Terracotta Filters
TERAFIL Terracotta Filter
The TERAFIL terracotta filter consists of two cylindrical metal buckets with a TERAFIL ceramic disc filter fitted in the middle. The raw water is stored in the upper bucket and the lower bucket has a spigot and serves as a collection vessel. The TERAFIL filter ceramic disc is manufactured from a mixture of red silt clay (ordinary pottery clay), river sand, wood sawdust and burnt at a high temperature in a low cost kiln. The design of this filter came from Surendra Khuntia, Scientist and Divisional Director of the Regional Research Laboratory in Bhubaneswar, India. The red terracotta clay, which is used to prepare domestic earthenwares, is abundantly available in many parts of India and elsewhere in the world. The wood sawdust is burnt and the clay particles are sintered around the sand particles, leaving pores in between. According to Khuntia, the pores in a well-sintered TERAFIL are within 1 to 5 microns, and the pores are not interconnected. A thin clay membrane of 50-100 micron thickness separates the pores and is responsible for the separation of most larger-sized bacteria. The removal of most suspended particles occurs at the top surface of the TERAFIL, forming a layer of sediments, which over time, may cause clogging to the filter and reduce flowrates. Therefore, it is recommended that the top of the TERAFIL clay disc is scrubbed once a day with a soft nylon brush or similar material to remove the sediments and open new pores. Since the pores of the filter are not continuous and interconnected, the core of the TERAFIL should not get clogged and with proper maintenance, it is expected to last more than 5 years. (Khuntia, 2001)
|
|
There are 2 TERAFIL filters that have been tested: One in MIT and the other in ENPHO, Kathmandu. Both TERAFIL filters came from the original manufacturer although their performance vary quite significantly. The MIT version has a flow rate of about 1.5 L/hr and the ENPHO version has a flow rate up to 5L/hr. The filter in MIT reduces turbidity from 5 NTU to <1 NTU while the filter reduces turbidity from 40 NTU to <2 NTU. Both filters are also able to reduce up to 95% of bacteria with no disinfection, under laboratory conditions.. However, high bacteria removal rates do not necessarily imply that the filtered water is drinkable. World Health Organization (WHO) drinking water guidelines require zero total coliform bacteria (an indicator organism for drinking water) per 100ml sample in all drinking water supplies. Therefore, it is recommended that some form of disinfection be carried out in addition to filtration to ensure 100% bacteria free drinking water.
Thimi Terracotta Filter
|
The Thimi terracotta filter cake is fabricated by a local potter maker using locally available materials in Thimi, a town half hour by car from Kathmandu. The photo shows the prototype filter top and bottom receptacle that are used to house a similar terracotta filter cake in the middle. These filter cakes are made from local pottery clay, saw dust, and rice husk ash. The materials are mixed by hand and molded into a simple cake shape using a pre-cast plaster mold. The filter cakes are then fired at a high temperature of 1000 deg C for 2-3 hours, depending on how dry they were. Then they are fixed at the bottom of the top container with white cement.
Two of such filters were brought back to MIT from Nepal in February. Preliminary laboratory tests are currently being carried out in the MIT lab.
|
 |