Researchers from KAUST have found a novel salt-tolerant bacterium from the Red Sea that can remove nitrogen from salty wastewater. The bacterium could be used to treat sewage water coming from seawater-based toilets.

Muhammad Ali tests the effectiveness of Candidatus Scalindua sp. AMXII at treating salinated wastewater. Source: © 2019 KAUST; Anastasia Khrenova

Less than 1% of the Earth’s water is fresh and accessible to humans. As populations grow, the demand for freshwater also grows. Toilet flushing accounts for 30% of the world’s total domestic water demand and the average person flushes 50 liters of water per day. A natural next step to conserve the world’s freshwater supply is to change the kind of water used in toilets.

Using seawater in toilets could partially alleviate pressure on freshwater resources. This practice is already in place in Hong Kong, Tokyo and Singapore. Coastal cities are the most likely to adapt to using seawater toilets because of their proximity to a saltwater resource. Using saltwater in toilets would reduce the dependence on freshwater and energy-intensive desalination.

This method hasn't been used worldwide due to the nitrogen in wastewater. Nitrogen must be removed from wastewater because of its negative effects on the environment and human health. The high salt content in seawater toilets wastewater limits the performance of conventional nitrogen-removing bacteria used in treatment plants because they have a low salt tolerance.

The team conducted three years of tests to find if the bacterium Candidatus Scalindua sp. AMXII could be used to remove nitrogen from salty wastewater. This bacterium was cultured from the Red Sea. Candidatus Scalindua sp. AMXII was around 90% effective in treating wastewater with a salinity of about 1.2%. This bacteria demonstrated high nitrogen removal rates.

The team’s findings demonstrate the proof of concept, now they are focusing on demonstrating the technology in the microbial granual system with the Candidatus Scalindua sp. AMXII bacteria in a full wastewater treatment process. The team is working with a Saudi fertilizer company to test the new bioprocess.

This study was published in Water Research.