Zapping sewage: microbes and electricity clean wastewater

If you've ever wondered, a city the size of, let's say, Shanghai, with more than 20 million residents, flushing, showering, and cooking every single day produces a massive volume of wastewater. Making it safe to return to the environment (or even reuse) requires sophisticated treatment plants. But these systems face a stubborn enemy: clogging. Filters that are supposed to clean the water gradually gum up with grease, proteins, and microscopic “slime,” reducing efficiency and driving up costs.

A team of researchers at Tongji University in Shanghai, led by Dr. Zhiwei Wang, may have found a clever solution: give the microbes a tiny electric “nudge.” Their study, published in Engineering, introduces an electroactive biofiltration dynamic membrane, a mouthful of jargon that boils down to this: a living, self-organizing filter that not only cleans wastewater but also produces extra energy in the form of methane.

Traditional wastewater treatment plants use special membranes to separate clean water from the muck. Over time, though, particles of food waste, dead microbes, and sticky polymers build up. Engineers call this “membrane fouling.” For treatment operators, it means more maintenance, higher energy use, and frequent replacement of expensive filters.

Scientists have long experimented with “dynamic membranes”: filters that rely not just on synthetic materials, but also on a layer of natural biomass (basically, a slime of microorganisms and organic matter) that builds itself. These dynamic membranes are cheaper and can, in principle, clean themselves. But they also tend to overgrow and harden into a dense, stubborn layer that resists water flow.

Here’s where electricity enters the picture. The Tongji University team wondered: what if you added a gentle electric field to the system?

Their setup, called an anaerobic dynamic membrane bioreactor, already relies on microbes that thrive without oxygen, breaking down organic waste and producing methane, a usable biogas. By wiring in a cathode (a negatively charged electrode), the researchers discovered that the microbes began behaving differently. The electric field subtly rearranged the slime layer. Instead of forming an impenetrable mat, the microbial community built a looser, more open structure, like a sponge instead of a brick wall. Water flowed through more easily, and the whole system stayed cleaner for longer. Think of this membrane as a self-regulating biofilter. Instead of floating randomly, microbes are guided by the electric field to assemble in a balanced way.

This innovation has several advantages. First, less slime, more flow. Proteins and sugars that normally clump into sticky networks were less abundant. Under the microscope, the treated filters had fewer dead cells and smaller clusters of gunk than untreated ones. Second, they use smarter microbes. Metagenomic sequencing (a kind of genetic census) showed that electricity encouraged certain “electroactive” bacteria like Geobacter. These microbes can literally shuttle electrons, helping break down waste more efficiently and boosting methane production. Finally, this method produces extra energy. Over 240 days of continuous operation, the membrane system removed over 93% of pollutants (measured as chemical oxygen demand) and produced 7.2% more methane than the non-electrified system.

In short: better water out, less clogging inside, and more energy on top.

Wastewater treatment is a huge energy sink. Many plants spend more electricity running pumps and filters than they can recover from methane. This new membrane makes filters less prone to clogging and simultaneously boosts methane output, thus moving treatment plants closer to being energy-neutral or even energy-positive.

There’s also the matter of cost. Replacing fouled membranes is one of the priciest headaches for water utilities. If electroactive membranes can last longer with less maintenance, cities could save millions, while also reducing the environmental footprint of treatment plants.

And finally, there’s resilience. As urban populations grow and freshwater supplies shrink, wastewater treatment is a matter of recycling water for reuse. Technologies that keep the system flowing smoothly are vital for sustainable cities. For now, this is still lab-scale research. The reactors tested were only 1.5 liters each, about the size of a soda bottle . Scaling up to an entire city’s treatment plant poses many challenges, from maintaining stable electrical conditions to managing costs. But the principle is exciting. The researchers have shown that by marrying biology with electricity, we can coax nature into working more efficiently for us. Instead of constantly fighting slime and clogs, treatment plants of the future might use living, electro-tuned membranes that clean themselves while generating renewable energy. Until even the dirtiest wastewater will not just be waste, but a resource, flowing back into the city as clean water and power.

If you want to learn more, the original article titled "Development of Electroactive Biofiltration Dynamic Membrane (EBDM) for Enhanced Wastewater Treatment and Fouling Mitigation: Unraveling the Growth Equilibrium Mechanisms of Fouling Layer" on Engineering at http://dx.doi.org/10.1016/j.eng.2025.02.003.