Process and plant for the oxidative treatment of drinking water, process water and wastewater

Abstract

Processes for the oxidative treatment of drinking water, process water and wastewater with the following characteristics: - the process water (1) to be treated and, if necessary, purified of particulate impurities is directed into a gas-filled, closed reactor vessel (3) and distributed there over an electrode stack (4) consisting of a plurality of high-voltage electrodes (15) and mass electrodes (16) provided with a dielectric (17), wherein the electrodes are subjected to high-frequency high-voltage pulses at direct current and a quasi-planar low-temperature plasma is formed at the electrodes by corona and dielectric barrier discharges, - oxygen-containing gases conducive to the generation of oxidative species, such as air, pure oxygen or oxygen-noble gas mixtures, are supplied to the reactor vessel (3), - Ozone is removed and destroyed from the reactor vessel (3) and - the treated water is then directed into a water reservoir (19), where the necessary reaction time for the more persistent, oxidative species generated in the process water (1) with other water constituents is ensured, and then discharged.

Description

[0001] The invention relates to a method and a plant for the oxidative treatment of drinking water, industrial water and waste water according to the preamble of claims 1 and 6.

[0002] Generally, oxidation processes are used in water treatment to degrade water constituents that are very difficult or impossible to remove by mechanical, biological or adsorptive processes.

[0003] In the municipal and industrial treatment of drinking water, industrial water and wastewater, various technologies are used to oxidise undesirable water constituents, which differ primarily in the type and quantity of oxidising agents produced.

[0004] The focus in research and technology is increasingly shifting towards advanced oxidation processes (AOPs). These processes involve various, often combined, processes based on the fundamental principle of directly breaking bonds in the molecular structures of organic trace substances via electrochemical, photolytic, or thermal energy input, or indirectly attacking trace substances oxidatively by generating several highly reactive species. This makes it possible to convert substances that are difficult to biodegrade into smaller, hydrophilic structures, which are often (but not necessarily) more bioavailable. Depending on the process conditions, the degradation can even proceed to the formation of short-chain carboxylic acids or even to the total conversion to carbon dioxide, water, and possibly anionic species.

[0005] The most commonly used oxidative process is ozonation. In addition, photolytic, photocatalytic and photochemical, chemical and electrochemical, and physical processes are used for specific applications—some on a large scale, but sometimes only on a laboratory scale.

[0006] The effectiveness of an AOP process is mainly discussed in the literature with the formation of short-lived but highly reactive hydroxyl radicals (•OH) (half-life < 1 µs). Hydroxyl radicals are, measured according to their standard potential (E 0 = 1.8 V at pH = 7 or E 0 = 2.8 V at pH = 0) in addition to the sulfate radicals (E 0 = 2.5 to 3.1 V) and after fluorine (E 0= 3.06 V) is the strongest oxidizing agent. In addition to certain electron transfer reactions, hydroxyl radicals initially cause hydrogen addition reactions at unsaturated carbon-carbon bonds and aromatic ring systems, as well as hydrogen abstraction at CH, NH, or OH groups. Hydroxyl radicals tend to react with larger, electron-rich molecules that offer a variety of attack points. The kinetics of such reactions are usually extremely high. Second-order reaction rates are often in the range of k ≈ 10 9 l mol -1· s -1 .

[0007] In addition to the hydroxyl radicals, many other radical species with short half-lives are directly or indirectly involved in the oxidation processes, although their oxidation potentials are lower. These species include singlet oxygen (O), the superoxide radical anion (O2), the hydroperoxyl radical (HO2), peroxyl radicals (ROO), ozonides (O3 - ) and also various nitrogen-oxygen radicals, such as peroxynitrite (ONOO - ). In the course of a variety of subsequent reactions, longer-lived oxidative species are also formed, such as ozone (O3) and hydrogen peroxide (H2O2). They can also react with organic trace substances, but much more selectively than radicals [6]. The kinetics of these reactions are usually higher by a factor of 10 compared to hydroxyl radical reactions, based on the second-order reaction rate. 6 up to 10 12smaller. However, ozone and hydrogen peroxide can in turn be the starting point for radical reactions (e.g. O3 + H2O2 → HO2• + -OH + O2 and H2O2 + e - → OH - + •OH).

[0008] FI 125772 B describes a technical system for purifying liquids based on electrical discharges generated by high-voltage pulses in a water-air mixture. The system consists of a water distribution unit that allows irrigation of the discharge reactor located below, which has two vertical plate electrodes and at least one high-voltage electrode. The pulse parameters (voltage [18-20 kV], frequency [1-1400 Hz], and pulse duration [100-400 ns]) are adjustable.

[0009] A disadvantage of this process is that the arrangement of the plate electrodes with the high-voltage electrodes in between requires a very narrow and tall reactor. The lack of ventilation or gassing in the reactor severely limits the formation of oxidative species.

[0010] RU 02136600 C1 relates to a process for treating water for drinking and industrial water supplies, wastewater treatment, and disinfection. The system consists of a reactor in the upper part of which a water-air mixture is generated by an ejector. This is additionally supplied with air by a ventilation-based aeration system, which flows through the reactor from bottom to top. The air enrichment is further enhanced by the installation of ventilation grids. The water-air mixture then passes through the electrode stack mounted below. The electrode stack is coupled to a high-voltage pulse generator. The electrode stack consists of comb-like high-voltage and ground electrodes, each coated with a dielectric.The dielectric barrier discharge then occurs in the interstitial spaces by generating high-voltage pulses, producing ozone, short-lived reactive species, and UV light, which interact with the water droplets and their constituents. The water then passes through the post-reaction chamber, which is also equipped with aeration grilles and ventilation to increase the water's contact time with the ozone formed. The treated water is then discharged from the system via a sand filter.

[0011] A disadvantage of this process is that a high concentration of residual ozone is to be expected, which makes post-treatment with polymer membranes, for example, impossible. Although excess ozone in the water phase can be removed with an activated carbon filter, this results in constant consumption of activated carbon, which results in additional costs. In this configuration, the water residence time can only be controlled via the flow, which becomes critical if a longer water treatment time is necessary, as this reduces the contact time of the water with the plasma and thus the formation of oxidative species. A large ozone-containing gas space exists above the water surface in the post-reaction chamber, resulting in a low ozone concentration in the aqueous phase.

[0012] CN 103496761 A relates to the field of wastewater treatment based on combined plasma, ultrasound, and UV treatment. Here, the process gas and water are mixed together in the atomizer nozzle and introduced into the system as a fine mist above an electrode stack. The water passes through the electrode stack, which consists of a multitude of rod-shaped electrodes with dielectric barriers (closed quartz glass tubes) and a high-voltage pulse generator. The system is housed in an "ozone collection tower," the lower end of which is connected to a "box reactor." The treated water and the resulting ozone enter this tower and are in contact through the open water surface.When the box reactor reaches a certain fill level and the ozone concentration is high, an ultrasound treatment system, a UV lamp, and an aeration unit installed in the bottom (with air supply + air pump + gas flow meter + ozone concentration measurement) are activated. The water is mixed in the box reactor using a circulation pump. The ozone then reacts with the water constituents in the box reactor. If the water does not meet the quality target determined by a simultaneous water quality analysis, it is recirculated via the atomizer nozzle and the electrode stack.

[0013] Once the quality target has been met, the process water is transferred to a filter tank, which in turn is connected to a downstream water storage tank. If the water in the storage tank does not meet the quality target due to turbidity, the water is returned via the filter tank.

[0014] The system features a water chemistry measuring section, as well as flow meters and water level indicators, all of whose data is fed into a data recording and control unit. A photovoltaic-based power supply is provided.

[0015] A disadvantage of this process is that there is no regulation or controllability of the high voltage. Simultaneous mixing of air and the water to be treated is very expensive due to the necessary compressor operation. Simultaneous mixing of air and the water to be treated is critical due to the risk of clogging.

[0016] DE 44 40 813 A1 describes a process for treating liquids. It involves converting pollutants or undesirable substances into harmless compounds that can remain in the water, followed by disinfection. The process combines ozone treatment with UV irradiation. The liquid to be treated is dripped or nebulized before passing through the electrodes, but without touching the electrode area, in order to mix process gases, i.e., ozone, generated during plasma formation, into the water.

[0017] The water must not completely fill the discharge chamber, as otherwise a dielectric short circuit would occur and a gas discharge would not be ignited. Only a thin film of water can pass through, and likely only an extremely low flow rate. This configuration is not suitable for industrial-scale application.

[0018] DE 199 51 117 A1 describes a process known as the "KVOLTOX" process. The system consists of a high-voltage reactor that can be independently fed with any gas (of any composition, even without O2 content) and water (of any conductivity, turbidity, and color) in the form of a trickling film. The gas and liquid phases are separated by the free water surface. The background of the process is the formation of redox-reactive substances via corona discharge above, on, and in the aqueous phase and the subsequent reactions with water constituents, without the need for additional (chemical) agents.

[0019] The process appears to be of little use, since the water film thickness for a flat corona discharge can be only a few mm (at most 3 mm). With a reactor area of ​​1 m 2Only 3 liters could be treated. Furthermore, approximately 100 electrode tips would be required for a reasonably large discharge. A high concentration of residual ozone is to be expected. No provision is made for removing other oxidizing agents remaining in the aqueous phase.

[0020] DE 10 2007 028 580 A1 relates to a device consisting of a reactor through which liquids can flow, containing opposing flat stainless steel electrodes with a porous ceramic coating spaced 1 to 3 mm apart, in which pulsed corona discharges are generated. The minimum voltage requirement is 12 to 15 kV, and the pulse width is 10 to 100 ns. The invention specifically relates to specifications of the electrode configuration and the coupling with a high-voltage pulse generator, which is intended to fulfill the task of cleaning and disinfecting liquids.

[0021] EP 1 782 841 A1 relates to the use of atmospheric plasma and chemical photocatalysis for the treatment of liquids and / or gases. The field of application extends to the disinfection and purification of drinking water and industrial wastewater, antifouling of industrial cooling water systems, remediation of contaminated surface and groundwater sites, organic farming including hydroponics, and the purification and disinfection of industrial and recreational water systems.

[0022] The device can be operated either as a batch process or as a closed circuit, or with continuous flow, with respect to the gas and liquid phases. The process gases generated during the plasma discharge are to be reused as far as possible in the closed process. The invention has a modular design and can therefore be adapted to higher throughput requirements. The generated plasma is not generated in the gas-water mixture. Therefore, highly reactive species cannot react at the water surface or directly with the target substances in the water. The photocatalytic effect is limited to the interface between the aqueous phase and the catalytically active support material and is therefore ineffective for industrial purposes.

[0023] The cited prior art has general disadvantages. For example, an ozone generator requires dry air or pure oxygen to produce ozone. The ozone generator itself requires only a relatively low power consumption. However, the air drying device or the provision of pure oxygen are the actually relevant cost factors. Conventional ozonation primarily uses ozone as an oxidizing agent. However, this is particularly ineffective against water constituents with σ-bonds and many functional groups. Furthermore, it is known that when ozone is used, only a small portion of the organic matter contained in the water is mineralized, i.e., completely converted into CO2 and H2O.

[0024] Photocatalytic processes are only active at the interface between the light source, possibly the semiconductor material, and the water phase. These processes require a complex reactor geometry. Undesirable polymerization reactions can occur due to a lack of oxygen.

[0025] Electrochemical processes may require stringent pH adjustment of the process water and the addition of certain additives (e.g., H2O2). Furthermore, the use of certain electrodes can result in locally high overvoltages, which promote the formation of halogenates and other species toxic to humans.

[0026] Electrolysis processes can produce hydrogen. This must be safely removed. This involves considerable effort. Scale formation on the electrodes is a major problem. Electrodes in electrolysis processes are subject to significant wear.

[0027] Physical processes are generally of little practical relevance, are only partially effective and are sometimes not permitted by drinking water regulations.

[0028] The object of the invention is to propose a process and a plant for the oxidative treatment of drinking water, industrial water, and wastewater. The treatment should be possible on an application-oriented scale without chemical additives, with flexible plant control in terms of electrical, hydraulic, and atmospheric control elements, with simultaneous data acquisition, and with safety features. By generating highly oxidative species, even persistent water constituents should be removed with minimal effort. Effective post-treatment should be enabled.

[0029] The object is achieved according to the invention by the subject matter of claims 1 and 6. Further features are described in subclaims 2 to 5 and 7 to 13.

[0030] In this process for the oxidative treatment of drinking water, industrial water, and wastewater, the process water to be treated, purified of particulate contaminants if necessary, is fed into a reactor vessel and distributed there via an electrode stack. The electrodes are subjected to high-frequency, high-voltage pulses using direct current. Corona and dielectric barrier discharges create a quasi-areal low-temperature plasma at the electrodes. The treated water is then fed into a water reservoir. There, the necessary reaction time is ensured for the persistent oxidative species generated in the process water. The treated water is then discharged.

[0031] According to the invention, the process water is distributed in a closed, gas-filled reactor vessel via an electrode stack consisting of a plurality of high-voltage electrodes and ground electrodes provided with a dielectric. Gases conducive to the generation of oxidative species are fed into the reactor vessel. Ozone is extracted or expelled from the reactor vessel and destroyed. The gases supplied can be air, pure oxygen, or oxygen-noble gas mixtures, for example, with argon.

[0032] In a special design, the water from the water reservoir is returned to the reactor vessel and distributed again.

[0033] The properties of the low-temperature plasma can be changed by varying the voltage, pulse width and pulse frequency via the settings on the high-voltage pulse generator.

[0034] The properties of the low-temperature plasma can be changed by varying the quantity and composition of the gases or gas mixtures.

[0035] Gas exchange takes place at a free water level in the reactor vessel to remove ozone from the gas and water phases.

[0036] After extraction and subsequent thermal destruction of ozone, exhaust air cooling should preferably be carried out.

[0037] The system used to carry out the process has an inlet of process water to be treated, which is distributed via a distribution device into a reactor vessel containing an electrode stack, for example, by spraying or atomizing it with a nozzle. The electrodes in the electrode stack can be subjected to high-frequency high-voltage pulses using a high-voltage pulse generator operating at direct current. A flat, low-temperature plasma is formed at the electrodes by corona and dielectric barrier discharges. The reactor vessel is connected to a water reservoir from which the treated water can be drained.

[0038] According to the invention, the electrode stack consists of at least one row of several high-voltage electrodes arranged side by side and at least one row of several ground electrodes provided with a dielectric. The high-voltage electrodes and the ground electrodes are arranged at an angle of 5° to 45° relative to the horizontal. The water flowing over the electrode stack is connected to a separate water reservoir via an outlet. Two connections on the reactor vessel enable the supply and removal of gases conducive to the generation of oxidative species. A thermal ozone destructor is connected to the closed reactor vessel.

[0039] In a preferred embodiment, a row with several ground electrodes arranged next to each other is always arranged between two rows each with several high-voltage electrodes arranged next to each other.

[0040] The reactor vessel is designed to be conical or round and the distribution device and the electrode stack arranged therein are positioned so high that no static gas space can form above the distribution device.

[0041] For multiple recirculation, a return line can lead from the water reservoir into the reactor vessel.

[0042] The connections for the supply and removal of gases conducive to the generation of oxidative species should preferably be located diagonally opposite each other.

[0043] An exhaust air cooler is advantageously arranged downstream of the thermal ozone gas destroyer to cool the discharged gases.

[0044] An activated carbon filter can be arranged in the process water effluent after the water reservoir.

[0045] In the reactor vessel there is a free water level, for example in the form of a sump, at which gas exchange can take place, for example by exchange with different concentrations of ozone still contained in the water, which can reduce the ozone concentration in the water even further.

[0046] The volume of the water reservoir can be changed by varying the number of individual segments of the water reservoir.

[0047] The process engineering core of the present invention is based on the fact that, in a reactor vessel shielded from the outside, water and air (or alternative process gases or gas mixtures) are mixed together and transferred into a low-temperature plasma in which highly reactive oxidative species are formed in situ and react simultaneously with the water constituents carried in the water.

[0048] The mixing of water and gas is preferably done via an atomizing nozzle. It then passes through the low-temperature plasma directly below as a fine mist.

[0049] The low-temperature plasma is generated in the area of ​​an electrode stack system, which consists of a large number of layered high-voltage and ground electrodes with dielectric.

[0050] A high-voltage pulse generator generates high-frequency high-voltage pulses with a very short rise time and transmits them to the high-voltage electrodes. Within a few nanoseconds, the application of a limited discharge current (Townsend phase) causes a significant acceleration of the naturally present free electrons in the few millimeter gaps between the high-voltage and ground electrodes. The initiated current increases linearly, but is limited by the number of free charge carriers and reaches a maximum – the saturation current.

[0051] A further increase in voltage exceeds the ignition voltage, at which point the acceleration of the electrons becomes so great that their kinetic energy is sufficient to release further electrons through collision reactions with gas and water molecules and ions. The number of electrons multiplies, resulting in an avalanche formation, which increases the current practically independently. Filamentary, irregularly distributed micro-discharge channels are formed across the entire electrode stack surface. During this phase, numerous excitation, ionization, and recombination processes occur, during which at least 75 reactive, mostly very short-lived species are formed in the water-air mixture in more than 500 reactions. These species then react in situ with the organic trace substances in the water matrix.The presence of water in the spaces between the high-voltage and ground electrodes reduces the formation of ozone, but promotes the formation of hydroxyl radicals through electron attachment to the water, through the dissociation of the water caused by the action of electrons, or through subsequent reactions of water with singlet oxygen.

[0052] As time progresses, the electrons gather in front of the dielectric of the ground electrodes (anode barrier), resulting in a self-reinforcing acceleration of the free charge carriers in the gas gap between the high-voltage and ground electrodes. This results in an increase in the internal electric field and a consequent shift in the external electric field, which triggers photoelectrons. These form the basis for the formation of secondary avalanches, which ultimately create conductive channels, the "streamers," and thus deposit more and more electrons on the anode barrier ("streamer phase"). While hardly any ozone is formed during the primary phase, most of the ozone is formed during this period. The internal field in front of the ground electrodes eventually grows to such an extent that the external electric field is weakened to such an extent that the conductive channel breaks open and the discharge extinguishes (decay phase).The internal electric field then remains for the period in which the electrons have not yet flowed away. In order for the discharge process to be initiated again, the external electric field must be temporarily switched off.

[0053] The creation of low-temperature plasma using dielectric barrier discharge is thus possible by applying alternating current. However, with regard to the generation of oxidative species, the method using high-frequency pulsed direct current has proven to be significantly more effective.

[0054] The invention is a compact water treatment solution that can be used both stationary and mobile. Its electrical and hydraulic design allows for very flexible control. The process according to the invention essentially requires no additives. However, they can also be used if necessary. It is designed so that, with continuous flow of the process water, the water can be simultaneously pumped multiple times over the electrode stack, allowing the water to be treated multiple times.

[0055] The system can be operated with normal air, although it is also possible in principle to operate it with other oxygen-containing process gases. The power consumption of the high-voltage pulse generator used in the invention is below the level of an ozone generator with an ozone production of approximately 10 g / h. A large number of highly reactive oxidative species are initially formed and introduced in situ into the water to be treated. Due to the generation of a large number of different species, a more extensive degradation of complex molecular structures is possible.

[0056] The invention involves the formation and mixing of the oxidizing agents in a single step at atmospheric pressure. Unlike other ozonation systems, no special safety measures such as a pressure vessel are necessary. Unlike photocatalytic processes, the entire water phase is enriched with oxidizing agents. This results in more efficient degradation of the organic water constituents. Furthermore, this also prevents fouling problems in water treatment. Unlike photocatalytic processes, no complex reactor geometry is required.

[0057] The concentrations of oxidative species in the low-temperature plasma can be controlled by varying the electrical parameters of the high-voltage pulse generator and by regulating the gas supply and removal in the area of ​​the electrode stack. Furthermore, the supply and removal of gases also causes a continuous gas exchange in the rest of the reactor, which has the effect that the ozone entrained in the water in the reactor sump is almost completely expelled before it passes through the outlet. A key advantage of this is the very short post-reaction time required between the remaining persistent oxidative species and the water matrix, which allows the water reservoir and the downstream activated carbon filter to be extremely small.This configuration allows for a direct downstream connection of a membrane system for further water treatment, which would not be possible with the current state of the art due to the destruction of the membrane by residual ozone.

[0058] The invention is explained in more detail below using an exemplary embodiment. The figures show: Fig. 1 high-voltage pulse system for the treatment of liquids Fig. 2 reactor vessels

[0059] The plant is designed to degrade persistent organic trace pollutants by in situ generation and transfer of hydroxyl radicals, ozone, and other species with unpaired bonds to the aqueous phase.

[0060] Substances that are difficult to degrade in drinking water include humic substances and their precursors, active pharmaceutical ingredients and other organic trace substances whose molecules predominantly contain σ-bonds and many functional groups.

[0061] An example is shown in Fig. 1. It shows a possible configuration of a high-voltage pulse system for the treatment of liquids, preferably drinking water, industrial water, and wastewater.

[0062] In the present embodiment, the process water 1 to be treated is pumped to the reactor vessel 3 by means of a pump 2, for example, a centrifugal pump or alternatively a submersible pump. Depending on the application, the process water 1 can be drawn from a free water surface, for example, from a well, or, in industrial applications, from a pipe or sewer system or from a storage tank. The pump 2 can be controlled via a frequency converter or an external controller via a programmable logic controller (PLC).

[0063] The process water 1 is pumped towards the reactor vessel 3 with the electrode stack 4 contained therein.

[0064] Pressure- and chemical-resistant tubing made of polytetrafluoroethylene (PTFE) is used as the transport medium. Alternatively, piping made of stainless steel and / or polyvinyl chloride (PVC) or other pressure- and chemical-resistant materials is also possible.

[0065] The flow is monitored by a turbine flowmeter 5 with a Hall sensor with coupled readout and storage functions. Other flow sensors, such as float sensors, could also be used.

[0066] The process water 1 is cleaned of particles ≥ 100 µm in diameter via a dirt trap 6 before passing through the reactor vessel 3. Any blockages in the transfer line to the reactor vessel 3 can be detected by a readable pressure sensor 7.

[0067] The process water 1 is atomized inside the reactor vessel 3 at its upper end by means of a distribution device 8 designed as a mist nozzle. The upper part of the stainless steel reactor vessel 3 is pyramid-shaped, thus following the shape of the spray cone 9 below the mist nozzle. This ensures that the spray cone 9 covers the entire cross-section of the outwardly shielded gas space of the reactor vessel 3.

[0068] Below the distribution device 8 is the also cuboid-shaped electrode stack 4 located in the cuboid-shaped middle part of the reactor vessel 3. The distribution device 8 is connected to the reactor vessel 3 by an adaptable thread and can be positioned such that the resulting spray cone 9 wets the entire surface of the electrode stack 4.

[0069] The distribution device 8 can be replaced as needed, i.e., depending on the desired water flow rate and the fineness of the atomization. It is accessible via the removable, sealed front panel of the center section of the reactor vessel 3. In principle, the installation of all types of single-medium atomizing nozzles is possible, for example, solid cone or hollow cone nozzles.

[0070] The interior of the reactor vessel 3 is further supplied with air or, if necessary, other process gases or gas mixtures at atmospheric pressure from the outside via a ventilation connection 10. The ventilation connection 10 is located in the pyramid-shaped part of the reactor vessel 3 below the electrode stack 4.

[0071] The gas or gases are supplied either via a ventilation device or via a hose or pipe connection to a pressurized system (compressor, compressed gas cylinder, or similar). The process gas flow is controlled by a float meter with a control valve or similar device, optionally with readout and storage functions.

[0072] The process gas is removed via an exhaust port 11, identical in size to the inlet port, which is connected to a thermal ozone gas destruction system 12 with subsequent exhaust air cooling 13. The exhaust port 11 is positioned diametrically opposite the gas inlet 10, so that the spatial diagonal runs directly through the electrode stack system 4. This ensures a continuous supply and removal of the beneficial process gases throughout the entire area of ​​the electrode stack 4, thereby maximizing the formation of oxidative species.

[0073] The ozone-containing air discharged from reactor vessel 3 is fed via a stainless steel hose 14 to a thermal ozone destructor 12. There, the gas is heated to at least 320°C, kinetically forcing the reaction of ozone to oxygen. Commercially available catalytic ozone destructors 12 are unsuitable due to the toxic effects of accompanying nitrogen oxides, as are activated carbon-based ozone destructors, which pose a significant fire hazard due to the exothermic reaction of the activated carbon with ozone in the gas phase.

[0074] To ensure the safety of the plant operators, the hot exhaust gas stream is transferred via a thermally insulated stainless steel hose 14 to an exhaust air cooler 13. The inlet is located at the bottom of the plant section. The rising air is cooled to below 50°C via two separate copper cooling coils, each of which is fed with water at a temperature of 1 to 20°C at a rate of at least 1 l / h. The ozone gas destroyer 12 and the exhaust air cooler 13 were dimensioned in this specific case for an air flow of maximum 8 Nm. 3 / h. However, the dimensions can be scaled upwards or downwards as required. The water vapor carried in the exhaust air condenses on the cooling coils.

[0075] The water is collected in a reservoir below the cooling column and can be drained through a drain line after the plant is shut down.

[0076] The electrode stack system 4 located in the reactor vessel 3 is coupled to an external high-voltage pulse generator 26 on the high-voltage and ground sides via two shielded cables. The electrode stack system 4 is also connected to a building ground. The high-voltage pulse generator 26 generates negative high-voltage pulses whose amplitude (voltage U = 0..30 kV), width (pulse duration t = 20..500 ns), and frequency (f = 0..10 kHz) can be controlled via the high-voltage pulse generator.

[0077] The electrode stack system 4 consists of a cuboid-shaped PVC housing with round, rod-shaped electrodes 15, 16 built into it. The 18 electrodes 15, 16, shown here, are arranged parallel and equally spaced at a distance of 6 mm in three levels. The inserted electrodes 15, 16 of each level are connected to each other by busbars, which are connected to the cables leading to the high-voltage pulse generator 26.

[0078] The middle level comprises the ground electrodes 16 coated with quartz glass as dielectric 17. The electrode levels above and below each consist of individual high-voltage electrodes 15 made of stainless steel without dielectric 17. Between the high-voltage electrodes 15 and the ground electrodes 16, a limited, planar and pulse-shaped discharge current is initiated, which causes diverse ionization processes both in the gas and at the interface of the water droplets depending on the high-voltage pulse shaping.

[0079] This results in the formation of a large number of highly reactive, oxidatively effective, but with the exception of ozone and hydrogen peroxide, mostly very short-lived species, which interact with the ingredients of the aqueous matrix.

[0080] The process water 1 sprayed into the electrode stack 4 partially collects on the surfaces of the electrodes 15, 16. To prevent water accumulation in the spaces between the electrodes and the resulting problem of uneven discharge between the electrode stack levels, the electrode stack 4 is tilted by 5° relative to the horizontal. This causes the water to flow along the electrodes 15, 16 and is evenly distributed. This also reliably cools the electrodes 15, 16. Depending on the process water volume flow, a steeper inclination of the electrodes 15, 16 may be necessary. For this purpose, the entire reactor vessel 3 can be tilted as needed. Accordingly, adjustable suspension or tilting devices are attached to the four outer sides of the reactor vessel 3.

[0081] After passing through the electrode stack 4, the water flows by gravity to the outlet 18 at the bottom of the reactor vessel 3. The reactor vessel 3 is pyramid-shaped below the electrode stack 4, mirroring the top. As a result, the process water 1 is collected centrally above the outlet 18 and slightly dammed or, as in Fig. 2 is collected in a sump 30. A free water level 31 is formed, through which residual ozone can escape from the water. This prevents ozone-enriched water from leaving the reactor vessel 3, while allowing sampling 29 of the aqueous phase to be taken from the side of the outlet 18 or the sump 30. Depending on the angle of inclination of the reactor vessel 3, three outlet positions are provided.

[0082] The water at the outlet 18 of reactor vessel 3 is transferred via a hose or pipe into a stainless steel water reservoir 19 located below. Because no gas phase escapes from reactor vessel 3 via this route, no gas space forms in water reservoir 19. The ozone dissolved in the water cannot escape. As a result, water reservoir 19 forms a secondary reaction space. The efficiency of this system component depends on the ozone concentration in the water, the properties of the water matrix, and the reaction kinetics of the ozone and its byproducts with the respective water constituents.

[0083] The most important control element here is the water's residence time. This is controlled, on the one hand, by the selected volume flow of the process water. On the other hand, the residence time depends on the volume of the water reservoir 19 itself. This can be adjusted in this system by the segmented design of the water reservoir 19. Depending on requirements, any number of flange-like individual segments 20, which feature ozone-resistant seals, can be bolted together and to a base and cover plate. Equivalent to the inlet, the water is drained from the bottom of the water reservoir 19 via an activated carbon filter 21 and a drain 28. The drain line to the activated carbon filter 21 is arranged so that its highest point runs above the water reservoir 19. This prevents the water reservoir 19 from draining.

[0084] Furthermore, a mixing of the water in the water reservoir 19 is provided. From the mixing unit 22, designed as a pump, a branch is installed to a water chemical measuring section with probes 23. The measuring section consists of a variable area flow meter for flow control, a measuring probe socket with pH - , conductivity and ozone electrodes, associated analog-to-digital converters, and a display, measuring, and storage unit. The water is then returned to the water reservoir 19 via a ball valve connection at the top of the water reservoir 19.

[0085] On the underside of the water reservoir 19, there is also a line to another controllable pump 24, for example, a gear or centrifugal pump, which can be used to pump the water back to the point of water atomization via the distribution device 8 in the reactor vessel 3 as needed. The flow can be regulated via a PLC control or directly at the frequency converter of the pump 24 and can be read via a turbine flow meter 25 with a Hall sensor. This enables a controlled statistical multiple transfer of the water over the electrode stack 4.

[0086] Another possible connection at the bottom of the water reservoir 19 may be available for sampling the aqueous phase. List of reference symbols 1 Process water 2 pumps 3 reactor vessels 4 electrode stacks 5 turbine flow meters 6 mud flaps 7 Pressure sensor 8 Distribution device 9 spray cones 10 Ventilation connection 11 Exhaust air connection 12 ozone gas destroyers 13 exhaust air coolers 14 stainless steel hose 15 high-voltage electrodes 16 ground electrodes 17 Dielectric 18 Outlet 19 Water reservoir 20 individual segments 21 activated carbon filters 22 Mixing unit 23 probes 24 Pump 25 turbine flow meters 26 High-voltage pulse generator 27 Return line 28 Procedure 29 Sampling 30 swamp 31 free water level

Claims

[1] Process for the oxidative treatment of drinking water, industrial water and waste water with the following characteristics: - the process water (1) to be treated and, if necessary, purified from particulate contaminants is fed into a gas-filled, closed reactor vessel (3) and distributed there via an electrode stack (4) consisting of a plurality of high-voltage electrodes (15) and ground electrodes (16) provided with a dielectric (17), wherein the electrodes are subjected to high-frequency high-voltage pulses at direct current and a quasi-areal low-temperature plasma is formed at the electrodes by corona and dielectric barrier discharges, - oxygen-containing gases, such as air, pure oxygen or oxygen-noble gas mixtures, which are conducive to the generation of oxidative species are fed into the reactor vessel (3), - Ozone is removed from the reactor vessel (3) and destroyed and - the water thus treated is then fed into a water reservoir (19), where the necessary reaction time for the more persistent, oxidative species generated in the process water (1) with other water constituents is ensured, and then discharged. [2] Method according to claim 1, characterized by that the water from the water reservoir (19) is returned to the reactor vessel (3) and distributed again. [3] Method according to claim 1 or 2, characterized by that the properties of the low-temperature plasma can be changed by varying the voltage, pulse width and pulse frequency via the settings on the high-voltage pulse generator (26). [4] Method according to one of claims 1 to 3, characterized by that the properties of the low-temperature plasma can be changed by varying the quantity and composition of the gases or gas mixtures. [5] Method according to one of claims 1 to 4, characterized bythat after extraction and thermal destruction of ozone, exhaust air cooling takes place. [6] Plant for carrying out a method according to one of claims 1 to 5 with the following features: - an inlet of process water (1) to be treated flows via a distribution device (8) into a reactor vessel (3) with an electrode stack (4), wherein the electrodes in the electrode stack (4) can be subjected to high-frequency high-voltage pulses by means of a high-voltage pulse generator (26) at direct current, and wherein a quasi-areal low-temperature plasma can be formed at the electrodes by corona and dielectric barrier discharges, - the electrode stack (4) consists of at least one row with several high-voltage electrodes (15) arranged next to one another and at least one row with several ground electrodes (16) arranged next to one another and provided with a dielectric (17), - the high-voltage electrodes (15) and the ground electrodes (16) are arranged at an angle of 5° to 45° relative to the horizontal, - two connections (10, 11) on the reactor vessel (3) enable the supply and removal of oxygen-containing gases, such as air, pure oxygen or oxygen-noble gas mixtures, which are conducive to the generation of oxidative species, - a thermal ozone gas destroyer (12) is connected to the closed reactor vessel (3) and - the water passed over the electrode stack (4) flows via an outlet (18) into a separate water reservoir (19) and can be drained from there. [7] Plant according to claim 6, characterized by that a row with a plurality of ground electrodes (16) arranged next to one another is always arranged between two rows with a plurality of high-voltage electrodes (15) arranged next to one another. [8] Installation according to claim 6 or 7, characterized bythat the reactor vessel (3) is designed to be conical or round and the distribution device (8) and the electrode stack (4) arranged therein are arranged so high up that no static gas space can form above the distribution device (8). [9] Installation according to one of claims 6 to 8, characterized by that a return line (27) leads from the water reservoir (19) into the reactor vessel (3). [10] Installation according to one of claims 6 to 9, characterized by that the connections (10, 11) for the supply and removal of gases conducive to the generation of oxidative species are diagonally opposite each other. [11] Installation according to one of claims 6 to 10, characterized by that the thermal ozone gas destroyer (12) is followed by an exhaust air cooler (13). [12] Installation according to one of claims 6 to 11, characterized by that an activated carbon filter (21) is arranged after the water reservoir (19) in the process water outflow. [13] Installation according to one of claims 6 to 12, characterized by that the volume of the water reservoir (19) can be changed by varying the number of individual segments (20) of the water reservoir (19).

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