📄 chemistry

Ciprofloxacin remediation by photolysis, TiO₂ photocatalysis and high-voltage electrical discharges: kinetics, energy demand and ecotoxicity

This study demonstrates that TiO₂ photocatalysis is the most efficient advanced oxidation process for ciprofloxacin remediation, offering superior degradation kinetics and energy efficiency compared to photolysis and high-voltage electrical discharges, while highlighting that short-duration treatments can transiently increase ecotoxicity due to the formation of more toxic intermediate byproducts.

Original authors: Cristèle DELSART, Maryline PFLIEGER, Urška LAVRENČIČ ŠTANGAR, Nadia BOUSSETTA, Marwa BRAHIM, Aurélien TRIVELLA

Published 2026-07-08

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Cristèle DELSART, Maryline PFLIEGER, Urška LAVRENČIČ ŠTANGAR, Nadia BOUSSETTA, Marwa BRAHIM, Aurélien TRIVELLA

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the antibiotic Ciprofloxacin (CIP) as a stubborn, invisible stain in a glass of water. It's a powerful medicine for humans and animals, but when it ends up in our rivers and lakes, it acts like a toxic ghost, harming fish, plants, and even encouraging superbugs.

This study acts like a "cleaning contest" to see which of three high-tech methods can scrub this stain away the fastest, cheapest, and safest. The three contestants are:

Photolysis (PL): Just shining a bright UV light on the water. Think of this as using a magnifying glass to burn the stain.
TiO₂ Photocatalysis (PC): Shining that same UV light, but with a special "magic dust" (Titanium Dioxide) added to the water. This is like using the magnifying glass plus a super-charged sponge that actively eats the stain.
High-Voltage Electrical Discharges (HVED): Zapping the water with powerful electrical sparks, creating a mini-plasma storm. This is like using a lightning bolt to blast the stain apart.

Here is what the researchers found, broken down simply:

1. The Speed Race (Kinetics)

If you set a timer to see how fast each method destroys the Ciprofloxacin:

The Winner: The Photocatalyst (PC) was the clear champion. It broke down half of the antibiotic in just 2.6 minutes.
The Runners-Up: The plain light (PL) and the electrical zaps (HVED) were much slower, taking about 14 minutes to achieve the same result.
The Analogy: If the antibiotic were a wall, Photocatalysis was a sledgehammer, while the other two were just using a hammer and a chisel.

2. The "Deep Clean" (Mineralization)

Breaking the antibiotic down is good, but the real goal is to turn it into harmless stuff (like water and carbon dioxide) so nothing toxic is left behind. This is called "mineralization."

The Winner: Again, Photocatalysis (PC) won. It cleaned up the "trash" (organic carbon) 25 times faster than the plain light and 2 times faster than the electrical zaps.
The Loser: The plain light (PL) was very poor at this. It broke the antibiotic apart but left behind a lot of messy, half-destroyed pieces that were still organic waste.
The Analogy: Photolysis was like shredding a document; the pieces are smaller, but they are still paper. Photocatalysis was like burning the document to ash; it's gone completely.

3. The Energy Bill

How much electricity did it take to clean the water?

The Winner: Photocatalysis (PC) was the most energy-efficient. To clean 90% of the antibiotic, it used the least power.
The Losers: The plain light (PL) used 4.5 times more energy than the winner, and the electrical zaps (HVED) used 2.2 times more.
The Catch: Even though Photocatalysis was the "cheapest" of the three, the authors note that the total energy cost is still quite high compared to older, traditional methods like ozonation. It's the best of the new options, but not exactly "free."

4. The Toxicity Surprise (The "Worse Before Better" Effect)

This is the most surprising part of the story. The researchers tested the water after cleaning it on three different living things:

Tiny Bacteria (Vibrio fischeri): These glow in the dark. If the water is toxic, they stop glowing.
Water Fleas (Daphnia magna): Tiny shrimp-like creatures. If the water is toxic, they stop moving or die.
White Clover Plants (Trifolium repens): Seeds trying to grow roots.

The Shock: In the beginning, as the methods started breaking down the antibiotic, the water actually became more toxic than the original dirty water!

Why? When the antibiotic is smashed apart, it creates "intermediate" pieces (degradation products). For a short time, these pieces are more poisonous to the water fleas and glowing bacteria than the original medicine was.
The Difference: The electrical zaps (HVED) seemed to create the most toxic by-products for the water fleas. The plants (Clover) were much tougher and didn't react as strongly as the water animals did.
The Hope: The study suggests that if you keep treating the water long enough, these toxic pieces eventually get broken down further into harmless substances, and the toxicity goes down. But if you stop too early, you might be left with water that is worse than you started with.

The Bottom Line

If you want to clean Ciprofloxacin out of water:

Photocatalysis (Light + Magic Dust) is the best overall. It's the fastest, cleans the deepest, and uses the least energy of the three.
The Warning: You have to be careful not to stop the process too soon. If you do, you might leave behind "toxic fragments" that hurt aquatic life more than the original drug.
The Reality Check: While this new method is great, it still costs a lot of electricity compared to old-school cleaning, so it's not ready to be used everywhere just yet without more research.

Technical Summary: Ciprofloxacin Remediation by Photolysis, TiO₂ Photocatalysis, and High-Voltage Electrical Discharges

Problem Statement
Ciprofloxacin (CIP), a widely used fluoroquinolone antibiotic, persists in aquatic environments due to incomplete metabolism and uncontrolled release from human and veterinary sources. Its accumulation poses risks to ecosystems, including the disruption of microbial communities, the development of antibiotic resistance, and direct toxicity to non-target organisms. Conventional wastewater treatment methods often fail to fully degrade CIP, merely transferring pollutants between phases or generating toxic by-products. Consequently, there is a critical need for advanced oxidation processes (AOPs) capable of achieving genuine degradation and mineralization while minimizing energy costs and ecological toxicity.

Methodology
This study conducted a comparative evaluation of three AOPs for CIP remediation in synthetic freshwater:

Photolysis (PL): UV-A irradiation using low-pressure mercury lamps.
TiO₂ Photocatalysis (PC): UV-A irradiation combined with immobilized TiO₂ (P25/PC500 mixture) films.
High-Voltage Electrical Discharges (HVED): Pulsed electrical discharges generating plasma in the aqueous phase.

The experimental design focused on three primary metrics:

Kinetics and Mineralization: Degradation rates were monitored via HPLC. Mineralization was assessed by tracking Non-Purgeable Organic Carbon (NPOC) removal and the formation of fluoride and nitrate ions (indicative of defluorination and nitrogen mineralization).
Energy Efficiency: Electrical energy consumption ( $E_c$ ) was calculated based on power, time, and treated volume to determine the energy required for 90% degradation.
Ecotoxicity: The toxicity of treated samples was evaluated using three distinct organisms representing different trophic levels: Vibrio fischeri (bioluminescent bacteria), Daphnia magna (planktonic crustacean), and Trifolium repens (white clover).

Key Results

Degradation Kinetics: All three processes followed apparent first-order kinetics. TiO₂ Photocatalysis (PC) was the most effective, with a half-life ( $t_{1/2}$ ) of 2.6 minutes. This was significantly faster than Photolysis (PL, 14.1 min) and HVED (13.9 min).
Mineralization: PC demonstrated superior mineralization capabilities. The time required to reduce NPOC by 50% was 39.2 minutes for PC, compared to 81.5 minutes for HVED and 990.2 minutes for PL. PC was 25 times faster than PL and 2 times faster than HVED in mineralization. Nitrate ion analysis confirmed that PC achieved higher mineralization levels at extended reaction times, whereas PL showed negligible nitrate formation.
Mechanistic Insights: Fluoride ion monitoring indicated that nucleophilic substitution was the dominant degradation pathway for PL and PC, whereas HVED relied less on this mechanism.
Energy Consumption: To achieve 90% CIP degradation, PC required the least energy. PL consumed 4.5 times more energy than PC, and HVED consumed 2.2 times more.
Ecotoxicity Evolution: Short-duration treatments (15–30 minutes) across all methods resulted in increased toxicity compared to the parent CIP molecule.
- Vibrio fischeri and Daphnia magna showed significant inhibition and immobilization, respectively, suggesting that intermediate degradation products were more toxic than the original antibiotic.
- Trifolium repens exhibited lower sensitivity to the treated samples compared to the aquatic organisms, with germination and root growth effects being less pronounced.
- HVED treatments generally induced higher toxicity levels in aquatic organisms compared to the photochemical processes.

Significance and Claims
The authors conclude that TiO₂ photocatalysis is the superior treatment method among the three evaluated for CIP remediation in synthetic freshwater. It offers the fastest degradation kinetics, the most efficient mineralization, and the lowest electrical energy demand. However, the study highlights a critical ecological nuance: rapid degradation does not immediately equate to reduced toxicity. Short-term treatments can generate transient intermediates that are more toxic to aquatic life than the parent compound.

The paper asserts that while PC is the most efficient single process tested, its energy consumption remains substantial for large-scale application compared to conventional ozonation. The authors emphasize that a comprehensive assessment of water treatment technologies must consider not only removal efficiency but also energy costs and the evolving ecotoxicity of degradation by-products. They suggest that future work should focus on identifying specific degradation structures and potentially combining processes to further enhance degradation rates and mineralization while mitigating the formation of toxic intermediates.

1. The Speed Race (Kinetics)

2. The "Deep Clean" (Mineralization)

3. The Energy Bill

4. The Toxicity Surprise (The "Worse Before Better" Effect)

The Bottom Line

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