shape of the electrodes (3), as shown in Figure 3, is a double helix. Due to their shape, the energy spent is significantly less when compared to other electrode options reported in literature ¹ . The MMO electrodes made of IrO2 and RuO2/Ti are reported in literature as having low anodic potential, as well as, oxidation potential. Therefore, their choice for micropollutants and microorganisms removal from aqueous matrices is not obvious and it was never studied before. This material is mostly used for cathodic protection (i.e. used in concrete structure reduce costs for future repair work and extends the life expectancy.)

Moreover, this electrode material shows the advantage of being a low-cost investment, which can be 10 times less comparing with other shapes, as well as, materials. Also, the electrodes showed to be resistant even when high current intensities were applied.

The electrodes (3), their material and shape, designed for micropollutants and microorganisms removal, have the benefit of a high specific surface area available for electrochemical reactions, which allows a low energy consumption and high oxidizing agents production with subsequent high removals.

In one embodiment the flexible electrodes (3) have the minimum of 20 mm wide x 0.9 mm thick, placed interchangeably, and at least 5 cm apart from each other depending on the capacity of the reactor, as well as the electrode design chosen. For a reactor with 0.4 m ² is required at least 105.80 cm ² of area for each electrode. These dimensions are not limitative of the present technology. Additionally, the power supply (6) is connected to the electrodes (3), as shown in the Figures, and used to maintain a constant direct current to the electrodes (3). A minimum of 0.25 A should be kept during the treatment, and it varies with the size of the reactor.

Outlet and inlet:

The reactor (1) additionally comprises an inlet (4) for the untreated aqueous matrix to enter the reactor chamber (2). This inlet (4) is positioned at the top of the reactor chamber (2), as shown in Figures 1, 2 and 3 in order to facilitate the entrance of the matrix by gravity forces, no pumps are used in this process. At the bottom of the reactor chamber (2), there is an outlet (5) through which the treated matrix will come out, facilitated by gravity forces. The flow in the inlets (4) and outlets (5) is performed by tubes and controlled by valves (7). In one embodiment the valves (7) are globe valves.

In one embodiment more than one reactor (1) can be assembled in series. In another embodiment more than one reactor (1) can be assembled in a parallel assembly.

The reactor (1) herein disclosed shows the following advantages :

• high removal of organic micropollutants with low energy consumption (e.g. removals up to 98% for 0.45 and 0.90 L);

• removal of microorganisms: > 4-Logio reduction

• removal of dissolved organic matter;

• hydrogen peroxide generation;

• electrode durability and price cost;

• protection of the environment by safer effluent discharge; • low initial investment, maintenance and disassembling;

• easy to operate;

• green process, no reagents added, replicable units that decrease the treatment time or increase the treatment volume;

• no byproducts resulting from oxidation processes from specific addition of products to promote oxidation (iron from fenton, chloride promoting CIO2) that dramatically change the matrix or produce reactive products that may lead to further contamination;

• avoids filtration processes that represent high costs;

• no waste stream associated;

• reactor design allows contaminants degradation;

• do not require the use of membranes or any physical barrier separation, which avoids fouling problems or membrane saturation and regeneration;

• bypass technology with quick and easy installation in, e.g., WWTPs. Also, possible to be used in containers as long as there is place for a power supply and electrodes;

• no pH changes to the matrix required, which do not compromise the quality of the aqueous matrix, when e.g. discharged or re-used.

Examples :

Example 1

The reactor working with 0.5 L (lx anode and lx cathode; circular shape with 105.80 cm ² of area for each electrode) showed removals up to 94% in only 2 hours of 100 mA applied current. Comparing with the same electrode material (MMO electrode made of IrO2 and RuO2/Ti) but in a different shape, bar shape, significant differences (p<0.05) were found for the micropollutants considered recalcitrant i.e. harder to remove: caffeine and carbamazepine (bar shape removed less 35% and 50%). It was expected that the degradation of the compounds would increase with a higher surface area-to- volume ratio as stronger reactions are provided between the electrodes and the compounds may suffer direct and/or indirect anodic oxidation and/or cathodic reduction.

Example 2

Doubling the size of the reactor (0.9 L) and the number of electrodes placed interchangeably (2x anode and 2x cathode; circular shape with 105.80 cm ² of area for each electrode, such as shown in Figure 1, MMO electrode made of IrO2 and RuO2/Ti), a removal efficiency up to 90% was achieved for all the target micropollutant in only 2 hours of 100 mA applied current in overall reactor.

Using the same reactor an E.coli reduction of ³ 5-Logiowas obtained. The conditions of the experiment (MPN/100 mL) were: Initial sample: 1.6 E+06;

Doped initial sample (with the micropollutants of table 1): 2.0 E+05;

Sample after treatment: < 1

Example 3

The rector assembled with 2x anode and 2x cathode; helix spring with 405.4 cm ² of area for each MMO electrode made of IrO2 and RuO2/Ti and placed interchangeably, such as shown in Figure 2, to treat 18 L of matrix showed a removal up to

40% in 2 hours of 2A applied current in overall reactor. Increasing the time of contact to 8 hours the removals significantly increased reaching 98% and below the limit of detection in some cases. Caffeine and ibuprofen were the two cases where the removals were around 50%. Using the same reactor, a reduction of ³ 4-Logio of colony forming units was obtained in 8 hours of treatment.

Overall, the pH and the conductivity were kept somewhat constant throughout the treatment. The reactor does not change matrix parameters, which is a big advantage comparing with other technologies.

The project leading to this application has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 778045.

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