Wastewater quality

Composition of raw sewage

Raw sewage contains 99.9% water and only 0.1% solids.

Out of the solid materials, 30% are inorganic, primarily salts, and 70% are organic materials.

The organic materials in the wastewater contain an average of 50% proteins, 40% carbohydrates and 10% fats.

The principal function of the treatment facility is to remove these organic materials from the water.

The solids in the wastewater are comprised of suspended materials and dissolved materials.

The suspended materials are removed using mechanical methods while the dissolved materials are treated using biological methods as explained in the previous sections.

The following table presents the typical characteristics of raw sewage during the last three years.

Average composition of raw sewage discharged into the treatment facility during the last three years (values in mg/L)

2009 2010 2011 Parameter/year
344 469 432 BOD
1195 1288 1156 COD
675 644 630 TSS - total suspended solids
105 102 TN – total nitrogen