Open Cut » Environment
Capacitive deionization is a robust, energy efficient and cost effective technology for desalination of water with moderate salt content. Including ion exchange membranes in front of the electrodes in a process called membrane capacitive deionisation is a promising recent development. This project used an onsite pilot scale trial to assess the viability of membrane capacitive deionisation, in combination with appropriate pre-treatment processes, to remove salt and other contaminants from mine water.
A pilot scale, fully off grid and powered through a PV system with storage, containerised mCDI system was successfully installed and operated to treat water. The unit was robust, flexible and able to desalinate water to a range of qualities. A digital twin of the plant was developed which allowed for real time supervision and operation of the plant remotely, and a preliminary investigation undertaken of how to interface a machine learning model to the digital twin to allow for automated optimisation of the plants operation. The digital twin provided a convenient and powerful environment for remote operation of the plant with benefits to operator training and also allowing for easier remote troubleshooting of anomalies to minimize time required on site when maintenance is necessary.
A performance model of the mCDI plant was developed to enable informed choice of operating parameters to meet a particular product water quality. Operation at the full extent of available parameter settings was undertaken during this model development to ensure the model was as robust as possible and captured the observed plant performance under all conditions. With mCDI it is typically possible to attain a desired product water quality over a range of parameter settings, with the performance model allowing for simple selection of the optimal condition that yields the lowest operating cost.
The performance model from this work and existing RO design tools were used to undertake an economic analysis of hypothetical full-scale RO and mCDI plants to treat 2 ML/day of Big Kahuna water. While mCDI was found to offer much lower routine maintenance costs, this was not sufficient to overcome the current high capital cost of the equipment unique to the mCDI technology.
mCDI seems unable to compete with existing technology in a large fixed installation at this time. Such an application however does not make full use of the unique strengths of mCDI such as simple ability to vary extent of desalination on-the-fly, minimal maintenance needs, and robustness to start-stop operation. Investigation of other applications that better utilise these strengths could be mobile operations, provision of drinking water to temporary settlements or smaller scale installations where the higher cost is less prohibitive and may well be overcome by the much lower needs for chemicals/labour, and applications where reliable operation and simple restoration when failure occurs is critical.
The demonstration of successful operation with PV power in an off-grid setting also indicates the technology should also be well-suited to powering as needed with other intermittent power sources.