Introduction to Reverse Osmosis Water Treatment Equipment

Introduction to Reverse Osmosis Water Treatment Equipment

I. Preparation Principle

Reverse osmosis water treatment equipment typically consists of three components: a raw water pretreatment system, a reverse osmosis purification system, and an ultrapure post-treatment system. The primary purpose of pretreatment is to condition the raw water to meet the feed requirements of the reverse osmosis membrane separation components, ensuring stable operation of the reverse osmosis purification system. The reverse osmosis membrane system represents the most economical and efficient purification method for removing over 98% of ions and organic matter, along with 100% of microorganisms (theoretically) from raw water in a single pass. The ultrapure post-treatment system employs multiple integrated technologies to further eliminate trace ions, organic compounds, and other impurities remaining in the reverse osmosis purified water, thereby meeting the final water quality specifications required for various applications.

II. Working Principle

Reverse osmosis represents the most sophisticated membrane-based liquid separation technology. By applying an operating pressure to the feed (concentrate) side that overcomes natural osmotic pressure, the direction of natural water molecule diffusion reverses when this pressure exceeds osmotic pressure. Water molecules from the feed (concentrate) partially pass through the reverse osmosis membrane to become purified product water on the dilute side. Reverse osmosis equipment blocks all dissolved salts and organic compounds with molecular weights exceeding 100 while allowing water molecules to pass through. Reverse osmosis composite membranes typically achieve a desalination rate exceeding 98%. They are widely used in industrial pure water and electronic-grade ultrapure water production, potable purified water manufacturing, boiler feedwater processes, and other applications. Employing reverse osmosis equipment prior to ion exchange significantly reduces operational water consumption and wastewater discharge.

III. Introduction to the Pretreatment System

A reverse osmosis water treatment system generally comprises a pretreatment system, reverse osmosis unit, post-treatment system, cleaning system, and electrical control system. The pretreatment system typically includes quartz sand filters, activated carbon filters, and precision filters. Its primary function is to reduce the pollution index and residual chlorine in the raw water, along with other impurities, to meet the feedwater requirements for reverse osmosis. Detailed classification of the pretreatment system:

1. Quartz Sand Filter

The quartz sand filter primarily removes suspended solids, colloids, silt, clay, humic substances, particulate matter, and other impurities from water. It reduces turbidity to clarify water quality and protects reverse osmosis membranes.

2. Activated Carbon Filter

This filter utilizes the abundant hydroxyl groups and other functional groups on activated carbon's surface to chemically adsorb various substances. It removes odors, organic matter, colloids, iron, and residual chlorine from water while reducing color and turbidity, thereby minimizing contamination of the reverse osmosis system.

3. Water Softener

This unit employs ion exchange resin to replace calcium and magnesium ions in water with sodium ions, thereby reducing water hardness. The resin is regenerated using water softening salt, also known as ion exchange resin regenerant.

4. Precision Filter

Employing a 5-micron PP melt-blown filter cartridge, this stage primarily removes particles larger than 5 microns not fully captured by the pretreatment system. It also intercepts filter media lost during the preceding three filtration stages, thereby protecting the RO membrane. The filter cartridge's ability to maintain normal operating conditions directly impacts the membrane's performance. Cartridges are typically replaced every 3-4 months.

IV. Reverse Osmosis System Overview

The reverse osmosis system primarily consists of multi-stage high-pressure pumps, reverse osmosis membrane elements, membrane housings (pressure vessels), and support structures. Its main function is to remove impurities from water, ensuring the output meets usage requirements. The high-pressure pump boosts the pressure of water from the security filter to the RO operating pressure, then evenly distributes it to the pressure vessels. The water flow is separated by the reverse osmosis membrane, forming two streams within the vessels. A portion of the feedwater permeates the membrane to form purified water, while the remaining inorganic salts and solid residues are retained and concentrated into concentrate, achieving separation of inorganic salts from water.

Purified water flows out from each pressure vessel housing reverse osmosis membrane elements, converges, passes through a flow meter, and exits the equipment outlet into the purified water tank. Concentrate flows out from the concentrate outlet of the pressure vessels.

Desalination Mechanism of Reverse Osmosis Membranes: The semipermeable membrane surface is densely covered with minute pores. Water molecules selectively adsorb onto the membrane surface, while salt solutes are repelled. Ions with higher valence states are repelled more strongly. Water molecules surrounding the pores flow through the membrane via capillary action under reverse osmosis pressure, producing purified water and achieving desalination.

When pore sizes exceed the reverse osmosis membrane's range, salt solutions leak through the membrane. Monovalent salts leak most readily, followed by divalent salts, with trivalent salts leaking least. With pore sizes <1.0 nm, RO membranes can filter out Pseudomonas aeruginosa (3000×10⁻¹⁰ m)—one of the smallest bacteria; It also filters various viruses, such as influenza virus (800×10⁻¹⁰m) and meningitis virus (200×10⁻¹⁰m); it can even remove pyrogens (10-500×10⁻¹⁰m). The characteristics of producing pure water using reverse osmosis are as follows: compact equipment structure with simple maintenance, small footprint, and high water production rate; without

When the pore size of the membrane exceeds the range of reverse osmosis membrane pores, aqueous salt solutions will leak through the membrane, with monovalent salts leaking the most, followed by divalent salts, and trivalent salts leaking the least. With a pore size <1.0 nm, RO membranes can filter out Pseudomonas aeruginosa (3000×10⁻¹⁰ m)—one of the smallest bacteria—as well as various viruses such as influenza virus (800×10⁻¹⁰ m) and meningitis virus (200×10⁻¹⁰ m). and even filter out pyrogens (10⁻⁵⁻¹⁰ m). The characteristics of producing pure water using reverse osmosis are as follows: compact equipment structure with easy maintenance, small footprint, and high water production rate; low energy consumption due to pure water production without phase change; no discharge of acidic or alkaline wastewater, making it a new energy-saving and environmentally friendly equipment;

The wastewater-to-pure-water ratio in reverse osmosis systems typically ranges from 3:1 for small household units to 1:1 for efficient small industrial systems, with large-scale systems achieving 0.3:0.7. Further reducing wastewater discharge increases costs and inevitably shortens membrane lifespan. This advanced membrane separation technology finds extensive applications across diverse fields.

V. Reverse Osmosis System Maintenance

1. Conduct daily water quality testing and maintain detailed records of operational parameters. Address any anomalies promptly. Regularly monitor and document critical metrics such as pure water conductivity, pressure readings at various points, and inlet/outlet flow rates.

2. Periodically replenish the salt tank with regenerant. Set regeneration intervals based on site conditions and production volume, typically every 3-4 days.

3. Replace security filter cartridges promptly (generally every 3-6 months).

4. Regularly wipe down the machine to maintain equipment cleanliness.

5. Frequently inspect piping for leaks and address promptly.

6. Ensure uninterrupted water and power supply to the equipment. In case of power or water outages, reset equipment timers accordingly—especially re-setting regeneration timing after power loss. Unauthorized personnel must not operate electrical control buttons or piping valves to prevent malfunctions.

VI. Emergency Measures

When power failure or damage to components like the main pump or membrane prevents pure water production, open the softened water valve to continue using softened water and maintain normal operation of water-using equipment. This method should be applied based on the actual requirements of the water-using equipment. 1. In case of severe leakage, immediately shut off the equipment's water inlet valve and power supply, then notify the service provider for handling. 2. During water production, promptly replace consumables such as resin, membranes, or activated carbon if the post-membrane pressure gauge exceeds 1.5 MPa, conductivity exceeds 15 μS/cm, or product water quality falls outside the standard range.

VII. Consumable Replacement Guidelines
As consumables like quartz sand, activated carbon, and softening resin are granular materials, accumulation can form porous structures that provide a breeding ground for microbial growth over time. Additionally, activated carbon and softening resin exhibit adsorption saturation limits, leading to diminished filtration efficiency with prolonged use. Replacement should occur when backwashing and regeneration fail to restore pretreatment effectiveness, ensuring optimal feedwater quality for reverse osmosis membrane modules.

Under optimal conditions, service life guidelines are: - Quartz sand: 10-24 months - Activated carbon: 10-12 months - Resin: 10-12 months - Precision filter cartridges: 3-6 months - Reverse osmosis membranes: Approximately 12 months Resin regeneration cycle: Under normal conditions, resin regeneration takes 1-3 days.

VIII. Application Fields

1. Power Industry: Boiler feedwater, cooling water reservoirs;

2. Electronics Industry: Ultra-pure water for semiconductor manufacturing, cleaning water for integrated circuits, formulation water;

3. Food Industry: Formulation water, production water;

4. Pharmaceutical Industry: Process water, formulation water, washing water, water for injection, sterile water preparation;

5. Beverage Industry: Formulation water, production water, washing water;

6. Chemical Industry: Production water, wastewater treatment;

7. Drinking Water Projects: Ultra-pure water preparation, drinking water purification;

8. Petrochemical Industry: Oilfield injection water, advanced treatment of petrochemical wastewater;

9. Seawater Desalination: Production and domestic water supply for islands, coastal water-scarce regions, ships, and seawater oilfields;

10. Environmental Protection: Recovery of precious metals from electroplating rinse water and water recycling to achieve zero or minimal discharge.