Finer Filtration - Australian Perlite

industry feature
The crystal clear water of Murwillumbah Pool,
which uses filters featuring Zelbrite filter media.
Finer filtration
F
iltration is one of the key components
of a sanitisation system necessary to
provide safe clear water for swimmers to enjoy.
The most common types of filters use
filter media (most commonly sand). In this
article we’ll be mainly looking at the different types of media used in filters, in both the
residential and commercial environments.
To start with, John McKenny, instructor and author of the Easy-to-Understand
Leisure Pool and Spa Handbook, has given
us a quick rundown of the different type
of media and filters. Further in the article,
we will get more specific information from
the manufacturers of some of the types of
filter media.
Sand
(a) Graded filter sand – By far the most
common media used. It is readily available
and transported in bulk bags or easier-tohandle 25kg bags. It’s washed and graded
and quite course compared to normal beach
sand. Although reasonably cheap to buy,
transport costs can make it expensive. It is
Media matters in
swimming pool filters.
known to last many years. Sand in gravity
filters fifty years old is common. It can be
regularly cleaned using common liquid soap
during a backwash, to assist in removing accumulated fats and oils, but regular removal
of the surface layers is recommended to
properly remove any build-up of salts from
the pool water and sanitisers. In small pools
such as private installations, a periodic acid
rinse during backwash can assist; but great
care is necessary to protect equipment,
persons and the environment.
(b) Ultra-Fine Sand – Ultra-fine sand
use in swimming pool filtration is so far
limited. It is used in other areas, often in
conjunction with additional equipment such
as centrifuges, to produce high quality air
and sometimes water, filtering down to
less than one micron (one micron = one
millionth of a metre). [Care should be taken
handling dry ultra-fine sand due to potential
health risk from inhalation.]
Sand replacements
(a) Zeolite – There are several brands and
grades on the market. Generally, those who
have experienced operational difficulties
using zeolite have used an inferior (imported)
product. Good quality Australian zeolite gives
excellent results. It is simply substituted
into any “sand” filter and provides an almost
instant improvement in water cleanliness, as
it is claimed to filter down to approximately 3
microns. Although slightly dearer than sand,
it enables less total chemical use, water consumption and heat loss, as times between
backwashing is often halved.
(b) Glass – Crushed glass can effectively
filter water, having similar properties to its
close relative, sand. Manufacturers advise
that this recycled glass is superior to normal
sand, as it provides better cleaning of the
water and requires less backwashing, saving
on water, heat and chemicals.
Other filtering methods
(a) Cartridge filters – These are common in
small installations. They are usually cheaper
than sand filters for the same pool size,
easier to install and use less water when the
filters need cleaning, as opposed to sand filter backwashing which can use considerable
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industry feature
Diamond Kleen filter media
quantities of water and therefore lose larger
amounts of chemicals and pool water.
(b) Diatomaceous earth filters (DE) –
Proven to be a reliable method of effectively
filtering small to large quantities of water
for both swimming and drinking. DE, in
the form of fine powder, is introduced into
the flow system to form a barrier to all
impurities including bacteria and pathogens such as giardia and cryptosporidium.
Its drawbacks are that as well as being
sometimes a bit expensive, the DE powder
is considered unsafe if inhaled. Its disposal
after backwashing requires special care.
(c) Perlite – This natural substance is
processed and crushed to a powder and
used in a similar way to DE. According to
those who have used and are still using perlite, it can be easily backwashed and doesn’t
require cleaning, and therefore replacing, as
often as DE. [However, some large commercial systems use no backwashing and simply
replace the media].
(d) Granular Activated Carbon (GAC) –
Already used in de-ozonation chambers
where ozone units are in use, GAC can
effectively remove almost all substances in
the water, including tastes, colours if any,
sediment and even chlorine and similar
added chemicals. Some GAC compounds
with special alloys added can filter out all
substances, including cryptosporidium,
giardia and other pathogenic bacteria.
(e) Cellulose fibre – This is used in openstyle filtering for large commercial projects.
Additionally, pre-filters such as MultiCyclone can be used to increase filter efficien-
cy and reduce the backwash requirements.
There are also other types of filtration
that are mainly used for water treatment
industry, such as reverse-osmosis filtration,
in which the water is forced under pressure
through a semi-permeable membrane. This
type of filter is used in desalination.
Glass filter media
Dan Kwaczynski of Poolrite, manufacturer of
Diamond Kleen, gives us a rundown on glass
filter media.
There are many forms of filtration available
to the market – DE, sand, zeolite, recycled
glass and more. In this short section, I will
focus on the performance of recycled glass,
(specifically Diamond Kleen) compared to the
performance of sand and other media.
The first question that must be asked is
what are we all looking for in a filtration
media (excluding price which we naturally
all care about). Here are some parameters,
by no means exhaustive list – pressure dif-
ference, level of cleaning (micron rating),
water saving (time between backwashes and
backwash duration), environmental footprint
and longevity/maintenance.
Cleaning ability/micron rating
The primary mechanism by which sand
and zeolites catch particles is by mechanical entrapment. This is based on
the porous nature with particles caught
in the gaps. Zeolite is far superior to sand
in this regard and cleans to a high level –
less than 10 micron. The performance of
sand, which has a less porous structure,
will naturally be worse than this, perhaps
filtering to 15-20 micron. Diamond Kleen
has a completely different entrapment
mechanism yet still manages to perform to
well below 10 micron. Research has shown
that this primarily relates to an electro
charge that attracts particles. In fact, glass
media is not very porous at all and is actually quite smooth on the surface. Why is
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industry feature
10 micron an important parameter? This is
generally believed to be the visible range, i.e.
below that and the water will look beautiful,
above and it won’t be quite as clear.
Pressure difference
The pressure difference is an important
parameter because this relates to the size of
pump and the flow rate delivered (and from
this, current draw and carbon footprint).
Porous media will generally have higher
pressure differentials because the water
flows into all the particle gaps, cracks and
pores. By comparison, glass media’s smooth
surface allows water to pass more easily,
hence reducing the pressure loss, and making the filter more energy efficient.
Another key factor in the performance of
a media is the grading – both in terms of the
minimum and maximum particle sizes and
the spread of media across this range. For
example, too large a grading range and the
smaller particles fill the gaps left between
the larger particles leading to higher differential pressure and easier clogging. Too
small a grading range or gradings that
are too fine can lead to quicker clogging
and therefore quicker pressure build up.
Diamond Kleen has been specifically engineered to optimise this delicate balance,
using a highly technical manufacturing process which includes particle activation.
Water saving
The water saving ability of a media is based
on two parameters – the ability of the media
to hold waste without increasing pressures
and the time taken to backwash once pressure has been built up. There is currently
independent research to verify exactly these
two water saving measures for both Diamond
Kleen and zeolite. Both Zelbrite (a brand
of zeolite) and Diamond Kleen have been
awarded the Smart Approved WaterMark. This
is an independent organisation that validates
the water saving capabilities of products.
From experience, both Diamond Kleen
and zeolite have excellent waste holding capacities, albeit that zeolite requires recharging at intermittent frequencies (in order to
clean out all the pores). This is not really
surprising when you consider the entrapment mechanisms mentioned above.
The other parameter to consider is backwash duration. Given zeolite and sand use
mechanical entrapment, it is clear that the
more deeply embedded particles are in the
structure, and so the longer the backwash
time is needed to completely clear these
particles from the porous structure. By com-
Zelbrite filter media in sizes 0.5 to 1.0mm (x200)
parison, glass backwash durations are usually
significantly reduced as the particles are held
loosely on the smooth surface of the particles.
Longevity and maintenance
The limitations of sand are that is breaks
down over time, while zeolite requires
recharging and replacement. Recycled glass
media, by comparison, has a much longer
life expectancy due to the increased hardness of the material. This can be further
broken down to separate clear sheet glass,
which has a relatively low smelting temperature and hence lower hardness reading
compared to bottle glass which has higher
smelting temperature and higher hardness
reading. It is therefore expected that glass
media (recycled or new) using bottle glass
will last longer than sheet glass.
Environmental impact of production
Zeolites, sand and new glass require quarrying operations to produce the base material.
This not only digs into our natural environment but also uses significant energy to
dig, convey, process, sort, ship, and bag the
product for market. New glass is even worse
– requiring large amounts of heat to melt
the product and transform it into glass.
Recycled glass media is by far the lowest
environmental impact of production. There
is no quarrying and there are no holes being
dug in the landscape. It uses existing material
that was previously destined for landfill, has
been saved and re-used. So in reality, for every
tonne of recycled glass used in filtration that
is one tonne of landfill saved – and potentially
many tonnes of quarrying saved (depending on
the yields of production for sand and zeolite).
The Australian market has embraced the
use of recycled glass media. It is interesting
that only now other markets in the world are
starting to see market growth in recycled glass
media, even though glass media per se has
been used for filtration for many years (there
are even reports that recycled glass was used
more than 20 years ago on Hamilton Island
when no sand was available at the time).
For more information go to www.poolrite.
com.au.
Australian zeolite
Peter Rabbidge of Zeolite Australia, manufacturer of Zelbrite, talks about zeolite in
general, and Australian zeolite in particular.
Zeolite is a natural mineral found in many
countries around the world and is the result
of volcanic activity.
Not all zeolites are the same. For example, the zeolites found in Europe, Asia and
New Zealand are very soft and therefore not
suitable to be used as a filter media. These
are mainly used as adsorbents such as Kitty
Litter and for soaking up oil spills.
Zelbrite’s zeolite is mined at Werris Creek
in Northern NSW and is one of the hardest
zeolites found in the world. This filter media
was introduced to the Australian swimming
pool market approximately 10 years ago and
has been used throughout Australia in both
backyard and commercial pools. It has been
exported around the world and Zelbrite has
recently been selected as the zeolite filter
media of choice by AstralPool in Spain.
Many people have made many claims and
sometimes their claims do not come from
independent testing. For this very reason,
Zeolite Australia chose to have Zelbrite
tested by the Australian Water Quality Centre
(AWQC) whose test results showed it would
give the performance of DE with the convenience of sand. In the past DE has been held as
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industry feature
Right: Perlite media under magnification
Above: Perlite media under 100 times closer magnification
the benchmark for filtration: that is, DE to 5
microns, while sand only filters to 15 microns.
The AWQC test showed Zelbrite could remove particles as small as 2 microns. Apart
from its superior physical properties, it is
also chemically active removing ammonium
by ion-exchange, resulting in less need for
ancillary chemical requirements to maintain
water quality.
Being a crushed rock it has a very large
surface area and therefore during summer it will take eight to 10 weeks to reach
backwash pressure, and secondly it takes
half the time to backwash as it roughness
causes it to swirl around inside the filter
shedding the dirt in half the time.
Zelbrite is the only zeolite filter media to
be awarded the Smart Approved WaterMark
and also recently gained Savewater approval.
For more information go to www.zelbrite.
com.au.
Perlite filter media
Perlite is another type of pool filter
media, used pretty much exclusively in
large commercial applications such as
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industry feature
regenerative media filters are the main
type of filters capable of using perlite, and
applications include WhiteWater World on
the Gold Coast.
David Biber from Australian Perlite
outlines the benefits of the media, and in
particular the Australian product.
Perlite is an important filtration media used
in the clarification of beverages including
beer, wine and fruit juices and in swimming
pool and other water filtration applications.
Perlite is a generic name for a naturally
occurring siliceous volcanic rock. A unique
property of perlite is that it expands up to
twenty times its original volume when it is
heated to its softening range.
This expansion process is caused by
the presence of water in the crude rock.
When perlite ore is rapidly heated to above
850°C, this water vaporises and causes the
softened rock to expand. Tiny glass-like
bubbles are produced which account for the
light weight and exceptional physical properties of expanded perlite.
It is these lightweight glass-like bubbles that are milled and classified under
stringent quality controlled conditions
to produce perlite filter aids. This material exhibits a unique, jagged interlocking structure with myriad microscopic
channels affording optimum flow rates
and clarities for a wide variety of applications. Perlite filter aids do not impart taste,
colour or odour to liquids being filtered and
they are virtually insoluble in mineral and
organic acids at all temperatures.
Comparative products such as diatomaceous earth (DE), sand and zeolite are also
used in filtration. DE does have high crystalline silica levels and accordingly it is listed
as a potential carcinogen and a Dangerous
Good (DG) under UN protocols.
DE, sand and zeolite are much heavier
than perlite and for a product that is sold by
the kilogram this makes it a more expensive
option than perlite (perlite is at least 30 per
cent lighter than any of these options).
Because perlite stays in solution, it can be
easily and legally disposed of in municipal
sewers while DE requires removal to a DGcertified land fill.
Australian Perlite (Ausperl) is the primary
supplier of perlite filter media in Australia
and New Zealand. Products are matched
to client requirements. Manufacturing
takes place in Sydney where a disciplined
testing regime ensures that the product is
highly consistent. Due to the bulk density of
perlite, local supply is likely to be the most
economic choice.
For more information go to www.ausperl.
com.au.
RMF and perlite
in water parks
June Holaday from Neptune Benson,
manufacturer of Defender filters, explains
the benefits of regenerative media filtration
(RMF) in large commercial applications such
as waterparks.
When it comes to waterparks, one of the
toughest obstacles to overcome is public
perception. The visitor sees what appears to
be an endless stream of water flowing all over
the park. What they don’t see are the very strict
measures that parks take to conserve water
behind the scenes. On average, a 100,000
square foot (9300 square metre) waterpark
resort might use 125,000 to 160,000 gallons
of water per day (473,000L to 600,000L). In
comparison, golf courses in the United States
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industry feature
Right: The Neptune Benson Defender
Above: The AquaBoss open filter tank using Purifibre
consume an average of 300,000 to 500,000 gallons of water per day (1.1ML to 1.9ML). Though
most people don’t seem to associate golf
courses with excessive water consumption.
New technologies are being implemented
throughout waterparks to reduce, reuse and
recycle water. One of the key elements is the
use of regenerative media filters (RMF) such
as Defender instead of high rate sand filtration. This popular filtration system requires
no backwashing, saving up to 90 per cent of
wastewater and eliminating the need for a
backwash holding tank.
The RMF technology operates on the
premise of surface filtration, has tremendous
Smart Approved Water
Mark favours four
filtration products
Smart Approved Water Mark,
the not-for-profit program that
helps consumers make informed
choices about saving water around
the home, garden and pool, has
included four swimming pool
filtration products.
Two are filter media – Zelbrite
zeolite media and Poolrite’s
Diamond Kleen recycled glass
filter media.
The other two are Waterco’s
MultiCyclone pre-filter and Ian
Coombes’ AquaBoss commercial
swimming pool filter system.
Products and services with the
Smart Approved WaterMark label
have been assessed by an independent technical expert panel.
dirt holding capacity, which extends filter
cycles to weeks or even months. The reduction in backwash water also means that less
‘make-up’ water needs to be reheated and retreated with chemicals. Operators report over
30 per cent savings on chemicals and heating
fuel which helps reduce the carbon footprint.
Additional features that reduce the carbon
and water footprints are reduced electricity usage and saving on construction room.
Regenerative media filters operate at a
lower head (TDH) compared to traditional
sand filters, saving motor horsepower. When
paired with a variable frequency drive (VFD),
electrical usage may be cut up to 30 per
cent. The RMF mechanical footprint requires
less than one-quarter of the space occupied
by sand filters, which significantly saves on
construction costs.
Since so much more waste water is being
eliminated, it becomes critical to maintain
optimum pool water quality. Regenerative
media filters can remove particles down to
1 micron. This allows for more than 99.9
per cent of cryptosporidium to be removed
in a single pass. The superfine filtration
of the water also increases UV sanitation
efficiency. So an additional benefit is that
a regenerative media filter combined with
a UV sanitation system becomes the best
defence against recreational waterborne
illnesses (RWIs).
Australia, suffering its worst drought in
a century, is home to WhiteWater World in
Queensland. According to Angus Hutchings,
the park’s Environmental Manager, the regenerative media filtration has the most impact on their water conservation. They use 90
percent less water and save approximately 23
million litres of water per year. Additionally, in
an independent, third party water efficiency
audit conducted by Environmental Resources
Management Australia (ERM), WhiteWater
World has been given the highest efficiency
rating possible for a waterpark.
For more information go to www.DefenderFilter.com.
Commercial filtration with
cellulose fibre
Ben Coombes from commercial filter manufacturer, Ian Coombes, describes a new
form of filter media – cellulose fibre.
AquaBoss fine media filters use the vacuum media filtration principal. They operate
by drawing the water through an open tank
full of filter elements. Each filter element is
coated with a cellulose fibre called Purifibre
which is a non-toxic, non-carcinogenic media
that provides filtration down to 2-3 microns.
This level of filtration is comparable to
diatomaceous earth without the unwelcome
handling issues. Purifibre is made from
wood pulp just like paper. This makes it a
safe and user-friendly product to work with.
It is a renewable resource and is 100 per
cent biodegradable allowing it to be discharged direct to the sewer without the need
for large backwash holding tanks.
AquaBoss filters in conjunction with Purifibre can give filter cycles of eight-to-16 weeks,
therefore using minimal water in comparison
to other filtration types. AquaBoss filters
require 3000 to 9000 litres per backwash,
compared with 10,000 to 15,000 litres used by
a conventional sand filter system.
The filter shell is open to the environment which makes trouble shooting quick
and easy as the filtration process is clearly
visible. This also has the added benefit of no
pressure in the filtration tank resulting in a
long product life.
For further information go to www.iancoombes.com.au.
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