Colloidal Silver Filter

Locally produced ceramics have been used to filter water for hundreds of years. Water is poured into a porous ceramic filter pot or in a pot containing a ceramic candle or disc, filtering the water. The filtered water is collected in another container (CAWST 2009c). The filter removes turbidity and traps and kills pathogens from drinking water (see also ceramic candle filters). 

To enhance ceramic candle filters, colloidal silver can be added. Colloidal silver helps in pathogen removal and prevents the growth of microorganisms within the filter itself (CAWST 2009). These enhanced forms of ceramic filters are called colloidal silver filters (CSF). CSFs were developed at the Central American Industrial Research Institute (ICAITI) in Guatemala in 1981 and are extensively promoted today. Currently, the most widely distributed ceramic filter is the Potters for Peace (PFP) colloidal silver filter, which is shaped like a flowerpot (see also pottersforpeace.org).

The filters are designed in particular for simple household use and are a recommended household water treatment and safe storage (HWTS). They can be produced locally by attending simple technical training.

Ceramic filters consist of a set of two containers. The upper unit contains the ceramic unit, which filters the water and the lower unit collects filtered and safe water. A tab device allows the users to withdraw the water for consumption while preventing recontamination by contact with hands or other objects that could bear bacteria. The porous ceramic devices can be either one or two candles, a disc or a pot. During use, tiny silver particles (colloidal silver) are suspended in the liquid acting as a disinfectant, preventing bacterial growth in the ceramic filter and enhancing inactivation of the bacteria in the filter (LANTAGNE et al., 2006). The colloidal silver is either added to the clay mixture before firing or impregnated on the fired ceramic pot (CAWST 2009c).

Pathogens and suspended material are removed from water through physical processes such as mechanical trapping and adsorption. Colloidal silver breaks down the pathogens’ cell walls causing them to die (CAWST 2009).

The filter operation is simple. First, the filter needs to be cleaned with clean water and left aside to dry naturally. Then, the filter units need to be assembled and the upper unit should be filled with water. Then, one has to wait until the water has passed the filter fort he first time. For security, the water filtered for the first time should not be used for consumption. Then, the filter can be refilled and the now filtered water collected in the lower storage unit can is ready to drink. To prevent clogging, water with a high turbidity (levels greater than 50 NTU) should first be strained (through a cloth) or settled before using the filter CAWST 2009c).

The filter pot should be regularly cleaned using a cloth or soft brush to remove any accumulated material. It is recommended that the filter pot, candle or disc be replaced every 1-2 years (CAWST 2009c). Cleaning prevents the formation of a biofilm and protects against fine invisible cracks, which may have developed over time. Any cracks will reduce the effectiveness since water can short-circuit without being filtered through the ceramic pores (CAWST 2009c). However, make sure not to remove all the silver when using a brush for cleaning.

Candle filters and disc filters normally have a lower contact surface for the water and therefore the filters produce less treated water per day than pot filters. However, the effective treatment rate (or flow rate) depends on the design). A typical pot filter can produce up to 1-3 L/hour while a candle filter produces only 0.1 to 1 L/hour (CAWST 2009a; CAWST 2009c).
The effectiveness of ceramic filters at removing bacteria, viruses and protozoa depends on the pore size of the ceramic material and the production quality of the filter unit. Most ceramic filters are effective at removing the majority of the larger protozoan and bacterial organisms and helminths, but not the smaller viral organisms (CDC 2008).

Laboratory testing has shown that although the majority of the bacteria are removed mechanically through the filter’s small pores, colloidal silver is necessary to inactivate almost 100 % of the bacteria (LANTAGNE, 2001a). The effectiveness of colloidal silver on viruses is not well known but estimated to be lower due to the smaller size of virus compared or silver particles.

Turbidity (solids) is efficiently removed by physical straining (filtration) and also taste, odour and colour of filtered water by CSF is generally improved. Iron is partially removed but other dissolved chemical pollutions are not removed. The effectiveness of CSF colloidal filter has been proven in many studies, where the reduction of diarrhoeal disease incidence among users has been documented (CDC 2008; EAWAG/SANDEC 2008).

For lack of residual protection, however, it is important for users to be trained on proper operation and maintenance of the ceramic filter and receptacle (CDC 2008).