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Which procedure should I follow to disinfect a well?

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This is a question that I've been asked in the field so I wanted to share it with everyone on KnowledgePoint

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Recently in August, we experienced a flood in some part of Nepal and we are using methods developed by WHO. Please check the link below.

http://www.who.int/water_sanitation_h...

https://www.unicef.org/cholera/Annexe...

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You have two main options for well’s disinfection: emptying or not emptying the well.

For example, in DRC, we organized a campaign of wells’ rehabilitation involving disinfection of some. The wells were not used since the inhabitants of the city ran away during the war. We were preparing their return.

Most of the time we did the wells’ disinfection without emptying it because we were simply not able to empty the well even with a motor-pump. The water yield was too high for that.

Chlorinated products and active chlorine

Function of the chlorinated product that you’ll use, the percentage of active chlorine is different. You need to take it into account when preparing your stock solution or when you’re cleaning your well without emptying it.

The HTH, the most commonly used chlorinated product contains 70% of active chlorine and its limit of solubility is 225 g/L (always check the constructor/supplier packaging indicating the exact proportion of active chlorine and also the limit of solubility).

For example, to prepare a 1% (10 g/L) stock solution you need to add 10 g of active chlorine to 1 L of clean water, or 200 g for 20 L of water, so 286 g of HTH.

Disinfection emptying the well

The main idea is to brush the whole lining manually while the well is empty.

  • Prepare a 1% (10 g/L) stock solution of active chlorine in a 20L jerry can;

  • Prepare a 200 mg/L solution of active chlorine in a 10L plastic bucket, by adding 200 mL of your stock solution in the bucket (= concentration g/L of solution in 10 L bucket x volume L bucket / concentration g/L of stock solution = 0.2 x 10 / 10 = 0.2 L = 200 mL);

  • Empty the well and brush the lining using the 200 mg/L solution (make sure that the cleaners use protective equipment, gloves, mask, boots, etc.). Depending on the yield of the well, you may continue pumping out the water while cleaning it;

  • Let the well refill itself;

  • Wait for 30 minutes.

Disinfection without emptying the well

With this procedure, you’ll clean the lining above the water level and disinfect directly the water inside the well.

  • Prepare a 200 mg/L solution like above; you’ll use this solution to brush the lining above the water level;

  • Calculate the quantity of chlorinated product (i.e. HTH or bleach) needed to mix with the water of the water to obtain a concentration of 100 mg/L of active chlorine:

  1. Calculate the volume of water in the well V (m3) V = π x r2 x h, where r is the radius of the well (m) and h the height of water in the well (m) and π=3.14;

  2. Estimate the quantity of chlorinated product to add to the well, always keeping in mind the proportion of active chlorine (g) = 0.1 x V / 0.7 (for HTH);

  3. Mix with water (from the well) into ...

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There is also a WGO/WEDC technical note specifically on "Cleaning and disinfecting wells" in emergencies - http://www.who.int/water_sanitation_h...

C Dietvorst gravatar imageC Dietvorst ( 2017-09-20 23:15:18 +0000 )edit
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