Wastewater Treatment Plant - Biosolids Disposal

North Shore City Council is to explore the feasibility of applying treated solid waste (biosolids) from its wastewater treatment plant onto forest areas.

The council has undertaken investigative work in the past without clear alternatives being identified. However pressure is intensifying to adopt more sustainable ways of dealing with the city's biosolids produced at the Rosedale plant.

Forest application - already used by some local authorities in New Zealand - is seen as providing an environmentally friendly and economic option for the disposal of the city's biosolids.

North Shore City's works and environment committee chairperson, Joel Cayford, says the council will thoroughly explore beneficial reuse alternatives to land filling biosolids.

The council will consider a proposal for a pilot trial for the forest disposal of biosolids at a cost of $450,000 over three years. It will also consider increasing the allowance for biosolids disposal to landfill pending the outcome of the forest disposal investigation.

Councillor Cayford says among the factors in the choice of any forest disposal site is the distance from the Rosedale plant - which affects transport costs - and the soil fertility needs of the forest area concerned.

The consideration of the study follows a report showing that the council will have to pay much more to landfill biosolids that are trucked away from the plant.

Although the plant's efficiency and capacity has been greatly increased over recent years, the solids fraction of the wastewater remaining after full treatment of approximately 12,000 tonnes is still trucked off site and landfilled.

North Shore City is to enter into a contract for the remainder of this and the next (04/05) financial year to land fill biosolids at Redvale. This will result in an increase in costs in the current financial year of approximately $500,000. The budget allowed in future years would also need to be increased by a similar amount.

Joel Cayford says the council is between a rock and hard place on this one.

"Landfill costs are sky-rocketing, sustainability pressures increasingly require organic biosolids to be reused on land rather than dumped, yet most farmers are reluctant to accept that biosolids can recondition soil, while more and more people come to live in the city."

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