Bioelectrochemical anaerobic oxidation of ammonia for sustainable N removal from wastewater

Project Information

ELECTRAMMOX

Grant agreement ID: 894525

DOI

10.3030/894525

Project terminated on 14 June 2022

EC signature date 16 March 2020

Start date 15 June 2020

End date 14 June 2022

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 172 932,48

EU contribution

€ 172 932,48

Coordinated by

METFILTER SOCIEDAD LIMITADA
Spain

Periodic Reporting for period 1 - ELECTRAMMOX (Bioelectrochemical anaerobic oxidation of ammonia for sustainable N removal from wastewater)

Reporting period: 2020-06-15 to 2022-06-14

Summary of the context and overall objectives of the project

The action “Bioelectrochemical anaerobic oxidation of ammonia for sustainable N removal from wastewater” looks at a novel method for the removal of N pollution from wastewaters at a decentralized level. In the last decade, the field of microbial electro catalysis has given birth to a wide variety of microbial electrochemical technologies (MET). MET use the extraordinary ability of some microorganisms to transfer electrons from a substrate in wastewater to a solid-state anode, which allows for different applications e.g. production of H2, CH4, or electricity, desalination or simply wastewater treatment. Recently, electroactive microorganisms were integrated in constructed wetlands (CW) for the treatment of municipal and industrial wastewater in a new technology called METland®. METlands allow for intensification of (previously considered extensive) CW for decentralized wastewater treatment. The majority of studies about MET focus on heterotrophic microorganisms but few works have studied anaerobic NH4+ oxidizing-, anode respiring microorganisms. The feammox reaction (anaerobic oxidation of ammonium using insoluble Fe3+ as electron acceptor) has been shown in natural environments but has yet not been exploited for wastewater treatment. Integration of feammox in wastewater treatment by replacing the iron by an anode can enable anaerobic nitrification, minimizing the most problematic issue for treating wastewater in thousands of European small populations: the costs derived from energy-intensive aeration for conventional nitrification. ELECTRAMMOX investigated anaerobic ammonia-oxidizing, anode-respiring microorganisms (electrammox bacteria) with the objective to integrate them in METlands for N removal from sewage.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The work comprised 3 work packages. In WP1 we enriched and characterised anaerobic ammonia oxidising cultures from wastewater treatment plants. In WP2 we evaluated the feasibility of anaerobic NH4+ removal in mesocosms and we investigated the interaction of anaerobic NH4+ oxidizing microorganisms with model electroactive heterotrophs, and in WP3 we investigated the application of bioelectrochemically enhanced constructed wetlands for the recovery of N from source separated urine.
The fellow participated in three international conferences during the course of the action,
In terms of communication and dissemination, the researcher has participated in several events oriented to general public: European Researcher’s night (2021 and 2022), Madrid Science day (local event targeting broad public), performing demonstrations and explanations and has collaboration in an art project including participation in a dissemination day at the Center for Contemporary Culture of Barcelona (CCCB).
In addition, the fellow has supervised a master student and a bachelor student, and co-supervises two PhD students working on topics related to the action in collaboration with Ghent University (Belgium). In parallel, the fellow has acquired funding in national competitive calls: A national grant under the program “Proyectos de generación de conocimiento 2021”, and the regional call “Programa de atracción de Talento”. This has enabled the fellow to join the Department of Chemical Engineering at the University of Alcalá, Spain, as an independent researcher. Furthermore, the researcher participated in the EBAME6 workshop on Microbial Ecogenomics (2021), organised by the Institut Universitaire Européen de la Mer (Brest, France).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The project investigated different aspects of the bioelectrochemical NH4+ removal from wastewaters. A series of screenings to identify and enrich electroactive anaerobic ammonia oxidizers from natural environments did not result in viable cultures. On the other hand, cultures enriched from engineered systems, i.e. full-scale wastewater treatment plants, showed evidence of NH4+ oxidation in bioelectrochemical systems.
Different tests performed during the project showed that anammox bacteria were involved in the bioelectrochemical anaerobic oxidation of NH4+ to N2 gas (this was confirmed by utilizing isotopically labelled NH4+), albeit at lower rates than expected. Cyclic voltammetries performed on anammox biofilms in glassy carbon electrodes showed that the observed phenomenon is compatible with an indirect exchange of electrons between bacteria and electrode, with Fe2+/Fe3+ as mediator that oxidizes at the surface of the electrode and is microbially regenerated via the feammox reaction. Additionally, we observed a negative effect of organic matter on the bioelectrochemical anaerobic ammonia oxidation, since spiking low concentrations of acetate immediately impaired the anammox activity in the biofilm, which raises the concern of whether anammox can be applied to wastewater treatment at relevant rates, when using an electrode as the sole electron acceptor.
Bioelectrochemical reactors inoculated with nitrifying cultures from full-scale bioreactors or developed in the lab showed capacity for the removal of N from wastewaters although at lower rates than reported in the literature (2-12 mg N/L/d in this work, vs 35 mg N/L/d observed by Vilajeliu-Pons (2018). In these experiments, higher NH4+ oxidation capacity was observed when treating a highly-conductive medium (hydrolysed urine) when compared to poorly conductive media (mimicking pre-treated municipal wastewater).
The application of constructed wetlands packed with electroconductive carrier material to the recovery of N from source separated urine showed good NH4+ oxidation capacity, with rates up to 284 mg N/L/d, although with low N recovery rates of 43%. The system was sensitive to free ammonia inhibition as well as free nitrous acid toxicity. High concentrations of NO2- caused by suppression of nitrite oxidizing bacteria and partial denitrification destabilized the system. This needs to be prevented to maximize nitrification rates, and minimize green house gas emissions.

Anammox culture forming biofilms on bioelectrochemical reactor