20 ENVIRONMENT AND ENERGY
<< Continued from page 19 Table 1: Content of typical wastewater in some major industries
Industry Pulp and paper
Iron and steel
Mines and quarries
Food industry
Brewing
Dairy
Typical content of effluent
• Chlorinated lignosulphonic acids, chlorinated resin acids, chlorinated phenols and chlorinated hydrocarbons – about 500 different chlorinated organic compounds identified
• Coloured compounds and absorbable organic halogens( AOX)
• Pollutants characterized by BOD, COD, suspended solids( SS), toxicity and colour
• Cooling water containing ammonia and cyanide
• Gasification products – benzene, naphthalene, anthracene, cyanide, ammonia, phenols, cresols and polycyclic aromatic hydrocarbons
• Hydraulic oils, tallow and particulate solids
• Acidic rinse water and waste acid( hydrochloric and sulphuric)
• Slurries of rock particles
• Surfactants
• Oils and hydraulic oils
• Undesirable minerals, i. e. arsenic
• Slimes with very fine particulates
• High levels of BOD and SS concentrations
• Variable BOD and pH depending on vegetable, fruit or meat and season
• Vegetable processing – high particulates, some dissolved organics, surfactants
• Meat – strong organics, antibiotics, growth hormones, pesticides and insecticides
• Cooking – plant organic material, salt, flavourings, colouring material, acids, alkalis, oil and fat
• BOD, COD, SS, nitrogen, phosphorus- variable by individual processes
• pH variable due to acid and alkaline cleaning agents
• High temperature
• Dissolved sugars, proteins, fats and additive residues
• BOD, COD, SS, nitrogen and phosphorus
Organic chemicals • Pesticides, pharmaceuticals, paints and dyes, petro-chemicals, detergents, plastics, etc.
• Feed-stock materials, by-products, product material in soluble or particulate form, washing and cleaning agents, solvents and added-value products such as plasticizers
Textiles
Energy
• BOD, COD, metals, suspended solids, urea, salt, sulphide, H 2
O 2
, NaOH
• Disinfectants, biocides, insecticide residues, detergents, oils, knitting lubricants, spin finishes, spent solvents, anti-static compounds, stabilizers, surfactants, organic processing assistants, cationic materials, colour
• High acidity or alkalinity
• Heat, foam
• Toxic materials, cleaning waste, size
• Production of fossil fuels – contamination from oil and gas wells and fracking
• Hot cooling water
Source: Based on IWA Publishing( n. d.); UNEP( 2010); and Moussa( 2008) mobility, and loading of industrial pollutants have potentially more significant impacts on water resources, human health, and the environment than actual volumes of water. This is reflected in Pollutant Release and Transfer Registries( PRTRs), which contain information from developed countries on the amounts of selected polluting substances( above certain thresholds) released by industry into water, land, and air. Such databases could be analysed to obtain a general idea about the overall level of potential recoverable resources among the many undesirable contaminants.
Widely varying industrial activities produce wastewater, which is characterised by a broad spectrum of pollutants( see Table 1). Technology is available to remove( or‘ mine’) these pollutants and is only limited by its cost-effectiveness in given industrial situations. This creates two products: the treated water and the materials recovered. The water may be recycled within a plant or by another linked industry, or it may be simply discharged, returning it to the hydrological cycle for others to use. In the USA, it has been estimated that for some major rivers the water has been used and reused over 20 times before it reaches the sea.
Useful materials may be recovered, such as minerals( phosphates) and metals. Cooling water may provide
March 2018 Volume 24 I Number 1 www. plumbingafrica. co. za