Question

Physical, chemical and biological clasiification of waste water

Answer 1

Answer:

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Explanation:

Characteristics of sewage

I. Physical characteristics of sewage:

1. Temperature:

Temperature of sewage depends upon season. However temperature is slightly higher than that of ground water.

High temperature of sewage is due to evolution of heat during decomposition of organic matter in sewage.

2. Color:

Color of sewage indicates its strength and age.

Fresh domestic sewage is grey in color but septic sewage is dark in color

When industrial effluent is mixed it give characteristic color to sewage

3. Odor:

Fresh domestic sewage is almost odorless.

Septic or stale sewage is putrid in odor which is due to generation of H2S during anaerobic decomposition of organic matters.

When industrial effluent is mixed, it give characteristics odor to sewage

4. Turbidity:

Sewage is highly turbid.

Turbidity of sewage is due to dissolved substances, colloidal matters, suspended solids and microbial cells.

II. Chemical characteristics of sewage:

1. Organic matter:

In general sewage contains large amount of organic matters. However amount of organic matter depends on types and condition of sewage.

Organic matter in sewage may be found in the form of dissolved substances, colloidal matter, suspended or sedimented form.

2. Chloride:

Human beings discharge large amount (8-15gm/day) of chloride in the form of NaCl, especially through urine and sweat. So domestic sewage from toilet and bathroom contains higher level of chloride.

Sulfite:

In sewage sulfite in the form of H2S (hydrogen sulfite) is generated during anaerobic decomposition of organic matters by anaerobic bacteria.

H2S gives putrid odor to sewage.

3. Biological oxygen demand (BOD):

Sewage usually have high BOD due to presence of large amount of organic matters.

Value of BOD ranges from 100mg/ltr for very dilute sewage to 600mg/ltr or more for concentrated sewage containing industrial effluent mix.

4. Dissolved oxygen (DO):

Due to high level of microbial cells and biodegradable organic matters, sewage have very low level of dissolved oxygen.

In some sewage, DO is completely absent.

Level of Do depends on age and condition of sewage. Low level DO is also due to lower solubility of oxygen in sewage. Oxygen is only 95% soluble in sewage than in pure water).

5. pH:

sewage is slightly alkaline in pH

6. Nitrogen:

In sewage nitrogen is found in variety of form like organic nitrogen, ammonia, nitrite, nitrate etc

Fresh sewage mainly contains organic nitrogen and very little inorganic form of nitrogen. On the other hand organic septic sewage contains high inorganic nitrogen and low organic nitrogen.

In sewage nitrite never accumulate in concentration greater than 1mg/ltr because it is intermediate product during conversion of ammonia into nitrate (NO3).

In sewage treatment plant, NH3 and NO2 are finally converted to NO3.

7. Oxidation-Reduction (O-R) potential:

Oxidation-Reduction potential indicates energy state of sewage in terms of its oxidizing or reducing potential.

O-R potential is very valuable index to monitor sewage treatment plant.

In aerobic treatment process like tripling filters, positive OR potential of about +2—to +600 is needed. In anaerobic treatment process like sludge digestion, negative OR potential of about -100 to -200 is needed