Table A lists the characteristics of domestic wastewater of different strengths. The strength of the domestic wastewater varies with the per capita water supply available. Since the per capita contribution of organic matter is constant (only a slight variation due to food habits) the strength of the wastewater depends on the per capita water available for dilution. Table B shows the per capita contribution of different characteristics of domestic wastewater

Table A . Major constituents of typical domestic wastewater

Table B.  Per capita contributions of domestic wastewater characteristics

Micro organisms present in wastewater are expressed in terms of total coliforms (TC) and fecal coliforms (FC) and the typical values of TC and FC vary between 10⁹ to 10¹⁰ per 100 ml and 10⁸ to 10⁹ per 100 ml of sample respectively.

POPULATION EQUIVALENT

The strength of the industrial wastewater is generally expressed as population equivalent by comparing with the per capita strength of domestic wastewater. Population equivalent (PE) is required to be determined so as to rationally charge the industries for the pollution caused by them when the industrial wastewater is discharged into a sewerage system. The population equivalent is determined by dividing the BOD5 of the industrial waste by the per capita contribution of BOD5.

Population equivalent (PE) = BOD of Industrial waste / Per capita contribution of BOD.

EFFLUENT STANDARDS

Effluent standards are the values for each parameter fixed by the BIS as the upper limit in the effluent to be discharged in to various environments such as land, water bodies etc. The tolerance limits fixed by the BIS for discharge of industrial effluent into various environments are furnished in Table C. The tolerance limits of discharge of wastewater effluent into the water bodies are furnished in Table D.

Table C. Tolerance limits for discharge of Industrial effluent

• a  as per IS 2490 – 1974 pt I
• b  as per IS 3306 – 1974
• c  as per IS 3307 – 1977
• d   as per  7968 – 1976

Table D.  Tolerance limits for discharge of domestic wastewater effluent into surface waters