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CONFERENCE: NZWWA 49th Annual Conference, Rotorua, New Zealand, September 2007

ABSTRACT:
Te Kauwhata wastewater treatment works comprises two waste stabilisation ponds and a wetland before discharging into Lake Waikare. Development in the region required an upgrade to the plant to deliver nutrient removal. Attached growth technology was retrofitted into the ponds to achieve this. During acclimatisation, it became apparent that the phosphorus removal would not achieve the target in the time available with significant cost implications for the client. It was decided to intervene and implement a chemical precipitation solution to deliver the performance needed in the time available. Jar tests were undertaken quickly to establish likely dosing rates for metal-based coagulants. Issues with sludge re-suspension after settlement were encountered and resolved. An initial 4 to 1 molar dosing ratio was derived from these tests and a full-scale temporary ferric chloride dosing system was designed, procured and commissioned in a matter of weeks in partnership with the process designers. Supplementary alkalinity dosing was implemented to ensure no impact on the nitrification process and to maintain a well-buffered final effluent. The system achieved the required phosphorus removal after a short period of optimisation and the upgraded wastewater treatment plant was approved to permit the connection of the new development.

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