18451 version 3
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Describe the management of pH, alkalinity, hardness, and corrosion
control
Level
5
Credits
5
Purpose
People credited with this unit standard are able to: describe the factors that
influence the pH, alkalinity, and hardness of drinking-water undergoing water
treatment; describe the processes used in drinking-water treatment to control
pH; describe the causes and treatment options for hardness in drinkingwater; describe the chemistry and parameters of corrosion and
plumbosolvency in water treatment; and identify critical points, hazards,
preventive actions, and corrective actions of the pH and alkalinity adjustment
process.
Subfield
Water Industry
Domain
Drinking-Water
Status
Registered
Status date
19 September 2008
Date version published
19 September 2008
Planned review date
31 December 2013
Entry information
Open.
Accreditation
Evaluation of documentation and visit by NZQA, industry
and teaching professional in the same field from another
provider.
Standard setting body (SSB)
Primary Industry Training Organisation
Accreditation and Moderation Action Plan (AMAP) reference
0179
This AMAP can be accessed at http://www.nzqa.govt.nz/framework/search/index.do.
Special notes
1
Reference
Drinking-Water Standards for New Zealand, Ministry of Health, Wellington, 2000 and
2005.
 New Zealand Qualifications Authority 2016
18451 version 3
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2
Definitions
Drinking-water supply – the supply catchment, treatment plant, and distribution. The
drinking-water supplier has responsibility for managing the public health risks of the
drinking-water supply.
Critical points – points in a process or in equipment where failure to function correctly
can lead to a public health hazard.
Organisational procedures – instructions to staff, and procedures which are
documented in memo or manual format and are available in the workplace. These
requirements include but are not limited to – site specific requirements,
manufacturers’ specifications, product quality specifications, and legislative or
regulatory requirements.
Elements and performance criteria
Element 1
Describe the factors that influence the pH, alkalinity, and hardness of drinking-water
undergoing water treatment.
Performance criteria
1.1
pH, alkalinity, and hardness are described in relation to the expected ranges in
the Drinking-Water Standards.
1.2
Organics and inorganics present in untreated water are described in terms of
their impact on water pH and alkalinity.
Range
1.3
includes but is not limited to – carbon dioxide, carbonate,
bicarbonate, sulphates, chlorides, organic colour.
Water treatment chemicals are described in terms of their effect on pH and
alkalinity.
Range
includes but is not limited to – alum, hydrated lime, soda ash,
caustic soda, carbon dioxide, sulphuric acid.
Element 2
Describe the processes used in drinking-water treatment to control pH.
Performance criteria
2.1
Chemical addition and removal techniques are described in relation to pH
control in water treatment.
Range
operational issues – solution strengths, material handling safety,
chemical transfer, line and pump blockage, chemical safety
handling, carry water, powder feeder control, line cleaning;
management techniques – material handling safety, equipment
selection, equipment maintenance;
pH control methods – measurement, calibration, time lags,
feedback control loops.
 New Zealand Qualifications Authority 2016
18451 version 3
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2.2
Equipment used to adjust pH is described in terms of their operational features.
Range
2.3
equipment – dry powder feeders, mixing tanks, dosing pumps.
Problems and operational difficulties are described in relation to the adjustment
of pH in drinking-water.
Range
chemical transfer, line and pump blockage, chemical safety
handling, carry water, powder feeder control, line cleaning.
Element 3
Describe the causes and treatment options for hardness in drinking-water.
Performance criteria
3.1
Naturally occurring chemicals present in raw water are described in terms of
their solubility and effect on the temporary and permanent hardness of the
water.
Range
includes but is not limited to – calcium carbonate, magnesium
carbonate.
3.2
The lime, soda ash, and caustic soda softening processes used in water
treatment are described in terms of their chemistry and methods of operation.
3.3
Ion exchange softening processes used in water treatment are described in
terms of their chemistry and methods of operation.
Range
includes but is not limited to – zeolites, greensands, synthetic
resins, brine regeneration.
Element 4
Describe the chemistry and parameters of corrosion and plumbosolvency in water
treatment.
Performance criteria
4.1
The chemistry of metal corrosion and plumbosolvency is identified and
described in terms of corrosion cell actions, and the drinking-water standards
maximum accepted values (MAVs).
Range
4.2
anodic/cathodic areas, pitting, tuberculation, iron, copper,
aluminium, cadmium, zinc, lead.
Metal corrosion parameters are identified and calculated in terms of the
Langelier Saturation Index (LSI), and guideline values in the drinking-water
standards.
 New Zealand Qualifications Authority 2016
18451 version 3
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4.3
Asbestos cement corrosion is described in terms of the impact of pH and
alkalinity.
Element 5
Identify critical points, hazards, preventive actions, and corrective actions of the pH and
alkalinity adjustment process.
Performance criteria
5.1
The critical points in the pH and alkalinity adjustment process are identified in
accordance with organisational procedures.
5.2
The hazards at each critical point are identified in terms of the causes of the
events leading to their appearance, and the risk factors.
5.3
The preventive and corrective actions for events related to each hazard are
identified.
Please note
Providers must be accredited by NZQA, or an inter-institutional body with delegated
authority for quality assurance, before they can report credits from assessment against
unit standards or deliver courses of study leading to that assessment.
Industry Training Organisations must be accredited by NZQA before they can register
credits from assessment against unit standards.
Accredited providers and Industry Training Organisations assessing against unit standards
must engage with the moderation system that applies to those standards.
Accreditation requirements and an outline of the moderation system that applies to this
standard are outlined in the Accreditation and Moderation Action Plan (AMAP). The
AMAP also includes useful information about special requirements for organisations
wishing to develop education and training programmes, such as minimum qualifications for
tutors and assessors, and special resource requirements.
Comments on this unit standard
Please contact the Primary Industry Training Organisation standards@primaryito.ac.nz if
you wish to suggest changes to the content of this unit standard.
 New Zealand Qualifications Authority 2016