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MARCH 2010

The design build team of Hawkins Infrastructure and Harrison Grierson has been appointed by Hamilton City Council to deliver an upgrade to the Sludge Treatment Plant at the City’s Pukete Wastewater Treatment Plant.  The plant is the fifth largest in the country and treats an average of 54 MLD of wastewater per day and services a population of 120,000 people.

The Hawkins/Harrison Grierson team has offered to design and build a Thermal Hydrolysis Plant to treat and stabilise the city’s sludge and produce biosolids that will be capable of being composted or applied directly to land. The upgrade will incorporate technology developed by Cambi AS from Norway.  The project is valued at just over $11 million.

A brief description of the process is, solids removed from the liquid waste stream at the plant will be dewatered in centrifuges and then pumped to a high pressure/high temperature reactor vessel where the pathogenic bacteria is pasteurised.  This process is followed by depressurisation, resulting in the hydrolysis of the sludge. The hydrolysed sludge is then fed to the existing digester system that will be reconfigured to operate as duty/standby parallel trains.  The digested sludge will then be further dewatered to a dry solids concentration (solids cake) of around 30% and exported from the site for beneficial reuse.

The centrate from the centrifuges will be treated to remove nutrients and other contaminants and returned to the main plant inlet for treatment through the liquid stream.  Biogas generated in the process will be conveyed to the existing cogeneration plant on site to produce “green” electricity that will be used on site.

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