An antiscalant is a substance that disperses sparingly soluble inorganic salts in water, preventing or interfering with the precipitation and scaling of insoluble inorganic salts on metal surfaces, thus maintaining good heat transfer performance in metal equipment. Reverse osmosis antiscalants effectively prevent membrane scaling, do not condense with iron and aluminum oxides and silicon compounds to form insoluble substances, effectively inhibit silicon polymerization and deposition, increase water production and quality, and reduce operating costs.

Reverse osmosis antiscalants mainly include some natural dispersants, phosphonic acids, phosphonic carboxylic acids, phosphonic sulfonic acids, and high molecular weight polymers. Currently, most antiscalant dispersants are polymers, which can disperse insoluble inorganic salts in water and prevent or interfere with the deposition and scaling of sparingly soluble inorganic salts.

Circulating water treatment antiscalants are organically compounded with antiscalants, corrosion inhibitors, dispersants, special surfactants, and permeabilizers. It exhibits strong inhibition of scale formation caused by carbonates, sulfates, and phosphates, and demonstrates excellent corrosion resistance for metal equipment such as carbon steel, stainless steel, copper, aluminum, and galvanized pipes.

When selecting a scale inhibitor, the quality of the treated water should be the primary consideration. If the water quality fluctuates significantly, the worst-quality water should be chosen, especially for wastewater. In such cases, upstream wastewater systems should be appropriately diverted to prevent particularly polluted water from entering the wastewater recovery system. For relatively stable water quality, only scale inhibition requirements should be met, and high-purity products should be selected to extend cleaning cycles. For wastewater systems, due to their complex and fluctuating water quality, diverse scale components, and obvious scaling trends, composite scale inhibitors should be considered. The synergistic effect of each component enhances overall scale inhibition performance.

Differences between Reverse Osmosis Scale Inhibitors and Circulating Water Scale Inhibitors

Because their application scenarios differ, their requirements also differ.

1. Circulating water systems require long-term antibacterial resistance. Large amounts of polymer dispersants can be used to disperse suspended solids, thereby increasing the scale inhibition effect. 1. Circulating water systems are large in volume, operate outdoors, and have low requirements for drug purity.

2. Reverse osmosis scale inhibitors require fast-acting and efficient cation exchangers and scale-forming ions. Furthermore, due to the narrow channels within the dry membrane, polymer dispersants can cause even greater problems. The cation exchange process is a concentration process on the membrane surface; high impurity content can also affect the stable operation of the system.

3. High cation exchanger concentration is a significant advantage, reducing transportation costs. As transportation costs account for an increasingly large proportion of product costs, this has attracted the attention of suppliers. For single-agent scale inhibitors, higher concentrations result in a narrower stability range. For composite scale inhibitors, the different stability ranges of single-agent agents make it even more difficult to increase the product concentration. In addition, higher scale inhibitor concentrations lead to faster changes during storage and higher impurity content.

The core difference between reverse osmosis and circulating water treatment chemicals lies in their completely different working environments, objectives, and precision. A circulating water system is an open, large-scale heat exchange system, while a reverse osmosis system is a closed, precise membrane separation system.

The table below visually illustrates their differences in five key dimensions:

Comparison Dimensions	Circulating water treatment chemicals	Reverse osmosis treatment chemicals
Application System	Suitable for open circulating systems such as cooling towers and heat exchangers.	Membrane separation systems (such as reverse osmosis membranes, nanofiltration membranes).
Core Objectives	Comprehensive management: scale prevention, corrosion prevention, sterilization, and algae control to ensure long-term stable operation of equipment.	Precise protection: Primarily prevents membrane scaling, ensuring permeate flux and desalination rate.
Types of Reagents	Various types, including corrosion and scale inhibitors, oxidizing and non-oxidizing bactericides.	Relatively specific, mainly including scale inhibitors, reducing agents (for removing residual chlorine), and non-oxidizing bactericides.
Key Requirements	Long-lasting, broad-spectrum, and antibacterial; allows for high concentrations of polymer dispersants and has low purity requirements.	Fast, efficient, and high-purity; avoids membrane contamination by impurities; prohibits the use of large molecular polymers.
Typical Chemicals	Often compounded with organophosphonic acids, polycarboxylic acids, azoles, etc., providing both scale inhibition and corrosion inhibition functions.	Mostly specialized scale inhibitors that need to quickly bind with scaling ions, such as controlling carbonate and sulfate scale.

Why do these differences exist?

These differences are primarily determined by the characteristics of the two systems themselves:
Circulating Water System: This is an open, large-volume system where water continuously evaporates and concentrates, accumulating dust and microorganisms, and directly contacting metal pipes. Therefore, chemicals must not only prevent scaling but also prevent corrosion and kill bacteria. Its operating environment is relatively “rough,” allowing the use of lower-cost, polymer-containing chemicals.

Reverse Osmosis System: The core of this system is a sophisticated reverse osmosis membrane with extremely narrow internal channels. To prevent membrane clogging, the purity of the chemicals is crucial; any impurities can cause irreversible fouling. Simultaneously, large-molecule polymers (commonly used in circulating water chemicals) exacerbate membrane fouling and are strictly prohibited. Chemicals need to work efficiently within a short time to prevent scaling caused by concentration polarization on the membrane surface.

Important Reminder: A critical risk is that residual or improperly introduced chemicals (especially bactericides and scale inhibitors) from the circulating water system into the reverse osmosis system can severely damage the reverse osmosis membrane. For example, residual antiscalants in circulating water can affect the flux and desalination rate of the reverse osmosis membrane, while some oxidizing bactericides can directly oxidize and damage the reverse osmosis membrane, causing permanent performance loss. Therefore, the chemical management of the two systems must be strictly separated and isolated.