Abstract Cold atmospheric plasma (CAP) is emerging as an environmentally friendly disinfection technology, but most plasma-liquid systems remain confined to millilitre‑scale volumes, limiting their applicability as bioprocesses for water treatment. Here, we designed and evaluated a bubble‑enhanced dielectric barrier discharge reactor, the Spiral Plasma Aeration Reactor Column (SPARC), as an environmental technology approach for litre‑scale inactivation of model bacteria in water. Direct CAP exposure achieved rapid, near‑complete inactivation of Escherichia coli and Bacillus subtilis in 200 µL, but performance decreased sharply at 100 mL, confirming strong volume dependence under surface‑limited plasma-liquid contact. Coupling CAP with gas bubbling (2 L·min−1) in SPARC markedly enhanced inactivation at 250–500 mL, achieving approximately 2–3 log reductions (≥ 99–99.9%) for E. coli and B. subtilis within 60 min, whereas non-aerated CAP remained below ≈0.8-log (≤ 60%) reduction under identical conditions. At 1 L under high initial loads (~ 106–107 CFU·100 mL−1), bubble-assisted CAP yielded ~ 4-log inactivation of E. coli and 3–3.5-log reduction of B. subtilis, including continued post-treatment inactivation consistent with plasma-activated water effects. In a protein‑rich organic matrix, early‑stage inactivation was attenuated, but SPARC still achieved ≈2–3‑log reductions, indicating robust yet matrix‑sensitive performance under wastewater‑like conditions. At fixed electrical input (34.5 W), specific energy consumption ranged from 60 kWh·m−3 (250 mL, 30 min, > 99% E. coli inactivation) to 30 kWh·m−3 (1 L, 60 min, ≈4‑log E. coli inactivation), corresponding to ≈7.5 kWh·log₁₀−1·m−3. These results position bubble‑assisted CAP as a promising environmental biotechnology and bioprocess platform for water disinfection and emphasise the central role of reactor and contactor design in determining microbial efficacy and energy demand. Key points • Direct CAP exposure in microlitre-scale water (200 µL) produces rapid ≥ 3-log₁₀ (> 99.9%) inactivation of E. coli and B. subtilis, but performance deteriorates at 100 mL, confirming strong volume dependence under surface-limited plasma-liquid contact. • The bubble-enhanced DBD reactor SPARC, operated at 250–500 mL, achieves ≈2–3-log₁₀ (≥ 99–99.9%) bacterial reductions within 60 min, whereas non-aerated CAP under identical electrical conditions generally remains below ≈0.8-log₁₀ (≤ 60%) reduction. • At 1 L, bubble-assisted SPARC attains ~ 4-log₁₀ (E. coli) and 3–3.5-log₁₀ (B. subtilis) inactivation under high initial loads, with specific energy consumption between 30 and 60 kWh·m−3 (≈7.5 kWh·log₁₀−1·m−3) for the laboratory prototype.

Bubble-enhanced cold plasma improves microbial inactivation in water under scalable conditions

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2026年8月3日

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José Gonçalves,
João Pequeno,
Jure Žigon,
Tom Koritnik,
Filipe Ferreira da Silva,
Davor Kržišnik,
Marija Trkov,
Israel Diaz,
Elisa Rodriguez,
Sebastian Dahle,
Andrej Steyer,
Rita Maurício,
Graça Martinho

摘要

Abstract

Cold atmospheric plasma (CAP) is emerging as an environmentally friendly disinfection technology, but most plasma-liquid systems remain confined to millilitre‑scale volumes, limiting their applicability as bioprocesses for water treatment. Here, we designed and evaluated a bubble‑enhanced dielectric barrier discharge reactor, the Spiral Plasma Aeration Reactor Column (SPARC), as an environmental technology approach for litre‑scale inactivation of model bacteria in water. Direct CAP exposure achieved rapid, near‑complete inactivation of Escherichia coli and Bacillus subtilis in 200 µL, but performance decreased sharply at 100 mL, confirming strong volume dependence under surface‑limited plasma-liquid contact. Coupling CAP with gas bubbling (2 L·min⁻¹) in SPARC markedly enhanced inactivation at 250–500 mL, achieving approximately 2–3 log reductions (≥ 99–99.9%) for E. coli and B. subtilis within 60 min, whereas non-aerated CAP remained below ≈0.8-log (≤ 60%) reduction under identical conditions. At 1 L under high initial loads (~ 10⁶–10⁷ CFU·100 mL⁻¹), bubble-assisted CAP yielded ~ 4-log inactivation of E. coli and 3–3.5-log reduction of B. subtilis, including continued post-treatment inactivation consistent with plasma-activated water effects. In a protein‑rich organic matrix, early‑stage inactivation was attenuated, but SPARC still achieved ≈2–3‑log reductions, indicating robust yet matrix‑sensitive performance under wastewater‑like conditions. At fixed electrical input (34.5 W), specific energy consumption ranged from 60 kWh·m⁻³ (250 mL, 30 min, > 99% E. coli inactivation) to 30 kWh·m⁻³ (1 L, 60 min, ≈4‑log E. coli inactivation), corresponding to ≈7.5 kWh·log₁₀⁻¹·m⁻³. These results position bubble‑assisted CAP as a promising environmental biotechnology and bioprocess platform for water disinfection and emphasise the central role of reactor and contactor design in determining microbial efficacy and energy demand.

Key points

• Direct CAP exposure in microlitre-scale water (200 µL) produces rapid ≥ 3-log₁₀ (> 99.9%) inactivation of E. coli and B. subtilis, but performance deteriorates at 100 mL, confirming strong volume dependence under surface-limited plasma-liquid contact.

• The bubble-enhanced DBD reactor SPARC, operated at 250–500 mL, achieves ≈2–3-log₁₀ (≥ 99–99.9%) bacterial reductions within 60 min, whereas non-aerated CAP under identical electrical conditions generally remains below ≈0.8-log₁₀ (≤ 60%) reduction.

• At 1 L, bubble-assisted SPARC attains ~ 4-log₁₀ (E. coli) and 3–3.5-log₁₀ (B. subtilis) inactivation under high initial loads, with specific energy consumption between 30 and 60 kWh·m⁻³ (≈7.5 kWh·log₁₀⁻¹·m⁻³) for the laboratory prototype.