Regional Research Laboratory
(Council of Scientific and Industrial Research),
Bhubaneswar-751013

Principle and State of art of Terafil water filter


Principle:

The red clay water filtration media, called as ‘TERAFIL’, is a burnt red clay porous media used for filtration and treatment of raw water into clean drinking water, which is invented by RRL (CSIR), Bhubaneswar since 1998. The ‘Terafil’ is produced from the mixture of red clay (silt clay), river sand and wood saw dust, which is sintered to make porous. During sintering process of the green Terafil, the wood particles are burnt, clay particles are sintered around the sand particles leaving elliptical / circular large size pores in between. The pores are not connected with each other, but separated by thin clay walls (membranes), which is semi-permeable and contains ultra-fine capillary openings. The capillary openings of the clay walls (membrane) bridge the large pores. The water travels from one pore to another pore through the capillary openings in the clay walls(membranes) of the Terafil during filtration process, and the large pores work like micro-reservoirs for holding water inside the Terafil. When the Terafil is fixed at the bottom of a container and raw water is allowed to pass through the Terafil, the raw water is filtered on the top surface of the Terafil leaving behind the sediments and impurities on top surface of the Terafil. Since diameter of the capillary openings of the clay walls (membranes) in the Terafil is in sub-micron size, almost all suspended particles & microbes etc. present in the raw water are restricted to travel along water inside the Terafil. These impurities are removed from the raw water on the top surface of Terafil without clogging its core, for which long operational life of the Terafil is obtained. The Terafil is activated during sintering process and the clay is negatively charged, for which soluble iron and some heavy metals present in raw water are also removed by ion-exchange or adsorption process, and the same get precipitated on the top surface of the Terafil. In this way the moderate raw water is filtered and treated to clean drinking water. 99% of turbidity, 95-99% of micro-organisms, 75-90% of soluble iron, colour etc. are effectively removed from the raw water during filtration process through the Terafil. The rate of filtration is dependant upon pressure of the raw water on the Terafil. The filtrates clog the top surface of the Terafil over time during use and hence reduce the flow rate. Therefore scrubbing or cleaning of top surface of the Terafil with a soft nylon brush or coir or similar materials is necessary to remove the sediments, open the new pores and rejuvenate the flow rate. The porous red clay media, TERAFIL, can be made in any shape; however circular disc shape is more preferable in view of strength, easy production & fixing with container, high flow rate, easy operation and maintenance. The quality of filtered water does not alter through out life of Terafil, although thickness of the Terafil reduces by scrubbing its outer surface during the filtration process.

‘TERAFIL’ is made in shape of a solid disc, having 50 mm thickness and 220 mm & 100 mm diameter at present. The Terafil disc can be fixed directly with bottom of any container through epoxy resin or cement or any adhesive which is not harmful to human being. The Terafil disc can also be fixed with a metallic or plastic holder with cement, which can be screwed to the bottom of any container to make a water filter. Domestic or community size Terafil water filtration system is consisting of two chambers; the upper chamber is placed on the top of lower chamber. A set of Terafil discs, depending on the rate of filtration, are fitted at the bottom of the upper chamber. The upper chamber holds raw water and lower chamber store the filtered water. The Terafils are fitted on the bottom of the upper chamber in such a manner that water can pass through the Terafil only without leakage through the joint between Terafil and the upper chamber. The filtered water is collected at the outlet of the Terafil holder, bellow the upper chamber, like any other water filters.

The water filtration system can work either by gravity force or by pressure of water. In case of gravity operated domestic water filter, two chambers are needed as mentioned above. The chambers can be made with any materials, such as stainless steel, Terracotta, food grade plastic, ferro-cement tank etc. Since the rate of filtration depends on the water pressure over the Terafil and total surface area of the Terafils; therefore the number of Terafils is decided as per requirement of the filtered water. The average rate of filtration in domestic size filter is in the range of 1 to 4 lit/hr depending upon turbidity of raw water, number of the Terafil disc or diameter of the Terafil used in the filter. Community size gravity flow water filter can be constructed with masonry chamber, ferro-cement or metallic containers. The rate of filtration depends on number & diameter of the Terafils fitted in the upper chamber. However, average rate of filtration in the standard gravity flow community size Terafil water filters is the range of 60-120 lit/hr, having dead storage capacity 1200-3000 liter. Fabrication cost of such community water filters are within range of Rs.10, 000/- to Rs.20, 000/- and its life will be more than 10 years. Cost of filtered water is within Rs.2/- per ton (neglecting cost of raw water). Rate of filtration and dead storage capacity of gravity flow Terafil water filter system can be increased or reduced as per water requirement of the community, up to 100,000 lit/day with masonry construction of the water treatment system.

The pressure flow on-line Terafil water filtration system is a closed system. It has also two water tight metallic chambers, upper and lower chambers. Terafils are fitted at the bottom of the upper chamber and raw water is supplied to upper chamber under pressure through a water pump or from overhead storage tank. The raw water is filtered through the Terafil under pressure to obtain high rate of filtration. The filtered water is collected in the lower chamber and the same can be supplied to the users through pipeline. The water tight chamber has a flanged opening for cleaning of the Terafils. The upper chamber is also connected with a sludge outlet for removal of sediments from time to time. However, the pressurized Terafil water filter can operate successfully up to the water pressure of 2.0 kg/cm2. The chambers can be made with stainless steel and food grade plastic depending upon the size and capacity of filter. The rate of filtration is dependent on number & diameter of Terafils, turbidity and pressure of raw water in the upper chamber. Presently on-line Terafil water filter with flow rate of 100 llit/hr to 2000 lits/hr are available. However, the rate of filtration can be increased up to 50,000 liter/hr as per requirement of the community with user’s friendly Terafil cleaning systems for removal of sediments can be designed easily for community water supply. The present cost of domestic on-line Terafil water filter with food grade plastic containers is within Rs.300/- per set, rate of filtration 60-100 lits/hr, life is about 10 years, and it operates with water pressure of overhead tank without electricity. The present cost of community size on-line filter having stainless containers is within Rs.30,000/-, rate of filtration 1500 lit/hr, operates by ½ hp water pump, and life is more than 15 years.
The life of Terafil is between 3-5 years, depending upon use, frequency of cleaning, turbidity of raw water etc. The cost of Terafil fitted with food grade plastic holder is about Rs.30/- per set for 100 mm diameter, and Rs.75/- per set for 220 mm diameter Terafil (including tax). The technology has been transferred to two SISI units for production of Terafil.

Dissemination :

More than 30,000 domestic size Terafil water filters, are being in operation in Orissa and Meghalaya through Government network, NGOs, and private users. Few numbers of community sizes Terafil water filters with ferro-cement tank have been installed in Orissa and Meghalaya.

Hon’ble Chief Minister of Orissa Shri Naveen Patnaik along with his cabinet ministers, secretaries of different departments, Chief Engineer, RWSS etc. have witnessed the operation of domestic size Terafil water filters in his office at Bhubaneswar. Shri S. Khuntia, Scientist-G and the Director Prof. B.K. Mishra presented the details of use and benefits of Terafil water filter to the Hon’ble Chief Minister and other ministers during the meeting in August, 2006. Thereafter the Hon’ble Chief Minister of Orissa and other concerned secretaries have taken few meetings during last year for formulation of extensive dissemination of Terafil water filter in Orissa for mitigation of drinking water problem. The Hon’ble Chief Minister has approved for distribution of 80,000 sets of domestic size Terafil water filters with food grade plastic containers in primary health centers, Anganwadi Centres, Self-help groups etc. for supply of clean dinking water to the children and creation of awareness of the benefit of Terafil water filter among the common people of Orissa. Different departments of Govt. of Orissa have started depositing the amount at RRL for production of the required Terafil water filter for the above purpose. The Terafil filter programme as required by Hon’ble Chief Minister will tentatively start from 1st week of March, 2007 after receiving the desired advance amount, i.e. Rs.1.0 crore from Govt. of Orissa. RRL-Bhubaneswar will develop the required shape and size of Terafil, plastic containers and test the filters before hand over the same to the Govt. of Orissa.


( S. KHUNTIA )
Scientist-‘G’ & Head
Design & Rural Technology Dept.
Regional Research Laboratory
Bhubaneswar.