Candle Filters
HJR Inc.
Heather Nelson
Jeannette Harduby
Rudi Schuech
Problem
• People in developing
countries do not have
access to clean water,
leading to a variety of
water-borne diseases
and high infant mortality
• According to a study by
Nat Paynter, women in
Nepal can spend up to
five hours a day carrying
15 kg (33 lb) of water for
their families
(Partial) Solution
• Low-cost POU water
treatment
technologies need to
be developed and
implemented around
the world.
• CANDLE FILTERS!
What is a Candle Filter?
• The most common ceramic water filter.
• Looks like an upside-down candle, screwed into
the base of the upper portion of a two container
water filter.
• Water poured into the upper basin, where it
filters through the candle and collects in the
lower container.
• A ceramic filter physically traps microorganisms
and other suspended contaminants in its pores.
Pictures
Candle Filters
Kisii Filter bucket with
ceramic filter
Candle Filter Design
• Mix clay with water and sawdust or flour
• Compress into mold
• Heat in oven to vaporize sawdust and leave
open pores
• Pore size ~ 1 – 5 micron diameter
• Can add more specialized filter material to
remove fluoride, arsenic
• Doulton filters made of Diatomaceous Earth
(DE) + activated carbon inside (for taste, odor)
• Often includes oligodynamic silver – kills
bacteria, slows biofilm formation (bacteriostatic
effect)
• Silver ions released into water, inhibit bacterial
enzymes
More Pictures
Candle filter constructed
By Voigt GmbH
Royal Doulton
Ceramic Filter Candle
Produced by
Australis Partners
All are similar in basic design and construction
What is removed
• parasitic worms, cysts (Crypty,
Giardia), spores, bacteria
What isn’t removed
• Many viruses are small enough to fit
through pores
– but viruses are often charged, and
adsorb to filter surfaces
• Any dissolved substances, unless
they adsorb (not guaranteed) or
additional filter materials are included
(activated carbon)
Example - Doulton
Candle Filter
Claims
•removes chlorine, bad
taste and odor,
pesticides,
herbicides,
industrial solvents
and heavy metals
•100% rejection of cysts
•Over 99.99% removal of
pathogenic bacteria
•But Doulton “premium” filters are
$60, not including housing container
Advantages
• Simple Technology behind design
– No special tools required to clean, just a metal brush
– Construction materials usually easily available
– Can be made by local potters
• Small-Scale - Each family can own a candle filter
• Effective- with proper use and cleaning they
have been shown to reduce contaminants
WOW! Candle Filters Are Great
• Kisii Water Filters states, “The only
‘problem’ that we heard of with the Kisii
Filter Bucket is that people who start using
it at home do not want to live without it
anymore. It becomes a true friend in the
family, to be used every day, day after
day.”
Problems with Candle Filters
•
Require Maintenance Work
– Must be cleaned at least once a week so pores don’t become
clogged. People often use unfiltered, dirty water to rinse the filter,
since they may not have clean water readily available.
– If people don’t clean the filters, they can become obstructed with
particles and reduce the filtration rate, making people less likely
to wait for their clean water.
– BUT, brushing physically removes a layer of material. Doulton
states filter is unsafe after about 100 cleanings.
– Doulton claims lifetime of 2,000-15,000 gal
– Typical lifetime of Madhyapur filter (Nepal) = 6 – 12 mo @ 2
L/day
– Partial Solution: research suggests that by coating and/or
impregnating the candle filters with colloidal silver, the growth of
microbes will be reduced.
More Problems
• Can often be expensive
– Even though the technology behind the
design and the raw materials are
cheap, the cost can still be prohibitive
for the poor because they are often
imported
• While importation allows for qualitycontrol, it drastically raises costs.
• For example, in India the prices of
candle filters range from $6 to $30 - a
lot considering the low per capita
income ($300).
• If made domestically, quality control
an issue
A Few More Problems
• They filter the water slowly. One candle
filter may not provide enough safe water
for one person, let alone an entire family.
– Estimates ranged from 100-700 liter per
WEEK for the Kisii Filter to only 3 liters per
day for a “slow speed” filter candle. Others
estimate 0.5 – 4 L/day!
– flow rate depends on how clogged filter is
– Sometimes multiple candles used to increase
total flow rate
Yet Some More Problems
• Break Easily – one tiny crack renders filter
useless
• Difficult to determine the optimal pore
diameter
– Too big: Many contaminants get through and
there will still be dirty water
– Too small: Takes too long to filter
– Filtration of viruses not reliable! Competing
particles can clog adsorption sites over time
Case Study in Nepal
• Sustainable???
– There was a group of MEng students from MIT who
developed clean water projects in Nepal.
– One village was given ceramic candle filters for free
several years ago, but when the MEng group
revisited, not even 10% of families were still using
them. "The main problems were that the filters broke,
or they came in aluminum containers which rotted or
became rusty. Some people bought a second filter,
but if that also broke, they decided that they didn't
want the aggravation and the expense of purchasing
yet another filter." (Dies)
Environment and Public Health
Organization (ENPHO) Study
• Survey Conducted in the Kathmandu
Valley
– The study concluded that generally, there was an
improvement in water quality. Before treatment
61% of water was uncontaminated (0 fecal
coliform (FC)/100ml)
• On average, the raw water had an average of
31 FC /100 ml and the treated water an average of
20 FC/100 ml.
• After treatment 73% of water was safe.
ENPHO Study
• Of water that was initially uncontaminated, water
quality in 12% of the households tested was
reduced in quality!
– Of the 93 households that were surveyed, 12 sites
actually made the water worse that it was before it
was filtered! (There were more contaminants and
water borne pathogens than before!)
Bottom Line
• Of the raw water that was contaminated, 87%
improved, 13% deteriorated, but only 50% was
made safe by the filter treatment.
ENPHO Study Conclusions
• Unsanitary handling of water
is a BIG problem!
• People were using candle
filters without understanding
how they work. Therefore,
they were not careful about
the use and cleaning of the
filters.
– Clear housing (Kisii) allows
people to see and trust filtering
process
The Next Step
• Better promotion of their use in developing
countries
• More instruction of local artisans and craftsmen
on the construction of candle filters according to
stringent quality levels
– Reduce cost
– Make the design more sustainable (reliable, durable)
• Colloidal silver allows larger pore size, higher
flow rate while maintaining good pathogen
“inactivation”
More Can Be Done
• EDUCATION
– Many people in undeveloped
countries don’t understand
the concept of water-borne
pathogens
– Personal hygiene, cleanliness
Resources
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<http://web.mit.edu/civenv/html/people/alumni_newsletters/summer_03/ar
t2.htm>
<http://www.firstwater.info/pdf/Ceramic%20Water%20Filter.pdf>
<http://www.handpump.org/handpump.htm>
<http://www.who.int/water_sanitation_health/dwq/wsh0207/en/index5.html
>
<http://www.irc.nl/page/7510>
<http://www.thinkcycle.org/tcfilesystem/download/development_by_design_2001/efficiency_of_househ
old_water_treatment_technologies_in_nepal_on_candle_filters,_biosand_
filters,_terracotta_filters_&_sodis/ENPHOsummary.doc>
<http://doultonusa.com>
<http://www.jamesfilter.com/frequently_asked_water_filter_qu.htm>
<http://www.australispartners.com.au/ceramic>