Biosolid removal with GEOTUBE dewatering units 

Overview

Desilting Solutions, a specialist contractor in biosolid removal and dewatering, partnered with Rockhampton Regional Council for a vital project to manage biosolids from sludge lagoons. The project targeted sludge removal at the Gracemere, North Rockhampton, and South Rockhampton sewerage treatment plants, addressing the critical need to manage over 150,000 m³ of biosolids within a constrained timeframe and challenging site conditions.

This initiative aimed to mitigate environmental risks, particularly the threat of lagoon overtopping into surrounding wetlands. The project's design maximized the site’s limited footprint, allowing efficient biosolid removal and dewatering while ensuring storage capacity was sufficient for the sludge quantity. Scheduled from July 2022 to February 2024, the project provided immediate environmental benefits and long-term sustainability advantages for the council and the surrounding communities.

Challenge

The project involved the complex removal of biosolids from operational treatment plants, each presenting unique spatial constraints. The sludge had accumulated over time, creating an urgent need for removal due to diminishing lagoon capacities. The volume of biosolids, coupled with the requirement to maintain the plants' operations during the works, added logistical complexity.

The process required constructing bunded areas to house the dewatering GEOTUBE® units, levelling the ground to achieve desired grades, and ensuring the containment areas were watertight. This meticulous preparation was vital to minimize disruptions and environmental hazards. A further challenge arose from weather variability, which had the potential to impact the dewatering process.

Space constraints at all three sites necessitated strategic planning. The operational status of the treatment plants required maintaining uninterrupted functionality, ensuring the sludge removal did not hinder day-to-day operations. Furthermore, handling a significant quantity of biosolids demanded a highly efficient dewatering solution.

Solution

To address these challenges, Desilting Solutions employed GEOTUBE dewatering containers of varying sizes, with the largest measuring 18.3m wide and 30.6m long. The GEOTUBE units were chosen for their ability to accommodate the constrained footprints of the sites while delivering high production rates and effective dewatering performance.

The project began by constructing bunded areas lined with a watertight plastic layer, ensuring environmental safety during dewatering. Floating pontoon dredges were deployed in the sludge lagoons, pumping the biosolids through a polymer dosing unit before depositing them into the GEOTUBE units. The polymer was selected based on detailed spoil analysis conducted by Geofabrics, ensuring optimal dewatering results.

Once inside the GEOTUBE units, the sludge underwent a dewatering process, gradually reducing its volume. After dewatering, the GEOTUBE dewatering containers were cut open, and the resulting solids were excavated and transported for disposal. This approach allowed the project to handle the high sludge volumes efficiently and effectively, avoiding the logistical challenges and cost implications of alternative methods, such as centrifuges.

The scale of the project set it apart, with over 150,000m³ of biosolids requiring removal. The combination of operational site constraints, the environmental risks of lagoon overtopping, and the precision needed for polymer selection underscored the complexity of the undertaking.

GEOTUBE units offered several advantages, including flexibility in size to suit confined spaces and compatibility with the site's dewatering requirements. Additionally, their ability to handle high production rates without compromising environmental safety proved critical.

The project was completed within the set timeframe of July 2022 to February 2024, meeting the client’s expectations for efficiency and environmental compliance. The use of GEOTUBE units significantly minimized the risk of environmental hazards, particularly the potential overtopping of lagoons into sensitive wetlands:

1. Successful removal of over 150,000m³ of biosolids.

2. Mitigation of environmental risks associated with lagoon overflow.

3. Efficient use of constrained site footprints with tailored GEOTUBE units.

Rockhampton Regional Council commended the project team for their expertise and professionalism. Top reasons for their positive feedback include:

1. Customizable solutions: The variety of GEOTUBE units sizes allowed seamless adaptation to each site’s spatial constraints.

2. Expertise in polymer selection: Detailed spoil analysis ensured the use of optimal polymers, maximizing dewatering efficiency.

3. Superior service: Geofabrics’ support and technical guidance ensured the project proceeded smoothly and successfully.

This project highlighted the importance of customized solutions for large-scale sludge removal projects, particularly in operational environments with spatial limitations. The use of GEOTUBE units demonstrated their value as a cost-effective and efficient alternative to traditional methods such as centrifuges, particularly when space and production rate considerations are key.