Treatment – Chlorine Disinfection - PowerPoint Presentation

1. Treatment – Chlorine DisinfectionDWQR Risk Assessment Training2018

2. Overview

3. Usage

4. Usage

5. Key Points to Watch For

6. Key Points to Watch For

7. Questions TCL1Could undisinfected water pass into supply? (Has the chlorine dosing system appropriate alarms or an automatic shutdown arrangement?)Automated chlorine dosing units may operate with a standby system in place, ensuring that chlorine continues to be dosed at the appropriate level if the main chlorination system fails (for example if the supply runs out, or a dosing line blocks). This will help ensure water is subject to disinfection at all times. TCL2Could lack of maintenance compromise the disinfection process?Refer to the maintenance regime recommended by the manufacturer and ask for written documentation that this is being adhered to, including servicing. Such documentation includes entries in a log book, diary records, and full records.TCL3Is there a risk of loss of chlorine dosing going undetected due to lack of appropriate alarms and shutdowns?Determine what alarms are in place to alert the operator to any loss of chlorine dosing, and whether this is linked to any automatic shut down of the supply to prevent undisinfected water entering the supply.TCL4Is there a risk of contamination due to use of chemicals of inappropriate grade, i.e. not approved for use in drinking water supplies? Chemicals used in a chlorination system must be approved for use with drinking water supplies and comply with Regulations.TCL5Could disinfection be compromised due to incorrect storage of chemicals or excessive storage times? Hypochlorite storage should not exceed 6 months as its strength will reduce and there is an increasing risk of byproducts such as chlorate forming. Poor storage conditions can exacerbate this degradation or render the disinfectant ineffective.TCL6Is there a possibility of incorrect making up / diluting of hypochlorite solution?Users should be aware of the strength of hypochlorite solution required and how this is made up. Clear instructions should be present on site and all chemicals and equipment should be clearly labelled.TCL7Could there be confusion over the target chlorine residual (is it documented and appropriate?)The target chlorine residual should be set at an appropriate level and this must be clearly documented on site.TCL8Is there a risk of poor control of disinfection due to lack of residual monitoring?Chlorine demand can vary rapidly, meaning that the amount of chlorine available to disinfect the water can change, putting effective disinfection at risk. It is important that chlorine residual is monitored regularly (ideally continuously via online monitors) and chlorine doses are adjusted accordingly. TCL9Is there a risk of inadequate contact time under some flow conditions?Chlorine needs adequate contact time (Ct) with the water in order to disinfect effectively. A suitable contact tank or pipe should be present that ensures sufficient contact time at all flows (it may be necessary to restrict the maximum flow to enable this). Ct is a measure of disinfection and is calculated by multiplying the chlorine residual in mg/l by contact time in minutes. The appropriate Ct for a given system and water quality is best decided by an expert, but 10 is a reasonable minimum value for a good quality raw water. TCL10Is there potential for by-product formation (primarily THMs?)Where waters are high in organic material and/or chlorine doses are poorly controlled or very high, disinfection by-products such as trihalomethanes may be formed. Formation of these can be controlled by improving removal of organics (colour) prior to chlorine addition, improving control of chlorine dosing and minimising water age.