Forschungsdaten – Titel und Zusammenfassungen von Publikationen, extrahierte Daten und Katalogeinträge – erscheinen in ihrer Originalsprache Englisch.
Simulation tests of in situ groundwater denitrification with aquifer-buried biocathodes
Daniele Cecconet, Silvia Bolognesi, Arianna Callegari, Andrea G. Capodaglio
KI-Zusammenfassung
78 % KonfidenzThis study evaluated buried biocathodes for in situ groundwater denitrification in sand and gravel media, comparing power-supply and potentiostat control. Nitrate removal was 20–36% slower in sand/gravel than in unstirred control, and N₂O accumulated in all buried configurations. Gravel outperformed sand due to lower packing density. Power-supply operation adapted cathode potential dynamically and achieved better total nitrogen removal than fixed potentiostat control, suggesting that electrode potential flexibility is critical for complete denitrification in porous media.
Zentrale Erkenntnisse
Zielkonflikt Buried biocathodes in sand and gravel showed 20–36% lower NO₃⁻-N removal rates than control (50.06 vs 32.04–36.04 gNO₃⁻-N m⁻² d⁻¹ in BES-PS), attributed to lack of recirculation limiting biofilm–substrate contact.
Was heißt das. In situ buried electrode designs must incorporate active recirculation or electro-kinetic mixing to maintain removal rates; passive burial alone is insufficient.
Mechanismus N₂O accumulated to >92% of non-nitrate total nitrogen in all tests, indicating incomplete reduction of N₂O to N₂ regardless of medium type, whereas NO₂⁻ was nearly absent.
Was heißt das. Operators should monitor and mitigate N₂O emissions; the rate-limiting step is N₂O→N₂ reduction, not earlier denitrification steps, suggesting need for cathode potential optimization or biofilm enrichment for N₂O reductase activity.
Zielkonflikt Power-supply operation (BES-PS) achieved 38–76% higher TN removal rates than potentiostat control (BES-Pot) in sand and gravel, despite similar NO₃⁻ removal, because cathode potential adapted dynamically to changing N-form composition.
Was heißt das. Fixed-potential control is suboptimal for denitrification in heterogeneous media; adaptive or variable-potential strategies should be prioritized to track shifting redox requirements as intermediates accumulate.
Schwellenwert Gravel (3 mm, lower packing) outperformed sand (0.6 mm, higher packing) in both BES-PS and BES-Pot, with statistically significant differences (p<0.05) in TN removal rates, particularly evident in TN removal.
Was heißt das. Aquifer-scale deployment should prioritize coarser porous media or engineered void space to minimize mass-transfer resistance; fine sand burial is contraindicated.
Leistung Energy consumption (SECTN) increased when intermediate N-forms accumulated in sand/gravel setups compared to control, reflecting lower TN removal efficiency despite similar or lower SECN in BES-Pot.
Was heißt das. Incomplete denitrification penalizes energy efficiency metrics; operators must balance power input against complete N removal to avoid paying for partial treatment.
Widersprüche1
Nur Konflikte, die die Publikation selbst zeigt, jeweils am Text geprüft.
Innerhalb der Publikation BES-Pot showed lower SECN in sand/gravel than control, opposite to BES-PS trend and prior author experience
Eine SeiteBES-PS: SECN increases with sand/gravel (higher energy per kg NO₃⁻-N removed)
“In the case of BES-PS, it is possible to observe how the energy consumption in terms of SECN (Fig. 5A), and SECTN (Fig. 5B) is lower in the control reactor (thus in absence of sand/gravel)”
Andere SeiteBES-Pot: SECN decreases with sand/gravel (lower energy per kg NO₃⁻-N removed)
“Surprisingly, in case of BES-Pot, the values of and SECN are lower in the presence of sand and gravel fillers than in the absence of a medium, with a trend exactly contrary to that of the BES-PS system. This pattern is in contrast with previ”
Einordnung der Autoren. Authors acknowledge the contradiction but do not fully resolve it; likely due to different current/power dynamics under potentiostatic vs galvanostatic control, but mechanism remains unclear.
Ansatzpunkte6
Konkrete Lücken in dieser Publikation, jeweils mit einem Experiment, das sie schließen würde.
Hoch No measurement of N₂O or NO₂⁻ concentration profiles over time; only day-5 endpoint reported. Kinetics of intermediate accumulation unknown.
N₂O >92% of non-nitrate TN at day 5 in all tests, but no time-series data on when/how it accumulates. Understanding whether N₂O forms early and plateaus or continuously increases would guide cathode potential timing strategies.
Versuch. Daily sampling for NO₃⁻-N, NO₂⁻-N, and N₂O-N (via headspace gas chromatography or dissolved N₂O probe) in sand/gravel setups to map denitrification pathway kinetics.
Hoch No variation of applied voltage or cathode potential in BES-PS or BES-Pot; only one voltage (1.0 V) and one potential (-0.303 V vs SHE) tested.
BES-PS outperformed BES-Pot, but the paper does not test whether a different fixed potential in BES-Pot would match or exceed BES-PS performance. The optimal cathode potential for complete N₂O reduction in buried media is unknown.
Versuch. Potentiostatic sweep of cathode potential from -0.2 to -0.6 V vs SHE in sand/gravel setups, measuring NO₃⁻-N, NO₂⁻-N, N₂O-N removal rates and SECTN at each potential.
Mittel No measurement of dissolved oxygen, pH, or ionic strength in cathode chamber during operation; only initial and final pH/conductivity reported.
Mass-transfer limitation and electro-kinetic effects depend on local pH and conductivity gradients. Lack of spatial/temporal profiles limits mechanistic understanding of why gravel outperforms sand.
Versuch. Continuous or daily monitoring of cathode chamber pH, DO, and conductivity; optional: microelectrode profiling of potential and pH within sand/gravel bed.
Mittel No test of intermediate recirculation rates or flow velocities; control used magnetic stirring but no quantification of mixing intensity or residence time distribution.
Paper attributes 20–36% performance loss to 'lack of recirculation' but does not define the recirculation rate needed to recover performance. Unclear whether low-rate pumping or diffusion-only operation would suffice.
Versuch. Buried electrode tests with variable recirculation rates (0, 0.1, 0.5, 1.0 mL min⁻¹) and measure NO₃⁻-N, TN removal rates and SECTN.
Mittel No variation of initial NO₃⁻-N concentration or C/N ratio; only one feed composition (0.216 g L⁻¹ KNO₃ ≈ 48.6 mg NO₃⁻-N L⁻¹) tested.
Groundwater NO₃⁻ concentrations vary widely (10–100+ mg L⁻¹). Unknown whether N₂O accumulation is concentration-dependent or whether higher/lower loads shift the denitrification pathway.
Versuch. Batch tests with NO₃⁻-N feed ranging 25–200 mg L⁻¹ in sand/gravel setups; measure NO₃⁻-N, NO₂⁻-N, N₂O-N removal rates and SECTN.
Mittel No characterization of biofilm composition, denitrifying enzyme activity (Nar, Nir, Nor, Nos), or microbial community structure on buried electrodes.
N₂O accumulation suggests low Nos (N₂O reductase) activity or abundance. Biofilm composition may differ between sand/gravel due to packing and oxygen gradients, but no molecular data provided.
Versuch. 16S rRNA gene sequencing and qPCR of denitrification genes (narG, nirS, norB, nosZ) on electrode biofilm from sand vs gravel setups; correlate with N₂O accumulation.
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Zusammenfassung
Bioelectrochemical systems (BES) application was proposed for a variety of specific uses, due to these systems' characteristics: electrodes can act as virtually inexhaustible electron acceptors/donors, offering a growth-support surface for microorganisms, and stimulating naturally-occurring microbial degradation activities. In situ, groundwater denitrification therefore seems to be a potential candidate for their use. In this study, buried biocathodes were operated in laboratory settings for the simulation of in situ groundwater denitrification. Two alternative configurations were tested: biocathode buried in sand, and biocathode buried in gravel. A control test with a biocathode in absence of sand/gravel was also performed. In all the cases, biocathodes were driven by power supply or potentiostat to guarantee a steady electron flux to the cathode. The presence of sand and gravel strongly influenced the denitrification process: in both configurations, accumulation of intermediate N-forms was detected, suggesting that the denitrification process was only partially achieved. In addition, a significant decrease (in the 20-36% range) in nitrate removal rates was measured in sand and gravel setups compared to the control reactor; this issue could be attributed to lack of recirculation that limited contact between substrate and electrode-adherent biofilm. Biocathodes buried in gravel obtained better results than those buried in sand due to the lower packing of the medium. The results of this study suggest that, in order to achieve successful in situ treatment, special design of submerged-biocathodic BESs is necessary.
Schlagwörter
Kennungen
- PubMed
- 31388574
- Zeitschrift
- Heliyon
- Jahr
- 2019
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