Comparison of Denitrification Induced by Various Organic Substances-Reaction Rates, Microbiology, and Temperature Effect

Widespread groundwater pollution with nitrate (NO3-) and the finite and decreasing geogenic NO3- degradation capacity in aquifers require a better understanding of potential treatment methods. This project aimed at exploring and comparing the efficiency of four organic substances as electron donors for heterotrophic denitrification. Circulation column experiments using sediment without NO3- degradation capacity and high agricultural NO3- groundwater were conducted. Acetate, glucose, ascorbic acid, and ethanol were added to these columns in three concentration steps to induce biological denitrification, whereby also temperature dependence of denitrification rates (room temperature and typical groundwater temperature of 10 degrees C) was taken into account. Results show denitrification with all four carbon (C) sources with intensities varying considerably between electron donors. Comparison of the two temperature approaches shows substantial differences between applied organic substances and indicates T as an important variable for denitrification. Ethanol is clearly the most effective electron donor for biodenitrification in groundwater investigated in this study, with a stronger and more effective NO3- degradation at 10 degrees C than at room temperature. In contrast, much higher reaction rates are achieved with glucose at room temperature, compared to 10 degrees C. Denitrification with ascorbic acid is very low at both temperatures; its addition produces biomass which repeatedly led to column clogging. In the entire test series, nitrite (NO2-) accumulation occurred more frequently and in higher concentrations at 10 degrees C. Analysis of microorganisms shows a strong modification in microbial community in reaction to the addition of different organic C as well as between the two temperature approaches.

Automated summary

The study investigated the efficiency of four organic substances as electron donors for denitrification, finding ethanol to be the most effective carbon source for enhancing NO3- degradation at 10 degrees C. Temperature was identified as a key variable in denitrification, with substantial differences observed in reaction rates between different organic substances and temperatures.