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Problems & Solutions

Description of the CWTC

Physical/Chemical Treatment

Continuous Neutralisation
This serves two purposes: (1) to neutralise acid wastes (2) to serve as an alkaline precipitator for a number of metal containing waste streams. The feed streams to the neutralisation tanks are:

  • Acid wastes from bulk storage
  • Miscellaneous inorganics from bulk storage
  • Non-chelated ferric chloride etchant from bulk storage
  • Reduced chromium solution from the reduction reactor

All residues resulting from the neutralisation and precipitation processes are dewatered and further treated in the stabilisation unit. The treated water is sent onward for final polishing before discharge.

Image of Effluent Tanks
Effluent Tanks

Waste Etchant Treatment
Spent ammoniacal chloride etchants and cupric chloride etchants are treated with caustic soda to recover copper oxide.

Chromium Reduction
In the chromium reduction reactor hexavalent chromium is reduced to a non-toxic trivalent state. The reduced material is sent to the Continuous Neutralisation System for precipitation and dewatering.

Other Aqueous Treatment
Treatment processes for chelated zinc, copper and nickel waste solutions are essentially the same as those for chelated ferric chloride etchants. Due to the multiple waste streams involved and a multitude of chelated compounds in these streams, two parallel treatment trains are used. The treatment trains consist of multi-reagent tank, precipitators and the filtration systems. Filter cake produced by these systems is sent to the stabilisation unit and the filtrate is sent to the Continuous Neutralisation system.

 

PO*WW*ERTM System
The PO*WW*ERTM system is a two step wastewater treatment system comprised of evaporation and catalytic oxidation. The incoming oil/water mixtures can also be treated with this system. The mixtures are concentrated in the evaporation stage to produce brine slurry. This slurry is sent to stabilisation. The wastewater with volatile organics is heated to a vapour state in the evaporator and forwarded to the oxidation unit. There, the volatile organics are oxidised to carbon dioxide and water vapour. The exiting vapour from the oxidiser is then condensed to recover high quality water. The water is reused throughout the system for boiler feed water make-up, container rinsing, filter cake washing and chemical reagent mixing.

Image of The PO*WW*ERTM Treatment System
The PO*WW*ERTM Treatment System

Stabilisation
All solid residues, solid metal bearing chemical wastes and some liquid wastes, including slurries and brine are chemically stabilised in this system prior to disposal at landfill. The system utilises a batch mixer and specific reagents to achieve chemical fixation or stabilisation.

Image of Waste Stabilisation System
Waste Stabilisation System

 

 

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Tuesday, 19 June, 2012