In the search for solutions to combat climate change, it seems counter-intuitive that one may involve emptying industrial waste into our oceans.
Yet such is the urgency around global waste that it has led Associate Professor Kai Schulz and fellow scientists to investigate how industrial waste – a product associated almost entirely with the negative – may be harnessed for the positive.
"Industrial inorganic waste has the capacity to be an effective, ocean-based conduit for carbon capture and storage," said Associate Professor Schulz, of Southern Cross University's Faculty of Science and Engineering.
"As an example, steel and iron production leave a lot of slag waste, most of which is stockpiled on land. If this waste was pulverised and, with strict controls, put in the oceans, the prospects for carbon capture/storage and enhanced climate change mitigation are extremely favourable."
"The reason is that, upon dissolution of the alkaline components in slag, oceanic pH increases. This leads to a conversion of carbon dioxide (CO2) to bicarbonate and carbonate ions in seawater. The result is reduced oceanic CO2 concentrations, allowing the surface ocean to absorb additional atmospheric CO2.
"Even so, there are pH thresholds that we must not cross without full knowledge of what it would mean for the oceans themselves and their delicate balance of marine ecosystems. Potential issues around such ocean alkalinity enhancement (OAE) -- including the addition of chemical elements within the waste itself – must all be investigated."
With emissions targets set by the 2015 Paris Agreement under pressure, the time is right for innovative thinking. OAE is one example.
In 2022, over several weeks in the picture postcard Norwegian city of Bergen, Associate Professor Schulz and fellow scientists were engaged in a research collaboration that placed large enclosures in a fjord to investigate OAE effects on marine communities.
"OAE looms as an efficient method to remove CO2 from the atmosphere, raise pH and counteract ocean acidification," he said. "Concomitant addition of certain elements contained in slag, such as silicates and iron, could also stimulate primary production by phytoplankton – microalgae vital to marine food systems – taking up additional CO2 and producing oxygen."
Born in Germany, Associate Professor Schulz joined Southern Cross University in 2013 on a Future Fellowship. His scientific work investigates potential impacts of ocean change on biogeochemical element cycling and feedbacks to the planet's climate system. He also analyses proposed approaches to climate change mitigation, including the potential use of industrial waste products to store atmospheric CO2 in the oceans.
OAE and waste-carbon strategies are not new to science. Studies have tested the efficacy of materials such as pulverised fuel ash, municipal solid waste ash, cement kiln dust, biomass and paper sludge ash and sewage sludge ash for collecting and storing carbon.
"We will not meet the Paris Agreement targets simply by reducing carbon dioxide emissions. We need to explore other options," said Associate Professor Schulz. "For instance, you can plant trees, except trees take up space at a time when space is at a premium. You can also do direct CO2 capture from air by filtering, which is costly.
"Then there is the ocean, which already absorbs more atmospheric carbon dioxide than anything else and perhaps, through strategies like OAE, it might be helped to do even more.
"Utilising what is otherwise considered industrial waste products in the ocean for carbon capture and storage would tackle one of the great global challenges while complementing the job that the oceans are already doing.
"But again, understanding the impact of such approaches on the oceans and marine ecosystems is the driving force for research, especially as it pertains to these precious and already vulnerable entities."
