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Industrial effluent treatment

Control panel at Levi Strauss

Control panel at Levi Strauss

Industrial effluent has generally been regarded as an unimportant and troublesome by-product of a manufacturing process.  In a few cases, industrial effluents contain useful resources that can be viably recovered.  In South Africa, industrial effluent discharge is ultimately regulated by the Department of Water Affairs and Sanitation (DWS).  If an industry is located within a Municipal boundary, the industrial effluent will most likely find it’s way to the Municipal sewage treatment plant.  Treated waters discharged from all sewage plants in South Africa are regulated by standards enforced by DWS. For industries located within Municipal boundaries, effluent is usually discharged to sewer.  Traditionally Municipalities have imposed minimum discharge standards.  These standards were primarily imposed to protect the sewage network.  For example low pH was discouraged to prevent corrosion of cement pipes.  A limit was imposed on suspended solids to prevent clogging of pipes.  Flammable liquids are not allowed to be discharged for obvious reasons.  Other standards, such as minimum COD limits are imposed to avoid over-burden of the local treatment works. Due to public and environmental pressure, DWS has become stricter with Municipalities that do not meet minimum discharge criteria.  As a consequence of this pressure, Municipalities have had to examine the capacities of their treatment plants, sewage networks and customers.  Bye-laws are in place to ensure that Municipalities can recover treatment and piping costs from individual polluters.  The Municipal bye-laws are becoming stricter, with South African industry facing unprecedented discharge fees. Currently the discharge tariff for an industrial effluent situated in the Cape Town Metropole is calculated from the following formula; Vw *(SVC) + Vie*T*[ (COD-1000)/1500 + Vie*(SF)] Where
  • "Vw" is the total volume, expressed in kilolitres, of wastewater discharged from the premises during the period concerned.
  • "SVC" is the sewerage volumetric charge in terms of the sanitation tariff.
  • "Vie" is the total volume, expressed in kilolitres, of industrial effluent discharged from the premises during the period concerned.
  • "T" is the cost, as determined by the council, of treating 1 kilolitre of wastewater.
  • "COD" is the chemical oxygen demand of the effluent in milligrams per litre .
    • In the event of the COD being less than 1 000, the COD factor falls away.
  • "SF" is the surcharge factor of the effluent calculated according to the formula:
    • SF = (X-L)/L
Where "X" is the concentration of one or more of the parameters listed in Schedule 2. "L" is the limit applicable to that particular parameter. Municipalities throughout South Africa have adopted similar discharge tariffs.  From the equation above it can be seen that industrial effluent disposal costs increase when COD concentrations are measured above 1000 mg/l.