Discharge of dangerous substances in industrial effluent
Industrial wastes usually contain traces or larger quantities of the raw materials, intermediate products, final products, co-products and by-products, and any ancillary or processing chemicals used. The composition and amount of pollutants discharged by a specific industry can usually be determined only by detailed analysis of its effluents. The complete enumeration of the substances present in industrial waste waters as a whole would run into thousands. They include detergents, solvents, cyanides, heavy metals, mineral and organic acids, nitrogenous substances, fats, salts, bleaching agents, dyes and pigments, phenolic compounds, tanning agents, sulphides and ammonia. Of the compounds mentioned, many are biocidal and toxic. In spite of this variety, many industrial wastes can be measured by the same parameters as those applicable to municipal wastes, such as biological oxygen demand (BOD) and chemical oxygen demand (COD), turbidity, and suspended solids; however, the lack of information on the composition of industrial discharges has caused the greatest difficulties in water management.
Industrial wastes are significant sources of water pollution, often giving rise to contamination with heavy metals (lead, mercury, arsenic and cadmium) and persistent organic compounds. A study of 15 Japanese cities, for example, showed that 30 per cent of all groundwater supplies are contaminated by chlorinated solvents from industry; in some cases, the solvents from spills travelled as far as 10 km from the source of pollution (UNEP 1996b).