Electrochemical pretreatment increased microbial activity on tested plastics, study reports

A University of Girona research team reports that a five-hour electrochemical pretreatment made tested polyethylene and polypropylene more amenable to microbial activity. Its study, published on 24 September in the Journal of Environmental Chemical Engineering, offers a possible route for treating persistent plastic waste associated with wastewater systems. The reported laboratory measurements do not establish how much plastic was completely broken down or whether the process would work at a treatment plant.

The researchers combined mild electro-Fenton treatment with a second stage using an enriched microbial consortium. They tested pure commercial plastic granules as well as polyethylene and polypropylene fragments collected from agricultural fields. The field-collected material makes the experiment more relevant to waste handling than tests on pristine granules alone, although it does not represent a trial in mixed wastewater.

What the two stages changed

The first stage used an electrical current and iron(II) to generate reactive hydroxyl radicals. The reported operating conditions were 5 amperes per square metre and 0.2 millimolar iron(II), at room temperature. After five hours, the researchers observed fragmentation, cracks on particle surfaces and oxygen-containing chemical groups. Those changes provide a plausible route for microbes to reach material that would otherwise be difficult to attack.

In the second stage, the team exposed the treated plastic to an enriched microbial culture. Its metagenomic analysis found genes associated with enzymes involved in alkane oxidation. That finding describes the culture's potential biological machinery; the presence of genes alone does not show how much plastic the organisms consumed.

Higher BOD supports the authors' conclusion that the pretreatment made the tested material more biodegradable to their microbial culture. It is a narrower finding than complete disposal of the plastic. The reported relative changes do not specify what fraction of the original material became carbon dioxide, water or microbial biomass, or how much plastic remained after the test.

Why wastewater treatment matters

The authors frame the process around a problem for wastewater treatment plants: physical separation can capture microplastics, but it also creates a concentrated plastic waste stream that still needs management. A process that changes persistent particles into material more accessible to microbes could be useful at that later stage. The study tests that idea through sequential laboratory treatment, rather than documenting operation at a wastewater facility.

The choice of polyethylene and polypropylene matters to that proposed use because both were the target polyolefins in the experiment. Testing field-collected fragments alongside commercial granules also checks whether the reported effect appears in material gathered outside the laboratory. The study record reports increased BOD for those fragments, but it does not establish treatment throughput or performance in the varied mixture a wastewater plant would handle.

The distance from a plant process

A separately authored 2025 review of electrochemical approaches to microplastic treatment identifies high energy consumption, expensive electrodes and operational complexity as challenges across this broader field. The review predates the Girona study and did not test this particular two-stage process. Its value here is to identify questions that would matter when assessing practical use, rather than to confirm the new experimental result.

That review points to electrode materials, operating conditions, integration with other technologies and energy or resource recovery as areas for further work. For the Girona process, the accessible study record does not report a wastewater-plant pilot or full-scale operation. It also does not provide plant-scale energy use or operating costs with which to assess the authors' description of the method as energy efficient.

The next evidence needed for a deployment judgment is therefore more specific than another relative BOD result: measurements of the plastic left after treatment, performance in mixed real wastewater, and the energy and operating demands of a process handling meaningful volumes. On the evidence reported so far, the study shows a measurable improvement in microbial response after pretreatment. Whether that response can become an effective wastewater-plant treatment remains open.