Candle Filters

HJR Inc.Heather Nelson

Jeannette HardubyRudi 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 quality-control, 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

• <http://web.mit.edu/civenv/html/people/alumni_newsletters/summer_03/art2.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/tc-filesystem/download/

development_by_design_2001/efficiency_of_household_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>