3. Economics:

• Average unit cost of a 100 mm diameter and 50 mm thickness Terafil disc fitted with food grade plastic holder costs about Rs 25. This disc can purify 1 LPH (litre per hour) in a domestic filter for about five years.
• Terafil disc can also be fitted with any domestic container to make a water filter, the cost of cleaning water is below Rs 2 per ton considering total cost of Terafil filter/plant (excluding cost of raw water), therefore poorest of poor can afford the Terafil water filter.
• An entrepreneur with four skilled workers can produce complete 500 sets of 100 mm dia Terafil water filtration disc per day, or 12,000 sets with an expenditure of Rs 2 lakh towards materials, labour & power in a month.
• An investment of about Rs 3 lakh (excluding cost of land & building) is required for production of various kinds of Terafil filter units (50-30000 liter per day). Total investment can be recovered back within six months period.
• For community level water filters a space ranging from 1 to 300 m2 would be required for a plant of 1000 to 100000 LPD capacity respectively.
• Technology fee for licensing manufacture of Terafil filter:
  
  • Rs 15000 onetime payment for DIC registered micro and small entrepreneurs
  • Rs 60000 onetime payment for other entrepreneurs (10.3% service tax extra).
• Tentative Cost of different kind of Terafil water filters:
  
  • Domestic (30 liter through CIPET) : About Rs 450 including VAT & Packing
  • Domestic (22 liter through CSIR-IMMT) : About Rs 385 including VAT & Packing
  • On-line Terafil water filter Unit price of a complete (without water tap & pipe) : Rs 1000 VAT
  • Community Level construction cost of 1000 lit capacity/day Stand-alone Terafil water purification plant (without water pipeline) : Rs 10,000.

4. Technical Details about Terafil

The dough of the mixture is sintered at high temperature in a low cost coal / wood fired furnace to make the terracotta disc porous. During sintering process, the wood particles are burnt and clay particles are sintered around the sand particles leaving elliptical / circular large size pores in between. These pores are not connected with each other, unlike white ceramic filter candles, but sepa- rated by very thin clay walls which are semi-permeable in nature. The thin clay walls contain large numbers of ultra-fine capillary openings. A set of pores are connected by these ultra-fine capillaries only. Average diameter of the capillary openings is in sub-micron size. During filtration process, water flows from one pore to another pore through the capillary openings by pressure of raw water over the Terafil disc. The pores inside the Terafil disc always work like micro-reservoirs of filtered water. Since opening of the capillaries are in sub-micron, almost all suspended particles & microbes etc. cannot enter into the capillaries; hence sediments & impurities are deposited on top of the Terafil disc during filtration. Therefore the core of Terafil disc is never clogged unlike white ceramic candle during filtration.

Rate of filtration is dependent upon turbidity and pressure of raw water as well as diameter of Terafil disc inside the filter. The filtrates clog the top surface of the Terafil over time during use and hence reduce the flow rate. Therefore scrubbing or cleaning the top surface of the Terafil disc with a soft nylon brush or coir or similar abrasive materials or by water jet is necessary to remove the sediments and open the new pores for rejuvenation of filtration process. The thickness of the Terafil keeps reducing on scrubbing its top surface; however quality of filtered water is not altered during entire life of Terafil.