Researchers in Japan have developed a wastewater treatment technology that could transform nitrogen pollution from an environmental liability into a recoverable resource. A team 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, has demonstrated a method for redirecting microbial communities in fermentation-industry wastewater plants away from conventional nitrogen removal and toward ammonium recovery. The approach, called the Microaerobic Activated Sludge process, uses carefully controlled oxygen and acidity levels to stop biological nitrogen conversion at the ammonium stage instead of allowing it to continue until nitrogen gas is released into the atmosphere.
Nitrogen is indispensable to modern society. It is used in fertilizers that support food production and serves as a raw material for pharmaceuticals, chemicals, and industrial products. Yet the large-scale movement of nitrogen through human systems has become an increasing environmental concern. When excessive nitrogen compounds enter rivers, lakes, and coastal waters, they can trigger eutrophication, stimulate harmful algal growth, reduce oxygen concentrations, and damage aquatic ecosystems. Nitrogen-related emissions also contribute to acid rain and climate change, particularly through nitrous oxide, a powerful greenhouse gas. Researchers are therefore seeking treatment systems that can manage nitrogen without simply transferring it from wastewater into the atmosphere.
Most industrial wastewater treatment facilities use activated sludge, a biological process in which dense communities of microorganisms consume and transform pollutants. In conventional nitrogen-removal systems, microorganisms first convert ammonium into nitrite and nitrate through nitrification. Other microbial groups then carry out denitrification, transforming these oxidized nitrogen compounds into nitrogen gas. The gas is released into the atmosphere, completing the removal process. Although effective for reducing nitrogen discharge, the system requires substantial aeration. Supplying oxygen to the treatment tanks is often one of the most energy-intensive parts of wastewater treatment, especially when large volumes of water containing relatively low concentrations of nitrogen must be processed continuously.
The Japanese research team pursued a different strategy: rather than driving nitrogen all the way to nitrogen gas, they attempted to preserve it in a recoverable form. In this approach, nitrogen compounds are biologically converted into ammonium ions, which can potentially be separated, concentrated, and reused. Ammonium can serve as a nitrogen-containing resource for fertilizers, chemical production, or emerging energy systems. Achieving this goal, however, requires precise control over the microbial community inside the activated sludge. If oxygen levels rise too high, nitrifying microorganisms can resume converting ammonium into nitrite and nitrate. If conditions are not properly balanced, additional nitrogen reactions can also undermine recovery efficiency.
To address this challenge, the researchers used scaled-down treatment processes modeled on actual fermentation-industry wastewater plants. They also prepared simulated wastewater based on real production streams, allowing the team to reproduce the chemical conditions that microbial communities encounter in industrial facilities. The central breakthrough came during the start-up and acclimation phase, when the existing microbial population had to transition from a nitrogen-removal configuration to a nitrogen-recovery configuration. The researchers found that operating the sludge under low dissolved oxygen, known as microaerobic conditions, together with a low-pH environment, helped suppress the microbial pathways responsible for further nitrogen oxidation.
Dissolved oxygen is a critical control parameter in activated sludge because different microbial groups respond differently to oxygen availability. Conventional nitrification requires oxygen, and reducing the oxygen supply can limit the activity of microorganisms that convert ammonium into oxidized nitrogen compounds. However, oxygen cannot simply be eliminated, because the wastewater still requires biological treatment and the microbial community must remain active. The Microaerobic Activated Sludge process therefore operates within a narrow range in which enough oxygen is present to support the desired reactions, but not enough to sustain unwanted nitrogen conversion. The low-pH condition provides an additional selective pressure, changing the balance of microbial activity and helping the recovery-oriented community become established.
According to the researchers, the optimized process successfully converted nitrogen compounds in fermentation wastewater into ammonium while preventing subsequent biological transformations. This is significant because the treatment objective shifts from destruction to capture. In a conventional plant, nitrogen is removed from the wastewater but lost as atmospheric nitrogen gas. In the new configuration, ammonium remains available for downstream separation and concentration technologies. Those technologies could produce a more concentrated ammonium stream suitable for reuse, potentially allowing wastewater treatment facilities to recover valuable nitrogen while reducing their aeration-related energy demand.
Fermentation-industry wastewater presents a particularly interesting target for this technology. Facilities that produce food, beverages, pharmaceuticals, and related products can generate organic wastewater containing relatively low concentrations of nitrogen compounds. Treating such streams efficiently is difficult because the nitrogen may be too dilute to recover economically, while biological removal still requires continuous energy input. The researchers’ results suggest that controlling the microbial ecosystem before downstream separation could improve the feasibility of recovery. Because the proposed process is based on activated sludge, it may also be integrated into existing infrastructure without requiring a complete redesign of treatment plants.
The work could mark a broader change in how wastewater is viewed: not simply as a stream of pollutants to be neutralized, but as a source of materials that can be reclaimed. The researchers emphasize that their demonstration was conducted using scaled-down systems and simulated wastewater derived from real production conditions, meaning further testing will be needed at larger operational scales. Long-term stability, fluctuations in industrial wastewater composition, ammonium recovery rates, and the economics of downstream concentration will all be important in determining commercial potential. Even so, the ability to guide a complex microbial community toward ammonium preservation represents a major step toward lower-energy, resource-recovering wastewater treatment. If validated in full-scale facilities, the Microaerobic Activated Sludge process could help industries reduce nitrogen emissions, cut aeration demand, and turn a traditionally discarded nutrient into a reusable industrial resource.
Subject of Research: Microbial control in wastewater treatment and ammonium recovery from fermentation-industry wastewater
Article Title: Acclimation of microbial communities in low dissolved oxygen and low pH driven start-up of microaerobic activated sludge process to recover ammonium from fermentation industrial wastewater
News Publication Date: 19-Jun-2026
Web References: https://doi.org/10.1016/j.watres.2026.126305
References: Water Research, DOI: 10.1016/j.watres.2026.126305
Image Credits: National Institute of Advanced Industrial Science and Technology (AIST)
Keywords
Wastewater treatment, ammonium recovery, fermentation wastewater, activated sludge, microaerobic process, microbial communities, low dissolved oxygen, low pH, nitrogen removal, nitrogen recovery, sustainable water treatment, resource recovery, AIST
