A Towering Success of CSIR, Terafil for the Thirsty by Dr P. Cheena Chawla

Water — the elixir of life — is abundant on our planet but alas, access to safe drinking water is a major challenge faced by most developing countries including India. About 800 million people that represent the face of rural India are severely prone to water-borne diseases, primarily diarrhea in children. Sure, it is the lack of adequate drinking water — the basic requirement for survival — that poses a major health burden on our people.

It is a heartening fact that today CSIR stands strong with an ingenuously developed technology, which amply suits the needs of people in rural areas who use water from both surface and ground water sources like dug wells, ponds, tube wells and rivers for drinking purpose.  One simply needs to ‘see’ to ‘believe’ it, for how such a low cost device by the name Terafil magically cleans impure, turbid water into sparkling drinking water. This filter has astounding ability to remove sediments, suspended particles, iron and harmful microorganisms from contaminated water. 

The credit to this achievement goes to the painstaking research efforts of the team of scientists at the Institute of Minerals and Materials Technology (IMMT), (formerly known as Regional Research Laboratory), Bhubaneswar. With its filtration discs being prepared under license and training from IMMT, Terafil is gaining widespread popularity, and is already being used by thousands of households in the States of Orissa, Karnataka and Meghalaya.

Technically, Terafil disc is formed from a mixture of red clay (silt clay/terracotta), river sand and wood saw dust without using any chemicals. The dough of the mixture, in specific proportion, is sintered at high temperature in a low cost coal/wood fired furnace to make the disc structure porous. During sintering process, the wood particles are burnt and clay particles are sintered around the sand particles leaving large elliptical/circular pores in between.

If Terafil is over sintered, then the size of the pores is reduced. Thus, proper sintering of Terafil is important for obtaining the required thickness of membrane as well as the shape of pores, which defines the strength of the filter. These pores are not connected with each other, unlike that in white ceramic filter candles, but are separated by semi-permeable, thin clay walls of 50-100 micron thickness. These clay walls contain several ultra-fine capillary openings. The average diameter of the capillary openings is sub-micron in size.

During the filtration process, water flows from one pore to another pore through the capillary openings due to pressure of water over the Terafil disc. The pores inside the Terafil disc, therefore, work like micro-reservoirs of filtered water. The opening of the capillaries are, however, too small for the impurities to enter into the capillaries, which is why such impurities, comprising suspended particles and microbes, get deposited on the top of Terafil disc as water is filtered through it. It is for this reason that the core of Terafil disc is never clogged unlike the ceramic candle filters that are in vogue in most currently available filters.

The water filtered through Terafil is thus free from turbidity, colour, bad odour while the process also effectively removes microorganisms, soluble iron and heavy metals from raw water. Terafil also removes fluoride, chromium, nickel, cobalt, lead, and chloride from raw water. All these impurities get precipitated on the top surface of Terafil, which can be periodically removed by cleaning the filter disc. Thus regular cleaning of the top surface of Terafil is important as over a period of time the collected impurities may clog the outer surface of Terafil, thereby reducing the flow rate of filtered water. Besides, the rate of filtration is also dependant upon the turbidity and pressure of raw water as well as the diameter of Terafil disc inside the filter.

The outer surface of Terafil, therefore, needs to be scrubbed, once a week or as and when required, with a soft nylon brush or coir to remove the sedimented impurities to open new pores for facilitating the filtration process. Although the thickness of Terafil may slightly reduce by scrubbing its top surface, the quality of water filtered by it does not change for about five years. As the pH of filtered water is also improved, Terafil water filter is well suitable for treatment of both surface and ground water with affordable cost and without significant maintenance for a long period.

The circular, disc shape of Terafil filter is more preferable due to its high strength, long operational life and for easy maintenance, besides being simple to produce and fix with the container. The Terafil discs in both domestic or community filters are easy to dismantle/reassemble. Generally Terafil discs of 50 mm thickness and 100 & 220 mm diameter are produced to obtain maximum benefits.

Domestic Terafil water filter is available in 20 and 30 liter sizes with 1 to 4 litre/hr rate of filtration. The cost comes to just Rs.2/- per ton of filtered water. Domestic Terafil water filters are normally made with chambers made from food grade plastic. For installing community Terafil water filters, space required is 1 to 300 square meters for filters of 1,000 to 1, 00,000 litres/day capacities. The chambers of Terafil filters, for community use, are usually cemented structures where filtration and collection of filtered water occurs. Besides, electricity is not required for operation of the Terafil water filters. On-line pressure Terafil filter with capacity of 60 to 10,000 litres/day have also been developed.

IMMT, Bhubaneswar had distributed 1000 sets of Terafil water filters to the victims of cyclone in affected areas of Orissa during November 1999 to March 2000 for evaluation of the performance of these filters. Different Govt. departments, NGOs, International organizations like UNICEF and OXFAM have distributed about 30,000 sets of water filter in rural areas of Orissa. These filters are being installed in schools, community centers and villages in Orissa by Rural Development (RD) Department, Govt. of Orissa. Such efforts are being replicated in other States as well, under Central Govt. Schemes like Bharat Nirman Yojana and Jalmani (a Ministry of Rural Development scheme for Installation of Stand Alone Drinking Water Purification Systems in Rural India).  

Meanwhile, CSIR scientists are working to develop more advanced versions of Terafil discs that have nano-silver impregnated into them for complete removal of microorganisms from raw water. Sure then, there is a bright ray of hope that as Terafil filter goes places touching the lives of common masses, it could emerge as the most promising solution to providing sustainable drinking water to our people.