In lab, low oxygen points to ammonia recovery from wastewater

At a fermentation-industry wastewater plant, nitrogen normally follows a one-way route: microbes help convert it through several compounds until it becomes nitrogen gas. Researchers at Japan’s National Institute of Advanced Industrial Science and Technology (AIST), working with Kirin Holdings, Tokyo University of Agriculture and Technology, and Kyoto University, have now shown a way to interrupt that route and retain the nitrogen as ammonium in scaled-down treatment processes.

The lever is counterintuitive: low dissolved oxygen and low pH. The team used wastewater modeled on real industrial streams to acclimate the activated-sludge microbial community—the mix of microbes that performs the treatment—away from nitrogen removal and toward nitrogen recovery. Their work appears in Water Research.

Today’s nitrification-denitrification process uses aeration to supply large amounts of oxygen. Nitrogen compounds are converted through ammonium, nitrite, nitrate, nitric oxide and nitrous oxide before ultimately being released as nitrogen gas. Holding the process at ammonium could preserve a compound useful in fertilizers and as a potential energy resource, rather than treating nitrogen only as something to eliminate.

The proposed Microaerobic Activated Sludge process does not recover a commercial product on its own. It is designed to feed downstream separation and concentration technologies, which could extract ammonia from the treated stream. AIST says the approach may allow existing treatment plants to move from decomposition and removal toward energy recovery without major modifications.

So what changes in practice? If the microbial control can be transferred from the scaled-down systems to full-sized plants, fermentation and pharmaceutical wastewater facilities could use less oxygen-intensive treatment while retaining nitrogen for reuse. For now, the reported tests used scaled-down processes and simulated wastewater, so the process has not yet been demonstrated at full scale.