VPE 511: Environment and Environmental Hygiene (2+1)

THE NITROGENOUS CONSTITUENTS

• Uncontaminated water supplies are rarely completely free from nitrogenous constituents, and in such waters nitrogen may be present in the form of humic acids or nitrates.
• Waters contaminated with sewage or other decaying organic matter may contain, in addition to these, ammonium salts or easily decomposable amides , and nitrites.
• As ammonium salts and nitrites are quickly oxidised in natural waters to nitrate, their presence is taken as a strong indication of recent contamination with sewage.
• Quantitatively the ammonium salts and easily decomposable amides are estimated by distilling a sample of the water made alkaline with sodium carbonate; the amount of ammonia distilling off is estimated calculated to part per 100,000 and reported as “Free Ammonia.”
• Humic acids and the more complex nitrogenous compounds such as protein do not liberate ammonia on boiling with sodium carbonate, but do so when distilled with an alkaline solution of potassium permanganate. This ammonia is estimated calculated to parts per 100,000 and reported as “Albuminoid Ammonia.”
• Satisfactory waters rarely contain any free ammonia at all, and the presence of more than 0.005 parts per 100,000 must be regarded as significant of pollution.
• If the amount of free ammonia present is greater than the amount of albuminoid ammonia then sewage contamination is certain. Many satisfactory waters, e.g. peaty waters, contain appreciable quantities of albuminoid ammonia but such waters yield their albuminoid ammonia slowly, and they contain only traces of free ammonia.
• In waters other than moorland waters, the albuminoid ammonia may be significant of sewage pollution if it is a present in concentrations greater than 0.01 parts per 100,000.
• The presence of nitrate is of no significance in the absence of other nitrogenous constituents. If, on the other hand, free ammonia is present then the presence of nitrate is an added indication of pollution.