Electricity and Plastic Created by Harnessing Waste Water

Treat waste water to create energy and biodegradable plastics

TREATING wastewater is energy intensive. But it does not have to be such a drain on resources; soon it might be able to earn its keep.

A team led by Hong Liu from Oregon State University in Corvallis has plans for microbial fuel cells that will reclaim energy from waste water and produce around 2.87 watts of electrical power per liter of waste water. That is almost double the amount of electrical power usually required for such a cell. Its by-products could be harnessed to create cheap and biodegradable plastics.

Waste water holds huge amounts of energy, bound up in organic molecules, but difficult to access. The Oregon fuel cells run on microbes that would normally digest organic matter to produce water. In a fuel cell, though, isolated from oxygen, that conversion stalls and electrons, which are bundled with protons and oxygen to form water, are pulled away from the microbes by the potential between a cathode and an anode, producing electrical current.

As well as tweaking the mixture of microbes on the electrodes, the Oregon design has also managed to squash far more electrodes into the fuel cell than on previous versions. Liu says her lab aims to scale up the device within the next five years and make it cheaper. The by-products of waste water treatment can be harnessed too. Engineers are working on a way to convert methane into biodegradable plastics.

The dream plastic would be would be made from organic material that are biodegradable and breaks easily. At the moment, Polyhydroxyalkanoate (PHA) seems to be the best bet. But PHA plastics are manufactured by genetically modified bacteria fed on sugars in a process that is both expensive and complex, making it hard to compete with conventional plastics.

So Molly Morse of Mango Materials in California and colleagues are now using methane, another major by-product of treating waste water. Methanotrophs, simple organisms that feed on methane, are much better at converting it into polymers than typical bacteria are at converting sugar into plastics. Methane is pumped into a vat of Methanotrophs harvested from the waste water treatment plant itself - along with a bubbling stream of oxygen and a few other nutrients. The end result is a polymer powder that can be separated from the mass of bacteria and turned into pellets for shaping into commercial plastic products.

Morse envisions that their waste water plastic could be used for all kinds of temporary or disposable applications, ranging from packaging materials to beauty products.