- Boiling:
- Very effective method of purification
- Boiled or rolled over for 10-20 mins
- Taste is slightly altered but harmless
- Care should be taken for vessels during storage as there is chance of contamination
- It kills bacteria spores, cysts, ova and also removes temporary hardness by removing carbon dioxide and precipitating calcium carbonate.
- Bleaching powder:
- It contains about 33% of “ active chlorine”
- It’s a unstable product
- To make it stable = excessive alum is added = chlorinated lime
- On exposure to environment leads to loss of active chlorine
- It should be stored in dark and dry place
- It gives pungent smell = hence not routinely used
- Chlorine solution:
- Prepared from 4 kgs bleaching powder in 20 liters of water
- 25% of activate chlorine
- But evaporates in the environement = stored in dark, dry and cold place
- High test hypochlorite
- Calcium compound containing 60 to 70% active chlorine.
- It is stable than bleaching powder and less deterioration
- Chlorine tablets
- Available readily in the market
- under various trade names like halazone tablets.
- Very economical = formulation used currently was developed by NEERI, nagpur
- 0.5 gm of chlorine tablet for 20 liters of water
- Iodine:
- It is used for emergency disinfection of water. Why?
- highly expensive
- physiological activity with respect to thyroid
- Two drops of 2% ethanol solution of iodine will be sufficient for one liter of clear water
- for a contact period of 20 to 30 min for effective disinfection.
- Remains active for longer time
- It is used for emergency disinfection of water. Why?
- Potassium permanganate:
- This was widely used,but now no longer recommended for water disinfection.
- Effective against vibrio cholera but not against other pathogens
- It also alters the color, taste and smell of water.
- Filtration:
- On a small scale, water can be purified by using THREE TYPES OF filters
- PASTEUR CHAMBERLAND FILTER = made up of percelian
- BERKEFELD FILTER = made up of kieselguhr or infusorial earth.
- KATADYN FILTERS = silver coating on filters = when bacteria touch silver- it dies due to oligodynamic effect
- Heart of the filter is = candle = ONCE PER WEEK
- Wash it under running water using hard brush followed by boiling = to remove impurities clogging the filters