STREAM POLLUTION

Wairarapa Times-Age, 24 February 1940, Page 8

STREAM POLLUTION

SELF PURIFICATION PROCESS. “Pollution and self purification of streams" was the subject of an address delivered by Mr L. 11. Davis, M.Sc., A.N.Z.T.C. of the Dominion Laboratory at the annual conference of the New Zealand branch of the Royal Sanitary Institute. The lecturer stated that owing to its solvent, nature pure water was really a curiosity and with our modern civilisation all manners of impurities found their way into our streams, including effete matters from mon and animals, manures, Irom cultivated land. etc. This being so it was an essential fact that streams did have within limits the power to purify themselves. Self purification could be divided into zones: a first zone of degradion during which a stream became grossly polluted; a second zone of active decomposition in which organic matter was attacked by bacteria being broken down to inorganic matter, by which various gases were produced, and a third zone of recovery, in which were certain physical forces of gravity, light and aeration, chemical forces of oxidation. reduction and coagulation, and biological—bacteria, algae, protozoa, rotifera and Crustacea—aquatic plants and aquatic animals, and finally a zone of cleaner water. Bacteria broke down organic matter, algae used C 0.2 and produced oxygen, protozoa lived on bacteria, aquatic plants took up chemical matter and produced oxygen, and aquatic animals lived on smaller organisms and plant life. Streams with an alternating flow, of slow stretches and then rapids were of the best type for self purification.