Ceramic pot filter

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Ceramic filter icon.png
Potters for Peace filter model.

A ceramic pot filter consists of a flowerpot-shaped pot, made from a porous ceramic material. Water poured into a ceramic pot filter percolates through the pot material, and is collected in a second container.

There are many variations of the ceramic filter: some are made entirely from ceramics such as the Potters for Peace filters, some have a ceramic pot hanging in a plastic container such as Filter Pure (Agua Pure). Frequently, a colloidal silver coating is added to the ceramic filter. Some ceramic pot filters also include activated charcoal in the clay mixture to improve odour, taste, and colour.

Locally produced ceramics have been used to filter water for hundreds of years. Today, 150,000 filters are used in Central America, Asia and Africa.

CARE, UNICEF, Red Cross amongst others use the filter.

In Nicaragua, Guatemala and Cambodia the production of this filter is a commercial activity and production is starting up in six other countries.

Suitable conditions

The ceramic pot filter is suitable to process 8 litres of water per batch. This produces a daily water supply of 20-30 litres.


Advantages Disadvantages
- The filter is small and lightweight

- Removes most pathogens and suspended solids
- The silver coating ensures disinfection, so further disinfection is not needed.
- Sustainable, minimal outside resources require. Ceramic for example is produced locally in most developing countries
- Household and voluntary labour can be used in the manufacturing process
- Simple and cheap
- Water tastes good

- Low flow rate (1-3 litres per hour)

- Set up is fragile, breaks easily, allowing bad water through undetectable cracks.
- Turid water plugs filter
- Cleaning results in removal of ceramic layer; over time, filter needs replacing.
- Quality control difficult to ensure.
- Dissolved compounds are not removed (same as other filters)


Highly effective for: Somewhat effective for: Not effective for:
- Bacteria

- Protozoa
- Helminths
- Turbidity
- Taste/odour/colour

- Viruses

- Iron

 - Dissolved Chemicals
Treatment process:
Filtration
Inlet water criteria:
Turbidity < 50 NTU

Construction, operations and maintenance

Cross section through a Ceramic Pot Filter.

Ceramic pot filters usually have a diameter of about 30 cm by 25 cm deep, with an 8 litre capacity. Two variations of ceramic filters, flat-bottom and round-bottom, are currently manufactured. The ceramic pot typically sits or hangs in the top of a larger plastic or ceramic container (20-30 litres), which is fitted with a tap at the bottom. A lid is placed on top of the filter to prevent contamination.

Ceramic pots are usually made from local clay mixed with a combustible material like sawdust, rice husks or coffee husks. The clay and combustible material are sieved through a fine mesh, and then mixed together with water until it forms a homogeneous mixture. The mixture is pressed into shape using a mold. When the pot is fired in a kiln, the combustible material burns out, leaving a network of fine pores through which the water can flow through.

Colloidal silver is sometimes applied to the ceramic pot after firing or added to the clay mixture prior to firing. Colloidal silver is an antibacterial which:

  • Disables the enzyme that pathogenic bacteria and fungi use for oxygen metabolism, thus suffocating them.
  • Destroys pathogens with an electric charge, causing their internal protoplast to collapse.
  • Renders pathogens unable to reproduce.
  • Kills parasites while in their egg stage.

Pathogens and suspended material are removed from water through a combination of biological and physical processes.

Quality control on the size of the combustible materials used in the clay mix ensures that the filter pore size is small enough to prevent contaminants from passing through the filter. Colloidal silver aids treatment by breaking down pathogens’ cell membranes, causing them to die.

Operation

Contaminated water is poured into the ceramic pot. The water slowly passes through the pores and is collected in the lower container. The treated water is stored in the container until needed, protecting it from recontamination. The user simple opens the tap at the base of the container when they need water.

For turbidity levels greater than 50 NTU, the water should first be strained through a cloth or sedimented before using the ceramic filter.

The estimated flow rate is 1-3 litres/hour. This is highest when the pot is full. It declines with use and accumulation of contaminants within the filter pores.

Manufacturing

Hydraulic press used to make the filters.
Small local filter factory.

Local production of the filters is common and preferable. A quality control process to ensure filter effectiveness is required. The lower container, lid and tap can usually be purchased locally.

Materials and facilities required are:

  • Clay
  • Combustible material (e.g. sawdust, rice husks, coffee husks)
  • Colloidal silver (optional)
  • Lid
  • 20-30 litre ceramic or plastic container with tap
  • A ceramic factory requires at least 100 m2 of covered area
  • 15 to 20 ton hydraulic press (can be fabricated locally)
  • Filter molds (can be fabricated locally)
  • Mixer for clay and combustible material (can be fabricated locally)
  • Hammer mill (can be fabricated locally)
  • Kiln with an internal area of at least 1 cubic metre (can be fabricated locally)
  • Racks
  • Work benches
  • Miscellaneous tools (e.g. traditional pottery tools)

A professional potter with experience in collecting clay, making ceramic articles, semi-industrial or mass production is required. Assistants, preferably potters are required. Skill and quality control in manufacturing is essential to ensure optimum pore size, flow rate and effectiveness.

Working with presses and kilns is potentially hazardous and adequate safety precautions should be used.

Treatment Efficiency

If properly constructed and operated, a ceramic filter can be very effective in producing good quality water. Ceramic filters with the silver coating have consistently tested to 99-100% removal of bacteria and parasites. These filters also eliminate the suspended sediments in the water, including any organic compounds that are adsorbed to the particles.

Bacteria Viruses Protozoa Helminths Turbidity Iron {{{extra_Field}}}
Laboratory >98-100 % 12 19-99% 1 34 Up to 100% 5 up to 100% 5 83-99% 16 not available -
Field 88 - >95.1% 27 not available Up to 100% 5 Up to 100% 5 <5 NTU 2 >90% 6 -

Treatment efficiencies provided in the above table require colloidal silver. The treatment efficiency is also affected by pore size and construction quality. Taste, odour and colour of filtered water is generally improved.

Maintenance

It is recommended that the filter pot be replaced every 1-2 years. This is in part to protect against fine cracks which may have developed and are not be visible. Any cracks will reduce the effectiveness since water can short-circuit through the crack without being filtered through the ceramic pores.

There are no moving or mechanical parts to break in the ceramic pot filter. Small cracks can occur which are not visible to the naked eye, but which allow pathogens to pass through the filter. Poor transportation of filters can lead to cracking and/or breakage. Plastic taps in the lower container can break, metal taps last longer but increase cost.

A supply chain and market availability for replacement filters and taps is required. A quality control process is required to ensure filter effectiveness. Recontamination is possible during cleaning; care should be taken to use clean water, not to touch the ceramic with dirty hands, and not to place the filter on a dirty surface.

Continued use of the filter causes the pore openings in the ceramic to become clogged with debris. As a result, the flow rate of water through the filter decreases.

Filters are cleaned by lightly scrubbing the surface when the flow rate is reduced. Some manufacturers recommend to boil the filter every three months to ensure effectiveness. Some manufacturers recommend that soap and chlorine should not be used to clean the filter. The lower container, tap and lid should be cleaned on a regular basis.

Estimated Lifespan

The estimated lifespan of the filer element and the receptacle is up to 5 years. But generally it lasts for 1-2 years until partial replacement (exhausted/ broken filter element, broken plastic taps, or plastic bucket) is needed. Replacement is strictly needed when there are any visible holes that allows pathogens to enter.

Suppliers

Free press and kiln designs are available from Potters for Peace.

Costs

Captial Cost Operation Cost Replacement Cost Estimated 5 years Cost Cost/liter treated
US$ 10-25 US$ 0 US$ 4 US$ 18-31 US$ ~0.001

Note: Program, transportation and education costs are not included.

Cost of introduction: US$ 15,000 - 30,000 for project incl. training, machinery and a first production of 500 filters. US$ 50,000 - 100,000 for project incl. production shop, training, first promotion, and 5,000 filters.

Field experiences


Akvorsr logo lite.png
RSR Project 351
Cost effective means of financing WASH


Manuals, videos and links

ClaySure Filter Construction
Filtro Atabey, por Ideac
The Pot with the
Silver Lining - Part 1
The Pot with the
Silver Lining - Part 2

References

  1. ↑ 1.0 1.1 1.2 Lantagne (2001)
  2. ↑ 2.0 2.1 2.2 Smith (2004)
  3. ↑ Van Halem (2006)
  4. ↑ Some additives to the clay may increase virus removal.
  5. ↑ 5.0 5.1 5.2 5.3 Not researched, however helminths and protazoa are too large to pass between the 0.6-3 μm pores. Therefore, up to 100% removal efficiency can be assumed.
  6. ↑ 6.0 6.1 Low (2002)
  7. ↑ Brown and Sobsey (2006)

Acknowledgements

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