Method for treating a permeate from a mobile water treatment plant

Abstract

Method for the preparation of a permeate (13) obtained from a reverse osmosis separation stage (10) of a mobile water treatment plant, comprising the steps: • Production of a stock solution (50) by dissolving sodium bicarbonate in water and stirring in one or more chemicals for chlorination selected from the group containing calcium hypochlorite, sodium hypochlorite, sodium dichloroisocyanurate and sodium dichloroisocyanurate dihydrate, • Addition of the stock solution (50) to the permeate (13) to obtain a stabilized and chlorinated permeate such that, after addition of the stock solution (50), the stabilized and chlorinated permeate (13) contains 30 to 50 mg / L sodium bicarbonate and 0.1 mg / L to 5.0 mg / L free chlorine.

Description

[0001] The invention relates to a method for processing a permeate obtained from a reverse osmosis separation stage of a mobile water treatment plant.

[0002] EP 0 352 779 A2 describes a mobile water treatment plant with a reverse osmosis system. The resulting permeate is treated with a mixed-bed ion exchanger, a salinization unit, an ozonation unit, an activated carbon filter, and a depot chlorination unit.

[0003] DE 10 2005 004 063 A1 discloses a process for producing a sodium hypochlorite solution. The sodium hypochlorite solution is used to treat a permeate obtained from a reverse osmosis separation stage of a mobile water treatment plant.

[0004] US Patent 5,788,858A depicts a mobile water treatment plant with a reverse osmosis separation stage. To protect components of the reverse osmosis separation stage, the raw water, if chlorinated, is passed through a pre-treatment dechlorination unit.

[0005] German patent DE 44 46 211 C1 concerns a mobile water treatment plant. The reverse osmosis separation stage used can also process raw water contaminated with chemical warfare agents.

[0006] US Patent 2014 / 0021115A1 discloses a process for treating permeate obtained from a reverse osmosis stage of a mobile water treatment plant. Additives can be added to the permeate. These additives can include, for example, minerals, iodide, chlorine, vitamins, potassium, and calcium.

[0007] A NATO standardization agreement, STANAG 2136, describes minimum standards for drinking water in an operation.

[0008] The operating manual ("Water Treatment Equipment for Decontamination Purposes WAA Dekon", German, 5.959-0074.0 Version 0.9 - 10 / 20.19) describes a mobile water treatment plant of the German Armed Forces, specifically the WAA Dekon from Kärcher Futuretech. The manual outlines a process for treating permeate obtained from a reverse osmosis stage of the mobile water treatment plant, including the following steps: • Generation of an initial solution by dissolving sodium bicarbonate in water, • Production of a second solution, which is partly also a suspension, by stirring calcium hypochlorite into water, • first addition of the first solution to the permeate to obtain a stabilized permeate, • Subsequent second addition of the second solution to the stabilized permeate to obtain a stabilized and chlorinated permeate.

[0009] In the known state of the art, the weight and space requirements are high because a separate dosing container and a separate dosing device are required for both the first solution with sodium bicarbonate and the second solution with calcium hypochlorite.

[0010] The object of the invention is to improve the method for processing a permeate obtained from a reverse osmosis separation stage of a mobile water treatment plant.

[0011] This problem is solved according to the invention by the features of claim 1, which is directed to a method.

[0012] Advantages of the invention result from the following process steps: • Production of a stock solution by dissolving sodium bicarbonate in water and adding and stirring in calcium hypochlorite, sodium hypochlorite, sodium dichloroisocyanurate or sodium dichloroisocyanurate dihydrate or a mixture thereof for chlorination, • Addition of the stock solution to the permeate to obtain a stabilized and chlorinated permeate.

[0013] Since both the sodium bicarbonate and the chlorination chemicals are dissolved in the stock solution, only one dosing tank and one dosing unit are required. This advantage is irrelevant for the WAA Dekon, as it has sufficient space for the various components. Therefore, a qualified technician sees no need to modify the WAA Dekon. However, this advantage becomes fully apparent in other mobile water treatment plants where there is neither enough space nor the capacity to accommodate the additional weight required for separate dosing tanks and units for the first sodium bicarbonate solution and for the second calcium hypochlorite solution.

[0014] After the addition of the stock solution, the stabilized and chlorinated permeate contains 30 to 50 mg / L sodium bicarbonate. At a sodium bicarbonate concentration of 30 to 50 mg / L, the pH value ranges between 7.7 and 8.0. This narrow concentration range not only provides corrosion protection for metallic materials and optimal chlorination effectiveness, but also corrosion protection for cementitious materials.

[0015] After the addition of the stock solution, the stabilized and chlorinated permeate has a free chlorine concentration of 0.1 mg / L to 5.0 mg / L.

[0016] Exemplary embodiments of the invention are described below with reference to the Fig. Figure 1 explains this in more detail. It shows a device for processing a permeate obtained from a reverse osmosis separation stage of a mobile water treatment plant.

[0017] The Fig.Figure 1 illustrates a process for the preparation of a permeate 13 obtained from a reverse osmosis separation stage 10 of a mobile water treatment plant, comprising the following steps: • Production of a stock solution 50 by dissolving sodium bicarbonate in water and adding and stirring in one or more chemicals for chlorination selected from the group containing calcium hypochlorite, sodium hypochlorite, sodium dichloroisocyanurate and sodium dichloroisocyanurate dihydrate. • Addition of stock solution 50 to permeate 13 to obtain a stabilized and chlorinated permeate 13.

[0018] In the apparatus for carrying out the process, a dosing container 30 receives the stock solution 50 and is connected to a dosing device 20, which adds the stock solution 50 to the permeate 13.

[0019] The reverse osmosis separation stage 10 removes ions, such as carbonate and bicarbonate ions, from the raw water 11. However, the carbon dioxide dissolved in the raw water 11 can readily pass through the membrane. Furthermore, atmospheric carbon dioxide dissolves in the permeate 13 until a solution equilibrium is reached. Since the permeate 13 lacks a pH buffer due to the absence of carbonate and bicarbonate ions, the pH value drops to values ​​below pH 5, thus failing to comply with the German Drinking Water Ordinance (TrinkwV 2001) and the STANAG 2136 standard.

[0020] The low pH value and the absence of a pH buffer after the reverse osmosis separation stage lead to corrosion in certain metallic materials, such as copper or hot-dip galvanized iron. This water is also corrosive to cement-bound materials.

[0021] In order to comply with the Drinking Water Ordinance 2001 and STANAG 2136, and to prevent corrosion on Bundeswehr facilities and connected systems, the pH value must be raised to • pH 7.0 to pH 8.7 in the presence of metallic materials or • A pH of 7.7 to 8.7 is required in the presence of cement-bound materials, necessitating pH buffering. Considering legal requirements, operating conditions, and the technology of the Bundeswehr's existing mobile water treatment plants, stabilization using sodium bicarbonate is the most suitable method.

[0022] The stabilization is intended to prevent the treated water from undergoing chemical changes during distribution, for example through corrosion.

[0023] Because the pH value remains within the permissible pH range of the German Drinking Water Ordinance (TrinkwV 2001) and STANAG 2136, regardless of whether the sodium bicarbonate addition is low (10 mg / L) or high (250 mg / L), continuous pH monitoring is unnecessary. At concentrations up to 50 mg / L, it is also ensured that the optimal effective range of free chlorine (≤ pH 8.0) for residual chlorination is maintained. The pH value is adjusted by the amount of sodium bicarbonate added. Ideally, after the addition of the stock solution, the stabilized and chlorinated permeate should contain 30 to 50 mg / L of sodium bicarbonate. This narrow range of 30 to 50 mg / L of sodium bicarbonate fulfills all subsequent requirements: • Compliance with the limit values ​​for pH value and maximum addition quantity according to the Drinking Water Ordinance and STANAG 2136 (for routine situation), • Optimal effect of chlorination, • Corrosion protection for metallic materials, • Corrosion protection for cement-bound materials.

[0024] The following table supports this: feature Application concentration of sodium bicarbonate (mg / L) Resulting pH value at least maximum at least maximum Compliance with the limit values ​​for pH value and maximum addition quantity according to the Drinking Water Ordinance and STANAG 2136 (for routine situations) 1,7 250 6,5 8,7 Optimal effect of chlorination 1,7 50 6,5 8,0 Corrosion protection for metallic materials 6,7 250 7,0 8,7 Corrosion protection of cement-bound materials 30 250 7,7 8,7 Optimal effect of chlorination and corrosion protection of metallic materials 6,7 50 7,0 8,0 Optimal effect of chlorination and corrosion protection of cement-bound materials 30 50 7,7 8,0

[0025] The chemicals used for chlorination protect the treated drinking water against microbial contamination during distribution. This results in residual chlorination with long-lasting microbial protection.

[0026] Due to the different stoichiometric compositions of the chemicals used for chlorination, the concentrations listed in the following table result for each chemical. chemical Sum formula Molar mass of chemical (g / mol) Free chlorine Mass concentration of chemical (mg / L) Mass concentration (mg / l) Molar concentration (mmol / L) from until from until from until Calcium hypochlorite Ca(ClO)2 142,99 0,1 5 1,9*10 -3 97,2*10 -3 0,28 13,90 Sodium hypochlorite NaClO 74,44 0,14 7,24 Sodium dichloroisocyanurate C3N3O3Cl2Na 219,98 0,43 21,38 Sodium dichloroisocyanurate dihydrate C3N3O3Cl2Na H2O 256,02 0,50 24,88

[0027] A specific example of implementation is described below. Fig.The device shown in Figure 1 for processing permeate obtained from a reverse osmosis separation stage of a mobile water treatment plant is weight- and space-reduced. The device comprises only one dosing container and one dosing unit. This is because it was found that both sodium bicarbonate and calcium hypochlorite can be dissolved in a common stock solution. Both sodium bicarbonate and calcium hypochlorite can then be added to this common stock solution.

[0028] The stock solution is prepared in a mixing vessel 40. First, 437 g of sodium bicarbonate are dissolved in 10 L of water.

[0029] Then, 5.5 g of calcium hypochlorite (60%) are stirred in. After the addition of the calcium hypochlorite, the solution becomes milky-cloudy, white particles precipitate out and settle over time. Alternatively, 27.6 g (22.6 mL) of a sodium hypochlorite solution (13%, density: 1.22 g / mL) could be stirred in. Alternatively, 5.6 g of sodium dichloroisocyanurate (62%) could be stirred in. Alternatively, 6.4 g of sodium dichloroisocyanurate dihydrate (55%) could be stirred in. Alternatively, a mixture of the aforementioned chemicals could be stirred in for chlorination.

[0030] Stock solution 50 consists of 100% by weight of water, sodium bicarbonate, and the chlorination chemicals. Alternatively, the stock solution could also contain a small amount of other substances, such as additives or supplements. Preferably, the stock solution consists of more than 75% by weight of water, sodium bicarbonate, and the chlorination chemicals specified in claim 1.

[0031] The resulting stock solution 50, which may also be a suspension, is then added to the dosing container 30. The downstream dosing device 20 continuously adds the stock solution 50 to the permeate 13 obtained from the reverse osmosis separation stage 10. Any white particles present in the stock solution 50 did not cause any malfunction of the dosing device 20. Alternatively, the stock solution could be mixed directly in the dosing container 30, deviating from the illustrated embodiment.

[0032] After the addition of the stock solution, the stabilized and chlorinated permeate has a pH value between pH 7.7 and pH 8.0.

[0033] After the addition of the stock solution, the stabilized and chlorinated permeate has a free chlorine content of 0.1 mg / L to 0.3 mg / L.

[0034] The stabilized and chlorinated permeate is fed into a pipe system (not shown) or directed into a water tank. Consumers then draw water from the pipe system or the water tank. Reference symbol list 10 Reverse osmosis separation stage 11 Raw water 12 Retentat 13 Permeate 14 Pressure pump 20 Dosing device 30 dosing containers 40 mixing containers 50 Stock solution

Claims

[1] Method for treating a permeate (13) obtained from a reverse osmosis separation stage (10) of a mobile water treatment plant, comprising the steps: • Producing a stock solution (50) by dissolving sodium bicarbonate in water and stirring in one or more chemicals for chlorination selected from the group comprising calcium hypochlorite, sodium hypochlorite, sodium dichloroisocyanurate and sodium dichloroisocyanurate dihydrate, • Dosing the stock solution (50) into the permeate (13) to obtain a stabilized and chlorinated permeate such that after dosing the stock solution (50) the stabilized and chlorinated permeate (13) has 30 to 50 mg / L sodium bicarbonate and 0.1 mg / L to 5.0 mg / L free chlorine.

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