An official website of the United States government
Removal of selenate (SeO42-) from selenate-contaminated wastewater is challenging due to the commonly coexisting and competing anions of sulfate (SO42-) and nitrate (NO3-). This study investigates SeO42- reduction to elemental selenium (Se0) in a cathode-based bioelectrochemical (BEC) reactor and a conventional biofilm reactor (i.e., an upflow anaerobic reactor). The simulated wastewater contained SeO42- at a typical concentration of 5 mg Se/L, SO42- at a typical concentration of 1000 mg S/L, and NO3- at concentrations that varied from 0 to 10 mg N/L. The impact of sulfate on the BEC reactor was much lower than that on the conventional reactor: The selenium removal, defined as (selenate in influent – dissolved selenium in effluent)/selenate in influent, was 99 % in the BEC reactor versus 69 % in the conventional biofilm reactor. The lower selenium removal in the conventional reactor was mainly due to the >10 times higher reduction of sulfate, which directly caused competition between sulfate and selenate for the common resources such as electrons. The more reduction of sulfate in the conventional reactor further led to 45 times higher production of selenide. Selenide is usually assumed to be minimal and therefore not measured in the literature. This simplification may significantly overestimate selenium removal when the influent sulfate concentration is very high. NO3- in the influent of the BEC reactor promoted selenium removal when it was less than 5.0 mg N/L but inhibited selenate removal when it was more than 7.5 mg N/L. This was supported by the microbial community analysis and intermediate (nitrite) analysis.
more »
« less
Real-Time Control of Exogenous Carbon Dosing in a Denitrifying Woodchip Bioreactor Treating Agricultural Drainage
Nature-based treatment technologies such as denitrifying woodchip bioreactors (WBRs) are employed to manage nitrogen (N) pollution from agricultural nonpoint sources. Due to variability in environmental conditions like temperature and discharge, it is challenging to achieve consistent treatment effectiveness with these passive systems. To improve nitrate (NO3–) load reductions in a field-scale WBR in New York State during cool spring weather, we designed a system for controlled exogenous carbon (C) dosing, allowing rates of C dosing to respond in real time to changing discharge and NO3– concentrations. Treatment efficiencies for NO3–, acetate mass balances, and other bioreactor properties were monitored from April 5 to June 10, 2023. Biostimulation with 7.5 mg C/L acetate (assuming complete mixing of injected acetate with bioreactor pore water) increased NO3– removal rates up to 5-fold compared to a model-based scenario of baseline bioreactor performance, and were as high as 0.4 mg NO3––N L–1 h–1 while water temperatures were <12 °C. Increasing acetate concentrations beyond 7.5 mg C/L did not confer a clear improvement in NO3– removal rates. Cumulative N load reductions increased from 11.3% under the baseline scenario without C dosing to 24.1% with C dosing. The mass ratio of metabolized C to additional N removal was 2.5:1, although the total dosed C/N mass ratio was 5.1:1 due to incomplete acetate utilization in the reactor. We found evidence that C dosing could enhance the future release of dissolved organic N (DON) and dissolved organic C related to biofilm sloughing. The expense of acetate, with a cost efficiency of 86 USD/kg N, was the main cost driver of the real-time control approach. Our results demonstrate the potential of real-time control of C dosing to meaningfully improve nonpoint source N removal during cool spring conditions but also highlight opportunities for methods to improve acetate utilization efficiencies in order to improve the overall cost-effectiveness of the approach.
more »
« less
- Award ID(s):
- 2237947
- PAR ID:
- 10525759
- Editor(s):
- NA
- Publisher / Repository:
- NA
- Date Published:
- Journal Name:
- ACS ES&T Engineering
- Volume:
- 4
- Issue:
- 6
- ISSN:
- 2690-0645
- Page Range / eLocation ID:
- 1433 to 1443
- Subject(s) / Keyword(s):
- woodchip bioreactor nitrate
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
This study evaluated the performance of sequencing batch reactors (SBR) in the fate and transport of dissolved organic nitrogen (DON) using a blend of wastewater and landfill leachate. Most nitrogen removal methods concentrate on inorganic nitrogen, whereas some biological processes add DON to the effluent. Two reactors were introduced with wastewater and landfill leachate of high and low organic carbon and compared them to a reactor without leachate. DON transformation, characterization, and microbial community dispersion were examined to understand the effects of leachate-induced effluent DON on the biological nitrogen removal process. The ammonium removal efficiencies were found 96, 97, and 98%; COD removal efficiencies were 75, 59, and 63%; and total nitrogen (TN) removal efficiencies were 83, 86, and 88%, for R1, R2, and R3, respectively. The effluent nitrate concentrations were found 1.67 ± 0.89 (R1), 3.05 ± 2.08 (R2), and 1.31 ± 1.30 (R3) mg/L and DON went down from 9.67 ± 2.5 to 6.02 ± 2.8 mg/L (R1), 9.29 ± 3.4 to 7.49 ± 3.6 mg/L (R2), and 3.59 ± 1.6 to 2.08 ± 1.1 mg/L (R3). Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and excitation-emission matrices (EEMs) with parallel factor (PARAFAC) analysis were used to characterize DON. Microbial community analysis was also conducted. Leachate-induced DON discharge's environmental effects were assessed using in-situ aquatic ecosystem algal bioassay. SBR system removed most inorganic nitrogen species and a small amount of leachate-induced DON. The study emphasizes the need for independent investigations to assess their effects on receiving water bodies.more » « less
-
null (Ed.)The increased environmental abundance of anthropogenic reactive nitrogen species (Nr = ammonium [NH4+], nitrite [NO2−] and nitrate [NO3−]) may increase atmospheric nitrous oxide (N2O) concentrations, and thus global warming and stratospheric ozone depletion. Nitrogen cycling and N2O production, reduction, and emissions could be amplified in carbonate karst aquifers because of their extensive global range, susceptibility to nitrogen contamination, and groundwater-surface water mixing that varies redox conditions of the aquifer. The magnitude of N2O cycling in karst aquifers is poorly known, however, and thus we sampled thirteen springs discharging from the karstic Upper Floridan Aquifer (UFA) to evaluate N2O cycling. The springs can be separated into three groups based on variations in subsurface residence times, differences in surface–groundwater interactions, and variable dissolved organic carbon (DOC) and dissolved oxygen (DO) concentrations. These springs are oxic to sub-oxic and have NO3− concentrations that range from < 0.1 to 4.2 mg N-NO3−/L and DOC concentrations that range from < 0.1 to 50 mg C/L. Maximum spring water N2O concentrations are 3.85 μg N-N2O/L or ~ 12 times greater than water equilibrated with atmospheric N2O. The highest N2O concentrations correspond with the lowest NO3− concentrations. Where recharge water has residence times of a few days, partial denitrification to N2O occurs, while complete denitrification to N2 is more prominent in springs with longer subsurface residence times. Springs with short residence times have groundwater emission factors greater than the global average of 0.0060, reflecting N2O production, whereas springs with residence times of months to years have groundwater emission factors less than the global average. These findings imply that N2O cycling in karst aquifers depends on DOC and DO concentrations in recharged surface water and subsequent time available for N processing in the subsurface.more » « less
-
null (Ed.)The increased environmental abundance of anthropogenic reactive nitrogen species (Nr = ammonium [NH4+], nitrite [NO2 ] and nitrate [NO3 ]) may increase atmospheric nitrous oxide (N2O) concentrations, and thus global warming and stratospheric ozone depletion. Nitrogen cycling and N2O production, reduction, and emissions could be amplified in carbonate karst aquifers because of their extensive global range, susceptibility to nitrogen contamination, and groundwater-surface water mixing that varies redox conditions of the aquifer. The magnitude of N2O cycling in karst aquifers is poorly known, however, and thus we sampled thirteen springs discharging from the karstic Upper Floridan Aquifer (UFA) to evaluate N2O cycling. The springs can be separated into three groups based on variations in subsurface residence times, differences in surface–groundwater interactions, and variable dissolved organic carbon (DOC) and dissolved oxygen (DO) concentrations. These springs are oxic to sub-oxic and have NO3 concentrations that range from < 0.1 to 4.2 mg N-NO3 /L and DOC concentrations that range from < 0.1 to 50 mg C/L. Maximum spring water N2O concentrations are 3.85 μg N-N2O/L or ~ 12 times greater than water equilibrated with atmospheric N2O. The highest N2O concentrations correspond with the lowest NO3 concentrations. Where recharge water has residence times of a few days, partial denitrification to N2O occurs, while complete denitrification to N2 is more prominent in springs with longer subsurface residence times. Springs with short residence times have groundwater emission factors greater than the global average of 0.0060, reflecting N2O production, whereas springs with residence times of months to years have groundwater emission factors less than the global average. These findings imply that N2O cycling in karst aquifers depends on DOC and DO concentrations in recharged surface water and subsequent time available for N processing in the subsurface.more » « less
-
Nitrogen and phosphorus contained in stormwater runoff contaminate both surface and groundwaters, causing problems for natural aquatic systems and human health. Pervious concrete specifically designed for pollutant removal, otherwise known as permeable reactive concrete (PRC), may be used as a novel component of existing infrastructure to remove nutrients from runoff. This research compares the removal and retention of dissolved, inorganic nitrate-nitrogen (NO3-N) and orthophosphate-phosphorus (PO4-P) for three PRC mixtures. The control PRC was ordinary portland cement (OPC) and was compared against other mixtures containing 25% replacement with Class C fly ash or with drinking water treatment residual waste (DWTR). Concrete specimens were jar-tested for 72 h in three different concentrations of nitrate or phosphate. The control mixture removed 60% of NO3-N and more than 80% PO4-P, and the fly ash mixture removed up to 39% of NO3-N and more than 91% PO4-P. The DWTR mixture leached NO3-N while removing more than 80% PO4-P. Linear isotherms were determined for the range of nutrient concentrations tested. Column leach tests were conducted on specimens after initial jar testing and used as an indication of removal permanence. Inorganic removal mechanisms were investigated, including crystallographic substitution, adsorption, and physical solute filtering in cement pore space. Results indicate PRC can be one of the leading methods to remove nitrate from surface waters and is as efficient as other methods for orthophosphate removal.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acsestengg.4c00020
