Researchers from the National Institute of Advanced Industrial Science and Technology (AIST), working with Kirin Holdings Co., Ltd., Tokyo University of Agriculture and Technology, and Kyoto University, have developed a technology to transition microbial communities in fermentation-industry wastewater treatment plants from nitrogen-removal to nitrogen-recovery types.

Current treatment plants for industrial wastewater containing nitrogen compounds use biological reactions to convert these compounds into nitrogen gas, which is then released into the atmosphere. This nitrification-denitrification process requires significant energy consumption through aeration to supply large amounts of oxygen.

The newly developed "Microaerobic Activated Sludge process" aims to halt microbial conversion reactions at the intermediate ammonium ion stage. By recovering the ammonium ion, the process could reduce energy consumption and allow the ion to be used as an energy resource through downstream separation and concentration technologies. This approach is expected to enable energy recovery without requiring major modifications to existing treatment plants.

To address the bottleneck in acclimating activated sludge microbial communities, the study utilised scaled-down processes of actual treatment plants and simulated wastewater derived from real streams. The researchers applied the following conditions to achieve the transition:

• Low dissolved oxygen (DO)
• Low pH conditions

The study, published in the journal Water Research, addresses the environmental impact of nitrogen compounds, which can lead to the eutrophication of lakes and coastal waters, acid rain, and global warming driven by nitrous oxide emissions.