Water Sanitation by ORP
Fruits and Vegetables
In the ever-increasing need and awareness for food safety and HACCP, Water
has become a focus point for proper disinfection treatment as pathogens
and harmful microorganisms can become a danger for contamination of fresh
fruits and vegetables during growing and post harvest contact. Water is
a critical control point of contact where proper treatment can greatly
reduce these microbes, thereby reducing the chances of food borne illness.
water applications include:
Field and growing water including irrigation water
Post Harvest Pre-cooling operations
Wash and Dip Tanks
Flume wash systems
Spray wash systems
Many water treatment sanitizers have been introduced in the market such
as Chlorine, Bromine, Ozone, Peroxyacetic Acid, Hydrogen Peroxide, Ultraviolet
light (UV), as well as many derivatives of Chlorine such as Chlorine gas,
Sodium Hypochlorite, Calcium Hypochlorite, Chlorine Dioxide, Dichlor,
Trichlor, Hypochlorous Acid.
With so many chemical choices and food commodities, it becomes very difficult
to standardize upon an adequate treatment level. How much chemical (ppm)
of each type to use for which product under varying conditions of organic
matter, dirt load, wash contact time, temperature, pH and pressure or
The objective of using any sanitizer is to disinfect the water and destroy
pathogens. All mentioned sanitizers except UV are oxidizers and they all
create oxidation. The stronger the oxidation, the faster the microbe is
killed. By measuring this oxidation level, we can directly measure the
rate at which these microbes are killed. ORP (Oxidation Reduction Potential)
is a measure of the oxidation level in the water and is measured in mV
(millivolts) and thereby measures the activity of the sanitizer rather
than its concentration levels (ppm). The choice of sanitizer may be left
up to the user bearing in consideration, their own process requirements.
for Water Disinfection:
Research has shown that at a level of 650 mV of ORP, bacteria such as
E. Coli are killed on contact or within a few seconds. Yeasts and molds
may require typically 750 mV or higher in order to be killed. Regardless
of any type of oxidizer or any combination of sanitizer, and regardless
of other varying water conditions, if there is adequate ORP, there will
be proper disinfection. Balancing pH and keeping the organic and dirt
load low helps in the strain and demand of the water, therefore it is
recommended that clean water quality be maintained as best possible which
will also reduce the amount of sanitizer needed to reach effective ORP.
There are several types of ORP measurement meters that vary depending
on the process requirements and design. Regardless of their style and
design they all have a sensor (electrode) that measures the ORP made of
Platinum, and an instrument that reads the ORP electrode value.
All ORP meters and electrodes need to be kept moist and require periodic
cleaning and calibration check with standards of known value to ensure
reliability and accuracy. Measurement is made by simply dipping the electrode
in liquid and observing the display. A stable reading is normally reached
within a couple of minutes.
Typically low cost and small in size to fit in the pocket or in a small
case and very portable. Both meter and electrode are integrated together
in to a compact design. These are low cost disposable meters and very
affordable with expected useful life of approx. one year. Readings are
reasonably reliable and provide a good indication of the water ORP. Calibration
test and cleaning is recommended at least once a week to ensure ongoing
Portable hand held meter offers a high degree of accuracy and reliability.
Electrodes may be either built-in or external on a cable and are replaceable.
Useful life of the electrode may be 1 to 2 years. Most hand held meter
also provide a pH and temperature measurement which may be useful in many
applications. Calibration check and cleaning is recommended at least once
Used in a fixed location for continuous monitoring of ORP and provides
a highly reliable up to date measurement as conditions continually change
in most process water applications. These instruments may also be used
as a source of reading only and manually dosing chemicals, however continuous
monitoring instruments are commonly used to automatically inject sanitizer
on demand, and provide a reliable method of process control as well as
recording for automated record keeping.
All ORP and pH electrodes need periodic maintenance and cleaning. A simple
cleaning procedure of dipping the electrode tip in dilute (1:100) acidic
solution for two minutes and rinsing with clean water. Then dip in electrode
checking solution to verify accurate readings. Some ORP meters allow calibration
adjustment but most do not. Inaccurate ORP readings are usually a result
of electrode contamination, which may be corrected by cleaning, or depletion
of useful life, which needs electrode replacement. Some ORP meters allow
slight slope offset adjustments to accommodate these errors.
Unlike a pH measurement
that follows a logarithmic curve and therefore requires more calibration
adjustments, ORP follows a linear relationship and does not need instrument
adjustment as much as it needs electrode maintenance.
ORP has proven to be a reliable method of measuring water disinfection
and provides the operator with a single value of measurement regardless
of which product, commodity, operation, treatment or sanitizer is used,
and regardless of varying field conditions or method by which chemical