Pascal Saikaly, KAUST Assistant Professor of Environmental Science and Engineering, works with his research group and Prof. Bruce Logan from Pennsylvania State University on tackling one of the world's most important issues: the provision of fresh, clean water for the growing global population.

"To meet the world's demand for water, we must explore the use of non-traditional water sources through the reclamation and reuse of domestic wastewater," Prof. Saikaly explained. "My group at KAUST is conducting fundamental and goal-oriented research to optimize and create sustainable biotechnologies for wastewater reclamation that are robust, scalable and capable of providing tailored-quality water with a minimization of energy, resources and footprint."

Prof. Saikaly notes that domestic wastewater is estimated to contain approximately 2 kWh/m3 of energy in the form of organic substrate. "An opportunity exists for us here to offset energy consumption for domestic wastewater treatment through the recovery of this inherent energy, thereby moving forward towards energy-neutral or energy-positive wastewater treatment," he said.

DEVELOPING NEW BIOTECHNOLOGY TO TREAT WASTEWATER

In two papers published in the journal Environmental Science & Technology (DOIs: 10.1021/es4030113; 10.1021/es504392n ), Prof. Saikaly and his research team outlined the development of a novel biotechnology for wastewater treatment and reuse based on microbial electrochemical technologies (METs), which include microbial fuel cells (MFCs) and microbial electrolysis cells (MECs). These technologies are used to treat wastewater and recover energy at the same time. Bacteria in the MET device are able to transfer electrons in soluble organic material present in the domestic wastewater directly into electricity (as in MFCs) or biogas (as in MECs).

Prof. Saikaly notes, however, that METs alone are not enough to produce high-quality water necessary for reuse applications. To achieve higher water quality levels, the researchers combined MET technology with membrane filtration using an electrically conductive and porous flat sheet membrane cathode. They created a hybrid air-biocathode microbial fuel cell-membrane bioreactor (MFC-MBR), which treats the wastewater and carries out ultrafiltration at the same time, producing water for direct reclamation.

Their work was done in collaboration with Suzana Nunes, Professor of Environmental Science and Engineering from the KAUST Water Desalination and Reuse Center (WDRC). Prof. Nunes and her team provided complementary expertise in synthesizing conductive membranes specifically tailored for the team's applications.

"Our novel system has an electrically conductive ultrafiltration membrane that functions as both a biocathode for electricity generation, with passive oxygen transfer to the cathode, and as a membrane for wastewater filtration," explained Prof. Saikaly.

The researchers' MFC-MBR system is unique because it is "truly integrated and single chambered," said Dr. Krishna Katuri, KAUST research scientist and an author of both papers. Unlike with some MFC systems, the air biocathode MFC-MBR does not require wastewater aeration, and it achieves simultaneous organic and nitrogen removal. "This is important because aeration typically consumes more than 50 percent of the energy required to operate conventional biological wastewater treatment systems," noted Dr. Katuri.

INTERNATIONAL RECOGNITION FOR RESEARCH TEAM

The researchers' innovative work has received international recognition, winning the 2014 International Society for Microbial Electrochemistry and Technology (ISMET) Innovation Award for Best Technological Advancement for 2013.

Prof. Saikaly and his team also collaborated with Zhiping Lai, Associate Professor of Chemical and Biological Engineering, and other researchers in KAUST's Advanced Membranes and Porous Materials (AMPM) Center to increase the packing density of the cathode, a "critical aspect of the design of METs for practical applications for wastewater treatment," said Prof. Saikaly.

"A disadvantage of using a conductive porous flat sheet cathode is its low specific surface area, or cathode surface area per reactor volume," he explained. To tackle this problem, the teams of Prof. Lai and Prof. Saikaly synthesized nickel-based conductive and porous hollow fiber membranes (Ni-HFMs), which function as both the cathode for the hydrogen evolution reaction (HER) and as the membrane for the filtration of the effluent.

In addition, the researchers were able to minimize the problem of membrane fouling, a "major drawback of all membrane processes," Prof. Saikaly said. They attribute their system's reduced membrane fouling to the formation of hydrogen bubbles at the electrode's surface, which may provide a mechanism of self-cleaning (or scouring) the surface of the membrane.

"We believe our technology, with its energy-positive potential and small footprint, has the potential to be used for decentralized wastewater treatment and reuse," said Dr. Craig Werner, a KAUST Ph.D. graduate and second author of the second paper. "We hope that improvements and further optimization of the system will result in a more sustainable biological treatment system that has decreased energy requirements compared to traditional MBRs."

"It is also possible that our work may help shape further research aimed at the development of more efficient and cost-effective biotechnologies for resource recovery from different kinds of waste streams," he said.

"Extreme water scarcity is a pressing issue in the Middle East and in other countries around the world," noted Prof. Saikaly. "We hope that through our work, people will see that the integration of science and engineering will create opportunities to address this 21st century challenge. The membrane-based microbial electrochemical technology developed in our lab is a good example of marrying science and engineering to achieve the dual benefit of energy and water recovery from domestic wastewater."

- by Caitlin Clark, KAUST News