Project Background or Rationale
RSL Care’s Sunset Ridge Retirement Community resides near the Pacific coast in Zilzie, Queensland, Australia. The retirement community includes 100 independent living villas, a 120-bed aged care residential complex, and resort style facilities. Although Zilzie averages 31 in (79 cm) of annual rainfall, RSL Care sought to install a graywater recycling system because of the environmental benefits and to secure and maintain an adequate water supply for the community¡¦s residents.
Capacity and Type of Reuse Application
The graywater treatment plant installed at the Sunset Ridge Retirement Community treats approximately 6,600 gallons (25 m3) of graywater per day. The plant captures graywater discharged from the community¡¦s showers, bathtubs, and hand basins. The treated water is then reused in all of the toilets on site and for landscape irrigation.
Water Quality Standards and Treatment Technology
In Queensland, all graywater treatment plants must be granted Chief Executive Approval by the Queensland Department of Infrastructure and Planning before they are allowed to operate (Queensland Australia Government, 2011). Formal approval is based on 26 weeks of independent monitoring to demonstrate that the plant is able to treat graywater to the regulated quality standards. Once a system has been approved, it can be employed in other projects of similar nature.
Where treated graywater is used in high level reuse applications (e.g. toilets, urinals, laundry reuse, vehicle washdown) the Queensland regulations require the treated effluent to achieve the following minimum quality:
- BOD5 TSS E. coli (max) E. coli (95th percentile) turbidity (max) turbidity (95th percentile)
The challenge of meeting these effluent standards in decentralized scenarios is that wastewater quality and flows are often highly variable. As such, the design of the treatment plant needs to be robust enough to manage a range of situations.
The core technology at Sunset Ridge is a modular membrane bioreactor (MBR), which encompasses a bioreactor with ultrafiltration membranes of 0.04 micron. MBRs are an advanced low footprint treatment technology typically used for blackwater treatment. However, this technology has been adopted to treat graywater primarily because of the soluble and insoluble organics that are commonly seen in commercial graywater influents. Graywater is by no means clean water with a few dirt particulates. Filtration based processes are sometimes used to treat graywater, but they do not provide the resilience needed for commercial systems, which MBRs afford. Once the effluent has been through the ultrafiltration membrane in the MBR, it is disinfected with ultraviolet (UV) and chlorine to achieve a chlorine residual. This multi-barrier treatment approach is what ensures the treatment plant is able to confidently handle variable wastewater qualities that are typical of decentralized graywater schemes.
Project Funding and Management Practices
One of the key considerations that clients and regulators want addressed when establishing reuse treatment plants of any size is who will operate the plant in the long-term This is especially important if the scheme is to be implemented by the private sector for a specific private project. In this case, RSL Care privately funded the graywater scheme at Sunset Ridge.
Reuse schemes require a long-term strategy and cannot be treated as a fixed piece of plumbing equipment. The challenge for many private sector decentralized reuse schemes is that they typically do not have wastewater specialists located on site. Therefore, longer-term arrangements need to be considered early on and should inform decision making throughout the project. For example, a cheap solution with poor equipment may win on capital price, but may also lead to the highest overall life cycle costs because of poor performance and operational difficulties. Life cycle analysis (LCA) must be considered.
The Sunset Ridge graywater plant operation is managed as a shared responsibility between the onsite maintenance staff at Sunset Ridge and the graywater system contractor. Day to day servicing and management is provided by Sunset Ridge locally, with twice yearly full technical servicing, remote monitoring, and regulatory reporting being provided by the contractor. Different projects will have different maintenance arrangement outcomes.
The graywater contractor is able to provide local staff with a high level of support particularly due to the capabilities of its risk management methodology in combination with the system’s built-in remote monitoring system. Utilizing Hazard Analysis and Critical Control Points (HACCP), a risk management methodology most commonly used in the food and beverage industry, the graywater contractor can ensure the delivery of high quality treated water. Different Critical Control Points (CCPs) of the treatment process are monitored in real-time providing data to the contractor. Corrective actions are programmed into the system if any of the CCPs are out of range, thus providing Sunset Ridge an additional layer of confidence with the quality of the treated graywater. In addition to the safety provided by the HACCP risk management approach, remote monitoring and controls allow technical staff to take the reins of the graywater plant if necessary. Operational data from the CCPs is continuously relayed back to the contractor’s headquarters where technical staff can increase/decrease aeration levels, change chlorination dosing, turn pumps on/off and so on. Remote monitoring and controls means the client has the security of knowing operational experts always have an eye on the plants operation.
Results and Lessons Learned
The Sunset Ridge graywater plant has consistently met effluent quality expectations since commissioning in early 2010 and the success of the scheme can be summarized down to contractor experience. It is important that managing regulatory approvals, delivering a robust technology suitable for commercial applications (commercial and domestic approaches are very different), and ensuring the appropriate operational partnerships are established and considered at the onset of the project.