Pre-treatment Processes
– Waste-Liquor Reintroduction
Version 1, Ref P4.4
January 2014
Citation: Ministry of Health. 2014. Water Safety Plan Guide: Pre-treatment Processes – Waste-Liquor Reintroduction, Version 1, ref p4.4. Wellington: Ministry of Health.
Published in January 2014
by the Ministry of Health
PO Box 5013, Wellington, New Zealand
ISBN: 978-0-478-42722-6 (print)
ISBN: 978-0-478-42723-3 (online)
Previously published in 2001 as Public Health Risk Management Plan Guide: Pre-treatment Processes – Waste-Liquor Reintroduction, Version 1, ref p4.4. This publication’s title and any reference within the text to ‘public health risk management plan’ was 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
Introduction 1
Risk Summary 2
Risk Information Table 3
Contingency Plans 5
Water Safety Plan Performance Assessment 6
Ref P4.4, Version 1 Water Safety Plan Guide: iii
January 2014 Pre-Treatment Processes – Waste-Liquor Reintroduction
Ref P4.4, Version 1 Water Safety Plan Guide: iii
January 2014 Pre-Treatment Processes – Waste-Liquor Reintroduction
Introduction
This Guide is concerned with the process of recycling waste liquor from the treatment process back into the raw water entering the plant. This is done to reduce the amount of waste water requiring disposal and in some cases to improve the effectiveness of the coagulation-flocculation process.
The waste liquor is almost certain to contain germs and health-significant chemicals. Your treatment processes must be able to produce a safe water despite this additional demand on its capabilities, otherwise the process has a very high risk.
If an event occurs during the reintroduction of the waste liquor (ie, some goes wrong with the process), the following could happen:
· If previously removed contaminants are added back into the water, and following processes do not remove them, germs and chemicals may cause sickness
· If control over the coagulation process is lost, and following processes do not remove them, germs and chemicals may cause sickness.
The reintroduction of waste liquor, and the risks associated with it, cannot be viewed in isolation. If the process is used, it can influence how well the coagulation (see P5 series Guides) and filtration processes (see P6 series Guides) work. The amount of waste liquor that can be added back into the raw water without creating a risk to public health will depend on:
· the quality of the raw water
· the nature of the waste produced by the treatment processes
· how effective the treatment processes are in removing the contaminants.
Risk Summary
The event creating the greatest risk in the reintroduction of waste liquor is reintroducing contaminants that have already been removed (see P4.4.1).
The most important preventive measure is to make sure that as much of the solid material as possible is removed from the waste before it is reintroduced (P4.4.1.2).
(References in parentheses are to the Risk Information Table.)
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.
Abbreviation: DWSNZ – Drinking-Water Standards for New Zealand
Causes / Preventive measures / Checking preventive measures / Corrective action /What to check / Signs that action is needed /
Event: REINTRODUCTION OF PREVIOUSLY REMOVED CONTAMINANTS1
Possible hazards: Germs and health significant chemical determinands.
Level of risk: High
P4.4.1.1
Contaminants in the aqueous phase. / · Avoid waste treatment conditions that redissolve contaminants. / · Colour – natural organic matter.
· Polymers/ monomers.
· pH.
· Metals, including aluminium if used as the coagulant. / · Elevated concentrations of contaminants in combined raw water waste stream.
· Elevated coagulant demand. / · Cease reintroduction of waste stream.
· Alter waste treatment to reduce dissolved contaminants.
P4.4.1.2
Inadequate separation of solids from aqueous phase. / · Determine the range of contaminant concentrations in the waste, and the relative amounts in the solids and the reintroduced waste stream.
· Determine the turbidity of the waste stream above which reintroduction should be stopped because of excessive contaminant levels. / · Bacteria and protozoa.
· Turbidity, particle content.
· Colour – natural organic matter.
· Polymers/monomers.
· Metals, including aluminium if used as the coagulant.
· Turbidity. / · Elevated coagulant demand.
· Ensure that reintroduction can be stopped when the turbidity of the waste stream is too high. / · Stop reintroduction of waste stream manually.
· Install controller.
1 Contaminants will inevitably be reintroduced with the waste liquor; a small amount of particulate matter is needed if the coagulation process is to be seeded. You need to be aware of the levels that your treatment system can tolerate, and to keep contaminant levels within these limits. This event is concerned with reintroduced contaminants beyond these limits.
Causes / Preventive measures / Checking preventive measures / Corrective action /What to check / Signs that action is needed /
Event: LOSS OF PROCESS CONTROL (primarily coagulation, due to variation in the combined raw water/waste water composition).
Possible hazards: Germs and health significant chemical determinands.
Level of risk: Low–moderate
P4.4.2.1
Controller or pump malfunction (see Guide P10). / · Routine controller and pump maintenance schedule. / · Maintenance log. / · Maintenance log not signed off.
· Sudden change in coagulant demand. / · Identify cause of fault and rectify.
P4.4.2.2
Rate of reintroduction is not proportional to the raw water flow. / · Ensure reintroduction rate is proportional to the flow, not fixed rate. / · Flow and rate of waste stream reintroduction. / · Coagulant demand not proportional to flow rate. / · Install flow proportional controller.
P4.4.2.3
Control of coagulation processes does not take account of the composition of the combined raw water and waste stream. / · Ensure coagulation dose control (eg, turbidity, colour, streaming current detector) sited so that it responds to the combined stream, not just the raw water. / · Turbidity.
· Colour.
· Particle charge – streaming current. / · Elevated turbidity, colour and residual coagulant in filtered water. / · Re-site coagulant dose control.
P4.4.2.4
Poor or no control of waste stream composition. / · Avoid waste treatment conditions that re-dissolve contaminants. / · Colour – natural organic matter.
· Polymers/ monomers.
· pH.
· Metals, including aluminium if used as the coagulant.
· Bacteria and protozoa.
· Turbidity, particle content.
· Colour – natural organic matter.
· Polymers and monomers.
· Metals, including aluminium if used as the coagulant. / · Elevated concentrations of contaminants in combined raw water waste stream.
· Elevated coagulant demand.
· Elevated coagulant demand. / · Stop reintroduction of waste stream.
· Alter waste treatment.
· Ensure waste treatment adequately and consistently separates solids from the aqueous phase using, for example, polymers, centrifuge, press, gravity thickeners. / · Alter waste treatment.
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 – Previously-removed contaminants are reintroduced and not removedIndicators / · Bacteria and protozoa in the treated water.
· Elevated turbidity and colour.
· Elevated coagulant residual in the treated water.
Required actions: / · Follow Sections 3.4 and 4.4 of DWSNZ:2000.
· Identify the reason for the failure of the process and rectify.
· Monitor contaminant until it reaches acceptable limits.
· Record the reason for the failure and the steps taken to rectify.
· Modify the water safety plan if necessary.
Responsibility: / Manager designated responsible for water quality.
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 observe: / · Bacteria and protozoa.· Turbidity and colour.
· Coagulant residual.
· Reasons for variability in coagulant dose rate.
How often: / · Follow the protocols set out in DWSNZ:2000.
What to do with the results: / · Results need to be recorded to meet legislative requirements or to 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 waste-liquor reintroduction.
· 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 waste-liquor reintroduction processes are recognised in the plan.
Responsibility: / Manager designated responsible for the water quality.
Ref P4.4, Version 1 Water Safety Plan Guide: 5
January 2014 Pre-Treatment Processes – Waste-Liquor Reintroduction