APPENDIX A

CURRENT OPERATION OF THE HEC TRADE WASTE TREATMENT PLANT (TWTP)

As shown in following figure, the TWTP is separated into two functional areas, coolant emulsion-splitting and wastewater treatment. The coolant emulsion-splitting process takes oil-contaminated wastewater, such as spent coolant, metal working fluids and lubricant-contaminated water into aerated storage tanks prior to further treatment to separate the emulsified oil and grease component (emulsion splitting). This is achieved by dosing the coolant with a proprietary brand of polymer solution and ferric chloride and controlling the pH with caustic soda and hydrochloric acid. The specific batch dosage of chemicals is determined by the in-house laboratory. Occasionally, brine dosing is utilised to split the emulsion. Recovered oil and grease waste (containing up to 50% water) which is separated at the emulsion splitting stage is transferred to an 18,000 litre waste oil tank, which is periodically pumped out for disposal by a sludge removal contractor.

Wastewater from the emulsion splitting stage is then mixed with other process wastewater at the wastewater treatment plant.

The wastewater treatment stage of the TWTP primarily takes washing-machine wastewater from the plants and treated wastewater from the emulsion-splitting stage where it is aerated in two balance tanks and held until batch treatment is to be commenced. Batch treatment begins in the flocculating tank where ferric chloride is added to aid in coagulation. pH adjustment also occurs in this tank. Flocs are not settled out of the wastewater at this stage, with effluent flowing directly to the flash mixing tank where dosing with polyelectrolyte occurs to enhance floc development.

Treatment in the Dissolved Air Flotation unit (DAF) follows, with the DAF unit being entirely responsible for the removal of suspended solids from the wastewater stream. Effluent from the DAF is disposed to trade waste with the sludge being transferred to a series of holding tanks. Supernatant liquid from the holding tanks is returned to the balance tanks for re-treatment.

The process is operator dependant, to enable staff to monitor operating parameters such as ammonia production and sludge accumulation. Fully automated control at the waste treatment operation is utilised only when there is a personnel shortage.

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