Toward Sustainable Biosolids Management

Auckland, as one of the world’s most liveable cities, is supposed to be able to manage their sanitation facilities, including biosolids, more wisely. Even though Auckland City has demonstrated their advanced processes in wastewater treatment, there is an issue on how to manage biosolids, a by-product generated during the wastewater treatment process, in a sustainable and integrated way. Evidence has shown that the application of biosolids can be harmful, not only to human health, but also to the environment. This report aims to re-evaluate current and forthcoming practice in disposing of biosolids from the Mangere Wastewater Treatment Plant.

Currently, the biosolids are being disposed to rehabilitate an old oxidation pond, which seems to be in compliance with the standards set by The New Zealand Water and Wastewater Association. However it is a fact that the oxidation pond will be at full capacity shortly. With regard to this issue, Watercare has proposed to “rehabilitate” Puketutu Island by disposing biosolids into the quarry hole. Watercare’s proposal has attracted debates about the positive and negative effects of disposing of biosolids at Puketutu Island, which are discussed on this report.

Even though the proposal has been granted by the Environmental Court, this report concluded that Watercare’s plan may be economically viable but should be seen as the last resort. It is further proposed that Watercare places more controls on industrial wastewater and restricts the type of waste that can be discharged into the sewerage system, especially wastewater which contains toxic metals. Unless metal contaminated input to sewers is banned, the quality of biosolids will stay beyond the standards and cannot be applied back to the land as fertiliser or land conditioner.

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