A quiet threat is coursing through our rivers, invisible to the naked eye but potent enough to change the future of medicine. Imagine a rural clinic, somewhere in India, where a child receives a dose of ciprofloxacin to treat a bacterial infection. The child recovers, but the story doesn’t end there. What the body doesn’t absorb is flushed away, eventually making its way into local waterways. There, residues of antibiotics accumulate, often surviving treatment in conventional wastewater plants. This seemingly mundane act contributes to a global crisis: antimicrobial resistance.
Pharmaceutical waste, particularly antibiotics, has become a stubborn pollutant in water systems. These compounds, designed to kill or inhibit bacteria, are now implicated in the development of antibiotic-resistant superbugs. And they aren’t just a problem in India or low-income countries. Around the world, traces of drugs like ciprofloxacin, amoxicillin, and tetracycline have been detected in rivers, lakes, and even tap water.
But scientists from the Indian Institute of Technology Bombay are exploring a new, surprisingly elegant solution: a combination of light and sound.
The invisible menace in your water
Antibiotics are among the most persistent pollutants found in aquatic environments. They’re used in large quantities for human and veterinary medicine, and significant proportions are excreted unaltered. These compounds enter the wastewater stream, flowing from households, hospitals, and pharmaceutical manufacturing plants.
Conventional sewage treatment plants struggle to remove these micropollutants, which often pass through unscathed due to their complex molecular structures. Left untreated, they pose threats to ecosystems and human health, fostering antibiotic-resistant bacteria and disrupting aquatic life. The problem isn’t just about pollution; it’s about weakening our arsenal against future infections.
The science of sonophotocatalysis
To tackle this challenge, researchers Dr Amritanshu Shriwastav and Ansaf V. Karim have developed a novel hybrid treatment system using a process called sonophotocatalysis. In this technique, visible light and low-frequency ultrasound are used in tandem to accelerate the degradation of pharmaceuticals in water.
At the heart of his method is a specially designed hexagonal reactor fitted with light-emitting diodes (LEDs) and ultrasonic transducers. The magic lies in the synergy. Light activates a catalyst (nitrogen-doped titanium dioxide, or N-TiO2), generating reactive oxygen species that attack the drug molecules. Meanwhile, ultrasound induces cavitation, tiny implosions in water that enhance mixing and expose more pollutants to degradation.
Their studies found that this combined approach worked significantly better than using light or sound alone. For ciprofloxacin, a widely used antibiotic, degradation reached over 54 percent in just 90 minutes using the hybrid technique. On its own, visible light achieved only 41 percent and ultrasound 44 percent under similar conditions.
Targeting real wastewater, not just lab samples
Laboratory experiments often simplify reality. But the researchers went a step further. They tested their method using real wastewater samples collected from a local treatment plant. These samples, especially during monsoon season, contain a complex mixture of substances that can interfere with pollutant degradation.
Even under these realistic conditions, the sonophotocatalysis method held up. Although degradation efficiencies dropped slightly, the system still removed a substantial portion of the antibiotics. This matters, because treatment processes must perform reliably in the messiness of real-world applications.
Integrating with biological treatment systems
Yet even the most powerful chemical treatment is just one part of the puzzle. The IIT Bombay team also explored how sonophotocatalysis could be integrated with existing biological treatment methods, particularly sequencing batch reactors (SBRs). These reactors use bacteria to consume organic matter and nutrients from wastewater.
In this two-stage approach, the antibiotic-laden water first undergoes sonophotocatalytic pretreatment. This breaks down complex antibiotic molecules into simpler, less toxic compounds. Then, the pretreated water is fed into an SBR, where microbes can further digest the remaining contaminants.
This synergy between chemical and biological processes proved fruitful. The pretreated system achieved higher removal of ciprofloxacin and tetracycline compared to systems without the advanced oxidation step. Moreover, metagenomic analysis revealed greater microbial diversity in the pretreated reactors, a sign that the microbial community was healthier and more robust.
A cleaner future, or just a scientific curiosity?
So, can this light-and-sound cocktail realistically clean our rivers and lakes?
The short answer: not yet at scale. The reactors used in the IIT Bombay studies were lab-scale prototypes. Scaling them up for municipal treatment would require considerable investment, as well as changes to infrastructure and regulations. But the technology is promising.
With antibiotic resistance declared a top global health threat by the World Health Organization, solutions like this cannot be relegated to academic journals alone. The United Nations Environment Programme has also highlighted the role of environmental pollution in accelerating antimicrobial resistance, especially in developing countries with limited treatment capabilities.
These findings offer a roadmap for bridging the gap between laboratory success and real-world impact. By refining the process, reducing energy consumption, and integrating with existing facilities, sonophotocatalysis could become a key player in sustainable wastewater treatment.
Policy, awareness, and public health
No technology works in a vacuum. For sonophotocatalysis to gain traction, governments and industry must recognise the urgency of pharmaceutical pollution. This means investing in research and development, supporting pilot projects, and updating water quality regulations to address micropollutants.
Public awareness is equally crucial. Proper disposal of medications, reduced reliance on over-the-counter antibiotics, and stricter pharmaceutical manufacturing standards can collectively reduce the environmental load.
At the same time, innovations like this provide a compelling counter-narrative: that with ingenuity and science, we can develop cleaner, safer systems without overhauling everything from scratch.
References
Karim, A. V., & Shriwastav, A. (2020). Degradation of ciprofloxacin using photo, sono, and sonophotocatalytic oxidation with visible light and low-frequency ultrasound: degradation kinetics and pathways. Chemical Engineering Journal, 392, 124853. https://doi.org/10.1016/j.cej.2020.124853
Karim, A. V., & Shriwastav, A. (2023). Integrated sonophotocatalytic oxidation and SBR processes for the effective treatment of antibiotics with an emphasis on process optimization and microbial diversity. Journal of Environmental Chemical Engineering, 11(2), 109632. https://doi.org/10.1016/j.jece.2023.109632
