Greening And Environment

Seawater toilet to alleviate pressure on freshwater resources

A novel salt-tolerant bacterium cultured from the Red Sea effectively removes nitrogen from salty wastewater—and it could be used to treat sewage coming from toilets that use seawater for flushing in place of freshwater.

Less than 1% of Earth’s water is fresh and also accessible for human use. The world’s population is expected to grow to about ten billion by 2050 and will continue to place increasing pressure on this already rare resource.

Currently, toilet flushing accounts for about 30% of the world’s total domestic water demand, and using seawater could alleviate that pressure on freshwater resources. A research team from King Abdullah University of Science and Technology (KAUST) believes they have figured out how it can be done efficiently.

“Seawater toilet flushing is already in practice in Hong Kong, Singapore and Tokyo,” says KAUST research scientist Muhammad Ali.

More coastal cities might follow suit except that the high salt content of seawater would limits the performance of conventional nitrogen-removing bacteria used in the treatment processes “because they have low salt tolerance.” Nitrogen needs to be removed from wastewater due to its negative effects on the environment and human health.

Ali and Dario Rangel Shaw, both in Pascal Saikaly’s lab, conducted three years of tests to find whether the bacterium Candidatus Scalindua sp. AMX11, which they cultured from the Red Sea, could effectively remove nitrogen from salty wastewater.

Currently, the most energy-efficient method to do this involves the use of granules containing two types of nitrogen-removing bacteria. But one of these, an anaerobic ammonium oxidation bacteria, or anammox bacteria for short, has a very low tolerance for and effectiveness in saltwater.

On the other hand, Candidatus Scalindua sp. AMX11 was around 90% effective in treating wastewater with a salinity of about 1.2% and demonstrated high nitrogen removal rates. The tests were on real seawater—unlike other studies that used artificial versions.

“The findings demonstrate a proof of concept, and the next step is to demonstrate this technology in a microbial granular system containing Candidatus Scalindua sp. AMX11 bacteria and the other types of bacteria necessary for a full-scale wastewater treatment process,” explains Saikaly


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