Innovative water treatment solutions and experience of introduction at railway transport infrastructure facilities

. The experience of operating ozone-sorption water treatment plants in the structural subdivisions of Russian Railways OJSC is provided. Technical solutions that increase the efficiency of water treatment and reduce operating costs are described.


Introduction
Currently, strategic tasks are being implemented in the water protection activities of the Russian Federation on the basis of the approved national project "Ecology", one of the directions of which is the conservation of water bodies and improving the quality of drinking water.
A set of measures is defined for the period up to 2024, and is aimed at abandoning use of outdated and inefficient technologies, the transition to the principles of introducing new modern technologies included in the reference book "Best Available Technologies" (hereinafter referred to as еру BAT) [1].The BAT reflects the best technologies of domestic production considering the practice of introducing achievements in various production processes.
In the railway industry, for implementation of this direction, a reference book of Russian Railways OJSC -Greenbook was created, the technologies presented in it were included in the Pure Water investment project.In order to provide consumers (enterprises and infrastructure facilities) with drinking quality water located in different regions of the country.

Materials and methods
As part of implementation of the Pure Water investment project of Russian Railways OJSC, almost all known water treatment technologies have been applied, namely, pressure and nonpressure aeration, reverse osmosis, ozonation and softening.The choice of these water treatment technologies is dictated by the results of the analysis of the source water, the location features, the technical, economic and operational indicators of the equipment, as well as the equipment suppliers.
This article provides the experience in development and operation of ozone-sorption water treatment plants manufactured by NPF VIETO LLC for the facilities of the Pure Water investment project of Russian Railways OJSC.
The general provision for all objects of implementation was purification of source water from iron and other pollutants, as well as placement of ozone-sorption treatment plants in separately located block modules equipped with heating, ventilation, fire extinguishing systems and automation equipment, as close as possible to the source of water supply -a well.The block modules dimensions were determined based on the plant performance.
Technical solutions implemented in all introduced ozone-sorption treatment plants, namely, impact water-air regeneration of filtering coal and recovery of residual ozone, are protected by a patent [2].

Results and discussion
Source water at all implementation sites involves removal of mechanical impurities, a decrease in the turbidity index and iron content.After treatment, the water quality must comply with the requirements of SanPiN 2.1.3684-21[3].
The schematic diagram of the plant for ozone-sorption treatment of source water is shown in Figure 1.The main working element of the plant is the KE contact tank located on the mounting frame.The KE contains a residual ozone destructor D, four level sensors (U1, U2, U3, U4), ejectors for supplying ozone and source water E1 and ejectors for supplying a waterair mixture E2, which is connected to the tank cavity in its upper part through the pipeline T2.Inside the KE tank on the bottom there is a perforated collector for collecting treated water.It is covered with a layer of backfill made of gravel, on which a filter layer of activated carbon is placed.A pipeline is connected to the collector, which is the suction line M2 of the pump for supplying treated water H1.Source water is supplied to the ejector E1 through the source water line M1.Before entering the ejector E1 on the line M1, a solenoid valve KL1 is installed.An inlet valve V2 is installed at the inlet to the M1 line, and an outlet valve V3 and a solenoid valve KL3 are installed at the outlet of the M2 line.Both lines are interconnected by another bypass line M4 equipped with valve V1.A system of three valves (V1, V2, V3) ensures that the plant is turned off for routine maintenance and provides water to the consumer bypassing it.On the mounting frame there are an ozone generator, a control unit for the process of water treatment and regeneration of the filtering backfill.The ozone-air mixture is supplied to the ejector E1 through the original ozone supply pipeline T1.Regeneration of the filtering backfill on the KE is provided with the M7 line, one end of which is cut into the M1 line after the V2 valve (along the source water), and the other end branches out.One branch through the KL5 solenoid valve is connected to the same fitting as the M2 line, and the second branch is connected to the E2 ejector through the KL4 solenoid valve.
The KE contact tank is equipped with the M9 line for flushing water discharge into the sewer.The M3 line is cut into the line after the N1 pump, which is equipped with the KL2 solenoid valve and is connected to the M9 line.
Two operating modes are typical for the ozone-sorption water treatment plant: treatment of source water and regeneration of the built-in carbon filter, which consists of two successive processes -backwash and forward flushing.
Position of the chek valves for these modes is shown in Figure 2.
Operation Backwash The plant operation, including switching modes, is provided by a programmable control unit, a general view of which is shown in Figure 3.The plant control program provides for the continuity of its operation during water treatment for a specified time, which is determined by the composition and amount of contaminants in the source water, but does not exceed 48 hours.The frequency and duration of flushes, as well as the time of their implementation, are also programmed.Increasing the reliability of water supply is ensured by the parallel connection, if necessary, of an additional plant with the same capacity.All modules operate on one collector, through which treated water is supplied to the consumer.The connection diagram of three plant modules for operation on a common line is shown in Figure 4.The required power of the ozonator is selected based on the results of the analysis of the source water and its consumption, as well as ensuring the conditions for sterilization [4], [5], [6].The plants use a new type of ozone generators that operate on undried atmospheric air and have unique characteristics, such as specific energy consumption for ozone production and the maximum ozone concentration [7].

Direct flushing
Pumping station -according to the hydraulic characteristics of the pump and the supply pipeline.
The process of oxidation of iron Fe 2+ with ozone is provided in the following form (formula 1): The formula for the oxidation of manganese Mn 2+ with ozone is presented as follows (formula 2): In order to ensure a given degree of inactivation, the following ratio is established (formula 3): , mg/l*min, (3) where: С -ozone concentration in water, mg/l, T -time of contact of water with ozone, min In the practice of drinking water supply systems, the following is taken: C = 0.4 mg/l T = 4 min CT = 1.6 mg/l x min The chemical demand for ozone must be determined using prototype samples of source water at the facility using a pilot plant.
Ozone dose and generator performance (formula 4) Where: D -the dose of ozone for the oxidation of contaminants in water k -a dimensionless coefficient that considers the efficiency of ozone transfer from the gas phase to the solution, considering the calculated reserve C0 -the required initial ozone concentration at the inlet to the contact apparatus, mg/l Calculated ozone generator capacity (formula 5): where: Q -water consumption from the consumer, m 3 /h The hardware design of units with various capacities is shown in  Experience in the production operation of ozone-sorption water treatment plants confirmed the declared hydraulic characteristics and high quality of treated water that meets regulatory requirements.
Operating conditions of plants at st. Pytalovo, Oktyabrskaya railway, and st.Ryazan, Moscow Railway, had limitations due to the lack of centralized sewerage networks not far from it.
Therefore, a technology was developed and implemented for reuse of flushing water for regeneration of the filtering coal charge.The schematic diagram and hardware design of this technology at the Ryazan station are shown in Figure 6.Within production operation of the plant at the specific consumer site, waste water from the tank E2 is filtered.Moreover, the discharged water from E2 is supplied by the pump N3 through the filter F, where it is cleaned from mechanical impurities of ferric iron, which are in the form of flakes.After filtering, water enters the tank E1.The provided F filter consists of a housing with Krapukhin filter elements (KFE) located inside [8].The design feature of this filter is the complete restoration of the calculated flow characteristics (KFE -spring design with a pore size of 13 microns).When the filter with the pre-washed layer of perlite powder is used, the fineness of filtration is 1 μm, while the throughput of the filter decreases and, as a result, the time for cleaning the flushing water increases.

Flow diagram
At the stage of flushing water treatment, the precipitate of filtered iron is formed on the surface of the KFE, which is then sent from the filter housing to the sediment collection tank.Further, the complete regeneration of the KFE is carried out by back blowing with compressed air, while the gap of the spring filter element increases significantly.The mass volume of the suspension (a concentrated mixture of water and ferric flakes) for subsequent disposal is equal to the volume of the filter housing and is about 10 liters.
The plant is started by filling the tank E1 with subsequent compensation for water losses, which is carried out through valve 6 with treated water.
The process of plant operation is fully automated.Control is provided by means of the control panel PU, where level sensors, timers, and differential pressure sensors are used.

Conclusions
Summing up, it shall be emphasized that use of ozonation for production of drinking water is universal in relation to a diverse range of contaminants.The ozonation technology provided in the article has a modern promising direction in solving problems of providing drinkingquality water to railway transport infrastructure facilities, as well as production facilities, for the purpose of water treatment for technological needs.Operation of ozone-sorption water treatment plants has proven itself well since 2017; the parameters declared at the design, both in terms of consumption and quality of treated water, have been confirmed.

Fig. 2 .
Fig. 2. Scheme of water movement within the plant operation.

Fig. 3 .
Fig. 3.Control unit.Management commands are formed on the basis of signals from level sensors located in the KE, and the objects of control are the ozone generator, pumping station and electromagnetic valves.Increasing the reliability of water supply is ensured by the parallel connection, if necessary, of an additional plant with the same capacity.All modules operate on one collector, through which treated water is supplied to the consumer.The connection diagram of three plant modules for operation on a common line is shown in Figure4.

Fig. 4 .
Fig. 4. Connection diagram of three plant modules for operation on a common line: 1 -module for ozone-sorption water treatment, 2 -rotary gate, 3 -electromagnetic flow meter.Performance of ozone-sorption water treatment plants with volumes of 2 m 3 /h, 5 m 3 /h, 10 m 3 /h, 15 m 3 /h is justified by presence and use of serially produced tanks as a contact filter apparatus (ANION LLC) providing the recommended filtration rate up to 10 m/h.

Fig. 6 .
Fig. 6.Ozone sorption water treatment plant with the block for flushing water filtration.