What Contaminants Affect Reverse Osmosis Equipment

What Contaminants Affect Reverse Osmosis Equipment

In the field of purified water production, reverse osmosis technology has become the preferred process for numerous industries due to its exceptional desalination performance. The core of this technology lies in the reverse osmosis membrane—a precision filtration material with a pore size of approximately 10 angstroms. It effectively retains inorganic salts, bacteria, viruses, colloids, and organic matter in water, achieving deep purification.

However, this very precision in filtration makes reverse osmosis equipment highly susceptible to contamination from various pollutants during operation. Understanding the characteristics of these contaminants and implementing appropriate protective measures are crucial for ensuring the long-term stable operation of the equipment.

Three Primary Sources of Contaminants

Based on different contamination mechanisms, reverse osmosis membrane fouling is primarily categorized into three types:

- Physical fouling: Deposition of metal oxides, insoluble salts, colloidal particles, etc., on the membrane surface

- Chemical fouling: Adsorption of harmful chemical components within the membrane pores

- Organic Contamination: Adhesion of bacterial slime, fungi, and organic matter to the membrane surface and within pores

Among these, flux decline caused by organic contamination is the primary factor limiting membrane separation efficiency. This often compounds with concentration polarization, further accelerating performance degradation.

Characteristics and Countermeasures for Four Pollutant Types

1. Suspended Solids: The Most Manageable “Large Particles”

Characteristics:

- Commonly present in surface water and wastewater

- Particle diameter typically exceeds 1 micron

- Naturally settles in static water

Treatment Approach:

Effectively removed via fine sand filters and multimedia filters. Adding coagulants during pretreatment allows these impurities to be adsorbed by flocs, subsequently retained by the filtration system.

2. Colloidal Contaminants: Stubborn “Suspended Microparticles”

Characteristics:

- Particle size less than 1 micron

- Permanently suspended in water without natural settling

- Complex composition including silicates, iron/aluminum oxides, humic substances, etc.

Treatment Essentials:

Requires specialized flocculation and clarification processes for effective removal; conventional filtration is ineffective.

3. Biological Contaminants: The Most Covert “Destroyers”

Contamination Characteristics:

- Initially affects only front-end membrane elements

- Early signs include rapid pressure increase in front stages and abnormal increase in desalination rate

- Over time, contamination spreads throughout the entire system

Key Species: Bacteria, Biofilms, Algae, Fungi

Control Standards:

When raw water bacterial content exceeds 1000 cfu/100mg, dedicated sterilization and disinfection processes must be implemented. This is a critical indicator that cannot be overlooked during the design phase.

4. Organic Contaminants: The Most Complex “Invisible Killer”

Source Analysis:

- Natural sources: Humic organic matter formed from decaying plants and animals

- Anthropogenic sources: Industrial waste pollution

Contamination Characteristics:

- Strong adsorption to membrane surfaces, making cleaning difficult

- Impacts are unpredictable; certain trace organic compounds may cause membrane material degradation

Design Threshold:

When raw water TOC reaches 3 mg/L, specialized organic removal processes must be implemented. This is the critical threshold for ensuring safe system operation.

Organic Removal Process Selection

For surface water and wastewater treatment, a tiered treatment strategy is recommended:

1. Primary Removal: Eliminate most organic matter through coagulation, clarification, and oxidation processes.

2. Advanced Treatment: If effluent still fails to meet standards, employ activated carbon adsorption filters, organic scavengers, or ultrafiltration equipment for fine purification.

Practical Insights

The stable operation of reverse osmosis equipment relies 30% on the equipment itself and 70% on pretreatment. Understanding pollutant characteristics is only the first step; it is more crucial to configure corresponding protective measures based on raw water quality during the design phase. Particularly for organic and biological contamination, the principle of “prevention first, treatment as a supplement” must be established to control pollution risks at the source.