1. What is Total Chlorine Residual at Any Particular Time?

Definition: This calculator determines the chlorine residual concentration needed to achieve a specific reduction in coliform bacteria over a given contact time.

Purpose: It helps water treatment professionals ensure proper disinfection while maintaining safe chlorine levels in drinking water.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( C_t \) — Chlorine residual concentration (kg/m³)
• \( N_0 \) — Initial number of coliform bacteria
• \( N_t \) — Number of coliform bacteria at time t
• \( t \) — Contact time (seconds)

Explanation: The formula calculates the chlorine concentration needed to achieve the specified bacterial reduction during the given contact period.

3. Importance of Chlorine Residual Calculation

Details: Proper chlorine residual ensures effective disinfection while preventing excessive chlorine that could cause taste/odor issues or disinfection byproducts.

4. Using the Calculator

Tips: Enter the initial and final coliform counts, and the contact time in seconds. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical chlorine residual for drinking water?
A: Typically 0.2-2.0 mg/L (0.0002-0.002 kg/m³), with 0.5 mg/L being common for distribution systems.

Q2: How is coliform count measured?
A: Through laboratory tests like membrane filtration or multiple-tube fermentation methods.

Q3: Why is contact time important?
A: Chlorine needs sufficient time to inactivate pathogens. The CT value (concentration × time) determines disinfection effectiveness.

Q4: What factors affect chlorine demand?
A: Organic matter, ammonia, temperature, pH, and other water quality parameters influence chlorine demand.

Q5: How often should chlorine residual be tested?
A: Continuous monitoring is ideal; at minimum, daily testing at various points in the distribution system.