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