• There are two broad categories of waste water on the basis of their origin. They includes sewage and industrial effluent.
• Sewage is waste water generated from residential areas like community whereas industrial effluent is waste water generated from various industries.
• Domestic sewage and industrial effluent differ in their composition and nature of pollutant. For example, microorganisms and organic matter are main pollutant in sewage whereas various toxic chemicals are main pollutants in industrial effluent.

I. Industrial effluent:

• Waste water generated from various industries is called industrial effluent.
• In general various toxic chemicals alike acid, alkali, coloring agents etc are main pollutants. Microorganisms and organic matters are usually lower in industrial effluent.
• Actual composition and characteristics of industrial effluent depends on type of industry and nature of raw materials of industry.
• Pollutants in industries are generated during processing of raw materials and manufacturing of products.

Some of the common industries and characteristics of their effluents:

1. Leather industry effluent:

• In leather industry raw skin is processed to make leather tough. Steps in making leather from raw skin includes-removal of hairs, liming of skin with Na2S, deliming by NH4Cl or (NH4)2SO4, tanning with chromium and coloring.
• Each steps in skin processing adds pollutants in effluent.
• Some important characteristics of these leather industries effluent are:
  • Organic matter; mainly keratin protein, hairs, some fats and coloring dyes
  • BOD: 700mg/liter
  • Color: strong dark
  • Dissolved and suspended solids: high
  • pH: 9.5

2. Paper and pulp industry effluent:

• In paper and pulp industries, paper is manufactured from woods.
• Various operations are carried out during paper making such as- preparation of raw materials, pulping, washing, coloring and paper making.
• All of these steps adds some pollutants in effluent.
• Characteristics of these paper industries effluent are:
  • Organic matters; mainly cellulose, lignin and coloring agents
  • Inorganic matters: acids, alkali, bleaching agents etc
  • Color: dark brown
  • Suspended solids: 1350mg/ltr
  • Dissolved oxygen (DO): 1650mg/ltr
  • Effluent is highly resistant to biological oxidation.

3. Dairy industry effluent:

• In dairy industry, various products like cheese, yoghurt, butter etc are produced from raw milk.
• Some of the characteristics of these dairy industry effluent are:
  • Organic matter: very high, mainly casein and lactose
  • Odor: highly putrescible and bad odorous due to anaerobic decomposition of casein
  • BOD: high
  • Effluent is highly susceptible for microbial decomposition
  • Toxic inorganic matter: very low or absent

4. Distillery and wine industry effluent:

• In distillery and wine industries, carbohydrate is fermented to produce alcoholic products.
• Operations carried out in distillery industries includes- preparation of raw materials, fermentation and down streaming process like distillation of alcohol.
• Pollutants are generated in each steps.
• Some characteristics of these distillery industry effluent are;
  • Organic matters: mainly carbohydrates, organic acids, and some spill alcohol
  • BOD: high (29000mg/ltr)
  • COD: high (80000 mg/ltr)
  • Suspended solids:high (4000mg/ltr)
  • Color: strong dark
  • pH: Acidic

5. Edible oil manufacturing industry effluent:

• In edible oil industry, pollutant are generated during neutralization of excess fatty acids, filtration and distillation of oil.
• Characteristics of these edible oil industry effluent are;
  • Organic matter: high content of free and saponified (hydrolyzed) fat
  • Suspended solids: high content of suspended and dissolved solids
  • BOD: high
  • COD: high

6. Detergent industry effluent:

• Detergent industry effluent mainly contains emulsifying agents like phosphorus, borax, alkyl benzene, sulphonate etc
• Effluent is usually alkaline and are non-biodegradable and toxic to aquatic biota.

II. Sewage:

• Wastewater generated from residential area is called sewage.
• Sewage is extremely unpleasant in odor which contains large number of microorganisms, organic matters and other pollutants.
• Pure domestic sewage consists of discharge from bathroom, toilet, kitchen and laboratories. However sometimes industrial effluent are also mixed with sewage.
• Actual composition of sewage depends on type, condition and age of sewage.
• In general sewage contains:
  • Sullage: it is waste water generated from kitchen, bathroom, laboratories etc
  • Human and animal excreta from toilet and animal farm
  • Run-off waste water from street during raining
  • Some industrial effluent

Wastewater; Industrial effluent and domestic sewage

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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.

III. Biological characteristics of sewage:

1. Bacteria:

• Two types of bacteria are found in sewage.
  • Intestinal bacteria:
    • Non-pathogenic intestinal bacteria are normal flora of gastointestinal tract of human and animals and enter into sewage together with stool. Examples; faecal coliform, faecal streptococci, Clostridium perfingens, et
    • Pathogenic intestinal bacteria such as Salmonella, Shigella, Vibrio cholera, Yersenia enterocolitica etc enter into sewage through stool of patients.
  • Real sewage bacteria
    • The natural habitat of these bacteria is sewage.
    • Both aerobic as well as anaerobic are found in sewage.
    • Aerobic bacteria play important role in oxidation of organic matter during aerobic process.
    • Common anaerobic bacteria includes;
      • Clostridium sporogens
      • Bifidobacterium
      • Peptococcus
      • Methanogenic bacteria like Methanobacterium, methanosarcina
    • Common aerobic bacteria includes;
      • Zeoglea remigera
      • Noacrdia
      • Flavobacterium
      • Achromobacter
      • Nitrosomonas
    • ** Zeoglea remigera is the main organism found in trickling filter.

2. Algae:

• Some algae found in sewage includes Chlorella phormidum, Ulothrix etc
• Algae are used in trickling filter in sewage treatment plant

3. Fungi:

• Fungi like Fusarium and Sporotricum are found in sewage which play important role in trickling filter.

4. Virus:

• Some viruses causing human disease such as Poliovirus, Rotavirus, Hepatitis A and E etc are found in sewage which get access through stool of patients.

5. Protozoa:

• Some protozoa that cause disease of intestinal tract enter into sewage together with stool of patient.
• Examples: Entamoeba histolytica, Giardia, Balantidium coli etc are pathogenic protozoa
• Few protozoa such as Vorticella and Opercularia are found in trickling filter.

Physical, chemical and Biological characteristics of sewage

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