Development of bioelectrochemical systems for electricity generation from ammonia oxidation: metagenome and metatranscriptome study

Abstract

The necessity to reduce energy consumption in wastewater treatment plants (WWTP) combined with strict effluent quality standards, especially concerning nitrogen concentrations, carries global importance. This imperative is heightened in developing countries due to the pressing demand for expanding services in sanitation and energy sectors. Simultaneously, in developed countries, there is a focus on modernizing sanitation infrastructure, further underscoring the global relevance of this issue. A promising avenue for addressing this challenge lies in the recent discovery and advancement of bioelectrochemical processes capable of directly generating electricity from ammonia nitrogen oxidation, thereby potentially transforming the energy dynamics of WWTPs. However, a lack of knowledge regarding fundamental aspects of this process, such as the responsible microorganisms, reaction cascades, metabolic pathways, and electron transfer mechanisms, impedes a comprehensive understanding of its practical applicability for effluent treatment. Consequently, optimization and scalable implementation of the process become challenging. This research proposal seeks to address these knowledge gaps by elucidating the reactions and mechanisms involved in the bioelectrochemical conversion process of ammonia through metagenomic and metatranscriptomic analyses. Spanning a 12-month period, the project comprises three experimental phases centered around microbial fuel cell (MFC) studies, to be conducted at the Environmental Microbiology and Biotechnology laboratory of Prof. Kartik Chandran at Columbia University in New York City, USA. The initial phase involves cultivating conventional electroactive bacteria (EAB) by operating MFCs with synthetic wastewater simulating anaerobic sludge digesters' supernatant. Subsequently, the second phase entails feeding the MFCs with an inorganic version of synthetic wastewater to assess the system's adaptation, considering microbial community composition and function, for ammonia oxidation. In the third phase, the study aims to evaluate the influence of dissolved oxygen on bioelectrochemical ammonia oxidation, while also investigating the impact of sulfate, commonly present in anaerobic sludge digesters' supernatant. A control unit, maintained under open circuit conditions throughout the operation, will aid in understanding bacterial-electrode interactions and the influence of biofilm composition and function. The research employs extensive effluent characterization, electrochemical techniques (cyclic voltammetry and impedance spectroscopy), and whole-genome shotgun sequencing (DNA) in conjunction with metatranscriptome sequencing (RNA). These approaches aim to unravel reaction chains, metabolic pathways, and electron exchange mechanisms responsible for converting ammonia into electricity. The outcomes of this study are anticipated to contribute valuable insights into complex phenomena, fostering the development and prospective integration of this innovative bioelectrochemical process into wastewater treatment systems, with potential benefits for the energy sector.