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Waipawa & Waipukurau Sludge and Dry Solids Removal

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

What is the Wastewater Treatment Plant De-Sludge Project?

Sludge levels in the ponds at both the Waipawa and Waipukurau WWTP’s have 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.

Hydracare have continued with the desludge of the Waipukurau WWTP pond. They have encountered several obstacles in the pond - most appear to be old anchoring posts cut off close to the pond floor. Having to manoeuvre the dredging unit over/around these obstacles has limited progress to date.

Waipukurau Desludge

Hydracare have recommenced onsite at Waipukurau in preparation for the commencement of the desludging. This includes a complete replacement of the geobag storage area liner and addition of drainage aggregate, pipework welding and removal of the BAS curtains from the main pond. 

December

Central Hawke’s Bay District Council is beginning a project to remove sludge for the main WWTP pond in Waipukurau. Currently, the pond is approximately 40% sludge. The removal of this sludge will allow the pond and tertiary treatment systems to perform to their fullest capacity, improving the quality of the discharge.

desludge

November

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.

desludge 2021

October

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.

August

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.

July 

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. 

VID-20210701-114938-1.mp4

June

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. 

May

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 plan

What's the process?

  • Stage 1 – Removal of dried sludge from existing geobag areas

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. It will be removed and the storage areas repaired.

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

A dredge will remove the majority of the settled sludge form the floor of the main ponds at both plants, this is then pumped to the storage areas to dewater and dry in Geotextile bags.

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