Performance characteristics and maintenance techniques of reverse osmosis purified water equipment

Author: Hongjie Water

1、 Introduction to reverse osmosis purified water equipment

The application of membrane separation technology in reverse osmosis equipment can effectively remove charged ions, inorganic substances, colloidal particles, bacteria, and organic substances in water. It is a preferred equipment in high-purity water preparation, brackish water desalination, and wastewater treatment processes. 

1. Equipment system composition

Reverse osmosis purified water treatment systems generally include pre-treatment systems, reverse osmosis devices, post-treatment systems, cleaning systems, and electrical control systems.

Pretreatment system generally includes raw water pump, dosing device, quartz sand filter, activated carbon filter, precision filter, etc.Its main function is to reduce the pollution index of raw water and other impurities such as residual chlorine, in order to meet the inflow requirements of reverse osmosis.

The reverse osmosis device mainly consists of multi-stage high-pressure pumps, reverse osmosis membrane components, membrane shells (pressure vessels), brackets, etc.Its main function is to remove impurities from the water and ensure that the effluent meets the usage requirements.

The post-treatment system is an added configuration when reverse osmosis cannot meet the effluent requirements.It mainly includes one or more equipment such as anion bed, cation bed, mixed bed, sterilization, ultrafiltration, etc.

The cleaning system mainly consists of a cleaning water tank, a cleaning water pump, and a precision filter. When the effluent indicators of the reverse osmosis system cannot meet the requirements due to contamination, it is necessary to clean the reverse osmosis system to restore its effectiveness.

The electrical control system is used to control the normal operation of the entire reverse osmosis system. Including instrument panel, control panel, various electrical protection, electrical control cabinet, etc.

2. Design Features

(1) By increasing the pressure on water, deep filtration of water is achieved. The reverse osmosis purified water equipment not only includes general filters, but also includes fine filters, granular activated carbon filters, and compressed activated carbon filters. Fine filters have a finer filtration function than ordinary filters, which can better filter impurities in water. As we know, activated carbon has good adsorption and filtration functions for odors and impurities. Reverse osmosis pure water equipment uses dual activated carbon filters to achieve deep filtration processing of raw water, improving the filtration efficiency of the equipment. At the same time, increasing the pressure of water to enhance filtration capacity is also an innovation.

(2) The core of reverse osmosis purified water equipment is the application of reverse osmosis membranes. Reverse osmosis membrane is a type of filtration membrane with extremely small pore size, which can achieve ultra fine filtration of raw water and convert water into high and low concentrations. High concentration water can be recycled and reused, while low concentration water is pure water that can be used by humans.

3. Main process flow

(1) Raw water tank

Store raw water for settling large sediment particles and other precipitable substances in the water. Simultaneously buffering the impact of unstable water pressure in the raw water pipe on the water treatment system. (such as pressure sensing reactions caused by low or high water pressure).

(2) Raw water pump

Constant system water supply pressure and stable water supply volume.

(3) Multi media filter

The main purpose of using a filter with multiple filter layers is to remove sediment, rust, colloidal substances, suspended solids, and other particles above 20um in the raw water. Manual valve control or fully automatic controller can be used for a series of operations such as backwashing and forward flushing. Ensure the water production quality of the equipment and extend its service life.

(4) Activated carbon filter

The system adopts a fruit shell activated carbon filter, which can not only adsorb electrolyte ions but also perform ion exchange adsorption. The activated carbon adsorption can also reduce the oxygen consumption (COD) of Potassium permanganate from 15mg/L (O2) to 2-7mg/L (O2). In addition, because the adsorption increases the concentration of the surface to be adsorbed and replicated, it also plays a catalytic role, removing pigments, odors, a large number of biochemical organics in the water, reducing the residual chlorine value and pesticide pollutants in the water, and removing trihalides (THM) and other pollutants in the water. At the same time, the equipment has a self maintenance system and low operating costs.

(5) Ion softening system

In order to concentrate and discharge dissolved solids and utilize fresh water in the R/O device, and to prevent crystallization and precipitation of carbonate, SiO2, and sulfate crystals, especially on the concentrated water side of a membrane component after the RO device, which exceeds its equilibrium solubility constant and damages the inherent characteristics of the membrane components, an ion softening device or an appropriate amount of scale inhibitor should be used before entering the reverse osmosis membrane component to prevent the crystallization of carbonate, SiO2, and sulfate crystals.

(6) Precision filter

The use of precision filters to remove residual suspended solids, non curved particles, colloids, and other substances from the influent ensures safer and more reliable operation of subsequent equipment such as the RO system. The filter element is a 5um melt blown filter element, designed to prevent impurities larger than 5um from being removed by the superior filtering unit. Prevent damage to the surface of the membrane by entering the reverse osmosis device, thereby damaging the desalination performance of the membrane.

(7) Reverse osmosis system

The reverse osmosis device uses sufficient pressure to separate the solvent (usually water) in the solution through the reverse osmosis membrane (or Semipermeable membrane). Because this process is opposite to the direction of natural osmosis, it is called reverse osmosis.

The Anti-Infiltration Act method can adapt to all kinds of raw water with salt content, especially in water treatment projects with high salt content, and can obtain good technical and economic benefits. The desalting rate of the Anti-Infiltration Act method is improved, the recovery rate is high, the operation is stable, the floor area is small, and the operation is simple. While desalting, the reverse osmosis equipment also removes most bacteria, colloids, and organic substances with large molecular weight.

2、 Maintenance Techniques for Reverse Osmosis Pure Water Equipment

1. Strictly control the inlet water quality to ensure that the device operates under water quality conditions that meet the inlet water index requirements. If the inlet water quality does not meet the requirements, it is very easy to cause fouling and blockage of the reverse osmosis membrane, causing consumables to fail quickly and seriously affecting the outlet water quality.

2. The total inflow of reverse osmosis is controlled by the RO inlet regulating valve. If the inflow of reverse osmosis does not change, do not adjust the RO inlet regulating valve, and it is strictly prohibited to fully open or close. The RO drainage regulating valve is used to adjust the system recovery rate. If the recovery rate does not change, do not tamper with the concentrated discharge regulating valve, and do not fully open or close it.

3. The device cannot be shut down for a long time and should run for at least 2 hours per day. If it is ready to shut down for more than 72 hours, a chemical cleaning device should be used to fill the components with 1% sodium hydrogen sulfate and 18% glycerol for protection.

4. After each shutdown and start-up of the reverse osmosis device, the device should be flushed for 10 minutes under a water inlet pressure of less than 0.4 Mpa.

5. Operating pressure control should be carried out at the lowest possible pressure value while meeting the requirements of water production and water quality. This is beneficial for reducing the attenuation of membrane water flux and reducing membrane replacement rate.

6. Operators should record operating parameters every hour to check the usage of pure water equipment and the quality of effluent.

The main records are as follows:

(1) Inflow:

PH value, conductivity, pressure, SDI, water temperature.

(2) Water production:

Conductivity, flow rate, pH value;

(3) Concentrated water:

Flow rate, pressure, and inlet pressure of each section.

7. When a high and low pressure alarm occurs to the reverse osmosis device, first check whether the opening of the manual valve between the security filter and the high-pressure pump is too small, then check whether the RO water inlet regulating valve and the concentrated discharge valve are normal, and then press the high and low pressure alarm reset button to restart the purified water production equipment.

8. The inlet temperature control should be based on the actual water consumption, and the critical pressure (the pressure value at which the desalination rate significantly decreases when the inlet pressure is lower than this value) that cannot meet the requirements of water production and quality should be taken as the inlet temperature during this time period, which can reduce the attenuation of membrane water volume.