Water Safety Plan Guide: Treatment Processes Ultraviolet Irradiation Disinfection s1

Water Safety Plan Guide Treatment Processes – Ultraviolet Irradiation Disinfection Version 1, Ref P7.4

January 2014 Citation: Ministry of Health. 2014. Water Safety Plan Guide: Treatment Processes – Ultraviolet Irradiation Disinfection, Version 1, ref p7.4. Wellington: Ministry of Health.

Published in January 2014 by the Ministry of Health PO Box 5013, Wellington, New Zealand

ISBN: 978-0-478-42746-2 (print) ISBN: 978-0-478-42747-9 (online)

Previously published in 2001 as Public Health Risk Management Plan Guide: Treatment Processes – Ultraviolet Irradiation Disinfection, Version 1, ref p7.4. This publication’s title and any reference within the text to ‘public health risk management plan’ were changed in January 2014 to reflect the December 2013 legislation change of the term ‘public health risk management plan’ to ‘water safety plan’. No other changes have been made to this document.

This document is available at: www.health.govt.nz This work is licensed under the Creative Commons Attribution 4.0 International licence. In essence, you are free to: share ie, copy and redistribute the material in any medium or format; adapt ie, remix, transform and build upon the material. You must give appropriate credit, provide a link to the licence and indicate if changes were made. Contents

4 [Title]

Introduction

Shining intense ultraviolet (UV) light through drinking water (UV irradiation) can be used to disinfect it. This Guide is concerned with this process.

If an event occurs during UV irradiation (ie, the UV disinfection process doesn’t work properly), the UV dose may be too little to kill germs and stop them from causing sickness.

UV treatment can only kill germs while they are being irradiated. The UV treatment unit should therefore be installed as close to the point of use as possible. This reduces the likelihood of germs getting into the water after treatment, or germs that have been only damaged reviving.

The use of UV irradiation can present risks to the health of treatment plant staff. These are acknowledged, but are not discussed further as such risks are the subject of health and safety in employment legislation.

The UV disinfection process and the risks associated with it cannot be viewed in isolation. This Guide looks only at the UV irradiation of the water. The value of UV light as a disinfectant is also affected by elements of the water supply system dealt with in other Guides.

Several factors influence how effective disinfection is: intensity and wavelength(s) of the UV delivered; germs are killed fastest by intense light in a particular wavelength range exposure period; the longer germs are exposed to UV light, the higher the percentage that are killed design of the contact chamber where the water is irradiated; germs can escape full exposure to the light if design is poor water quality (turbidity, colour, iron, manganese, hardness); constituents of the water that absorb light or form deposits on lamp surfaces reduce the effectiveness of the light in killing germs (see the S1, P1, P5 and P6 series of Guides and Guide P8.2).

6 Water Safety Plan Guide: Ref P7.4, Version 1 Treatment Processes – Ultraviolet Irradiation Disinfection January 2014 Risk Summary

The event creating the greatest risk involved in UV irradiation of drinking-water is the UV dose not being too low to kill germs in the water (see P7.4.1).

The most important preventive measures are: regularly maintain the unit and clean the surface of the lamp, or lamp sleeve, to make sure enough UV light passes into the water (see P7.4.1.1) use a sensor to measure the UV irradiation (see P7.4.1.1) put an alarm on the irradiation sensor to let you know when the light intensity is too low and to cut off the water flow if this happens (see P7.4.1.1).

(References in parentheses are to the Risk Information Table.)

Ref P7.4, Version 1 Water Safety Plan Guide: 7 January 2014 Treatment Processes – Ultraviolet Irradiation Disinfection Risk Information Table

Reliable information about water quality is essential for the proper management of a water supply. Knowledgeable and skilled staff are also essential for minimising the public health risks associated with water supplies. Please read the staff training (Guide G1) and the monitoring guides (Guide G2). While we haven’t pointed out every detail of how these documents are linked with the present document, the links are many and are important.

Abbreviations: DWSNZ – Drinking-Water Standards for New Zealand

8 Water Safety Plan Guide: Ref P7.4, Version 1 Treatment Processes – Ultraviolet Irradiation Disinfection January 2014 Causes Preventive measures Checking preventive measures Corrective action

What to check Signs that action is needed

Event: UV DOSE TOO LOW Possible hazards: Germs not killed. Level of risk: High1

P7.4.1.1 Routine cleaning and Microbiological E. coli or aerobic Clean quartz sleeve and Inadequate UV maintenance schedule for lamp quality. bacterial spores is sensor lens. intensity at the sleeves and UV sensor. UV intensity. detected in 100 ml Replace UV lamp. sample of water required Regular replacement of UV Alarm. Relocate sensor, or wavelength. lamp. leaving the UV unit. Signs of scaling on purchase a unit with The sensor for measuring UV Activation of the UV correctly located sensor. the lamp’s quartz intensity alarm. radiant exposure should be on sleeve and sensor Lubricate sleeve seal. the wall of the irradiation Water flow shut off. lens. Check water hardness chamber farthest from the UV Water inside quartz lamp. Maintenance records. and treat to reduce if sleeve (ineffective necessary. Lubrication of seal each time seal). Manually disinfect the tube is removed (with Scale formation on water-based lubricant). storage tank (chlorine) the quartz sleeve. until satisfactory water Reduce water hardness to Absence of quality can be restored, minimise scaling on lamp maintenance records. or close the supply sleeves and UV sensor lens. down and arrange for Link UV sensor to alarm to another supply of water. show inadequate UV intensity, and a solenoid to shut off water flow.

1 The consequences of the event, and therefore the level of risk, will be influenced by the quality of the source water and the effectiveness of treatment processes prior to the UV disinfection process.

Ref P7.4, Version 1 Water Safety Plan Guide: 9 January 2014 Treatment Processes – Ultraviolet Irradiation Disinfection Causes Preventive measures Checking preventive measures Corrective action

Event: UV DOSE TOO LOW cont’d

P7.4.1.2 Independent check on Microbiological E. coli or aerobic Recalculate dose rates Time of calculations (especially after quality. bacterial spores is and change flow exposure to UV alterations to the system). UV dose (intensity x detected in 100 ml settings. radiation Routine maintenance and time). sample of water Identify cause of fault leaving the UV unit. inadequate due calibration checks on flow rate Maintenance records and rectify. to poor flow controller. of flow rate Undertake flow rate control, Establish how UV lamp output controller. controller calibration. incorrect dose is affected by temperature, and Minimum-maximum Calculated UV dose at Reduce water flow until calculation, or reduce water flow accordingly. low water thermometer readings wavelength of 240290 UV irradiation dose temperature. of water temperature. nm is less than exceeds 40 mW.s/cm2 is 400 J/m2 acceptable. 2 [40 mW.s/cm ]. Manually disinfect Calculations not storage tank (chlorine) cross-checked and until satisfactory water signed off. quality can be restored, Maintenance and or close the supply calibration checks not down and arrange for signed off. another supply of water.

P7.4.1.3 Install adequate filtration Microbiological E. coli or aerobic Obtain a more suitable Excessive system. quality. bacterial spores is filter system. colour or Regular replacement and Filter maintenance detected in 100 ml Replace filter cartridge. turbidity. maintenance of filters. schedule. sample of water leaving the UV unit. Turbidity/colour post- filter. Excessive turbidity or colour (sufficient to Pressure drop across reduce the UV the filter intensity to a level (breakthrough or that is too low). rupture may lead to low pressure drop). Absence of maintenance records.

P7.4.1.4 Regular maintenance of UV Alarm. No electrical power. Make arrangements for Power supply power supply. Power supply Absence of a more reliable power failure. An alarm to indicate power maintenance maintenance records. supply to be provided. failure. schedule. Manually dose chlorine Stand-by generator or battery into the holding tank, or bank. close the supply until power is restored and Solenoid shut-off valve to stop arrange for another flow. supply of water.

Event: UV DOSE TOO LOW cont’d

P7.4.1.5 Staff training for sample Audit staff training Inadequate records. Train staff. Monitoring analysis and record keeping. and sampling records. Monitoring schedule Put monitoring schedule samples not Develop monitoring schedule not followed. in place. taken or and roster. incorrectly recorded (see Guide D4).

10 Water Safety Plan Guide: Ref P7.4, Version 1 Treatment Processes – Ultraviolet Irradiation Disinfection January 2014 Causes Preventive measures Checking preventive measures Corrective action

P7.4.1.6 Develop a quality assurance Maintenance log and E. coli or aerobic Replace faulty Method of UV system for monitoring, and schedule for bacterial spores equipment. dose/turbidity/ instrument calibration. equipment. detected in 100 ml Start using approved colour Staff training in quality Monitoring schedule. sample of water methods for monitoring leaving the UV unit. measurement assurance methods. Audit staff training (see DWSNZ:2000 incorrect, or and methods used to Equipment fails where necessary). instruments monitor water quality. quality control Put in place a incorrectly checks. maintenance schedule calibrated (see Evidence that for instruments. Guide D4). monitoring schedule Train staff. has not been followed. Evidence of use of unsatisfactory methods and instruments for monitoring.

Event: AFTER TREATMENT, WATER IS RE-INFECTED, OR GERMS REVIVE Possible hazards: Germs. Level of risk: Low–High2

P7.4.2.1 Microbiological water E. coli or aerobic Periodic shock dose of A number of practices may lead to reinfection. quality. bacterial spores is the distribution system (See Guides D2.3 and D2.4 for causes and detected in 100 ml with a strong preventive actions.) sample of water disinfectant, eg, leaving the UV unit. chlorine. Resuscitation of micro-organisms is a natural process, therefore Corrective Actions, rather Heterotrophic plant than Preventive Measures, are required. count in distribution system is higher than that leaving the UV unit.

2 The level of risk will be high if UV disinfection takes place a long way from the point of use, or is stored after treatment before use.

Ref P7.4, Version 1 Water Safety Plan Guide: 11 January 2014 Treatment Processes – Ultraviolet Irradiation Disinfection Contingency Plans

If an event happens despite preventive and corrective actions you have taken, you may need to consult with the Medical Officer of Health to assess how serious a problem is.

Event – Dose of UV light is lower than minimum acceptable level

Indicators Action required if UV radiant exposure is less than 400 J/m2 at 240- 290 nm. In 100 ml samples of water leaving the treatment plant, E. coli or aerobic bacterial spores is continually detectable, or is present at elevated levels (more than 10 per 100 mL). Widespread illness in the community.

Required Immediately take the treated water off line. Provide another source of actions: potable water until water of acceptable quality can again be supplied. Then: if excessive turbidity detected in water after filtration: identify and rectify cause of inadequate filtration monitor turbidity until it reaches acceptable limits if excessive colour detected in water after filtration: identify and rectify cause of excess colour monitor colour until it reaches acceptable limits if low UV dose not due to poor influent water quality: identify and rectify cause of reduced UV reading at the sensor (ie, low tube output, dirty tube/quartz sleeve, increased flow, etc). Then, in all above situations: if indicator organisms or pathogens have entered the reticulation, inform MOH of the transgression restart plant operation record cause of system failure and steps taken to correct modify water safety plan if necessary.

Responsibility: Manager designated responsible for the water supply.

12 Water Safety Plan Guide: Ref P7.4, Version 1 Treatment Processes – Ultraviolet Irradiation Disinfection January 2014 Water Safety Plan Performance Assessment

To make sure that your supply’s water safety plan (formerly known as a Public Health Risk Management Plan, PHRMP) is working properly, periodic checks are needed. The overview document outlines what needs to be done. The following table provides the detailed information for checking this particular supply element.

What to measure or UV intensity (calculate UV dose). observe: E. coli (faecal indicator). Aerobic bacterial spores. Follow the protocols set out in DWSNZ:2000. Note that the presence of faecal indicators may be influenced by factors other than the adequacy of the UV treatment process (eg, reinfection downstream).

How often: For the monitoring frequency for E. coli measurements see DWSNZ:2000 Section 3.3.2.

What to do with the Results need to be recorded to meet legislative requirements or to results: allow water safety plan performance assessment. The WINZ database is good for this. The collected data need to be periodically reviewed to see whether problems with this supply element are developing. This should be done as frequently as the manager responsible considers necessary to minimise risk to public health arising from this supply element. Should this review show any unusual incidents, indicate that proper procedures are not being carried out, highlight poor laboratory results or indicate that poor water quality is reaching customers, then review the procedures for managing UV disinfection. Evaluate the monitoring results, and any actions taken as the result of having to implement a contingency plan, to see if the water safety plan needs modification – eg, preventive measures are up to date; the contingency plan steps are still adequate; and changes to the treatment processes are recognised in the plan.

Responsibility: Manager designated responsible for water quality.

Ref P7.4, Version 1 Water Safety Plan Guide: 13 January 2014 Treatment Processes – Ultraviolet Irradiation Disinfection