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Multimodal biofilm control strategies for spacecraft water systems: Evaluating coatings, nutrient removal, and biocides for improved sustainability

Madelyn K. Mettler

Madelyn K. Mettler

  • Center for Biofilm Engineering, Montana State UniversityBozeman, USA
  • Department of Chemical and Biological Engineering, Montana State UniversityBozeman, USA
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Mettler, Madelyn K.
 y 
Brent M. Peyton

Brent M. Peyton

  • Center for Biofilm Engineering, Montana State UniversityBozeman, USA
  • Department of Chemical and Biological Engineering, Montana State UniversityBozeman, USA
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Peyton, Brent M.
  
14 sept 2025
Multimodal biofilm control strategies for spacecraft water systems: Evaluating coatings, nutrient removal, and biocides for improved sustainability's Cover Image
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Categoría del artículo: Research Note
Publicado en línea: 14 sept 2025
Páginas: 75 - 89
DOI: https://doi.org/10.2478/gsr-2025-0005
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© 2025 Madelyn K. Mettler et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Figure 1.

Coupons for sampling biofilm accumulation in the CDC reactor.
Coupons for sampling biofilm accumulation in the CDC reactor.

Figure 2.

Biofilm control methods used in each of the eight iterations of experiments. The empty section in the upper left represents the base condition of unmitigated biofilm growth. This layout is used throughout the results to present data for each experiment.
Biofilm control methods used in each of the eight iterations of experiments. The empty section in the upper left represents the base condition of unmitigated biofilm growth. This layout is used throughout the results to present data for each experiment.

Figure 3.

Viable biofilm density for each of the eight iterations of biofilm control combinations. Continuous flow was initiated on Day 1 after the sample was taken. The grey dashed line represents the limit of detection, y=1.69. Error bars are standard deviation.
Viable biofilm density for each of the eight iterations of biofilm control combinations. Continuous flow was initiated on Day 1 after the sample was taken. The grey dashed line represents the limit of detection, y=1.69. Error bars are standard deviation.

Figure 4.

Viable planktonic cell density for each of the eight iterations of biofilm control combinations. Continuous flow began on Day 1 after the sample was taken. The grey dashed line represents the limit of detection, y=1.3. Error bars represent standard deviation.
Viable planktonic cell density for each of the eight iterations of biofilm control combinations. Continuous flow began on Day 1 after the sample was taken. The grey dashed line represents the limit of detection, y=1.3. Error bars represent standard deviation.

Figure 5.

Confocal images of biofilms accumulated on Inconel CDC coupons seven days after inoculation. Viable bacterial cells are in green, non-viable bacterial cells are in red, and fungal cells are in blue. The fluorescence of the coating can be seen in the three images on the lower right. The scale bar for each image is 30 μm.
Confocal images of biofilms accumulated on Inconel CDC coupons seven days after inoculation. Viable bacterial cells are in green, non-viable bacterial cells are in red, and fungal cells are in blue. The fluorescence of the coating can be seen in the three images on the lower right. The scale bar for each image is 30 μm.

Figure 6.

Confocal images of biofilms accumulated on Teflon CDC coupons seven days after inoculation. Viable bacterial cells are in green, non-viable bacterial cells are in red, and fungal cells are in blue. The fluorescence of the coating can be seen in the three images on the lower right. The scale bar for each image is 30 μm.
Confocal images of biofilms accumulated on Teflon CDC coupons seven days after inoculation. Viable bacterial cells are in green, non-viable bacterial cells are in red, and fungal cells are in blue. The fluorescence of the coating can be seen in the three images on the lower right. The scale bar for each image is 30 μm.

Figure 7.

Side views of tallest segments of biofilms on A) uncoated Inconel, B) coated Inconel, C) uncoated Teflon, and D) coated Teflon grown in full strength medium without biocide dosing. Scale bar in each image is 30 μm.
Side views of tallest segments of biofilms on A) uncoated Inconel, B) coated Inconel, C) uncoated Teflon, and D) coated Teflon grown in full strength medium without biocide dosing. Scale bar in each image is 30 μm.

Recipe for microbial ersatz MTN featuring final component concentrations_

Component Concentration Component Concentration
Propylene Glycol 8.971 μL/L Benzyl Alcohol 6.075 μL/L
Ethanol 44.946 μL/L Diethylphthalate 2.01 μL/L
Acetone 25.799 μL/L Trimethyl Silanol 0.635 μL/L
2-(2-butoxyethoxy) Ethanol 2.356 μL/L Benzothiazole 0.21 μL/L
N, N-Dimethylformamide 1.486 μL/L 2-Ethyl-1-Hexanol 0.48 μL/L
2-Ethoxyethanol 1.303 μL/L Decamethylcyclopentasiloxane 1.03 μL/L
1-Methyl-2-Pyrrolidinone 0.782 μL/L Dodecamethylcyclohexasiloxane 10 μL/L
2-Propanol 0.896 μL/L Octamethylcyclotetrasiloxane 1.02 μL/L
1-Propanol 0.876 μL/L Dimethoxydimethylsilane 35.1 μL/L
4-Ethylmorpholine 2.265 μL/L Calcium Sulfate 1.885 mg/L
Formic Acid 27.489 μL/L Dimethyl Sulfone 0.205 mg/L
Lactic Acid 8.55 μL/L Hexamethylcyclotrisiloxane 1.02 mg/L
Benzoic Acid 3.015 mg/L Monobasic Potassium phosphate 0.835 mg/L
Caprolactam 1.111 mg/L Magnesium chloride hexahydrate 0.397 mg/L
Urea 1.899 mg/L Manganese chloride tetrahydrate 0.319 mg/L
Zinc (II) Acetate dihydrate 1.425 mg/L Ferric chloride 0.129 mg/L
Nickel (II) Acetate tetrahydrate 0.518 mg/L Boric acid 0.268 mg/L
Acetic Acid 32.088 μL/L Cobalt chloride hexahydrate 0.004 mg/L
Ammonium Bicarbonate 101.457 mg/L Sodium molybdate dihydrate 0.016 mg/L
Sodium Fluoride 0.88 mg/L
Potassium Iodide 0.021 mg/L

P-values for statistical significance of individual factors comparing viable cell densities of the accumulated biofilms_ Bolded values represent those less than 0_05, indicating the factor had a significant impact on viable biofilm accumulation of the organism_ Table key: No P: no phosphorus medium; FS: full strength medium; AgF: silver fluoride biocide; Inc: Inconel; Tef: Teflon; SL: Sher-Loxane 800 coating; and Unc: uncoated_

Factor B. contaminans C. mutabilis M. organophilum R. insidiosa R2A (whole biofilm)
Medium (No P < FS) <0.00005 0.0556 <0.00005 <0.00005 <0.00005
Biocide (AgF < No biocide) <0.00005 <0.00005 <0.00005 <0.00005 <0.00005
Material (Inc < Tef) 0.0269 0.0003 0.0002 0.0497 0.9930
Coating (SL < Unc) <0.00005 <0.00005 <0.00005 <0.00005 <0.00005

P-values for statistical significance of individual fixed factors comparing viable cell densities of the planktonic cells in the reactor fluid_ Bolded values are less than 0_05, indicating the factor had a significant impact on the viable planktonic density of the organism_ Table key: No P: no phosphorus medium; FS: full strength medium; AgF: silver fluoride biocide; SL: Sher-Loxane 800 coating; and Unc: uncoated_

Factor B. contaminans C. mutabilis M. organophilum R. insidiosa R2A counts (total planktonic)
Medium (No P < FS) 0.0011 0.9320 0.0013 0.0003 0.0049
Biocide (AgF < No biocide) <0.00005 0.0110 0.0001 <0.00005 <0.00005
Coating (SL < Unc) 0.2827 0.0042 0.0464 <0.00005 0.0009

Selective agar used for microbial enumeration of planktonic and biofilm samples_

Organism enumerated Agar
B. contaminans Pseudomonas isolation agar
C. mutabilis Sabouraud dextrose agar, pH lowered to 3
M. organophilum Methylobacterium agar (Atlas, 2010) with amphotericin B (7.5 μg/mL)
R. insidiosa R2A with chloramphenicol (20 μg/mL) and amphotericin B (7.5 μg/mL)
No isolation, general counts R2A
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