CZ29833U1 - Apparatus for decontamination of water containing toxic metals - Google Patents

Description

The technical solution relates to the field of water purification, namely the equipment for decontamination of water containing toxic metals.

BACKGROUND OF THE INVENTION

At present, it is necessary to ecologically eliminate the increasing volume of toxic metals harmful to the environment occurring in contaminated waters. Toxic metals such as lead, cadmium, chromium, mercury, arsenic, antimony, nickel, copper and possibly zinc are important undesirable substances in wastewater with a significant environmental impact on aquatic ecosystems. They come from a wide range of industries, including, but not limited to, the chemical industry, non-ferrous metallurgy, the engineering industry (metal surface treatment), the electrical industry (printed circuit boards, etc.).

Chemical, physico-chemical and biological methods are used for wastewater treatment. One of these methods is precipitation or chemical coagulation using coagulating agents (eg Ca (OH) ₂ , NaOH, sulphides, ferric or aluminum salts, etc.) to allow the elimination of contaminated water-soluble compounds (mostly in ionic form), in the form of a small insoluble precipitate which passes into the coagulation sludge. The sludge can then be removed by settling, filtration or other mechanical methods. In water treatment, coagulation is used to remove calcium and magnesium, and to de-iron and de-manganize water. In wastewater treatment, the removal of toxic metal ions is of utmost importance. The disadvantages of this method of removing toxic metals from wastewater are mainly the low removal efficiency of alkaline metals in the form of anions (eg arsenates, antimonates), the consumption of coagulation agents and the production of larger volumes of contaminated sludge requiring further processing, will result in increased economic cost of the whole process.

Electrocoagulation methods are another group of toxic metal removal solutions. Electrocoagulation is principally similar to chemical precipitation in that it is also based on the interaction between the coagulating agent and the contaminants, which are excreted in the form of an insoluble precipitate, but the coagulating agent is generated directly in-situ. The electrocoagulation method uses an electrochemical cell, which includes a working electrode - an anode made mostly of iron or aluminum, cathode and electrolyte, which consists of a solution (waste water) containing the removed toxic metals. The electric current passes between the anode and cathode, whereby the anode is gradually oxidized, ions are released into the solution, gradually decreasing the anode and the released ions form clusters of metal oxides that sediment to the bottom and form a so-called sludge. The sedimented sludge is then mechanically removed. GB 2494299 and US 2010116650 disclose the removal of contaminants from water by this method. Electrocoagulation is a physico-chemical decontamination process, in which the dissolved metals or organic substances to be removed are transferred to sludge, which must then be removed from the purified water and treated in a similar way as in the case of chemical coagulation. The disadvantages of these solutions are, in particular, the necessity of frequent replacement of the continuously decreasing anode during the removal of toxic metals.

The object of the technical solution is to eliminate the drawbacks of the above known solutions and to create a device for decontamination of water containing toxic metals, which would efficiently and at low cost of operation decontaminate waters contaminated with toxic metals.

The essence of the technical solution

The above-mentioned drawbacks are eliminated by a device for decontamination of water containing toxic metals according to this technical solution. The apparatus comprises a reservoir for water contaminated with toxic metals and an electrocoagulation cell in which at least one pair of anode-cathode electrodes is connected, interconnected by connecting cables to the power supply. The essence of the invention is that an inverter is connected between the power supply and the electrodes

Of polarity for uniform electrolyte polarization and even anode and cathode consumption in electrocoagulation. The optimum value of the current that is fed to the electrocoagulation cell at a flow rate of purified water of 100 l.hr ^-1 is between 25 and 40 A, when the voltage then stabilizes at 3.5 to 15 V depending on the conductivity of the water, respectively. depending on the content of salts dissolved in water. The controlled electrolyte prepolarization results in an even depletion or dissolution of the anode over a period of time, and consequently the cathode over the same period of time during decontamination of toxic metal contaminated water. The dissolution time of the anode or cathode can be time controlled according to the current state and need after a set time interval. This solution also greatly extends the lifetime of the electrocoagulation cell and its operational stability, since without the pre-polarization, the cathode is gradually covered by the deposited layers of reduced metals and their oxides and salts, thus having significantly inferiority in terms of current flow. At the same time, the ecological aspect is not neglected, as the amount of waste in the form of unused cathode decreases significantly.

In a preferred embodiment, each electrode is formed by at least one plate and the plates are arranged opposite each other in a replaceable electrode cassette provided with insulated contacts, which is housed inside the electrocoagulation cell. The connection cables are insulated and pass from the polarity inverter through the sealing bushings inside the electrocoagulation cell to the insulated contacts of the electrode cassette. The contacts are sealed in this way, do not come into contact with water and the risk of personal injury or equipment damage is completely eliminated.

Preferably, the electrode cassette is provided with at least two consecutive pairs of plates of aluminum or iron based material. Each plate has a maximum thickness of 4 mm and has an area ranging from 0.1 to 0.35 m ² . The panels thus arranged have a long service life, stable operation and the possibility of decontamination of contaminated water for a long time. Preferably, the sum of the surfaces of the plates in the electrode cassette is in the range of 3 m ² to 3.5 m ² .

The storage tank is preferably connected to the electrocoagulation cell via plastic or stainless steel interconnecting piping via a circulation pump, control valve, flow sensor, pH sensor and conductivity sensor. These MaR control elements are necessary to ensure the proper operation of the electrocoagulation process, where pH values are particularly important, which must be in the range of 6 to 10 or the rate of pumping of polluted water into the electrocoagulation cell, which depends on the concentration of toxic metals in the water.

Electrocoagulation cell is preferably provided with an outlet which is connected to the coagulum homogenizer germ flakes, which is provided with an agitator rate of 250 rpm ^{the first} Rapid agitation ensures homogeneity of the formed ion flakes released from the electrodes and toxic metal ions throughout the coagulation homogenizer volume. Output coagulation homogenizer is connected to a precipitation vessel, fitted with a stirrer at a frequency of 10 to 30 rpm ^{the first} Slow agitation ensures sedimentation of the formed flakes of oxides and hydroxides of iron or aluminum with adsorbed toxic metal compounds to form sludge, which is subsequently drained.

The sedimentation tank is preferably provided with an overflow of purified water free of toxic metals and an outlet pipe of the separated sludge to the filter press, which is provided with a filtrate outlet pipe and a condensed outlet slurry outlet pipe. Purified water free of hazardous toxic metals, which is an environmental burden for the environment, is subsequently used for various applications. The thickened sludge is then removed by standard techniques such as stabilization / solidification or some metals can be recovered (eg Cu). The process of decontamination of water containing toxic metals can be set according to this technical solution in both batch and continuous mode.

In a preferred embodiment, the electrocoagulation cell is provided with an outlet that is connected to a coagulation seed flare homogenizer having a stirrer at 250 rpm. The output of the coagulation homogenizer is connected directly to the filter press, which is equipped with a filtrate outlet pipe.

The advantages of the toxic metal-containing water decontamination device according to the present invention are in particular the efficient removal of toxic metals from the water at a low cost for the operation of the plant. Another advantage is the even consumption of the anode and cathode due to the prepolari-2CZ 29833 UL of the electrode system compared to conventional electrocoagulation methods, where only the anode gradually decreases.

Clarification of drawings

This technical solution will be explained in more detail in the following drawings, where:

Fig. 1 shows a diagram of a device for decontaminating water containing toxic metals; Fig. 2 shows a tabular output of X-ray fluorescence analysis of a sedimented sludge sample after water treatment from the metallurgical industry.

Example of technical solution implementation

It is to be understood that the specific embodiments of the invention described and illustrated below are presented by way of illustration and not as a limitation of the invention to the examples given. Those skilled in the art will find or will be able to provide, using routine experimentation, more or less equivalents to the specific embodiments of the invention described herein. These equivalents will also be included within the scope of the following protection claims.

The toxic metal-containing decontamination device shown in Fig. 1 comprises a storage tank I for retaining toxic metal contaminated water. The storage tank 1 is further connected to the circulation pump 3, the control valve 4, the flow sensor 5, the pH sensor 6 and the conductivity sensor 7 to the electrocoagulation cell 8 via the connecting line 2. The connecting line 2 is made of stainless steel. be made of plastic. The electrocoagulation cell 8 is provided with plates representing six pairs of anode-cathode electrodes arranged in a replaceable electrode cassette 9 which is housed inside the electrocoagulation cell 8. The electrocoagulation cell 8 is further provided with interconnecting cables 12 for connecting the electrocoagulation cell 8 to the polarity inverter 11 allowing switching between cathode and anode for even dissolution of the electrode plates. Inverter polarity periodically changing the polarity of the direct current power source voltage generated by the 10th electrocoagulation cell 8 is further connected to a coagulation homogenizer 13 allowing rapid stirring germ flake with a speed of 250 revolutions ot.miri ^first Coagulation homogenizer 13 is connected to a settling tank 14 with slow stirring at 10 for ¹ ot.miri effective aggregation and sedimentation resulting flakes iron oxides and hydroxides. The sedimentation tank 14 is further provided with an overflow of toxic metal-free water to remove purified water from the plant, a sludge sludge outlet pipe 16 to a filter press 17, where the sludge sludge is filtered and the sludge is thickened. The filter press 17 is then provided with a filtrate outlet line 18. This arrangement is then used to decontaminate the waters contaminated with toxic metals.

Example 1

Example 1 describes a decontamination process of automotive wastewater in a plant according to the present invention in a continuous mode. The first series of tests was carried out with waste water coming from the paint shop and metal surface treatment in the automotive industry. Due to the initial pH of the wastewater at 7.1, there was no need to adjust it. Here, three independent tests, each with a starting volume of 50 L, were performed to monitor the efficiency of the electrocoagulation process as a function of increasing current applied to the electrodes. Contaminated water is passed from reservoir 1 through the electrocoagulation cell 8 with steel electrodes, wherein the Fe ions were dosed and then entering the coagulation homogenizer 13 where it was stirred at the speed of 250 rpm ot.miri ¹ and then entered into the sedimentation tank 14, in which mode has been slow agitation for 10 min at 20 rpm ot.miri ¹ and finally followed by gravitational sedimentation for 40 min. The flow rate of purified water through the electrocoagulation cell 8 was set at 50 l.hr ^-1 and the electrode dosing was for a period of 20 min. Depending on the input value of the current, the corresponding amount of iron was then dispensed. The basic technological data of the quarterly electrocoagulation test (EC) are summarized in Table 1 below.

-3EN 29833 Ul

Tab. 1 Technological data in the process of electrocoagulation OV from the automotive industry

EC mode Current [A] Voltage [V] Power [kW] Fe dosage [mg / 1] AND. 10 3.53 0.06 69.5 II. 20 May 6.40 0.12 138.9 III. 30 9.60 0.22 208.4

During the test, the color change of the purified water from greenish to light brown to brown was evident, because the Fe ²⁺ ions were gradually transformed into Fe ³⁺ oxides and hydroxides eg FeO (OH), Fe (OH) ₃ , Fe ₂ O ₃ .

During each test, samples were collected in a 1 L process beaker by performing external coagulation and sedimentation on a mixing set. Samples of incoming contaminated water and purified water were taken from the sedimentation tank 14 via a side bypass valve for analysis. The sediment sludge was not further processed or analyzed in this series of tests. The results of the analyzes of input contaminated and output purified water are summarized in Table 2.

ío Tab. 2 Parameters of input and purified water from the automotive industry in various electrocoagulation test modes.

Ozn. sample PH conductivity Zn Ni Fe TOC TIC - mS / m mg / l mg / l mg / l mg / l mg / l EC W input 6.9 725 32.2 21.3 1,02 20.8 5.2 EC Š 10A / 794 2.25 12.1 51.3 14.9 4.8 ECŠ20A / 865 0.42 6.73 39.0 14.5 4,5 EC Š 30A / 789 0.15 2.43 26.5 13.6 3.9

The presented results show an increase in the removal efficiency of all metals by the electrocoagulation process as a function of increasing the input current. In addition to metals, the total organic carbon (TOC) content of organic contamination decreased in all tests. The current value of 30 A was considered to be the limit in the configuration used, both from a technical point of view, when the cables used were designed for a maximum current of 36 A, exceeding this will cause overheating and switching off the power supply. magnetite Fe ₃ C> 4, which shows poor sedimentation properties.

Example 2

Example 2 describes a decontamination process of wastewater from the metallurgical industry in a continuous mode plant according to the present invention. The second series of tests was carried out with waste water from the non-ferrous metal industry. These are mainly waste water from the scrubbing of emissions and solid drift from high-temperature furnaces. Due to the initial pH of 7.5, no water treatment was necessary. Here, two independent tests of the continuous-mode electrocoagulation process were performed at a wastewater flow rate of 50 l / h, contaminated water passed from the storage tank and through the electrocoagulation cell 8 with steel electrodes where Fe ions were metered, then entered the coagulation homogenizer 13 agitation 250 rev / min to ensure the formation of flakes FeO (OH), Fe (OH) _3, Fe ₂ O ₃ and subsequently entered into the sedimentation tank 14 with slow stirring 10 to 20 rpm in ^{the first} The volume of the coagulation homogenizer 13 for rapid mixing was 10 L, the residence time in the coagulation homogenizer 13 was 6 min, and the volume of the sedimentation tank 14 for slow mixing 150 L with a residence time of 3 hours. The electrode dosing time was set to 40 min. Basic technological data are provided in the following table 3.

-4GB 29833 Ul

Tab. 3 Basic technological data of electrocoagulation process in wastewater treatment from metallurgical industry.

EC mode Current [A] Voltage [V] Power [kW] Fe dosage [mg / 1] II. 20 May 3.01 0.06 277.8 III. 30 4.12 0,124 416.8

Due to the high conductivity of the test effluent as shown in Table 4, which is an average of three times that of water from the automotive industry, a very low power source power is seen, which at 30 A is less than 60% compared to the automotive water test. This observation shows that the higher the conductivity of the treated water, the lower the electric energy consumption will be in the electrocoagulation process. The results of analyzes of incoming contaminated and effluent treated water from the metallurgical industry are summarized in Table 4.

Tab. 4 Parameters of input and purified water from metallurgical industry under various electrocoagulation test regimes.

Ozn. sample pH conductivity Tl CD Zn Pb TOC mS / m mg / l mg / l mg / l mg / l mg / l EC_input 7.50 2 030 27.8 1.73 1.53 0.15 24.6 EC_20A 9.13 2 070 21.2 0.020 <0.005 0,025 23.5 EC_30A 10.0 2 080 0.32 <0.001 <0.005 0,021 20.8

These results show a high removal efficiency of metals such as Cd, Zn, Pb even at low input concentrations and at the same time a slight decrease in the TOC content. Thallium is a more complex element since it is very difficult to precipitate into the form of poorly soluble compounds with a low solubility product. In the 20A mode, only 30% thallium loss occurred, but in the 30A mode, the removal efficiency exceeded 99%.

A sample of approximately 1 L was taken from the sludge after gravity sedimentation, which accounts for about 30% of the input water, which was filtered through a 0.45 μηι filter and subjected to X-ray fluorescence analysis, which provides information on the elemental composition of the matrix excluding light elements. The output of this analysis is shown in tabular form in Fig. 2. The analysis shows a high Fe content of about 83% by weight, which is due to the dissolution of the iron electrode and also the representation of other metals such as Tl, Mn, Zn, Pb, As. All these elements originally represented in the waste water were transferred to the sludge by the electrocoagulation process.

Example 3

The third series of tests was carried out with waste water from the non-ferrous metal industry. It is leakage water, the so-called landfill leachate from the landfill of inorganic substances such as fluxes and slag. Due to the initial pH of 9.5, no water treatment was necessary. Here, the continuous-mode electrocoagulation process was tested at a flow rate of 100 l.hr ^-1 for a single current value. Contaminated water is passed from a reservoir and through the electrocoagulation cell 8 with steel electrodes, wherein the Fe ions were dosed after entering the coagulation homogenizer 13 with rapid stirring 250 rpm for securing ^one of floc formation FeO (OH), Fe (OH) ₃ , Fe2O ₃ and subsequently entered into the sedimentation tank 14, with slow stirring, and 10 to 20 rpm in ^{the first} The volume of the quick-mix coagulation homogenizer 13 was 10 L and the residence time in the quick-mix coagulation homogenizer 13 was 6 min. For slow agitation in the sedimentation tank 14, the volume was 150 L with a residence time of 3 hours. The electrode dosing time was set to 60 min. Basic technological data from the quarterly EC operation test are provided in the following table 5.

-5GB 29833 Ul

Tab. 5 Basic technological data of electrocoagulation process in waste water treatment from landfill leachate of inorganic waste in metallurgical industry.

EC mode Current [A] Voltage [V] Power [kW] Fe dosage [mg / 1] AND 25 3.36 0,084 260.0

Due to the very high conductivity of the wastewater tested, as shown in the above table, a very low power source power is seen, which at 25 A reaches a value of less than 0.084 kW.

The following table 6 shows the removal of toxic metals from the landfill leachate of inorganic waste in the metallurgical industry by electrocoagulation (EC) technology.

Tab. 6 Parameters of input and purified water from landfill leachate of inorganic waste in metallurgical industry.

PH conductivity As Coll Zn CD Pb mS / m mg / l mg / l mg / l mg / l mg / l EC_Input 9.5 8 510 12.2 3.31 5.35 3.46 0.33 EC 25 A 9.8 8 480 1.9 2.43 0.01 1.24 0.009

These results show high metal removal efficiency (As, Zn, Cd), where the arsenic removal efficiency exceeded 84%.

Example 4

Example 4 describes a waste water decontamination process in a batch mode plant according to the present invention. The process for removing toxic metals from the waste water was carried out in a similar manner as in Examples 1 to 3, without the use of conveying elements of the apparatus such as a circulation pump 3, control valve 4, flow sensor 5, pH sensor 6 and conductivity sensor 7 because electrocoagulation cell 8. it is submerged in the waste water storage tank 1 and is decontaminated directly in the storage tank i.

Example 5

Example 5 describes a wastewater decontamination process in a plant according to this invention in a continuous mode. The process of removing toxic metals from the waste water was carried out in a similar manner as in Examples 1 to 3, but in which the coagulation homogenizer 13 is provided with an outlet connected directly to the filter press s7 with the outlet pipe 18 of the filtrate. The waste water therefore does not pass through the sedimentation tank 14.

Industrial applicability

The apparatus for the decontamination of water containing toxic metals according to the present invention is industrially applicable for the treatment of waters contaminated with dangerous toxic metals in a continuous operating or batch mode.

PROTECTION REQUIREMENTS

Claims (8)

An apparatus for decontamination of toxic metal-containing water, comprising a reservoir (1) for toxic metal-contaminated water, and an electrocoagulation cell (8) comprising at least one anode-cathode pair interconnected by connecting cables (12) to a source (10) and a polarity inverter (11) for uniformly polarizing the electrodes between the electrical voltage source (10) and the electrodes. -6GB 29833 Ul Device according to claim 1, characterized in that each electrode is formed by at least one plate and the plates are arranged opposite each other in a replaceable electrode cassette (9) provided with insulated contacts, which is housed inside the electrocoagulation cell (8), the interconnecting cables ( 12) are insulated and pass from the polarity inverter (11) through the sealing bushings inside the electrocoagulation cell (8) to the insulated contacts of the electrode cassette (9). Device according to claim 2, characterized in that the electrode cassette (9) is provided with at least two consecutive pairs of plates of aluminum or iron-based material, each plate having a thickness of not more than 4 mm and having an area of 0, 1 to 0.35 m ² . Device according to claim 2 or 3, characterized in that the sum of the surfaces of the plates in the electrode cassette is in the range of 3 m ² to 3.5 m ² . Device according to one of Claims 1 to 4, characterized in that the storage tank (1) is connected to the electrocoagulation cell (8) via a connecting pipe (2) of plastic or stainless steel via a circulation pump (3), a control valve (4). flow sensor (5), pH sensor (6) and conductivity sensor (7). 6. Device according to one of claims laž5, characterized in that electrocoagulation cell (8) is provided with an outlet which is connected to the coagulum with a homogenizer (13) of germ flakes, which is provided with an agitator rate of 250 rpm ¹ whose output it is connected to the sedimentation tank (14) which is provided with a stirrer rate from 10 to 30 ot.miri ^first Apparatus according to claim 6, characterized in that the sedimentation tank (14) is provided with an overflow (15) of water free of toxic metals and an outlet pipe (16) of the offset sludge to the filter press (17) which is provided with a filtrate outlet pipe (18). . 8. Device according to one of claims laž5, characterized in that electrocoagulation cell (8) is provided with an outlet which is connected to the coagulum with a homogenizer (13) of germ flakes, which is provided with a stirrer at a frequency of 250 ot.miri ¹ whose output is is connected to a filter press (17) which is provided with a filtrate outlet line (18).