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Cold Plasma as an Innovative Tool for Wastewater Pre-Treatment and Post-Treatment at Ravda WWTP: Bioindication by Means of Microbial Metabolic Potential
 
 
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Environments
Volume 13
Issue 1
10.3390/environments13010015
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This is an early access version, the complete PDF, HTML, and XML versions will be available soon.
Article

Plasma-Assisted Valorization of Liquid Digestate from the Ravda Wastewater Treatment Plant: Microbiological and Chemical Aspects

by
Yoana Sofronieva
1,2,*,
Irina Schneider
1,2,
Yovana Todorova
1,2,
Nora Dinova
1,2,
Magdalena Bogdanova
1,2,
Ivaylo Yotinov
1,2,
Todor Bogdanov
2,3,
Evgenia Benova
2 and
Yana Topalova
1,2
1
Faculty of Biology, Sofia University “St. Kliment Ohridski”, 8 Dragan Tzankov Blvd., 1164 Sofia, Bulgaria
2
Center of Competence “Clean Technologies for Sustainable Environment—Water, Waste, Energy for Circular Economy”, 1a James Bourchier Blvd., 1164 Sofia, Bulgaria
3
Department of Medical Physics and Biophysics, Medical University of Sofia, 1431 Sofia, Bulgaria
*
Author to whom correspondence should be addressed.
Environments 2026, 13(1), 15; https://doi.org/10.3390/environments13010015 (registering DOI)
Submission received: 19 November 2025 / Revised: 23 December 2025 / Accepted: 25 December 2025 / Published: 29 December 2025
(This article belongs to the Special Issue Advances in Wastewater Bio-Management: Microbial Community Relationships, Monitoring and Assessment)
Versions Notes

Abstract

Anaerobic digestion of sewage sludge generates large volumes of liquid digestate, which is often returned to wastewater treatment plants (WWTPs) due to the presence of pathogens and pollutants, limiting its safe reuse in agriculture. This study evaluated plasma-based post-treatment as a method to improve the sanitary quality of digestate. The liquid phase from mesophilic digesters at WWTP “Ravda” was treated for 5 min using two plasma sources, the β-device and the Surfaguide WR340 (SAIREM, Décines-Charpieu, France). Disinfection effectiveness was assessed for aerobic and anaerobic heterotrophs, fecal and total coliforms, Escherichia coli, Salmonella sp., and Clostridium sp. Physicochemical parameters measured included pH, COD, NH4+, NO2−, NO3−, and PO43−. The β-device achieved partial disinfection, with reductions ranging from 16.3% to 89.8% for different microbial groups, whereas coliforms persisted and Clostridium sp. reappeared. The Surfaguide produced near-complete disinfection, eliminating coliforms, E. coli, Salmonella sp., and Clostridium sp., and markedly reduced microbial diversity. Both treatments caused slight pH increases, COD decreases, release of NH4+ and PO43−, and rises in NO2− and NO3−. Plasma-based disinfection, particularly with the Surfaguide, effectively improves the sanitary quality of the digestate and modifies its chemical properties, supporting the potential for sustainable digestate valorization and its safe reuse in agriculture.
Keywords: digestate; plasma; wastewater treatment; agriculture; pathogen disinfection digestate; plasma; wastewater treatment; agriculture; pathogen disinfection

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MDPI and ACS Style

Sofronieva, Y.; Schneider, I.; Todorova, Y.; Dinova, N.; Bogdanova, M.; Yotinov, I.; Bogdanov, T.; Benova, E.; Topalova, Y. Plasma-Assisted Valorization of Liquid Digestate from the Ravda Wastewater Treatment Plant: Microbiological and Chemical Aspects. Environments 2026, 13, 15. https://doi.org/10.3390/environments13010015

AMA Style

Sofronieva Y, Schneider I, Todorova Y, Dinova N, Bogdanova M, Yotinov I, Bogdanov T, Benova E, Topalova Y. Plasma-Assisted Valorization of Liquid Digestate from the Ravda Wastewater Treatment Plant: Microbiological and Chemical Aspects. Environments. 2026; 13(1):15. https://doi.org/10.3390/environments13010015

Chicago/Turabian Style

Sofronieva, Yoana, Irina Schneider, Yovana Todorova, Nora Dinova, Magdalena Bogdanova, Ivaylo Yotinov, Todor Bogdanov, Evgenia Benova, and Yana Topalova. 2026. "Plasma-Assisted Valorization of Liquid Digestate from the Ravda Wastewater Treatment Plant: Microbiological and Chemical Aspects" Environments 13, no. 1: 15. https://doi.org/10.3390/environments13010015

APA Style

Sofronieva, Y., Schneider, I., Todorova, Y., Dinova, N., Bogdanova, M., Yotinov, I., Bogdanov, T., Benova, E., & Topalova, Y. (2026). Plasma-Assisted Valorization of Liquid Digestate from the Ravda Wastewater Treatment Plant: Microbiological and Chemical Aspects. Environments, 13(1), 15. https://doi.org/10.3390/environments13010015

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