For users of sodium hypochlorite generators, accurate dosing directly impacts disinfection effectiveness, cost control, and compliance with water quality standards. Below is a comprehensive, standards-compliant dosing guide and application-specific recommendations (covering municipal water, wastewater, swimming pools, and more) to match your generator's output to your specific needs.
Dose Calculation Basis
Before determining the sodium hypochlorite generator dose, it is essential to confirm the available chlorine demand, which serves as the core basis for equipment model selection. The general formula is:
Available Chlorine Demand (g/h) = Design Water Volume (t/d) × Total Chlorine Demand Concentration (mg/L) ÷ 24 Hours
Note: There is currently no unified national standard for chlorine dosage across different water bodies. The following data are empirical references, and actual dosing should be determined through on-site testing to ensure compliance and effectiveness.
Application: Municipal Tap Water Disinfection
Applicable Scenarios
Small water supply stations and medium to large water plants, in accordance with GB5749-2022 Standards for Drinking Water Quality, which require free chlorine in plant outlet water to be 0.3–2 mg/L.
(1) Small Water Supply Stations
Surface Water Sources (rivers, reservoirs):
Design Dose = 1–2 mg/L
Reason: Surface water contains more algae and organic matter, requiring a higher chlorine concentration to oxidize impurities and achieve reliable disinfection.
Groundwater Sources (wells, springs):
Design Dose = 0.5–1 mg/L
Reason: Groundwater is naturally filtered and cleaner, allowing a lower chlorine dose to meet safety requirements while avoiding excess residual chlorine.
(2) Medium and Large Water Plants
Must coordinate with the three-stage disinfection process: pre-chlorination → post-chlorination → dosing chlorination.
Pre-Chlorination: 1–1.5 mg/L
Applied before the sedimentation tank for oxidation and algae inhibition.
Post-Chlorination: 2–2.5 mg/L
Applied before the disinfection tank; ensures ≥30 minutes contact time to fully eliminate pathogens.
Dosing Chlorination: 0.5–1 mg/L
Maintains ≥0.05 mg/L residual chlorine at pipeline ends to prevent secondary pollution.
Application: Domestic Sewage Disinfection
Applicable Scenarios
Sewage treatment plants at different treatment stages. The required dose depends on the degree of pollutant removal.
After Primary Treatment: 20–30 mg/L
Reason: High content of organic matter and suspended solids demands strong oxidation and disinfection capacity.*
After Incomplete Secondary Treatment: 10–15 mg/L
Reason: Moderate pollutant levels require a balanced dose for both efficacy and economy.*
After Complete Secondary Treatment: 5–10 mg/L
Reason: Lower BOD and turbidity allow reduced chlorine levels while still meeting discharge standards (total coliforms ≤1000 CFU/L).
Application: Swimming Pool Water Disinfection
Applicable Scenarios
Public and private swimming pools, following GB37488-2019 Hygienic Indicators and Limits for Public Places.
Residual Chlorine Requirement:
Maintain 0.3–1.0 mg/L free chlorine in pool water. Real-time monitoring is essential to prevent irritation from excessive chlorine.
Empirical Disinfection Dose:
2 mg/L free chlorine achieves full disinfection (99.99% removal of E. coli and fungi).
Dynamic Adjustment Principle:
Increase by 0.2–0.5 mg/L during high-traffic periods (weekends, holidays).
Reduce by 0.1–0.2 mg/L during low-traffic periods to minimize chemical waste.
Application: Hospital Sewage & Thermal Power Plant Circulation Systems
Applicable to domestic and medical wastewater, including laboratory and ward sewage.
Recommended Practice:
Conduct a pilot test with 15–25 mg/L doses, then adjust based on the "total coliforms ≤500 CFU/L" discharge standard.
Increase the dose by 5–10 mg/L for infectious disease ward sewage.
(2) Thermal Power Plant Circulation System
Used for cooling water disinfection, preventing algae growth and corrosion.
Low-Hardness Water (≤200 mg/L as CaCO₃): 3–5 mg/L
High-Hardness Water (>200 mg/L as CaCO₃): 5–8 mg/L
Target Residual Chlorine: 0.5–1.0 mg/L
Ensures effective inhibition of biofouling in circulating systems.
Important Operational Reminder
All dose data provided above are empirical references. For optimal performance:
Continuously monitor residual chlorine using a chlorine tester.
Adjust dosage dynamically based on actual microbial test results (e.g., increase by 10–20% if coliforms exceed standards).
Always comply with local water supply and environmental regulations, including sewage discharge and drinking water standards.
How to Adjust Sodium Hypochlorite Generator Dose Based on Actual Conditions
Adjusting the dose of a sodium hypochlorite generator is not a one-time setup-it requires dynamic optimization based on water quality changes, treatment goals, and external factors (e.g., flow, user load). Below is a scenario-specific adjustment guide, aligned with the previously mentioned standards (GB5749-2022, GB37488-2019) and empirical data.
Core Principle for Dose Adjustment
First, recall the core calculation formula for chlorine demand (to anchor adjustments):
Required Available Chlorine (g/h) = Design Water Volume (t/d) × Target Chlorine Concentration (mg/L) ÷ 24
All adjustments revolve around modifying either the "target chlorine concentration" (based on water quality) or matching the "design water volume" (if flow changes), while ensuring the final residual chlorine meets relevant standards.
1. Adjustment for Tap Water Treatment (Small/Mid-Large Water Plants)
Key Monitoring Indicators
Residual free chlorine (must meet GB5749-2022: 0.3–2 mg/L in plant water)
Water source quality: Turbidity (NTU), algae content, organic matter (COD/Mn)
Water flow rate (if it deviates from the original "design water volume")
Adjustment Triggers & Methods
2. Adjustment for Domestic Sewage Treatment
Key Monitoring Indicators
Residual chlorine (no mandatory national standard, but refer to empirical ranges: 5–30 mg/L based on treatment stage)
Sewage quality: COD (chemical oxygen demand), BOD (biochemical oxygen demand), suspended solids (SS)
Treatment stage (primary/secondary/unfinished secondary)
3. Adjustment for Swimming Pool Water Treatment
Key Monitoring Indicators
Residual free chlorine (GB37488-2019: 0.3–1.0 mg/L; empirical effective dose: 2 mg/L)
User load (number of swimmers per hour)
Water temperature (≥28℃ accelerates chlorine consumption)
pH value (optimal 7.2–7.8; pH >8 reduces chlorine efficacy)
4. General Adjustment Steps (Applicable to All Scenarios)
Monitor First: Use a portable residual chlorine detector (or online sensor) to test current residual chlorine; simultaneously record water quality (turbidity/COD) and flow/load.
Calculate Adjustment: Based on the trigger factor (e.g., flow up 15%, residual down 0.2 mg/L), recalculate the required available chlorine (g/h) via the core formula.
Adjust Generator: Modify the generator's output (via control panel: increase/decrease salt input or electrolysis current) to match the new required chlorine amount.
Verify & Stabilize: Test residual chlorine 30 minutes–1 hour after adjustment; if it meets standards, keep the new dose; if not, repeat steps 2–3 (fine-tune by 0.1–0.3 mg/L each time).
