A new pathway for ammonium oxidation coupled to iron reduction in the absence of oxygen and nitrate/nitrite has recently been described by the PI and co-workers for wetland soils in New Jersey, by researchers from UC Berkeley in tropical rainforest soils, and by researchers in Japan in a bioreactor, and has been referred to as Feammox. Further Studies have been conducted in incubations of NJ wetland sediments, confirming that Feammox is a biological process, and that an Acidimicrobiaceae bacterium A6, previously unknown, is responsible for it. Samples have been enriched and the PI has isolated the pure Acidimicrobiaceae bacterium A6 strain. Preliminary results from augmenting an anoxic bioreactor with ferrihydrite and Acidimicrobiaceae bacterium A6 have shown that there is a potential to exploit this process for anaerobic biological ammonium oxidation. Having isolated the Acidimicrobiaceae bacterium A6 raises the potential to determine the functional gene responsible for Feammox and to gain new fundamental insights into this process and its applications.
Virtually all wastewater treatment plants in the developed world as well as in many developing countries oxidize ammonia to nitrate ion, before discharging the treated wastewater. This is done to decrease oxygen demand in the receiving waters. Biological ammonium oxidation is conduced by aerobic (in the presence of oxygen) nitrifying bacteria and requires aeration, the step with the highest energy input in wastewater treatment plants. An alternative is the partial nitrification + Anammox system, which has been implemented in some treatment plants over the past 15 years, with the goal of saving energy costs, since only half of the ammonia is converted to nitrite ion aerobically, while the rest is converted to nitrogen gas anaerobically via Anammox. However, these Anammox-based wastewater treatment systems need to operate at temperatures between 28 and 35 Celsius. In contrast, we have shown that the Feammox pathway is still active at below 10 Celsius. Hence, a Feammox-based process could result in further energy savings, by requiring no aeration or heating of the wastewater water in temperate climates, although the cost of an Fe(III) source will have to be taken into account. Furthermore, N excess in near-shore environments has been identified as a major environmental problem leading to eutrophication and anoxia (Chesapeake Bay, Gulf of Mexico, etc.). Therefore legislation is being drafted which will require conversion of nitrate to nitrogen gas in conventional wastewater treatment plants. Potentially the Feammox process could achieve N removal in a single stage reactor with low energy utilization.
