ABSTRACT
In recent years, the problem of water pollution has been complicated by the introduction of many new chemical contaminants whose effect is more indirect, latent and more difficult to diagnose and eliminate. Oxygen-demanding wastes are usually destroyed by bacteria if there is sufficient oxygen in the water. The report defines "water-quality criteria" as "a designated concentration of a constituent that, when not exceeded, will protect an organism, an organism community, or a prescribed water use or quality with an adequate degree of safety". Bacteria and other small organisms in the water consumed the sewage or other organic matter, turning it into new bacterial cells, carbon dioxide, and other products. In primary treatment, solids are allowed to settle and are removed from the water. Secondary treatment, a further step in purifying waste water, uses biological processes. The discharge of oxygen-consuming wastes will increase despite the universal application of the most efficient waste treatment processes now available.
