Application of Sodium Dichloroisocyanurate in Water Source Disinfection

Application of Sodium Dichloroisocyanurate in Water Source Disinfection

I. Basic Properties of Sodium Dichloroisocyanurate

Sodium Dichloroisocyanurate, abbreviated as SDIC, has the molecular formula C₃Cl₂N₃NaO₃. It is a commonly used organic chlorine disinfectant belonging to the isocyanurate family. At room temperature, it appears as a white crystalline powder or granules with a faint chlorine odor. Its available chlorine content is approximately 55%–60%. It is stable, easy to store and transport. Compared to traditional chlorine disinfectants such as bleaching powder and sodium hypochlorite, SDIC dissolves rapidly in water and slowly releases hypochlorous acid upon hydrolysis. Through the oxidation of hypochlorous acid, it destroys the nucleic acids, enzyme systems, and other active substances of microorganisms, thereby achieving effective disinfection. It exhibits good killing effects against a wide range of pathogenic microorganisms, including bacterial vegetative cells, bacterial spores, viruses, and fungal spores.

The germicidal efficacy of SDIC is relatively less affected by water pH. It performs best in neutral to weakly acidic water environments. In water source disinfection scenarios, it adapts well to the pH range of most natural water sources, with no significant loss of disinfection efficiency due to pH fluctuations. Additionally, cyanuric acid, a residual product of hydrolysis, helps maintain a certain level of residual chlorine in the water, prolonging the disinfection duration and reducing the risk of secondary contamination.

II. Mechanism of SDIC in Water Source Disinfection

When SDIC is added to a water source, it rapidly hydrolyzes to produce hypochlorous acid and cyanuric acid. The reaction equation is:

C₃Cl₂N₃NaO₃ + 2H₂O → 2HClO + C₃H₃N₃O₃ + NaCl

The hypochlorous acid generated is the core disinfecting agent. The hypochlorous acid molecule is small, uncharged, and can quickly penetrate microbial cell walls. Once inside the microorganism, it oxidizes and destroys key enzyme systems such as sulfhydryl enzymes, interfering with microbial energy metabolism and nucleic acid synthesis, ultimately leading to microbial death.

Compared to other chlorine disinfectants, SDIC releases hypochlorous acid more slowly and steadily, maintaining an effective residual chlorine concentration in water for a longer period. It not only rapidly kills common pathogenic bacteria in water sources but also inhibits the regrowth of residual microorganisms after disinfection. This makes SDIC suitable for both centralized water supply systems and temporary emergency water treatment. Moreover, cyanuric acid, the hydrolysis product, stabilizes hypochlorous acid in water, reducing the rapid consumption of hypochlorous acid by organic matter, thereby improving disinfection efficiency and lowering the required disinfectant dosage.

III. Application Scenarios and Dosage Guidelines

1. Routine Disinfection of Drinking Water Sources

For conventional centralized treatment of surface water or groundwater as drinking water sources, SDIC is typically used in both pre‑disinfection and final disinfection stages.

· Pre‑disinfection: Applied to raw water at a dosage of approximately 0.5–1.0 g per cubic meter (m³) of raw water. Its main functions are to kill plankton and algae in the raw water, inhibit bacterial growth, and reduce microbial contamination of filter media and membranes in subsequent treatment steps.

· Final disinfection: Applied after the filtration process at a dosage of 1.0–2.0 g per cubic meter of water. This ensures that the effluent residual chlorine meets the requirements of the Standards for Drinking Water Quality (e.g., residual chlorine at the end of the distribution network not less than 0.05 mg/L).

2. Emergency Water Source Disinfection

In scenarios such as natural disasters or public health emergencies, SDIC is widely used for disinfection of decentralized emergency water supplies due to its solid granular form, ease of transport, and simple application without complex preparation equipment. For contaminated temporary water sources, the recommended dosage is generally 2.0–5.0 g per cubic meter of water, adjusted according to the degree of contamination:

· Good sensory quality (clear, no obvious odor or turbidity): Reduce dosage to 1.5–2.0 g/m³.

· Mild contamination (some suspended solids or visible impurities): Pre‑treatment by sedimentation and filtration is recommended, followed by disinfection at 3.0–4.0 g/m³ SDIC.

· Obvious contamination: Increase dosage to 5.0 g/m³. After disinfection, residual chlorine must be tested and confirmed as acceptable before the water is used.

3. Disinfection of Storage Containers and Private Water Sources

For small‑scale water sources such as household wells or storage tanks, SDIC can be used for periodic disinfection. A typical dosage of 1.5–2.5 g per cubic meter of stored water is sufficient. After adding, the water should be mixed thoroughly and allowed to stand for at least 30 minutes before use. Regular application helps inhibit the formation of biofilm on inner surfaces of storage containers, maintaining water quality in compliance with hygienic standards.