单选题 Treating waste water is energy intensive. In the US, it sucks up the equivalent output of four of the country's biggest power plants every year. But it needn't 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 per litre of waste water. That is almost double the amount of electrical power usual for such a cell. And its by-products could be harnessed to create cheap, biodegradable plastics.
Waste water holds huge amounts of energy, bound up in organic molecules, but it can be difficult to access. The Oregon fuel ceils run on microbes that would normally digest organic matter to produce water. In a fuel cell, though, isolated from oxygen, that conversion stops 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, creating an electrical current.
As well as transferring 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 biodegradable, made from organic materials, and break down easily. At the moment, polyhydroxyalkanoate (PHA) seems like 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 for them to compete with conventional plastics. In the past, researchers have used the by-products of waste water treatment to generate fuel and sometimes even to create plastics, but nearly all these attempts have focused on the solid waste and chemicals. Because the solid waste is made of many diverse components, it produces a less stable plastic.
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.

单选题 What can we learn about Hong Liu's plans?
A. They will call for recognition of the pubic.
B. They will protect energy from further losing.
C. They have failed to properly preserve energy.
D. They can recover useful things from waste products.

单选题 According to the passage, the energy in waste water
A. doesn't reach the amount for usage.
B. is easy to be acquired and stocked.
C. can be transformed into electrical power.
D. can only be used in producing plastics.

单选题 Which of the following is true about PHA plastics?
A. Their producing is cheap and simple.
B. They can break down easily after usage.
C. They aren't as good as conventional plastics.
D. They can only be acquired from solid waste.

单选题 With methane, Molly Morse and colleagues
A. can treat waste water with less by-products.
B. will convert sugar into plastics much easily.
C. can break away from waste treatment plants.
D. will create more commercial plastic products.

单选题 What's the main idea of this passage?
A. How to make electricity from water.
B. Plastics and environment protection.
C. Waste water treatment and recycling.
D. Waste classification and treatments.