RU2569350C1 - Method for obtaining portable quality water - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method for obtaining portable quality water includes separation of mechanical admixtures and pollutants from it by means of mechanical purification filter and reverse osmosis unit, working with a stop between working cycles for hydraulic purification of membrane element of reverse osmosis unit and concentrate removal. Pressure tank of reverse osmosis unit is filled with permeate for the time of technological break. First, mechanical admixtures with particle size larger than 5 mcm are separated from processed water. After that, it is supplied into pressure tank of reverse osmosis unit with periodic hydraulic washing of membrane element during working cycle without stopping equipment with interval, determined by formula: $$\tau (час)\le \frac{\alpha }{{\displaystyle {\sum }_i^n{C}_i}},$$

where a is empiric constant, equal 3.5 mg/dm³ hour; C is concentration of dissolved ions, resulting in formation of colloidal particles, mg/dm³.

EFFECT: simplifying method of purification and increasing its efficiency.

4 cl, 1 dwg

Description

The invention relates to the field of water supply for collective users and can be used to obtain drinking water from surface or underground sources.

Currently, due to the unsatisfactory environmental situation, the reduction of water sources and the violation of the integrity of existing water mains and centralized water treatment systems, one of the main problems of life support has become the problem of providing the population with drinking-quality water.

This problem is especially acute in areas of natural disasters due to unforeseen disasters (earthquakes, storms, floods, droughts, etc.), destruction of the water supply system and pollution of water sources (springs, wells, rivers, ponds, etc.) by various types pollution.

For the rural population and residents of villages remote from the central water treatment plants, drinking water is either absent or becomes very expensive and unclaimed, since laying highways and building centralized water treatment plants is a very costly and long-term undertaking, and drinking-quality water, the consumption of which for drinking needs is 5-7% of the total volume of water consumption, is unclaimed due to high tariffs at a price.

For this reason, the development of new affordable methods for producing drinking-quality water and the production of autonomous stations for their implementation in order to provide the population of natural disaster areas and remote rural settlements of the constituent entities of the Russian Federation with drinking-quality water, as well as providing clean water for socially significant facilities (schools, kindergartens and hospitals), is a very urgent task.

A known method of reverse osmosis desalination of water, comprising introducing additives into the treated water, followed by filtering the water through the reverse osmosis membrane, using inert carbon particles, for example, fullerene or soot, as additives [Description of the invention to RF patent No. 2216521 of 04.01.2003, IPC ⁷ C02F 1 / 44, publ. November 20, 2003]. The method prevents permeate contamination by substances added during desalination and reduces their consumption.

The disadvantages of the method include a decrease in productivity due to clogging after some time the surface of the membrane with mechanical particles of additives.

A known method of purification of natural waters, comprising two stages of machining, desalination by reverse osmosis, after two stages of machining, is dechlorinated with sodium sulfite, then water is purified by microfiltration and an inhibitor is added, desalination by reverse osmosis is carried out in two stages, after the first stage the concentrate is dumped, and permeate is added an inhibitor and caustic soda, raising the pH to 10.4, then the second stage of desalination by reverse osmosis is carried out, and the concentrate is mixed into the second stage of reverse osmosis into the flow to the inlet of the first desalination stage, and acid is added to the permeate and passed through filter-conditioners with calcium-magnesium loading [Description of the invention to RF patent No. 2225369 of 03/13/2003, IPC ⁷ C02F 9/08, publ. 03/10/2004]. The method provides a reduction in capital costs and maintenance costs of desalination plants, improving the quality of purified permeate water to a level that meets WHO recommendations, including boron and hardness salts.

The disadvantages of this method include its multi-stage and the complexity of the hardware design. In addition, the performance of the method is unstable and depends on the degree of contamination of reverse osmosis membranes.

There is a method of deep desalination of fresh and brackish water, including sequential processes in steps: clarification, treatment of clarified water on ion-exchange filters and desalination in the reverse osmosis stage with the removal of concentrate from each cleaning stage, while the reverse osmosis desalination process is carried out in two stages at a higher pressure of the treated water at each subsequent stage of desalination, and the pressure of the purified water is set at the first stage not more than 1.6 MPa and not more than 4.0 MPa on after stages when the ratio of permeate to concentrate of the reverse osmosis stage is within n = 7-99, the concentrate is removed from the reverse osmosis stage in each stage to regenerate ion-exchange filters, and the permeate is subjected to H-OH ionization after the reverse osmosis purification step [Description of the invention to the RF patent No. 2283288 dated 11/23/2004, IPC ⁷ C02F 9/08, B01D 61/12, C02F 1/42, C02F 1/44, publ. 09/10/2006]. Achieved results are an increase in the permeate yield, a decrease in the concentrate consumption, an increase in the quality of demineralized water, a reduction in the concentrate discharges along the desalination steps, and a decrease in water consumption for the plant’s own needs.

The disadvantages of the method, as in the previous case, include the multi-stage and complexity of the hardware design, as well as the frequency of work associated with the need to restore the working functions of the equipment.

Also known is a method of producing clarified water for feeding the water circulation cycles of ammonia production, which consists in taking the initial water, its subsequent clarification, flocculation, filtering from mechanical and suspended particles and feeding nanofiltration and reverse osmosis to the installation for producing demineralized water, and, as membrane elements become contaminated, their cleaning by feeding and soaking in time washing solutions: 50% sulfuric acid and 42% alkali or 20% sodium hypochlorite [Description of the invention to the patent of the Russian Federation No. 2294794 from 25.1 1.2004, IPC B01D 61/14, C02F 9/08, C02F 1/52, publ. 03/10/2007]. The use of the invention provides high-quality water suitable for reliable and efficient operation of nanofiltration and reverse osmosis plants used in water treatment schemes of chemical plants.

The disadvantages of the method include large capital costs for the preparation of water for supply to the reverse osmosis unit.

Closest to the essential features of the claimed method is a method of purification and disinfection of water, comprising sequentially separating from it in several stages of mechanical impurities and impurities using two pressure sorption filters and a reverse osmosis unit, working with a stop between working cycles for hydraulic cleaning of the membrane element of the reverse osmosis unit and removal of concentrate, moreover, during idle time, the pressure channel of the membrane element (pressure vessel backward otic block) filled with filtrate (permeate) [Disclosure of the invention to RF patent №2360870 from 25.10.2007, IPC C02F 9/08, publ. 07/10/2009]. The method provides a unit productivity of 250-500 dm ³ / hour for 8-20 hours / day for compactly located collective users, while ensuring the quality of drinking water specified by the physicochemical properties.

Despite the fact that this method has been widely used for desalting water with various initial concentrations of dissolved substances, like all similar separation methods, it has significant drawbacks, which include its multi-stage process, the need for thorough preparation of water for reverse osmosis treatment, which entails large capital and operating costs, insufficient productivity and, consequently, the complexity of the hardware design.

For this reason, the development of technological schemes, including reverse osmosis desalination and control of their operation modes in order to reduce capital and energy costs, is paramount, relevant and in demand.

The problem solved by the first invention of the group and the technical result achieved are to simplify the cleaning method and increase its productivity to 250-60000 dm ³ / hour for 8-20 hours / day.

To solve the problem and achieve the claimed technical result in a method for producing drinking-quality water, including the separation of mechanical impurities and impurities from it using a mechanical filter and reverse osmosis unit, working with a stop between work cycles for hydraulic cleaning of the membrane element of the reverse osmosis unit and removal of concentrate, moreover, at the time of the technological break, the pressure vessel of the reverse osmosis block is filled with permeate, while first from mechanical water with a particle size of more than 5 microns is isolated using the filter, after which it is fed into the pressure vessel of the reverse osmosis unit, while also periodically hydraulically flushing the membrane element during the working cycle without stopping the equipment with the interval defined by the formula:

где

Where

a is an empirical constant equal to 3.5 mg / dm ³ hours;

C is the concentration of dissolved ions leading to the formation of colloidal particles, mg / DM ³ .

The dimension of the constant a is milligram per decimeter cubic per hour - mg / dm ³ hours, and the physical meaning is the specific temporal concentration, which has no other applied value, except as declared as a certain empirical constant.

Besides:

- in the water, purified from mechanical impurities with a particle size of more than 5 microns, before inhibitors are fed into the pressure vessel of the reverse osmosis unit, 1.5-4.5 g / m ^{3 of} treated water is introduced;

- use inhibitors based on polyphosphates or polyacrylates;

- during the technological break, after hydraulic washing of the membrane element of the reverse osmosis block and removal of the concentrate from the surface of the membrane, the salts of inorganic acids are dissolved by filling the pressure tank of the reverse osmosis block with permeate with pH = 5.0-6.0.

The invention is illustrated in the drawing, which shows a diagram of an autonomous station that implements a method for producing drinking-quality water.

The method of producing drinking-quality water is implemented at an autonomous station, which includes a mechanical (coarse) cleaning filter 1 installed in the technological sequence, a pressure pump 2 connected to a pressure tank 3 of the reverse osmosis unit 4, pressureless tank 5 of which is connected to a storage tank 6 of permeate, while the pressure tank 3 of the reverse osmosis unit 4 has a single nozzle 7 for draining the concentrate and supplying permeate from the storage tank 6 by means of an additional pump 8, and a control system (conditionally not shown), while the filter 1 mechanical cleaning is made with the possibility of separation of mechanical impurities with a particle size of more than 5 μm, and to the output 9 of the filter 1 mechanical cleaning connected to the flow tank 10 of the inhibitor.

It should be noted that the term "pressure vessel of the reverse osmosis unit" means the internal volume of pipelines adjacent to the membrane of the reverse osmosis unit 4, and where the water to be treated is concentrated. In turn, “pressure free capacity” is the internal volume of pipelines at the outlet of the membrane of the reverse osmosis unit 4, where purified water (filtrate, permeate) is concentrated.

Example 1

To isolate mechanical impurities and contaminants from the water using a filter 1 of mechanical cleaning and a reverse osmosis unit 4, working with a stop between working cycles for hydraulic cleaning of the membrane element 11 (shown conditionally) of the reverse osmosis unit 4 and removal of concentrate, moreover, during a technological break, the pressure vessel 3 the reverse osmosis unit 4 is filled with permeate, and first, mechanical impurities with a particle size of more than 5 μm are first isolated from the treated water using a filter 1, after which e is fed into the pressure vessel 3 reverse osmosis unit 4, the hydraulic perform periodic flushing of the membrane element 11 during the operating cycle without stopping the equipment at intervals of hours, determined by the formula:

, где

where

a is an empirical constant equal to 3.5 mg / dm ³ hours;

C is the concentration of dissolved ions leading to the formation of colloidal particles (concentration of suspended particles), mg / DM ³ .

The water purified from mechanical impurities with a particle size of more than 5 microns, before being fed into the pressure vessel 3 of the reverse osmosis unit 4, is injected with inhibitors based on IOMS-1 polyphosphate at the rate of 1.5 g / m ^{3 of the} treated water, and for the duration of the technological break, after hydraulic washing of the membrane element 11 (or membrane) of the reverse osmosis unit 4 and removal of the concentrate from the surface of the membrane, the salts of inorganic acids are dissolved by filling the pressure vessel 3 of the reverse osmosis unit 4 of permea ohm with pH = 5,0.

Example 2

In the water purified from mechanical impurities with a particle size of more than 5 microns, before being fed into the pressure vessel 3 of the reverse osmosis unit 4, inhibitors based on Aminat D polyphosphate are introduced at the rate of 4.5 g / m ^{3 of the} treated water, and for the duration of the technological break, after hydraulic washing of the membrane element 11 (or membrane) of the reverse osmosis unit 4 and removal of the concentrate from the surface of the membrane, the salts of inorganic acids are dissolved by filling the pressure vessel 3 of the reverse osmosis unit 4 ne meatom with pH = 6,0.

Example 3

Before water is supplied from mechanical impurities with a particle size of more than 5 μm, inhibitors based on VITEK polyacrylate are introduced into the pressure vessel 3 of the reverse osmosis unit 4 at the rate of 1.7 g / m ^{3 of} treated water, and after a technological break, after hydraulic washing the membrane element 11 (or membrane) of the reverse osmosis unit 4 and removing the concentrate from the surface of the membrane, dissolve the salts of inorganic acids by filling the pressure vessel 3 of the reverse osmosis unit 4 of permeato with pH = 5,5.

Example 4

Before water is supplied from mechanical impurities with a particle size of more than 5 μm, inhibitors based on ROPUR polyacrylate are introduced into the pressure vessel 3 of the reverse osmosis unit 4 at the rate of 4.3 g / m ^{3 of the} treated water, and during the technological break after hydraulic washing the membrane element 11 (or membrane) of the reverse osmosis unit 4 and removing the concentrate from the surface of the membrane, dissolve the salts of inorganic acids by filling the pressure vessel 3 of the reverse osmosis unit 4 of permeato with pH = 5,9.

The advantage of the invention is due to the following. Traditionally, installations with reverse osmosis units include complex systems of preliminary preparation of water for its supply to the membrane. In fact, water is maximally purified from mechanical impurities. At the same time, between the operating cycles of the plants (as a rule, this is one working shift), the filters are restored and the membrane element of the reverse osmosis unit is hydraulically cleaned with the concentrate removed. At the time of the technological break, the pressure vessel of the reverse osmosis unit is filled with permeate to prevent salts from precipitating onto the surface of the membrane element.

In the present technical solution, the method of producing water is greatly simplified.

First, mechanical impurities with a particle size of more than 5 microns are isolated from the treated water using a filter 1. This is the most simple, affordable, high-performance and cheap form of water treatment. Such obviously “under-treated" water is supplied to the pressure vessel 3 of the reverse osmosis unit 4. When operating on such water, the membrane of the reverse osmosis unit 4 becomes contaminated and its permeate productivity decreases rapidly. Observations of the operation of reverse osmosis systems on various types of contaminated water showed that after one month of operation, productivity decreased by 3 times.

To remove loose sediment of suspended particles and colloidal iron from the surface of the membrane element 11 in the reverse osmosis units 4 of the roll type, a scheme was used that used periodic hydraulic washing of the surface of the membranes. The analysis of flow hydrodynamics in the roll membrane element 11 of the reverse osmosis unit 4 was carried out, and the influence of hydrodynamic parameters on the reverse osmosis cleaning process was examined.

It turned out that to achieve effective hydraulic flushing it is enough to increase the water flow rate in the pressure channel 12 by about 2-3 times by depressurizing the membrane (in the pressure vessel 3). To achieve this, a magnetic valve 14 is installed on the concentrate line 13, including a quick hydraulic flushing process.

In this regard, it seems important to determine the optimal frequency of hydraulic flushing of the membrane element 11 of the reverse osmosis unit 4. For this, the combined parameter S, the so-called the concentration of suspended particles, equal to the sum of the concentrations of dissolved ions, which can lead to the formation of colloidal particles C _i , mg / DM ³ :

Thus, the parameter S is determined based on the quality of the source feed water.

On the basis of our own array of experimental data on the operation of the reverse osmosis system on the source water of various compositions (with and without preliminary treatment) and literature data, it was established that the interval of hydraulic flushing t (hour) depending on S is described by an analytical expression

where a is an empirical constant equal to 3.5 mg / dm ³ hours.

Calculation example.

For example, the concentration of dissolved ions leading to the formation of colloidal particles (concentration of suspended particles) in water is 3.7 mg / dm ³ . The flushing interval will be 3.7 / 3.5 = 1.06 hours or less, which may be related to the duration of the shift at the water receiving station or the convenience of adjusting its control system. The duration of the hydraulic flushing interval, longer than the calculated one, will contribute to excessive contamination of the membrane element 11, and, consequently, to reduce the productivity of the station, depending on the excess of the normalized parameter.

It was experimentally established that the use of periodic hydraulic leaching allowed to increase the filter cycle of the reverse osmosis water treatment system by more than 2 times.

Since CaCO ₃ + CaSO ₄ compounds and suspended solids predominate in the concentrate, a scheme with sediment inhibition was considered.

An analysis of the amount and composition of the sediment showed that dense sediments of suspended solids, calcium carbonate and calcium sulfate form on the surface of the membrane element 11, which in turn significantly reduces the efficiency of reverse osmosis treatment systems. This fact is explained by the fact that the action of the inhibitor is based on the formation of films on the surface of the membrane element 11, which reduces the number of centers of crystal formation and prevents the formation of deposits of mineral salts on the surface of the membranes. In the case of using reverse osmosis treatment plants without preliminary water treatment, sediment of suspended and colloidal particles forms on the surface of the membrane elements 11, and the inhibitor ceases to act effectively. The action of inhibitors also reduces the high content of dissolved and colloidal iron in the source water.

From this we can conclude that the main contaminants of the membrane elements 11 are loose deposits rapidly accumulating on the surface of the membranes. It is also noted that these sediments are effectively removed by hydraulic flushing. At the same time, in the case of working with hydraulic flushing, the duration of the filter cycle directly depends on the accumulation of dense carbonate deposits, to prevent which nothing was previously used. Therefore, the behavior of the reverse osmosis system was investigated during a process with inhibition of sedimentation and hydraulic flushing. The data obtained showed that in the case of the use of sedimentation inhibitors together with hydraulic leaching, it is possible to significantly increase the filter cycle of the reverse osmosis treatment system in comparison with all known schemes. The effective removal of loose sediment, suspended solids and iron hydroxide allows inhibitors to work much more efficiently on the surface of the membrane element 11.

Inhibitors are administered at a rate of 1.5-4.5 g / m ^{3 of} treated water, depending on its quality composition. The smaller the number of inhibitors from the specified limit does not allow for effective protection of the membrane surface. More - leads to an overrun of the inhibitor, which is economically inexpedient. Numerous experiments have revealed the most effective inhibitors. They turned out to be polyphosphate-based inhibitors, such as, for example, IOMS-1, Aminat D, and others, or polyacrylates, such as, for example, VITEK, ROPUR, and others.

The use of hydraulic flushing and inhibition together gives good results and allows you to operate reverse osmosis systems in unprepared water, theoretically allows you to increase the duration of the filter cycles by 5-6 times before chemical washing of the membranes, while the service life of the membrane elements 11 is not reduced, which allows you to compete with systems having in their composition blocks of preliminary water treatment before it is fed into reverse osmosis blocks. In this case, the composition of the water after purification at the end of the filter cycle complies with regulatory requirements.

Supplementing the water purification technology described above by filling the pressure vessel 3 of the reverse osmosis unit 4 for the duration of technological breaks with a permeate, an even more effective scheme for carrying out the reverse osmosis cleaning process can be implemented - in combination with periodic hydraulic cleaning of the membrane element 11 and inhibition of sedimentation. The permeate of the reverse osmosis unit 4 is not only deeply demineralized water, which dissolves the remaining part of the precipitation, but also due to the lowered pH values (pH = 5.0-6.0) it significantly increases the solubility of inorganic acid salts in it. Despite the fact that the amount of salts not removed as a result of washing is small, this allows you to restore the properties of the membrane element to its original state, and, therefore, improve its working conditions and provide higher performance. Using hydraulic flushing and inhibition, as well as filling the pressure vessel 3 of the reverse osmosis unit 4 with permeate while the station stops, it is possible to achieve almost complete removal of contaminants from the surface of the membrane element 11, which leads to the stable operation of the reverse osmosis cleaning system on water with a high content of contaminants.

When comparing various schemes for conducting reverse osmosis treatment (desalination), the implementation of the claimed method can significantly reduce not only capital but also operating costs without changing the quality of the water obtained.

As can be seen from the description and examples, a method for producing drinking-quality water has been created, which is distinguished by its availability and ease of implementation and provides a productivity of up to 250-60000 dm ³ / hour for 8-20 hours / day.

Claims (4)

1. A method of producing drinking-quality water, including the separation of mechanical impurities and impurities from it using a mechanical cleaning filter and a reverse osmosis unit, working with a stop between working cycles for hydraulic cleaning of the membrane element of the reverse osmosis unit and removal of concentrate, moreover, during the technological break, the pressure vessel of the reverse osmosis the block is filled with permeate, characterized in that first, mechanical impurities with p with a particle size of more than 5 μm, after which it is fed into the pressure vessel of the reverse osmosis unit, and periodic hydraulic washing of the membrane element is carried out during the working cycle without stopping the equipment with an interval determined by the formula:

where
a is an empirical constant equal to 3.5 mg / dm ³ hours;
C is the concentration of dissolved ions leading to the formation of colloidal particles, mg / DM ³ . 2. The method according to p. 1, characterized in that the water is purified from mechanical impurities with a particle size of more than 5 microns, before being fed into the pressure vessel of the reverse osmosis unit, inhibitors are introduced at the rate of 1.5-4.5 g / m ^{3 of} treated water . 3. The method according to p. 2, characterized in that they use inhibitors based on polyphosphates or polyacrylates. 4. The method according to p. 1, characterized in that at the time of the technological break, after hydraulic washing of the membrane element of the reverse osmosis block and removal of the concentrate from the surface of the membrane, the salts of inorganic acids are dissolved by filling the pressure vessel of the reverse osmosis block with permeate with pH = 5.0 -6.0.