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The domestic sewage of a town was tested for total solids and the following results were obtained : Weight of sample of sewage = 1000 gm Weight of solids after evaporation of liquid = 0.952 gm Weight of dry residue after ignition = 0.516 gm What is the value of volatile solids?

The domestic sewage of a town was tested for total solids and the following results were obtained : Weight of sample of sewage = 1000 gm Weight of solids after evaporation of liquid = 0.952 gm Weight of dry residue after ignition = 0.516 gm What is the value of volatile solids? Correct Answer 436 ppm

Concept:

Organic solids are called ‘volatile solids’ and these solids on heating at 650°C temperature get vaporized and leaving behind the inorganic solids or ‘non-volatile solids’.

→ Total Solids (TS) = Organic Solids (Volatile Solids) + Inorganic Solids (Non-Volatile Solids)

On heating, the water sample at 650°C all organic or volatile solids gets converted into vapors and leaving behind the inorganic solids

→ Weight of inorganic solid/Non-Volatile solids (NVS) = Weight of the residue after heating at 650°C – Weight of pan

On heating the same water sample at 110° which is the boiling point of water all water gets vaporized and leaves behind residue which consist of total solids.

→ TS = Weight of the residue after heating at 110°C – Weight of pan

Calculation:

Given,

Weight of sample of sewage = 1000 gm

Weight of solids after evaporation of liquid = 0.952 gm

→ Weight of liquid = 1000 - 0.952 = 999.048 gm

Weight of dry residue after ignition = 0.516 gm

As we know Organic Solids (Volatile Solids)

Weight of Volatile Solids after Ignition = 0.952 gm - 0.516 gm = 0.436 gm

Now,

0.436 gm of Volatile solids are in 999.048 gm

Assuming Sewage density = 1 kg/litre

(∴ 0.436 gm 436 mg of Volatile solids in 1 liter i.e. 436 ppm)

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