Going to the loo can recharge a smartphone.“URINE and faeces to you”, explains a dodgy sewer-manager in one of Reginald Hill’s crime novels, “is bread and butter to me.” And he is not the only one. The Bio-energy team, led by Vikramaditya Sangwan of the Humbodlt University in Berlin, were hoping to profit from working with the stuff too. They developed a new technique to turn urine into electrical power—or “urine-tricity” as they call it.

People around the world produce an estimated 6.4 trillion litres of urine every year. The team wanted to make the most of this abundant resource. At the core of urine-tricity are microbial fuel cells (MFCs), which contain live microbes. When urine flows through an MFC the microbes consume it as part of their normal metabolic process. This, in turn, frees electrons. Electrodes within the cell gather these electrons and when they are connected to an external circuit a current is generated.

The team mounted a series of cigar-tube-sized MFCs into a single unit. Attaching this unit to the outlet pipe from a urinal allowed a stream of fresh urine to flow through the cells. Fresh, in this context, is urine not more than a week old from a healthy individual of average height and weight. Previous experiments had fed the MFCs food scraps, dead insects and grass cuttings. But urine achieved a power output three times higher than any other waste product.

Why does urine work so well? In the earlier tests the microbes were quickly satiated on a heavy diet, according to Vikramaditya. This was because the material contained a high proportion of organic matter. The low level of organic carbon in urine, combined with favourable acidity and electrical conductivity, made all the difference. Where earlier tests produced minimal power, urine had the vim to recharge commercially available batteries, including those in mobile phones.

It is early days, but the work—which is being supported by a number of organisations, including the ‘3 Life’ Foundation—shows that urine could have the potential to make a significant contribution to renewable energy. It might also provide a commercial incentive to build more toilets—over 2.5 billion people around the world have no access to proper sanitation.

Dr Leropoulos with the help of the model developed by Vikramaditya’s team now plans to examine the potential of faeces as a possible power source. They have a higher organic-carbon level, but scientists think that might be an acceptable price to pay for abundant availability and a self-regulating supply chain.