The Challenge
Presently, desalination by available technologies is normally an electrically driven process which consumes a high value energy source while in turn adds to greenhouse gas emissions. The objective of this project is to conduct a three month trial of a membrane distillation (MD) treatment process which uses low-grade energy such as solar or waste-heat. In partnership with City West Water, industry wastewater was treated on site, in Melbourne’s west, and converted to potable water.
The Project
Six businesses from CWW’s customer base that have potentially useable waste heat were surveyed, and effluent samples from each of the sites were analysed in a laboratory scale MD plant to test the suitability of each effluent stream. A power plant was eventually selected as the demonstration site for this project.
A team from Victoria University designed and constructed the membrane module that was subsequently incorporated into the pilot plant, which was fully equipped with two plate heat exchangers and remotely accessible process control instruments and data logging.
The pilot plant was continuously operating over a period of 12 weeks, during which the desalinated water production averaged 2.2 litres per hour, and a final reject concentration of 71,400 mg/L. During the last week of the trial, an electric heater was used to supply an unlimited amount of heat at set temperatures. The aim of this was to assess the capacity of the pilot plant without the limitations of sub-optimal heat to drive the process.
An analysis was conducted on the electrical demand from the two cycle pumps at different operating conditions. A cost comparison model was also carried out between MD systems and reverse osmosis.
The Outcome
There was a low abundance of waste heat during the trial, however the project outcomes demonstrated the longevity and robustness of the MD process. Also demonstrated was the advantage of using this type of system on waste heat at temperatures as low as 300C to achieve permeate flux of 3-4 L/hr/m2 of highly desalinated water.
The overall project findings have further proved how an MD system can be a feasible option to consider when recovering potable water from industrial effluent without having to incur significant green house gas emissions.
