Some of the main pollutants in wastewater are various phosphorus and nitrogen compounds that cause eutrophication of water bodies, and some of them are highly toxic to aquatic life. One of the most toxic nitrogen compounds is nitrite (nitrite ions), so it is particularly important to ensure that they are not present in the effluent at all or that their concentrations do not exceed the permissible level. Electrochemical sensors – selective electrodes of various ions, dissolved oxygen – are most often used for continuous monitoring of the concentration of some substances in wastewater. Concentrations of other substances are determined only by periodic sampling for laboratory testing. Unfortunately, for the continuous measurement of nitrite ion concentrations in wastewater or other waters, there is no corresponding ion-selective electrode, and its concentration is determined only by spectrometric / photometric measurements. It is thought that an alternative to the selective electrode could be a microbial fuel cell (MFC), in which the microorganisms attached to the bioanode – bacteria-exoelectrogens – generate electricity. The parameters of electricity generated by microorganisms (voltage/current) are directly dependent on the bioelectrochemical activity of exoelectrogens, which is largely determined by the chemical composition of the anolyte. In addition, exoelectrogens, like other living organisms, are also adversely affected by many toxic substances. The aim of this project will be to determine the impact of toxic nitrite ions and their different concentrations on the operation of MFC. Determining the relationship between the change of MFC electrical parameters and the changing nitrite ion concentration in model wastewater-anolyte with different nutrient organic content would create preconditions for using MFC as an electrochemical sensor for long-term monitoring of nitrite ion concentration in real wastewater.
Project funding:
Project is funded by EU Structural Funds according to the 2014–2020 Operational Programme for the European Union Funds’ Investments priority “Development of scientific competence of researchers, other researchers, students through practical scientific activities” under Measure No. 09.3.3-LMT-K-712.
Project results:
After studying the microbial fuel cell as a nitrite ion sensor, it was found that the exposure of its bioanode to nitrite ions (0.1-1000 mg / L) contaminated model nitrate-anolyte results in a very clear and sudden drop in the voltage generated by the microbial fuel cell. It is then replaced by the same sudden rise in voltage (recovery) which is observed immediately after the exposure to nitrite ions has ceased, i.e. after the supply of model nitrate-anolyte without nitrite to the microbial fuel cell. A larger drop in the voltage generated by the microbial fuel cell was observed by increasing the nitrite concentration in the model effluent-anolyte and a slower return of the voltage to the initial level in the absence of nitrite contamination. It was found that the voltage drop of a microbial fuel cell-sensor depends logarithmically on the concentration of nitrite ions when it varies in the range of 0.1–10 mg / L in model wastewater-anolyte. This creates preconditions for the use of such a microbial fuel cell for quantitative monitoring of nitrite ion concentrations in wastewater, etc. Although higher concentrations of nitrite ions (in the range of 100-1000 mg / L) in model wastewater-anolyte cannot be accurately quantified due to a particularly significant voltage drop of the microbial fuel cell, it has the potential to be used as a bioelectrochemical early warning device for extremely high nitrite pollution.
Period of project implementation: 2020-11-03 - 2021-04-30
Project coordinator: Kaunas University of Technology
