AUSTRALIA - 2010
Bacteria Consumes Refining Impurity in Alcoa-Developed Process
An Alcoa-developed process that uses naturally occurring bacteria to consume an impurity in the alumina refining process is reducing carbon dioxide emissions and energy use and saving millions of dollars compared to conventional destruction technologies.
Oxalate is a natural product found in soil and some plants. When decaying plant matter is carried underground via water, some of it sticks to bauxite ore and enters the alumina refining process, where it degrades into oxalate. Considered an impurity, oxalate must be removed for the process to work efficiently and for the alumina to meet specification.
Alcoa’s conventional method for destroying oxalate removed from the alumina refining process has been to burn it in a kiln. This method results in the generation of carbon dioxide, volatile organic compounds (VOCs), and odors. It also requires expensive and energy-consuming emissions control equipment to meet Alcoa’s standards.
In 1999, scientists at Alcoa’s Technology Delivery Group in Australia began researching the use of naturally occurring bacteria in the refining process. The focus turned to oxalate, and over the next decade the group continued developing a process and identified naturally occurring bacteria to efficiently consume the impurity.
Known as continuous biological oxalate destruction, the process uses a series of tanks containing warm liquid and bacteria growing on strands of beads. Oxygen and nutrients are added, and oxalate is introduced as a feed source. The bacteria consume the oxalate, reducing carbon dioxide emissions to less than half that of a kiln and emitting minimal VOCs and odor.
Alcoa’s Kwinana refinery in Western Australia was the first to implement the process in mid-2009. The system destroys all oxalate produced at the refinery, which averages around 40 metric tons per day, and reduces carbon dioxide emissions by more than 8,000 metric tons annually. Kwinana also avoided approximately US$16 million in capital expenditures, and the refinery is saving approximately US$1.6 million in energy costs each year compared to conventional technology.
“Alcoa is always looking at opportunities to minimize its various wastes and emissions,” said Peter McKenzie, manager of environmental health services for the town of Kwinana. “Although members of the community have had some concerns with the Kwinana refinery’s operations, I believe they would look upon this oxalate process as good for the environment. Alcoa is certainly on the leading edge in waste avoidance and reuse.”
Alcoa plans to next introduce the bio-oxalate process at its Pinjarra and Wagerup refineries in Australia and Pt. Comfort refinery in the United States. Long-term, the process has the potential to consume all of the nearly 200 metric tons of oxalate removed each day by Alcoa’s nine refineries around the world, while reducing both greenhouse gas emissions and energy usage.
In 2010, the technology earned the Western Australia Engineering Excellence Award (Environment category) and the Australian Government Engineering Innovation Award at the Australian Engineering Excellence Awards. It was also recognized with the inaugural AIRG Medal from the Australasian Industrial Research Group in 2011.