Algae makes wastewater valuable

02 February 2020

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Navid Moheimani and Parisa Bahri are developing algal systems to turn wastewater into valuable food resources

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Algae are largely underappreciated...

Algae are plant-like organisms that can make food from sunlight. But they are different from plants because they lack roots, stems and leaves. And while they might be invisible to the naked eye, they play a huge role in sequestration of carbon dioxide, and they generate over 50% of the oxygen in the atmosphere. They live everywhere, from rivers, stream and freshwater ponds, to salt lakes and seawater. They can also be cultivated, and their clever chemical know-how used to clean up and recycle human waste, which is how we are seeking to exploit them.

Wastewater

Humans generate a huge amount of wastewater. This is mainly due to human population growth, and a worldwide increase in agriculture and animal husbandry. Not treating these wastes would result in vast environmental and health impacts. But conventional wastewater treatment systems are often ineffective, inefficient and can be very expensive. That means that there is a need for alternative wastewater treatment processes.

Algae and wastewater

Our team at Murdoch University Algae R&D Centre has developed a unique process that uses algae to treat effluent. The process involves first passing the effluent through an anaerobic digester, which converts the organic material in the waste into biogas (methane). This can be used to generate electricity. The remaining liquid and suspended material produced by the digester is then fed to our algae. This material is very high in ammonium, meaning it is toxic to most organisms, and only specific algae can grow under these conditions. As the algae multiply, consuming the organic material, nutrients and minerals, they also remove a significant amount of carbon dioxide. The result is algal biomass with a very high protein content, and clean water.

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Algae can turn wastewater into a protein-rich valuable feedstock

So far, we have successfully treated piggery effluent using this process. The biomass generated can be used as animal feed, fertiliser or an aquaculture feed. We have shown that the biomass can be safely used as a feed for juvenile marron and as a sustainable organic fertiliser. The biomass can also be digested by pigs. We've also started to investigate using our technique to clean up abattoir effluent, and further work with domestic and dairy effluents are also underway.

Integrating biology and engineering

This is a project requiring a very good understanding of biological and engineering systems and processes. While algal cultivation depends upon understanding the biology of algae, there are many aspects of engineering that also needs to be fully understood and integrated into the process. Our approach will only work if we successfully integrate the biology and engineering.

Economics

For any process to be successful, there needs to be an economic justification. Our process is a typical example of a circular economy: the process not only cleans the wastewater and reduces the carbon footprint, but it also generates revenue through the generated biomass. A preliminary economic analysis indicates that, overall, the cost of biomass is around $2 for each kilogram we produce. At this rate, the process seems to be generating positive cash flow for the industry, especially if the carbon credit and clean water value is added to the overall revenue. On the socio-economic side, we also significantly reduce the water way contaminations as algae concentrate most of them in their biomass.

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