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

Abstract

Nitrate pollution of water resources is a global problem (Almasri, 2007). In some regions, the guideline values of groundwater and drinking water regulations are considerably exceeded in surface waters, but also in groundwater (Carrey et al., 2014). Several European Union member states, including Germany, were penalized by the European Court of Justice for non-compliance with the Nitrate Directive (European Court of Justice, 2010Justice, , 2018. However, further infringements and sanctions are to be expected. This contamination results mainly from anthropogenic N fertilizers used to increase agricultural productivity (Hosono et al., 2013). Excess N enters groundwater as NO 3 − . Due to a geogenic NO 3 − degradation capacity of most aquifers (sulfide minerals and organic C), part of the NO 3 − can be degraded (Rivett et al., 2008). Based on sulfide-S and organic C contents of the aquifer, groundwater recharge and NO 3 − concentration, the remaining time until a NO 3 − breakthrough to drinking water production wells may be calculated (e.g., Ortmeyer, Volkova, et al., 2021). Overall, a link between hydrologic and water quality models is important because including transit times can improve understanding of NO 3 − transport in aquifers (Hrachowitz et al., 2016). In the future, considerable increases in NO 3 − concentrations and NO 3 − breakthroughs to raw water wells are expected, as this degradation capacity is decreasing and finite (Knowles, 1982;Schwientek et al., 2017). Climate change is expected to enhance this deterioration of water resource quality and quantity (Fleck et al., 2017;Ortmeyer, Mas-Pla, et al., 2021). In addition to a decrease in groundwater recharge and a drop in water levels, Stuart et al. (2011) point to possible increasing rates of NO 3 − leaching under future climate scenarios. The thickness of the unsaturated zone is crucial for reaching NO 3 − peaks at the groundwater table (Wang et al., 2012). Nitrate storage in the vadose zone is also important, but often not considered in

Modified microbiology through enhanced denitrification by addition of various organic substances—temperature effect

“…The 15-mL falcon tubes were then filled with groundwater which had NO 3 − concentrations of 200 to 250 mg/L. Natural groundwater was obtained from a piezometer in the Haltern Fm (Ortmeyer et al 2021b ). Consequently, the water corresponds hydrogeochemically to the sediment used.…”

“…In addition, each groundwater contained one of the four different selected C: acetate, glucose, ascorbic acid (manufacturer: CHEMSOLUTE), and ethanol (manufacturer: VWR) to initiate a heterotrophic denitrification. The individual substrates were added in three concentration steps, according to Ortmeyer et al ( 2021b ). In each of the column experiments in Ortmeyer et al ( 2021b ), with a water volume of 3.74 L, substances were added in the steps 2.5, 5, and 10 mmol of the four organic carbon ( C org ).…”

“…The individual substrates were added in three concentration steps, according to Ortmeyer et al ( 2021b ). In each of the column experiments in Ortmeyer et al ( 2021b ), with a water volume of 3.74 L, substances were added in the steps 2.5, 5, and 10 mmol of the four organic carbon ( C org ). Concentrations of C org in the 15-mL falcon tubes were adjusted to the concentrations from the column experiments.…”

“…Biostimulation is a promising method to decontaminate groundwater polluted by NO 3 − (Azubuike et al 2016 ). Biological denitrification enhanced by the addition of external C is one of the best known and most effective treatment methods for nitrate-polluted groundwater (e.g., Khan and Spalding 2004 ; Vidal-Gavilan et al 2013 ; Ortmeyer et al 2021b ). A great advantage is the selective NO 3 − removal.…”

“…Ortmeyer et al ( 2021b ) investigated the influence of temperature on enhanced denitrification. Four pure organic substrates (acetate, glucose, ascorbic acid, ethanol) were applied, which were investigated under realistic conditions on a laboratory scale in column experiments.…”