Index >> Waste Water Microbiology >> Chemical Characteristics of Sewage

Chemical  Characterestics of Sewage - A typical raw sewage contains about 99.9% water. The remaining 0.1 % is made up of about 70% organic and 30% inorganic solids. The solid content occurs in both suspended and dissolved forms. The inorganic components include ammonia, chloride, grit, salts and metals.

These inorganic chemicals are actually those which are present in the water supply initially. Metal industries and mines also contribute to the inorganics. Organic compounds may be either nitrogenous compounds such as proteins and amino acids or non nitrogenous compounds such as carbohydrates and lipids.

The next important chemical group found in sewage is lipid. Fat and fatty acids which escape digestion, adsorption or deposition in human digestive system accounts for the lipids in faeces. Proteins are the next groups which mainly originate from the excreta of humans and animals. In addition, dead/decomposing plants, insects and microorganisms also provide proteinaceous substances.

Since wastewaters from different sources accumulate in sewage, their chemical compositions vary depending upon the sources. Moreover, since the microorganisms are also part of sewage, they carry out certain changes in the chemical composition of sewage irrespective of the treatment processes. Industrial wastes from slaughter houses, sugar factories and paper mills add organic matters.