The Dominant Position of Cooling Water Treatment Agents in the Water-Saving Field Remains Unshaken

Key Takeaway: In the field of water conservation and reuse, although new technologies such as membrane technology and zero discharge are constantly emerging, corrosion inhibition, scale inhibition, and biocide remain fundamental requirements for protecting cooling water systems. These are closely related to water conservation and reuse and are irreplaceable.

At the recent 2013 China Water Treatment Technology Symposium, experts pointed out that chemical treatment remains the foundation of cooling water conservation and reuse, and its mainstream position is unlikely to change. Innovation in the variety of biocides and scale inhibitors will be the main focus of water treatment chemical research.

Circulating cooling water systems need to address three main problems: microbial fouling, sedimentation, and corrosion. These three problems are different yet related, all directly or indirectly related to microorganisms in the cooling water system. The best way to solve these three problems is to add chemicals. Bao Qinai, Deputy Director of the Industrial Water Treatment Professional Committee of the China Chemical Industry Society, pointed out that practice has proven that microorganisms cause the fastest and most obvious problems in cooling water systems, potentially leading to rapid water quality deterioration. Once a large amount of biological slime is generated, corrosion and scale inhibitors immediately become ineffective, directly harming the entire system, and this harm ranks first among the three major water treatment problems. Bao Qinai believes that whether it's water directly entering the cooling system after zero discharge or recycled water entering the membrane system, the microbial problem must be solved first. Therefore, developing biocides to prevent microbial fouling is paramount.

For a long time, oxidizing and non-oxidizing biocides have been used alternately. Oxidizing biocides were first used in cooling water systems and have been used for over half a century. Their low cost, broad spectrum, high efficiency, and cost-effectiveness have kept them dominant in the microbial control of cooling water systems. However, oxidizing biocides can have negative effects on other agents and even damage equipment in the system. Therefore, developing oxidizing biocides with high biocidal efficiency and minimal negative impacts is an important innovation goal. Non-oxidizing biocides are, in some respects, more convenient and effective than oxidizing biocides. Combining them for synergistic effects has been the mainstream direction of their development and application in recent years. The biocidal capacity of a combination of two agents is greater than the sum of the biocidal capacities of the individual agents.

According to a representative from the Shengli Refinery of Sinopec Qilu Branch, long-term use of biocides can lead to drug resistance in microorganisms, affecting their biocidal effectiveness. To effectively control microorganisms and biofilm, it's often necessary to increase the dosage of chemicals and frequently alternate the addition of multiple biocides to maintain water treatment effectiveness. Therefore, he believes that a composite non-oxidizing bactericide with characteristics such as high efficiency, broad spectrum, low toxicity, rapid and long-lasting effect, strong penetration, ease of use, and a wide applicable temperature and pH range should be developed.

Bao Qinai believes that innovation and quality improvement in biocides should not only include the development and application of oxidizing and non-oxidizing biocides, but also biodispersants, biocidal synergists, shellfish fouling, and improvements in dosing and monitoring systems.

Reverse osmosis desalination technology has been widely used in wastewater reuse and zero wastewater discharge. Due to the characteristics of reverse osmosis desalination, various inorganic salt scales easily deposit on the surface of the reverse osmosis membrane on the concentrate side, affecting the desalination performance of the reverse osmosis membrane, shortening its lifespan, and in severe cases, even causing the reverse osmosis membrane module to fail. The proliferation of bacteria and microorganisms has consistently impacted reverse osmosis systems. In recent years, 70%–80% of reverse osmosis system failures have been caused by organic biological contamination. Therefore, the application of scale inhibitors has become a crucial aspect of the reverse osmosis desalination process, and the selection of scale inhibitors directly affects the safe and economical operation of the reverse osmosis unit.

Commonly used scale and corrosion inhibitors are mostly phosphorus-based composite formulations. However, since phosphorus emissions can cause eutrophication of surrounding water bodies, experts point out that given the restrictions on the production and application of phosphorus-based scale and corrosion inhibitors in water treatment, developing phosphorus-free or low-phosphorus, non-nitrogen, biodegradable, and environmentally friendly scale inhibitors that meet environmental requirements will be another major direction for the water treatment chemical industry. According to Tao Wurong, an engineer at Sinopec Shanghai Petrochemical Co., Ltd., a newly developed scale inhibitor in recent years, polyepoxysuccinic acid (PESA), combines corrosion inhibition and scale inhibition functions, exhibits good thermal stability, is phosphorus-free and non-nitrogenous, and is environmentally friendly, earning it the reputation of a green water treatment agent.