Many industries produce saline wastewater that contains pollutants such as nitrate and nitrite, which are harmful for water bodies by causing eutrophication. Sustainable, nature-inspired processes that rely on microorganisms to remove these pollutants (e.g., denitrification) often face challenges when salt levels are too high. Some industrial effluents, for instance, can be three to four times saltier than seawater.
In his doctoral research, Alessio D’Aquino explored how a nature’s own strategy can be implemented in an optimised system to help overcome this challenge. In natural environments, microorganisms tend to live together in a protective layer called biofilm, which shields them from external stressors. By applying this principle in engineered biofilm reactors, D’Aquino investigated how to improve the biological removal of nitrogen-compounds from highly saline wastewater, by using bacteria commonly found in municipal wastewater treatment plants.
“Biofilm processes are widely used in wastewater treatment, but they need to be further optimised to cope with extreme salinity and maintain efficient pollutants removal” he says.
His research shows that both the type of biofilm reactor and of the microbial metabolism determine how well the denitrification system can tolerate salt. The biofilm reactor can be further optimised by choosing the right carrier for the biofilm to attach to, depending on the wastewater’s salinity. Thus, selecting the most suitable process design in the beginning plays a key role in improving salt tolerance and can make the treatment more effective and likely more cost-efficient over time.
Nature-inspired, smart applications for pulp and paper industry
D’Aquino got another important insight when dealing with a common problem for industrial wastewaters: the lack of a chemical that provides energy to bacteria. D’Aquino demonstrated that adding a waste stream rich in organic matter generated in pulp mills can not only supply the “food” for bacteria but can also boost nitrogen removal under saline conditions. This approach promotes a circular economy, turning one type of waste into a resource for treating another.
“These findings could be applied for example in the pulp and paper industry. Here, a saline nitrogenous wastewater is generated when NOx-SO2 scrubbers are used to clean flue gases and comply with air emission regulations. A well-designed biofilm reactor represents a valid option for a resistant and resilient process, while an organic-rich stream, as evaporator foul condensate, could be used as “food” for biological nitrogen removal, creating an effective, low-cost, and sustainable treatment solution,” he adds.
“By taking inspiration from how microorganisms cooperate in nature and carefully engineering key process elements, we can design smarter technologies for sustainable water management”, D’Aquino concludes.
Alessio D’Aquino is a Finnish-Italian researcher, who carried out his doctoral dissertation as part of a co-tutelle project between Tampere University and the University of Trento in Italy. He is currently a PhD student in the Bio- and circular economy unit, while working also as University Instructor in the Environmental Engineering degree programme at Tampere University.
Public defence on Friday 14 November
The doctoral dissertation of MSc (Tech) Alessio D’Aquino in the field of environmental technology/engineering titled Denitrification Under Salinity Stress in Biofilm Reactors will be publicly examined at the Faculty of Engineering and Natural Sciences at Tampere University at 12 o’clock on Friday 14 November at Hervanta Campus, in Festia building, auditorium Pieni Sali 1 (Korkeakoulunkatu 8, Tampere).
The Opponents will be Assistant Professor Anna Mikola from Aalto University, Senior Research Fellow Elisangela Heiderscheidt from the University of Oulu) and Associate Professor Stefano Papirio from University of Naples Federico II. The Custos will be Docent Marja Palmroth from the Faculty of Engineering and Natural Sciences at Tampere University.