NL1043234B1 - Method and device for the continuous removal of micropollutants from waste water - Google Patents

Abstract

The present invention relates to a method and device for advanced oxidation of micropollutants, such as medicine traces, antibiotics and pesticides, from water, characterized by a device in which at least a continuous flow filter, a radical producing source, such as UV-C irradiation in the presence of hydrogen peroxide, and an ultrasound producing source are integrated. The continous flow filter removes turbidity from the water to be purified as welt as nutrients such as dissolved organic molecules and nitrate. The ultrasound keeps the quartz protection sleeves of the UV-C lamps clean by preventing the formation of inorganic and organic scaling caused by precipitation and co-precipitation of inorganic salts and organic molecules onto the quartz surface. At the same time, the ultrasound catalyzes disinfection and the decomposition rate of micropollutants. This synergistic effect of ultrasound on the advanced oxidation process is caused by disturbing the phospolipid structure of cell membranes of micro-organisms and by deciustering aggregates of particles passing the continuous flow compartment of the filter, thereby exposing micropollutants to radicals in the bulk of the water phase.

Description

Method and device for the continuous removal of micropollutants from waste water The present invention relates to a method and device for advanced oxidation of micropollutants, such as medicine traces, antibiotics and pesticides, from water, characterized by a device in which at least a continuous flow filter, a radical producing source, such as UV-C irradiation in the presence of hydrogen peroxide, and an ultrasound producing source are integrated.

The continous flow filter removes turbidity and dissolved organic compounds from the water to be purified as well as nutrients such as nitrate and phosphate.

The ultrasound keeps the quartz protection sleeves of the UV-C lamps clean by preventing the formation of inorganic and organic scaling caused by precipitation and co-

precipitation of inorganic salts and organic molecules onto the quartz surface.

At the same time, the ultrasound catalyzes disinfection and the decomposition rate of micropollutants.

This synergistic effect of ultrasound on the advanced oxidation process is caused by disturbing the phospolipid structure of cell membranes of micro-organisms and by declustering aggregates of particles passing the continuous flow compartment of the filter,

thereby exposing micropollutants to radicals in the bulk of the water phase.

Introduction Growing urbanization and industrial growth result in higher demands for drinking water and industrial water.

This increasingly puts stress on our ecosystem to deal with traces of micropollutants, such as medicine traces and pesticides, that are present in the effluent of municipal waste water treatment plants (MWWTPSs) and industrial waste water purification plants. in order to prevent that micropoliutants affect our environment and drinking water quality, governments are implementing legislation regarding the maximum allowed concentration of micropoliutants in waste water streams.

An example is a new Dutch law that obliges all horticulturists in The Netherlands as per January 1, 2018 to remove at least 95% of the pesticides traces from their waste water streams before the waste water is discharged.

At this moment, it is investigated and evaluated by the Dutch government how to deal with the traces of medicines and pesticides that are now discharged to the surface water through

MWWTP effluent.

Since about 90% of all medicine traces in municipal waste water originate from households, it makes sense to work towards a centralized solution i.e., to implement an extra purification step at MWWTPs.

An exception to this approach might be hospital waste water since the concentration of medicines in these waste streams is relatively high and since these waste streams also contain so called "laste resort antibiotics" resulting in an increased risk for "unintentional breeding of antibiotic resistant bacteria" if traces of the medicines end up in MWWTPs.

Hence, it makes sense to purify hospital waste water locally before the water is dicharged to the sewer.

The present invention relates to a very efficient, continuous flow, advanced oxidation (AOP) reactor system, that is feasible as an extra purification step in MWWTPs and future hospital waste water treatment plants to remove micropollutants from (pre-purified) waste water.

It is noted that the applicability of the present invention is not limited to the purification of hospital waste water and MWTTP effluent.

It is a general general treatment technique for upgrading water streams to, for example, swimming water quality.

Technical description of the present invention Advanced oxidation through UV-C irradiation combined with hydrogen peroxide and advanced oxidation through ozonation are prior art techniques to efficiently remove micropollutants from waste water.

According to literature, UVC-irradiation combined with hydrogen peroxide results in less partially oxidized molecules (metabolites of the AOP process) as compared to ozonation since the photolysis of hydrogen peroxide results in the production of very reactive OH radicals.

This is an advantage since it is known that metabolites from medicine traces and pesticides may be very toxic.

However, application of UV-C lamps for the purification of MWWTP effluent is frustrated by rapid scale formation on the quartz protection sleeves of the UV-C lamps, resulting in unacceptable cleaning cost and an unacceptable reduction of the availability of the AOP installation.

A second challenge involved with the large scale application of AOP is that the efficiency of the process considerably increases with decreasing residence time distribution in the AOP reactor.

This is caused by the fact that the AOP process is first order in the micropollutant concentration, meaning that, from a kinetics point of view, the reactor should be operated as a plug flow reactor to achieve maximum efficiency.

In other words: any backmixing of reactor product with influent will decrease the reactor efficiency and increase both the amount of required UV-C irradiation and hydrogen peroxide for purifying the water.

A third challenge is that AOP processes are strongly influenced by the presence of organic and inorganic particles in the water to be purified.

The organic particles result in turbidity in the solution thereby decreasing the efficiency of the UV-C lamps and in consumption of radicals that otherwise would be available for oxidation of micropollutants.

Finally, organic particles may also absorb or adsorb micropollutants thereby slowing down the AOP process by mass transfer limitation.

The inorganic particles cause turbidity and adsorption of micropollutants as well and thereby also inhibit the AOP process through a decrease of the efficiency of the UV-C lamps and mass transfer limitation.

The technology of the present invention provides a solution integrated in one continuous flow reactor solving all problems and challenges mentioned above.

In the following, this reactor is referred to as the MBFAOP (Moving Bed Filtration Advanced Oxidation Process).

According to a first aspect, the technology according to the present invention relates to a moving bed biofilter (MBF) as described in open literature in for example: J.P.

Kramer, H.W.

Wouters, M.P.

Noordink, D.M.

Anink, J.M.

Janus Water Sci Technol (2000) 41 (4-5):29-33. In a nutshell such moving bed biofilter is a continuous flow filter that is operated upflow,

meaning that the influent flows upward through a filter bed.

The filter is operated at continous flow conditions and the filter material is continuously cleaned inline.

Cleaning of the filter material is done through an airlift at the bottom of the filter that washes and recirculates the filter material through a central pipe.

The MBF is characterized by continous flow operation without stops for backflushing and very efficient washing of the filter bed material at low pressure drop over the filter bed.

The characteristic design of the MBF and the continuous cleaning of the filter bed material results in plug flow of the fluid above the filter bed.

In prior art, this feature of the MBF is not considered relevant since the filter performance is completely determined by what happens in the filter bed and not by the residence time distribution of the fluid above the filter bed in the MBF.

However, the inventors according to the present invention realized that the plug flow conditions above the filter bed of a MBF provides a great opportunity to integrate a UVC irradiation / H202 AOP process in the such MBF.

By installing the AOP equipment in the fluid compartment of an MBF, a separate UV-C reactor, in which special measures have to be taken to realize plug flow, can be omitted completely.

It is noted that safeguarding plug flow conditions in both the filter bed and the fluid compartment above the filter bed are essential for a good performance of an MBF in which AOP equipment is integrated.

Plug flow conditions in both the filter bed and the fluid comparment above the filter bed are realized in case there are no preferential flow channels in the filter bed of the MBF.

In a first preferred embodiment of the present invention, filter bed homogeneity is monitored real time and inline by adding a number of passive low frequency RFID tags, typically operating in the frequency range between 40 kHz and 200 kHz, to the filter bed.

The RFID tags mimic the transport behavior of the filter package material and by measuring the residence time distribution of these RFID tags, filter bed homogeneity can be calculated.

This way, deviations in filter homegeneity e.g., filter bed stagnation and clogging are recognized at a very early stage so that operating conditions of the filter can optimized.

An MBF equipped with means to monitor bed homogeneity, through application of RFID tags and / or other particles mimicking the behavior of the filter bed particles, expressly makes part of the technology according to the present invention.

In a second preferred embodiment of the present invention, the operating conditions of the MBF are chosen such that turbidity and the total concentration of organic compounds i.e., Total Organic Carbon (TOC) [mg/l], are minimum.

It is noted that a MBF effectively removes particles and aggregates of particles from MWWTP effluent.

The filter performance can be further enhanced by applying primary and secondary flocculants like polyacrylates and iron hydroxide respectively.

In a nutshell, these chemicals are able to capture micron and submicron particles that otherwise would not be removed in the filter bed and would decrease the efficiency of the AOP process in the fluid compartment of the MBFAOP.

Additionally, the filter performance can be further increased by adding a carbon-source (e.g., bio-ethanol) to the solution in order remove nitrate from the solution through biological denitrification.

Biological activity in the filter bed may also result in partial oxidation of micropollutants so that further decomposition of these compounds can be achieved at lower energy and chemical cost.

Besides these parameters also the type of filter material (particle size but also particle composition such as granular activated carbon, sand, glass beads) is an important variable to achieve the desired filter performance, depending on the water quality of the MBR influent.

Additionally, it is possible to inject air / gas into the filter bed to enhance biological processes, such as nitrification.

Finally filter bed height, fluid velocity, average particle recirculation rate and washwater flow rate are important parameters to fine tune the filtration process for optimum performance of an MBR with integrated AOP process (MBRAOP). Some none limiting typical process parameters for operating an MBR with integrated AOP process are: a cross sectional fluid upward fluid velocity of 5 m/hr, and average particle circulation rate of 5 mm/min, a surface area per filter of 7 m2, 50 RFID tags per filter, a filter bed consisting of 0.8 mm - 1 mm particles, a filter bed height of 2 m to 4 m and a height of the fluid compartment in which plug flow occurs of 2.5 m.

The mentioned process parameters that can be used to optimize the MBRAOP as well as the mentioned preferred embodiments make expressly part of the technology according to the present invention.

According to a second aspect, the present invention relates to means for oxidizing micropollutants in the fluid compartment above the filter bed, where the freshly filtered water flows upward in plug flow towards the reactor outlet.

Preferably, said means to oxidize the micropoliutants consist of UV-C lamps, hydrogen peroxide and ultrasound transducers.

The UV-C lamps preferably consist of low pressure lamps producing UV-C irradiation with a wavelength of 254 nm and / or low pressure lamps producing UV-C irradiation with both a wavelength of about 185 nm and 254 nm and / or medium pressure UV-C lamps.

Most preferably, the UV-C lamps consist of low pressure lamps producing UV- C light with a wavelength of 254 nm.

Preferably, the length of the UV-C lamps is longer than 1 meter.

Most preferably, the length of commercially available low pressure UV-C lamps with an electrical power rating between 300 Watt and 400 Watt is between 1.50 m and 2 m. lt is noted that this length is preferred since it provides a good balance between the total amount of lamps required per m2 of filter area to expose each volume element in the reactor to the desired amount of UV-C energy per m3 of water. it is further noted that the characteristic distance between 2 UV-C lamps preferably amounts 5 cm to 30 cm.

The total electrical power input for producing UV-C irradiation with low pressure UV-C lamps typically amounts between 0.3 kWh / m3 of purified water and 3 kWh / m3 of purified water in order to achieve micropoliutant removal efficiencies in the ranging from 50% to 95%. It is noted 5 that the required power input strongly depends on water quality.

In MWWTP effluent,

especially the TOC content, the concentration of organic chromophores like humic acids and turbidity strongly influence the required dose of UV-C irradiation [kWh/m3] to remove micropollutants from the water by AOP.

In a third preferred embodiment, the present invention relates to low pressure UV-C lamps producing irradiation with a wavelength of

254 nm that are placed vertically above the filter bed of an MBRAOP i.e., parallel to the upward fluid flow direction.

Preferably, the lamps are positioned in such a way that they are equally distributed over the total surface area of the filter i.e., each lamp is placed at equal distance from its direct neighbours where this distance preferably amounts 5 cm to 30 cm.

In order to produce OH radicals, hydrogen peroxide is added to the MBRAOP.

Preferably this is done just above the filter bed ensuring an equal distribution over the surface area.

In a fourth preferred embodiment, the hydrogen peroxide is dosed to the filter influent.

In that case, biological activity in the filter bed may be inhibited but on the other hand, micropollutants will already be partially oxidized in the filter bed and the hydrogen peroxide will be perfectly distributed of the surface area of the filter.

Preferably, the dosing rate of hydrogen peroxide lies between 5 g/m3 of water and 50 g/m3 of water.

It is noted that the production of OH radicals may be catalyzed by the presence of iron ions or complexed iron ions in the solution (photo Fenton reaction). In open literature, it is reported that this iron catalyzed reaction only occurs at pH<4 but the inventors of the technology in this application have found that the presence of complexing agents in waste water e.g., humic acids or partially oxidized organic molecules, may result in a significant iron ion concentration in the water being treated, even at pH values of 7<pH<8. This means that dosing iron ions or salts as secondary flocculant may also catalyze the AOP process.

The dosing of iron ions or salts as a secondary flocculant and at the same time as a catalyst for the AOP process expressly makes part of the technology according to the present invention.

According to a third aspect, the present invention relates to means for keeping the quartz protection sleeves of the UV-C lamps clean through ultrasound.

The inventors of the present invention have found that application of low pressure or medium pressure UV-C lamps for the purification of waste water results in the formation of a hard light brown to dark brown scaling layer on the quartz protection sleeves at a very fast rate i.e., within 1 to 4 weeks, thereby reducing the efficiency of the UV-C lamps to zero.

The scaling layer on the quartz protection sleeves mostly consists of calcium carbonate that is co-precipitated with organic molecules.

This happens since the UV-C lamps produce heat, resulting in a temperature of the quartz sleeves that is higher than the surrounding water.

Since the solubility of calcium carbonate decreases with increasing temperature, scaling preferentially occurs on the surface of the quartz protection sleeves.

This scaling appears to be so hard that it cannot be removed by installing mechanical wipers in the reactor system.

It might be possible to remove the scaling by acid cleaning but at the scale of an MWWTP this solution is not acceptable since it requires a lot of chemicals and results in limited availability of the process installation.

The inventors of the present invention have found that the formation of scaling on the quartz tubes can be prevented completely by installing ultrasound equipment near the quartz protection sleeves.

The ultrasound equipment comprises several ultrasound transducers that are operatively connected to cilindrical resonators with a typical length between 1 m and 2 m and a typical diameter between 1 cm and 5 cm.

The resonators are preferably made of 316 L grade stainless steel or titanium.

Preferably the cilindrical resonators are hollow except at both ends over a length between 1 cm and 10 cm.

Preferably, each resonator is operatively connected to an ultrasound transducer with an electrical power input between 50 Watt and 1 kWatt.

The transducer preferably operates in a frequency range between 20 kHz and 300 kHz, more preferably in a frequency range between 25 kHz and 100 kHz and most preferably in a frequency range between 30 kHz and 50 kHz.

Preferably, the ultrasound transducer is powered by a software configurable frequency generator and amplifier producing a frequency sweep close to the resonant frequency of the transducer - resonator system.

The resonators are preferably installed parallel to the UV-C lamps at a distance smaller than 50 cm from the lamps and the transducer is preferably not present in the water but placed above the fluid level of the

MBRAOP.

The amplifier preferably comprises a class E amplifier in which at least 5% of the total power output is dissipated in a power resistor or in the drain to source resistance of the applied power FETs.

Although counter intuitive, it appears that this approach results in a higher energy efficiency of the ultrasound system since switching current peaks and higher order oscillations are considerably suppressed this way.

It is noted that the beforementioned preferred embodiments for the ultrasound system expressly make part of the technology of the present invention.

Besides preventing scaling on the quartz protection sleeves of the UV-C lamps, it appears that the ultrasound energy also breaks up aggregates of particles, thereby setting free encapsulated micro-organisms and micropollutants.

Also, the ultrasound disturbs the phospolipid structure in the cell membrane of micro-organisms so that it becomes permeable for ions.

As a result, the ultrasound appears to enhance disinfection and to some extent also the AOP process.

Now the core elements of the present invention have been described, a number of synergistic combinations of the present invention with other technologies are described. These synergistic technology combinations expressly make part of the present invention. In a first application, the technology according to the present invention is combined with the dosing of a limited amount of ozone i.e, preferably 1 to 5 g/m3, to the influent of the MBRAOP. As a result easily oxidizable compounds will be decomposed by the ozone so that the components that are more difficult to remove can be oxidized more efficiently through the UV-C, H202, ultrasound AOP process. An important process optimization parameter for this first application is the bubble size of the ozone or ozone containing gas that is dosed to the MBRAOP. In a second application iron ions are added to the influent of the MBRAOP through electrolysis with a sacrificial iron anode.

In a third application, granular activated carbon is applied as filter material in an MBRAOP and / or the filter medium is cleaned and washed using ozone enriched air.

Clauses

1. Device for the continous removal of micropollutants and / or bacteria from water characterized by e a first fluid compartment above the filter bed in the MBF with a minimum height of 1 meter in which e atleast a first UV-C lamp is installed thereby exposing the fluid in the first fluid compartment to UV-C irradiation e Atleast a first ultrasound resonator placed in the first fluid compartment at a distance smaller than 50 cm from said first UV-C lamp e means for dosing hydrogen peroxide into the influent of the MBR or into the

MBR

2. Device according to clause 1 where particles in the filter bed consist of sand.

3. Device according to clause 1 where the particles in the filter bed consist of granular activated carbon.

4. Device according to clause 1 where the particles in the filter bed consist of glass beads.

5. Device according to one of the previous clauses 1-4 and means for dosing iron ions as a secondary flocculant and AOP catalyst.

6. Device according to clause 5 where the means for dosing iron ions comprise an electrolysis unit with iron as a sacrificial anode.

7. Device according to one of the previous clauses 1-6 and means for dosing a polymer flocculant.

8. Device according to one of the previous clauses 1-7 where said first ultrasound resonator consists of at least a stainless steel or titanium hollow cilinder with a diameter between 0.5 cm and 5 cm and a length between 10 cm and 200 cm.

9. Device according to one of the previous clauses 1-8 where said first ultrasound resonator is operatively connected to a software configurable class E amplifier characterized by at least one dissipation resistor or a group of dissipation resistors, converting at least 5% of the total electric power input of the amplifier into heat.

10. Device according to one of the previous claims 1 to 9 and means for dosing ozone to the influent of the MBF.

11. Device according to one of the previous claims 1 to 9 and means for washing the particles int the filter bed with ozone enriched air.

12, Method for the continuous removal of micropollutants and / or bacteria from water characterized by a device according to one of the previous claims 1-11. e a continuous upflow moving bed biofilter (MBF) with a filter bed consisting of particles with a characteristic diameter between 0.2 mm and 5 mm

Claims (12)

ConclusiesConclusions 1. Inrichting voor de continue verwijdering van microverontreinigingen en / of bacterien uit water gekenmerkt door e een continu doorstroomd upflow moving bed biofilter (MBF) met een filterbed dat uit deeltjes bestaat met een karakteristieke diameter tussen 0.2 mm and 5 mm e een eerste vloeistofcompartiment boven het filter bed in the MBF met een minimale hoogte van 1 meter waarin e tenminste een eerste UV-C lamp is geplaatst die daardoor de vloeistof in het eerste compartiment blootstelt aan UV-C straling e tenminste een eerste ultrasone resonator die in het eerste vioeistofcompartiment is geplaatst op een afstand van de eerste UV-C lamp die kleiner is dan 50 cm.1. Device for the continuous removal of micro-pollutants and / or bacteria from water, characterized by a continuous flow-through upflow moving bed biofilter (MBF) with a filter bed consisting of particles with a characteristic diameter between 0.2 mm and 5 mm e a first liquid compartment above the filter bed in the MBF with a minimum height of 1 meter in which e at least one first UV-C lamp is placed, thereby exposing the liquid in the first compartment to UV-C radiation and at least one first ultrasonic resonator which is in the first liquid compartment placed at a distance from the first UV-C lamp that is less than 50 cm. e middelen om waterstofperoxide te doseren aan het influent van de MBR of aan een inlaat van de MBR.e means for dosing hydrogen peroxide to the influent of the MBR or to an inlet of the MBR. 2. Inrichting volgens conclusie 1 waarbij de deeltjes in het filterbed uit zand bestaan.2. Device as claimed in claim 1, wherein the particles in the filter bed consist of sand. 3. Inrichting volgens conclusie 1 waarbij de deeltjes in het filterbed uit granulaire geactiveerde kool bestaan.The device of claim 1 wherein the particles in the filter bed consist of granular activated carbon. 4. Inrichting volgens conclusie 1 waarbij de deeltjes in het filterbed uit glas bestaan.The device of claim 1 wherein the particles in the filter bed consist of glass. 5. Inrichting volgens een van de voorgaande conclusies 1-4 vermeerderd met middelen om ijzerionen als secundaire flocculant en AOP katalysator te doseren.Device according to any one of the preceding claims 1-4, in addition to means for dosing iron ions as secondary flocculant and AOP catalyst. 6. Inrichting volgens conclusie 5 waarbij de middelen om ijzerionen te doseren uit een electrolyse-apparaat bestaan met een ijzeren opofferingsanode.Apparatus according to claim 5, wherein the means for dosing iron ions consists of an electrolyser with a sacrificial iron anode. 7. Inrichting volgens een van de voorgaande conclusies 1-6 vermeerderd met middelen voor het doseren van een polymere flocculant.Device according to any one of the preceding claims 1-6, in addition to means for dosing a polymeric flocculant. 8. Inrichting volgens een van de voorgaande conclusies 1-7 waarbij de genoemde eerste ultrasone resonator uit tenminste een roestvrij stalen of titanium holle cylinder bestaat met een diameter tussen 0.5 cm and 5 cm en een lengte tussen 10 cm en 200 cm.Device according to any one of the preceding claims 1-7, wherein said first ultrasonic resonator consists of at least one stainless steel or titanium hollow cylinder with a diameter between 0.5 cm and 5 cm and a length between 10 cm and 200 cm. 9. Inrichting volgens een van de voorgaande conclusies 1-8 waarbij genoemde eerste ultrasone resonator werkzaam verbonden is met een software configureerbare klasse E versterker met het kenmerk dat tenminste een dissipatieweerstand of een groep van dissipatieweerstanden tenminste 5% van het totale opgenomen elektrische vermogen van de versterker dissipeert.Device according to any one of the preceding claims 1-8, wherein said first ultrasonic resonator is operatively connected to a software configurable class E amplifier characterized in that at least one dissipation resistor or a group of dissipation resistors is at least 5% of the total electrical power consumption of the amplifier dissipates. 10. Inrichting volgens een van de voorgaande conclusies 1-9 vermeerderd met middelen om ozon aan het influent van de MBF te doseren.Device according to any one of the preceding claims 1-9, plus means for dosing ozone to the influent of the MBF. 11. Inrichting volgens een van de voorgaande conclusies 1-9 vermeerderd met middelen om de deeltjes in het filterbed te wassen met lucht waaraan ozon is toegevoegd.11. Device as claimed in any of the foregoing claims 1-9, plus means for washing the particles in the filter bed with air to which ozone has been added. 12. Werkwijze voor de continue verwijdering van microverontreinigingen en / of bacterien uit water gekenmerkt door een inrichting volgens een van de voorgaande conclusies 1-15 met het kenmerk dat de hoeveelheid gedoseerd waterstofperoxide tussen 5 g/m3 water en 50 g/m3 water ligt.Method for the continuous removal of micro-pollutants and / or bacteria from water, characterized by a device according to any one of the preceding claims 1-15, characterized in that the amount of hydrogen peroxide dosed is between 5 g / m3 water and 50 g / m3 water.