The recently discovered microbial process of anaerobic ammonium oxidation (anammox) offers a more economical and environmentally sustainable option to nutrient nitrogen removal during wastewater treatment compared to conventional nitrification-denitrification. Anammox bacteria catalyze the reaction of nitrite with ammonium to form dinitrogen gas in the absence of elemental oxygen. The most important limiting factors of the process are the slow growth rates of the bacteria involved combined with their sensitivity to the substrate, nitrite. Preliminary research has demonstrated that nitrite inhibition is considerably more severe in the absence compared to the presence of the energy donating substrate, causing the biomass to become irreversibly inactivated. The dependency of the inhibition on starvation conditions may be related to the unusual organelle structures in anammox bacteria. The central metabolic reactions of anammox bacteria take place in a specialized organelle compartment, the anammoxosome, which protects the rest of the cell from reactive compounds and provides an intracellular membrane barrier for energy yielding proton gradients. The overarching goal of the project goal is to demonstrate the validity of the hypothesis and use it as a guide to develop strategies to prevent nitrite-inhibition during the application of anammox as an N-removal technology. The project will characterize two enrichment cultures of anammox bacteria and use them to describe and quantify the scope of the nitrite-inhibition. Experiments will be conducted to elucidate the mechanisms of nitrite inhibition by influencing the metabolic energy in anammox bacteria via starvation or dissipating proton gradients. The mechanistic insights gained will be used to design and test strategies of preventing inhibition during the operation of bioreactors including membrane bioreactors that provide improved cell retention.
Nutrient nitrogen compounds are important environmental contaminants causing depletion of oxygen, eutrophication, and fish toxicity in surface waters as well as a posing a public health threat via ground water resources. To mitigate these impacts, environmental regulations for nutrient nitrogen are becoming stricter. As a result, N- removal is becoming a necessary component of wastewater treatment. The current practice is based upon the nitrification-denitrification process, which requires costly aeration and electron-donating substrate additions. Anammox is an alternative N-removal technology that provides important savings in aeration costs (62.5%), more compact bioreactors and eliminates the need for substrate supplements. These benefits translate to less energy consumed for N removal and thus provide a lowered Carbon-footprint for wastewater treatment. Anammox is particularly suited for waste streams high in ammonia and low in organic carbon such as sludge liquor and landfill leachate. An important drawback for the application of the anammox process has been its unreliability due to the poorly understood cases of anammox organism inactivation. This project specifically aims to understand the problem so as to design strategies to provide a solution to make anammox technology more reliable and thus attractive to utilities and technology suppliers. The project will have benefits in education by supporting graduate and undergraduate student research as well as providing scientific results to develop modules in environmental engineering courses. Institutionally, the project will reinforce industrial partnerships to scale up the anammox technology.
