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Disinfection methods; alum and bleaching powder

Short answer

Common disinfection methods include boiling, chlorination, chloramine, ozonation, UV, and iodine. For25 MLD, alum at15 mg/L needs375 kg/day; chlorine dose0.5 mg/L requires12.5 kg/day chlorine, thus bleaching powder with30% chlorine=41.67 kg/day.

Mention the common methods of disinfection. Calculate the daily quantity of alum and bleaching powder required in a treatment plant of capacity 25 million liters per day. Consider optimum dose of alum as 15 mg/l and chlorine dose of 0.5 mg/l assuming 30% chlorine available in bleaching powder.

Common methods of disinfection

  1. Boiling (for small household quantities, 5 to 10 min).
  2. Chlorination (gas, bleaching powder, hypochlorite): the most common method.
  3. Chloramine and chlorine dioxide treatment.
  4. Ozonation: a strong oxidant, no residual.
  5. Ultraviolet (UV) radiation: for clear water, no residual.
  6. Iodine and bromine, potassium permanganate, silver (Katadyn) for small supplies.
  7. Lime and excess lime treatment for softening and disinfection.

Quantities required for 25 MLD

Flow = 25 MLD =25×106= 25\times10^6 l/day. 1 mg/l ×\times 1 MLD = 1 kg/day.

Alum (dose 15 mg/l):

15×25=375 kg/day15\times25 = 375\ \text{kg/day}

Chlorine (dose 0.5 mg/l):

0.5×25=12.5 kg/day0.5\times25 = 12.5\ \text{kg/day}

Bleaching powder (30 % available chlorine):

12.50.30=41.67 kg/day\frac{12.5}{0.30} = 41.67\ \text{kg/day}

Answer: alum = 375 kg/day; bleaching powder = 41.67 kg/day.

✓ Answer checked by Claude Opus 5.5 (high effort)

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