Start Made on Napier’s Wastewater Treatment Upgrade

Ground works are underway for the $30m upgrade of Napier’s waste water treatment at Awatoto.

The Waitangi Road site is being prepared for building a biological trickling filter (BTF) plant, scheduled for commissioning at the end of next year.

Planning for the development – one of biggest projects undertaken by the Napier City Council – started in 2007. In granting it a 25-year consent, the Hawke’s Bay Regional Council requires the new plant to be commissioned by 31 December next year.

Over a 10-week period, Holcim Hastings Quarry are delivering 30,000 cubic metres of crushed rock quarried in Mere Road, Fernhill, onto the site. Another month will be needed to compact the structural fill in 250mm layers, bringing the site for the planned new pump station up to ground level.

The site was excavated in 2004 as part of ground improvements required for the previous planned expansion of the plant. The new development is being built at the same location, next to the existing milliscreen plant, so the earthworks previously carried out are being utilised.

The Napier City Council expects a start will be made on constructing the main effluent pump station, the first major component of the plant infrastructure, in autumn next year.

Meanwhile, the High Court has instructed the Environment Court to hear the matter of Wayne Church’s appeal on the outfall discharge resource consent being lodged within the statutory time frame.

Tandem Treatment for Wastewater

The existing milliscreen plant has been treating the city’s wastewater since 1991. The BTF plant will provide a secondary treatment process to follow milliscreening and a new grit removal process.

BTF is a fixed-film biological treatment process that is very well established, both in New Zealand and overseas. Compared to many other treatment processes, it is relatively economical and simple to operate. Wastewater flows through tanks with plastic filter media on which an active bacterial mass establishes to feed on and transform human waste into a non-offensive bacterial biomass.

The Napier BTF plan will use structured media, which is used in the Gisborne BTF plant and has also been trialled in the pilot plant at Napier. The two tanks containing the media will be covered to control odour, with air treated in a biofilter field of chipped bark.

The system’s only moving part is a sprinkler arm for distributing the wastewater. Other major advantages of the BTF process are that there will be no sludge transportation or disposal costs and it avoids the use of chemicals, which would eventually become part of the discharge.

As the final stage in the process, the treated wastewater will flow through a Papatuanuku channel (an open channel filled with rocks) as a spiritual cleansing before discharge via a 1.5km outfall into Hawke Bay, south of the city at Awatoto. Scientific studies show that the receiving environment is well able to accept such a discharge.

A pilot plant has already been successful trialled on the Awatoto site under local climatic conditions and using Napier sewage.

The design will allow for other treatment stages to be added in the future if needed.

Preparatory work undertaken at the milliscreen plant earlier this year includes the installation of a new upgraded electrical system, new draft tubes for outfall pumps, the relocation of the internal wash water tank to outside the building, an upgrade of the ventilation system and cleaning down and repairing internal surfaces affected by corrosion.

At all stages in progressing plans for the upgrade, the Council has consulted with the Kaitiaki Liaison Group.
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