Chlorine dioxide removal of green algae, algae, chlorophyll, and toxin…
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Chlorine dioxide (ClO2) is attracting attention as a highly effective alternative for removing algae and green algae, which are major nuisances in aquatic ecosystems, based on its powerful oxidizing power. In particular, unlike conventional chlorine treatment, it is evaluated as an environmentally friendly water treatment agent because it does not generate harmful organochlorine compounds such as carcinogens, trihalomethanes (THMs), haloacetic acids (HAAS), haloacetonitrines (HANs), chloral hydrate, and chloroform.
1. Principle and Basis of Algae Removal (Scientific Basis)
Chlorine dioxide kills algae by penetrating their cell walls and oxidizing the amino acids and proteins inside.
• Destruction of Cell Walls: It alters the permeability of the algal cell membrane, inducing the leakage of intracellular substances. • Chlorophyll Destruction: Directly oxidizes chlorophyll (Chlorophyll-a), the core component of algal photosynthesis, causing the algae to lose their photosynthetic capacity.
• Metabolic Inhibition: Prevents reproduction by destroying intracellular enzyme systems.
• Toxin Decomposition: Effectively oxidizes microcystin, a toxic substance problematic during algal blooms, thereby neutralizing its toxicity.
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2. Key Benefits
• Rapid Reactivity: Rapidly reduces algal concentration within a short period, even at low concentrations.
• Byproduct Suppression: Eliminates off-flavors and odors resulting from reactions with phenols, and produces almost no trihalomethanes (THMs).
• Broad pH Effect: Unlike conventional chlorine, its sterilization and oxidizing power remains consistent across a wide pH range of 2 to 10. ________________________________________
3. Domestic and International Research Data and Case Studies
* Domestic Case Studies and Research
• Advanced Water Treatment at Water Purification Plants: In various water purification plants in Korea (such as the Nakdong River system), chlorine dioxide is used as an alternative to pre-chlorination to remove algae and off-flavors (Geosmin, 2-MIB) during the occurrence of algal blooms in the summer.
• Research by the National Institute of Environmental Research: Research results have been reported indicating that applying chlorine dioxide concentrations of 0.5–1.0 mg/L can remove over 90% of Microcystis, the causative agent of algal blooms.
• Korea Water Resources Corporation (K-water): The effectiveness of chlorine dioxide for controlling algal blooms in dams and reservoirs has been confirmed through demonstration experiments.
* International Case Studies and Research
• United States (EPA) and Europe: The EPA has approved chlorine dioxide as an official disinfectant for drinking water disinfection and algal control, and it is commonly used in water purification plants in Europe, particularly in Italy and France. • Chinese Cases: There are numerous research studies demonstrating that spraying chlorine dioxide during algal bloom outbreaks in large lakes, such as Lake Taihu, has reduced algal concentrations and improved water quality within a short period.
• Research Data: According to papers published in journals such as *Journal of Water Process Engineering*, ClO2 is known to decompose algal toxins approximately 3 to 5 times faster than chlorine.
• Research Data: According to papers published in journals such as *Journal of Water Process Engineering*, ClO2 is known to decompose algal toxins about 3 to 5 times faster than chlorine. (1) Water Supply & Purification Treatment (Domestic & International)
• When algae (especially cyanobacteria) occur
→ Used for chlorine dioxide pretreatment instead of chlorine
• Purpose:
o Destruction of algal cells
o Removal of odor substances (geosmin, MIB)
o Oxidation of toxin precursors
* In water treatment plants in the US and Europe, a combination of ClO₂ + activated carbon + ozone is utilized
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(2) Agriculture & Hydroponics
• Inhibition of algae/biofilms in culture water and nutrient solutions
• Application of fogging methods inside greenhouses
→ Confirmed effectiveness in inhibiting algal growth as well as pathogens
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(3) Water Quality Management (Aquaculture & Reservoirs)
- Reduction of floating microorganisms
- Inhibition of early algal growth
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4. Considerations for Application
* Optimal Concentration: Varies depending on the algal density of the target water, but typically shows optimal effects between 0.5 and 2.0 ppm. * Persistence: Due to its light-induced decomposition properties, it has low environmental persistence, eliminating concerns regarding secondary pollution.
* Injection Method: High-concentration (e.g., 6,000 ppm) liquid products are diluted and injected, or directly injected via an on-site generator.
Summary
Chlorine dioxide is a powerful oxidizing agent that simultaneously destroys chlorophyll and toxins in algae. Due to the low generation of environmental byproducts, it is one of the most trusted solutions in the water treatment field. In particular, it is applicable not only to large-scale water purification facilities but also to various environments requiring algae management, such as golf course ponds, fish farms, and wastewater treatment plants.
1. Dose Calculation Criteria
In typical water treatment sites, the requirement for chlorine dioxide follows the following formula: Total ClO2 Demand = (Flow rate * Target Dosage) + Organic Demand
• Low-concentration algal bloom (Prevention stage): 0.2 ~ 0.5 mg/L (ppm)
• Medium-concentration algal bloom (Early stage): 0.5 ~ 1.0 mg/L (ppm)
• High-concentration algal bloom (Severe stage): 2.0 ~ 3.0 mg/L (ppm) or higher
Note: As chlorine dioxide is consumed by substances other than algae first at higher organic matter concentrations, it is safer to design the actual dosage to be approximately 10–20% higher than the target concentration.
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2. Dosage Methods by Water System Type
① Water systems with regular inflow/outflow (Rivers, Streams, Water Treatment Plants)
Adopt a continuous dosing method.
• Design: Use a metering pump linked to a flow meter to spray directly at the downstream point of the inflow. • Key Point: Ensure a mixing zone between the flow velocity and chlorine dioxide to ensure even distribution throughout the entire water system.
② Closed Water Systems (Reservoirs, Golf Course Ponds, Fish Farms)
* Perform batch treatment or administration via a circulation system.
• Design: Calculate the total volume (V = Area * Average Depth) and then determine the total amount required to achieve the target concentration.
• Dosage Method:
- Surface Spraying: Spray across the entire water surface using a vessel or drone.
- Circulation Pump Interlocking: Inject into the intake of an existing circulation pump to induce mixing down to deep water.
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3. Design Example for Utilizing 6,000 ppm High-Concentration Liquid Phase
* The calculation for treating 1,000 tons (m³) to achieve 1 ppm is as follows:
1. Required amount of pure chlorine dioxide: 1,000 m³ * 1 g/m³ = 1,000 g
2. Required amount of 6,000 ppm liquid: 1,000 g / 0.006 = 166,666 g = 167 L
3. Conclusion: A concentration of 1 ppm is achieved by administering approximately 167 liters of stock solution per 1,000 tons of water.
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4. Monitoring and Control System (Feedback Loop)
* Post-administration management is essential for an efficient design.
• Residual concentration check: Measure residual chlorine dioxide at a certain distance from the administration point to verify that it is maintained at 0.1–0.2 ppm.
• Kill monitoring: Observe changes in Chlorophyll-a levels and any sudden fluctuations in dissolved oxygen (DO) 24–48 hours after administration. (DO may temporarily drop sharply in the event of mass algal die-off)
• Safety: To protect the aquatic ecosystem (fish, etc.), we recommend a design that maintains low concentrations for an extended period rather than making rapid changes in concentration.
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5. Step-by-Step Dosing Scenario (Standard Protocol)
1. Field Diagnosis: Calculate water volume and measure current algal density.
2. Preliminary Test (Jar Test): Collect field water, administer a small amount of chlorine dioxide, and determine the optimal reaction concentration after the experiment.
3. 1st Dosing (Shock Dosing): Administer 100% of the target concentration to achieve initial algal die-off.
4. Maintenance Dosing (Maintenance): Apply 1-2 times a week or continuously at a low concentration (0.2 ppm) to prevent recurrence.