Accumulation Of Denitrification Intermediates Research Articles

Modeling simultaneous carbon and nitrogen removal (SCNR) in anaerobic/anoxic reactor treating domestic wastewater

This paper presents a mathematical model based on the Anaerobic Digestion Model No. 1 (ADM1) to simulate the effects of nitrate concentration and hydraulic retention time (HRT) on the simultaneous carbon and nitrogen removal (SCNR) in anaerobic/anoxic reactor treating domestic wastewater. The model was calibrated using previously published experimental data obtained from anaerobic batch tests for different COD/NO3− ratios. Model simulations were performed to predict the SCNR in a completely mixed reactor (CSTR) operating under mesophilic conditions (35 °C). Six different scenarios were evaluated to investigate the performance of the SCNR based on typical influent characteristics of domestic wastewater. The variables analyzed were chemical oxygen demand (COD) removal, nitrate concentration, methane production, nitrogen gas, volatile fatty acids (VFA) concentration, pH and percentage of COD used by the denitrifying and methanogenic microorganisms. The HRT was decreased stepwise from 15 to 4 h. The results indicate that Scenario (S5) with a COD/NO3− ratio equal to 10 and an HRT equal to 15 h ensures the occurrence of the stable SCNR. Furthermore, the accumulation of denitrification intermediates and a significant reduction in the biogas production when the organic matter is limited was verified.

Feeding strategies for groundwater enhanced biodenitrification in an alluvial aquifer: Chemical, microbial and isotope assessment of a 1D flow-through experiment

Nitrate-removal through enhanced in situ biodenitrification (EISB) is an existing alternative for the recovery of groundwater quality, and is often suggested for use in exploitation wells pumping at small flow-rates. Innovative approaches focus on wider-scale applications, coupling EISB with water-management practices and new monitoring tools. However, before this approach can be used, some water-quality issues such as the accumulation of denitrification intermediates and/or of reduced compounds from other anaerobic processes must be addressed. With such a goal, a flow-through experiment using 100mg-nitrate/L groundwater was built to simulate an EISB for an alluvial aquifer. Heterotrophic denitrification was induced through the periodic addition of a C source (ethanol), with four different C addition strategies being evaluated to improve the quality of the denitrified water. Chemical, microbial and isotope analyses of the water were performed. Biodenitrification was successfully stimulated by the daily addition of ethanol, easily achieving drinking water standards for both nitrate and nitrite, and showing an expected linear trend for nitrogen and oxygen isotope fractionation, with a εN/εO value of 1.1. Nitrate reduction to ammonium was never detected. Water quality in terms of remaining C, microbial counts, and denitrification intermediates was found to vary with the experimental time, and some secondary microbial respiration processes, mainly manganese reduction, were suspected to occur. Carbon isotope composition from the remaining ethanol also changed, from an initial enrichment in 13C-ethanol compared to the value of the injected ethanol (−30.6‰), to a later depletion, achieving δ13C values well below the initial isotope composition (to a minimum of −46.7‰). This depletion in the heavy C isotope follows the trend of an inverse fractionation. Overall, our results indicated that most undesired effects on water quality may be controlled through the optimization of the C/N ratio determined from the amounts of injected ethanol vs. the amount of nitrate in groundwater, with a smaller C/N ratio causing a lower level of undesired impurities. Furthermore, the authors suggest that the biofilm life-time has a direct effect on microbial population and hence affects biodenitrification performance, influencing the accumulation of nitrite over time.

Response of methanogenic archaeal community to nitrate addition in rice field soil

Addition of nitrate strongly inhibits CH4 production from anoxic soil. The main mechanisms were considered to be the substrate competition and the toxic effect of denitrification intermediates on the methanogenesis. However, it is unclear whether these inhibitory effects are reflected in the structure and dynamics of methanogenic community in the soil. In the present study, the response of methanogenic archaeal community to nitrate addition was determined using terminal restriction fragment length polymorphisms in combination with cloning and sequencing of archaeal 16S rRNA genes. When nitrate was added at the beginning of an anoxic incubation of rice field soil, denitrification occurred rapidly and the denitrification intermediates were detected only for a short time. Total production of CH4 was reduced, but no obvious effect on the structure of methanogenic community was observed. In contrast, when nitrate was added 20 days after the anoxic incubation, the denitrification intermediates obviously accumulated. CH4 production was completely suppressed for 7 and 16 days from treatments of 5 and 10 mM nitrate respectively. The dynamics of methanogenic community also diverged greatly from the control. While the hydrogenotrophic methanogens increased and the acetoclastic methanogens decreased with the incubation in the control soil, the structure and abundance of the methanogenic community remained unchanged after the addition of nitrate. Methanogenesis resumed when the denitrification intermediates were depleted in soil. The analysis of carbon isotopic signals revealed that hydrogenotrophic methanogenesis recovered faster than acetoclastic methanogenesis. Our study suggests that the accumulation of denitrification intermediates has a strong inhibitory effect on the activity but not the structure of methanogenic community.

Inhibitory effects of nitrate reduction on methanogenesis in the presence of different electron donors

The preferential utilization of different electron donors and their effects on the nitrate reduction and methanogenesis in a mixed, mesophilic (35 degrees C) methanogenic culture were investigated. Batch methanogenic cultures were fed with dextrin/peptone (D/P), propionate, acetate, and H(2)/CO(2) at an initial COD of 500 mg/L and an initial nitrate concentration of 50 mg N/L. Immediate cessation of methane production was observed in all nitrate-amended cultures. Methane production completely recovered in the D/P- and acetate-fed cultures, and partially recovered or did not recover in the propionate- and H(2)/CO(2)-fed, nitrate-amended cultures, respectively. Accumulation of denitrification intermediates was observed in both the propionate- and H(2)/CO(2)-fed cultures, which resulted in inhibition of fermentation and/or methanogenesis. The fastest and the slowest nitrate reduction were observed in the acetate- and propionate-fed cultures, respectively.