Gunnedah Shire Council (GSC) identified that an upgrade was required to:
- Cater for additional hydraulic and treatment capacity for population growth and expansion of the sewage network
- Extend the working life of the existing treatment assets up till 2038
- Improve workplace safety around the site.
Hunter H2O won a project to upgrade the existing trickling filter Gunnedah Sewage Treatment Plant (STP) with preliminary treatment, biosolids handling and site services. The project involved:
- Development of a Review of Environmental Factors (REF)
- Development of a concept design
- Detailed process, civil, structural and electrical design
- Specification and tendering for Principal Supplied equipment
- Preparation of Contract Annexures and technical specifications
- Tender assessment and evaluation report
- Construction period assistance.
Hunter H2O worked closely with Gunnedah Shire Council’s (GSC) management and operations personnel during the conceptual design phase to ensure we understood their expectations regarding reliability, operation and maintenance.
GSC decided that to achieve certainty of the features and capacities of key equipment packages, the inlet works, sludge dewatering system and digester mixing equipment would be Principal Supplied. Hunter H2O worked closely with GSC to organise inspections of available equipment and to provide information on the pros and cons of different options and technologies. Hunter H2O then undertook the specification and call for tenders for the equipment packages.
The early identification of key equipment and its procurement in a competitive environment allowed the detailed design to be prepared with certainty regarding the installation requirements, operation and maintenance needs and how the equipment would be integrated in the new electrical and control system. A 3D model with walk through capability ensured GSC was satisfied with the layout and functionality of the new works.
Whole of life cycle costs were developed to confirm the consistency of the design with GSC’s budget.
The $8.1M upgrade of the STP included the installation of a new inlet works, anaerobic digester, sludge dewatering facilities and included the decommissioning of redundant assets. The upgrade maintained the existing trickling filters with 100% effluent reuse for cotton irrigation. By retaining the trickling filter process, we were able to provide a sustainable and cost-effective supply of effluent and nutrients which would otherwise need to be supplied from other water sources and commercial fertiliser products. The staged capital upgrade provided the required hydraulic capacity to service projected growth to 2038. The project highlights are shown on the annotated diagram attached for this example.
This project is an excellent example of where Hunter H2O worked with our client to produce an outstanding outcome. Our commitment to our client meant we were able to understand their needs and objectives and tailor the design and procurement model to ensure the finished plant met their objectives in regard to time, cost and quality.
GSC regards this as a very successful project where project objectives were met on time and on budget. The relationship between GSC and Hunter H2O and between GSC and the Principal Contractor was considered healthy and positive outcomes arose from those healthy relationships.
Aspects that will be of great value to GSC include:
- Technology Matching: this project showed the importance of adopting a designer that can tailor the process design to Council’s expectations in regard to robustness, operability and maintainability. The Principal Supplied inlet works, biosolids dewatering system and the cold digester mixing systems were all well regarded features of the project.
- Constructability: the detailed design approach with Principal Supplied equipment packages meant that risk allocation between the Principal and the Contractor was optimised. This approached ensured GSC that its expectations regarding materials, arrangements, details and features were delivered and the Contractor could focus on time, material and subcontractor management rather than undertaking “design on the run”.
- Value for money: our solution focused on extending the life of existing assets and deferring capital investment, thus providing a cost effective and sustainable solution for the community. The final project cost of $8.1M (2018) was very close to the original estimate of $8.0M (2015).
- Environmental – 100% of effluent is now re-used for cotton irrigation, reducing groundwater extraction. Nutrients (nitrogen and phosphorus) are retained within the effluent for beneficial reuse.