What is your goal?

Among naturally occurring bacteria, those without names that we have never seen and which are totally unknown to us account for 99.9%. These unknown bacteria are thought to include many “super bacteria” with excellent abilities and functions. If we can find such “super bacteria” and use them for wastewater treatment or energy production, we will be able to create new technologies that have higher efficiency and lower environmental load than conventional technologies.

For example, to protect our precious water environment, the wastewater we discharge must be properly treated. In addition, wastewater treatment processes that consume as little energy and emit as little greenhouse gases (such as CO₂ and N₂O) as possible are required. In particular, as illustrated in Figure 1, the removal of ammoniacal nitrogen from wastewater involves the oxidation of ammoniacal nitrogen (NH₄⁺) into nitrous acid (NO₂^-) and nitric acid (NO₃^-) using microorganisms (nitrifying bacteria) (nitrification process), along with the subsequent reduction of the obtained nitric acid into nitrogen gas (N₂) (denitrification process). This method requires a large amount of oxygen in the nitrification process and consumes a huge amount of energy to supply oxygen to wastewater. Furthermore, the denitrification process generates a large amount of N₂O, a greenhouse gas with a greenhouse effect approximately 310 times greater than CO₂.

 

Fig. 1 Comparison between the New Nitrogen Removal Method Using anammox bacteria and the Conventional Nitrification/Denitrification Method

Accordingly, we investigated a variety of sludge and wastewater, in an attempt to discover a “super bacteria” that can directly produce N₂ gas from ammoniacal nitrogen and nitrous acid. As a result, we have successfully cultured new bacteria with these abilities (“anammox bacteria”). Use of these “anammox bacteria” has led to an overall nitrogen removal rate approximately 30 times faster because they eliminate the need to supply oxygen and also because they have higher treatment abilities per single bacteria cell and can proliferate at higher densities. As described above, the discovery of “anammox bacteria” allows for a dramatic reduction in energy consumption and running costs, with a reduction in the footprint of treatment facilities also expected.

 

What equipment do you use and what experiments do you carry out?

Fig. 2 Nitrogen Removal Rate with the Use of Anammox Bacteria Anammox bacteria (biomass in red) accumulate inside the reactor over time. However, proliferation of these bacteria is extremely slow.

We mainly culture bacteria in flasks or using the bioreactors in Figure 2. Of course, we frequently use general microscopes and confocal laser scanning microscopes as we handle microorganisms. Recently, it has also become necessary to employ molecular biological techniques to identify bacteria and estimate their functions using the genetic information of bacteria. For example, we can also analyze where, how, and how many of our anammox bacteria exist based on genetic information (this method is known as the FISH method) (Fig. 3).

 

What is your next goal?

With the depletion of fossil fuels expected to become more serious going forward, future wastewater treatment must be efficient and produce energy (electric power). In fact, a large amount of potential energy (electrons) still remains in wastewater. Thus, we are developing a “biofuel cell” that can generate power and treat wastewater at the same time (Fig. 4). With this “biofuel cell,” organic matter in wastewater is decomposed (oxidized) into electrons and hydrogen ions by the action of electrical power-generating bacteria (still unidentified), with the emitted electrons seized by negative electrodes (such as carbon paper) to generate electricity. Since this system depletes the energy of bacteria (electrons), the proliferation of bacteria is inhibited, thereby making it a dream wastewater treatment system that provides the three benefits of power generation, wastewater treatment, and sludge reduction. Let’s discover “super electrical power-generating bacteria” together.

Fig. 4 Overview of Biofuel Cell

 

References

(1) Satoshi Okabe, Chapter 8 “Suishitu Osen to Aratana Seigyo Technologies (Water Pollution and New Control Technologies),” in Bunshi de Yomu Kankyo Osen (Reading Environmental Pollution from Molecular Perspectives), written and edited by Satoshi Suzuki, pp. 202-231, Tokai University Press (2009)