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Waipawa & Waipukurau Sludge and Dry Solids Removal

The Central Hawke's Bay Council is undertaking a project to de-sludge the Waipawa WWTP and remove the Dry Solids from Waipukurau and Waipawa's WWTP's.

This project integrates with the overall Wastewater Strategy as part of Project 1 and the Minor Improvements to the Waipawa, Waipukurau and Otane Wastewater treatment plants. These minor improvements aim to rectify known issues at the plants, improve compliance with discharge consent requirements, lessen the dependence on operator input and ultimately provide better environmental and community outcomes.

Waipawa Wastewater Treatment Plant De-Sudge Project:

Sludge levels in the ponds at the Waipawa WWTP has reached critical levels, and are impacting on operational performance and regulatory compliance. Oxidation pond de-sludge operations should be undertaken every 5-10 years, depending on the operation of the pond system. The pond desludging is overdue, and the accumulation of sludge has been impacting on compliance with the discharge consents.

By undertaking the desludging of the ponds, this will restore the treatment capacity.

The de-sludge project is a two-step process:

Stage 1 – Removal of dried sludge from existing geobag areas

Stage 2 – Pond de-sludge into geobag areas (Waipawa)

This sludge will then be dried in the geobag areas before being eventually removed as dry solids. 

Waipawa and Waipukurau WWTP Dry Solids Removal Project:

Currently, biosolids are stored within a series of geotextile bags (geobags) at Waipukurau and Waipawa WWTPs. The geobagged material has been in-situ since 2005, and over this time the material has stabilised to biosolids. 

The removal of the dried sludge from the geobag area frees up space for dewatering / dewatered sludge, thus enabling the desludging of the ponds.

Removal of sludge is continuing at pace - approximately 50% of the sludge has been now removed from the Waipawa WWTP main pond (about 1000 tonne). Hydracare have also removed the last small section of floating wetland.

Desludging 1

Waipawa - Desludging has commenced with good initial progress, approx. 13% of the pond has been completed in just under two weeks. When passing the plant you will now see the first four geobags being filled.



Waipukurau Geobag area

The dried solids removal at Waipukurau will be completed early this week, the liner repair company will be onsite later this week to inspect and provide CHBDC with a recommendation for any repairs that are necessary. Hydracare’s team will be back at the Waipawa WWTP preparing for arrival of the dredge that will desludge the pond and fill new geobags in the recently repaired storage area.

Last week Hydracare removed the last of the existing biosolids from the Geobag area at the Waipawa WWTP, revealing a large empty pond like area - see the video below to see the progress. This week the liner will be being completely replaced with a new layer of HDPE material over the top of the existing liner to make sure this will be durable and last well into the future. 


Last week saw Hydracare establish onsite at the Waipawa WWTP and start preparing for the removal of the old biosolids from the Geobag storage area, removal and transportation to the Landfill is planned to start this week. In order to move the material around while in the lined storage area they use this cool little tracked transporter called a Marooka, this spreads the weight over a greater area and protects against damaging the liner material. 

Desludging Marooka Onsite

Last week Council reached the end of the tender process and awarded a contract for solids removal at Waipawa and Waipukurau WWTPs and desludging of the Waipawa WWTP pond to Hydracare.

This will involve the removal of the old dried sludge (biosolids) from the geobag bunded areas at both sites, repair of the liners in preparation for pond desludging and then the desludging operation at Waipawa. This work is needed to increase the pond capacity (currently reduced to approx 59% of full capacity due to sludge build up), which in turn will improve the treatment ability of the plant.



 Waipukurau Wastewater Treatment Plant



 Waipawa Wastewater Treatment Plant


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