| Abstract [eng] |
Nitrites are widely found in a variety of waters: rivers, lakes, mineral and drinking waters. However, these compounds are highly undesirable in water bodies due to its toxicity to aquatic animals. The regulated maximum levels for nitrite ions in drinking water are very low (0.05-0.1 mg/dm3). Analysis of nitrites using sensitive and accurate methods can only be performed in laboratories. In recent years, more and more research has been conducted on microbial fuel cells (MFC) using them as sensors. Often, this type of sensor is used for wastewater testing to detect various chemical compounds. Due to the rapid reaction, this type of sensor could be used for the analysis of nitrite ions. In this reaserch, two MFC, which had two chambers, were constructed. In one microbial fuel cell mixed culture of bacteria (activated sludge) was cultivated, in another Shewanella putrefaciens bacteria. The shape and size of the bacteria were determined by scanning electron microscopy (SEM). The determined optimal MFC external load (passive resistance) was 1000 Ω, it was the same for both fuel cells. The maximum generated voltage was observed at a flow rate of 12 cm3/min. MFC was tested in two operation modes: flow through and recirculation. Optimal concentration of acetate (nutrient) in model wastewater (anolyte) was 3 mg/dm3. By reducing and increasing the nutrient concentration in the anolyte, the voltage generated in both MFCs decreases. It was found that the fluctuations of the MFC voltage are caused by the fluctuations of the ambient air temperature, as well as the temperature of the electrolyte (anolyte and catholyte): the voltage of the MFC increases with increasing temperature and decreases with decreasing temperature. The values of MFC voltage and oxidation-reduction potential (ORP) of anolyte depend on the concentration of nutrients in the recirculation mode. As nutrients decrease, the voltage of MFC decreases and the ORP increases. Both fuel cells were studied in a wide range of nitrite ion (NO2-) concentrations (0.1-1000 mg/dm3). Both fuel cells showed response to NO2- in wastewater - a decrease in the generated voltage. At low concentrations (0.1 mg/dm3 to 10 mg/dm3) MFC with mixed bacterial species showed logarithmic decrease of generated voltage. Whereas MFC with S.putrefaciens voltage decreased same amount (59%) in concentrations of nitrate ion from 0.1 to 10 mg/dm3. At high nitrite ion concentrations, a much higher decrease of generated voltage was observed in both MFCs. At 1000 mg/dm3 concentration of nitrite ions voltage generated in both MFCs have not recovered to level of voltage that was observed before experiments. It was observed by colorimetricmethod that the concentration of nitrite ions in the wastewater flowing from both MFCs decreased at concentration of NO2- 0.1-1.0 mg/dm3 or remained unchanged at concentration of NO2- 10-1000 mg/dm3. |
