TOKYO -- A Japanese publisher once had great success with an exercise book for learning kanji, or Chinese characters, by inserting the word "poop" into every sample sentence. But adults are now finding a more serious use for the pungent substance.

It is estimated that the total amount of excreta produced annually by cows, pigs and chickens in Japan could provide enough energy for a passenger car to travel around the world 750,000 times.

It could also be good for the environment.

In the town of Shikaoi, in a dairy farming area of the northern island of Hokkaido, the Environmental Preservation Center started a pilot project in January to develop infrastructure to process excreta into fuel for cars by producing hydrogen from manure.

Livestock excreta is brought in on container trucks to a biogas plant, where it is deposited in cylindrical tanks and left to ferment, producing biogas. The gas is then sent to an adjacent refining and hydrogen production facility, where impurities such as carbon dioxide are removed. The gas is then combined with water vapor to produce hydrogen, which is transported to hydrogen stations. There, the fuel is pressurized and pumped into fuel-cell vehicles and forklifts. It is also used to power households and shops.

Contained in cylinders, the gas can be used anywhere. The town plans to make sturgeon farming a key local industry, using the fuel to generate power and heat.

"Excreta is normally industrial waste, but here, it's a precious energy source," said Tomohiro Inoue, manager of the engineering business of Air Water, one of Japan's largest industrial gas manufacturers, which is working with the town along with general contractor Kajima, and Nippon Steel & Sumikin Pipeline & Engineering.

A cow produces enough dung annually that when converted to hydrogen, it can power a fuel-cell vehicle for about 10,000km, about the average that a person drives in a year in Japan. If all livestock excreta is converted into hydrogen, it could meet the annual fuel-cell needs of about 3 million cars.

But cost is still an issue. With demand for hydrogen limited, the Shikaoi plant operates only one week per month. Theoretically, the plant's cost efficiency is not much different than that of deriving hydrogen from natural gas, which is more widely used. But operating the plant at a lower capacity compromises efficiency.

Yet Inoue believes there will be more fuel-cell trucks and tractors in the future, and costs will fall as the fueling infrastructure grows. Eventually, that will create "a cycle of energy production and consumption" in the area, he said.

He added that if the hydrogen plant operates steadily, it may become efficient enough to be competitive with gasoline, which currently costs a fraction of manure-based hydrogen to produce.

The pilot project will run until the year ending March 2020.

Shikaoi is just one of 19 municipalities comprising the Tokachi region that are working together to promote gas and hydrogen production from excreta.

Around 80 million tons of livestock excreta is produced annually in Japan, according to the Ministry of Agriculture, Forestry and Fisheries. That is four times the amount of food waste. But much of it is used only as manure, or disposed of as industrial waste.

Manure stinks and the stench can become an regional problem. And it doesn't create new industries Hidenori Uematsu, a senior official of the municipal government of Obihiro

Hidenori Uematsu, a senior official of the municipal government of Obihiro, one of the towns participating in the initiative, says all that excreta is better used as a biomass resource.

"Manure stinks and the stench can become an regional problem. And it doesn't create new industries," he says.

The group plans to increase biomass power generation three-fold in the fiscal year through March 2023 compared to the fiscal year beginning in 2012.

"It will be great if the Tokachi initiative becomes a role model and helps Japan's farming to grow," he said.

Not only the excreta of livestock, but that of humans is also a potential energy source.

At a sewage plant in the southern city of Saga, there is an ongoing experiment to cultivate euglena, a kind of microalgae, for use as a source of jet fuel.

The experiment is being carried out by biotechnology start-up Euglena, which develops products using the microalgae. It was started in 2014 jointly with the Saga municipal government and the industrial giant Toshiba.

The microorganisms are cultivated in a 1.2-meter-high cylindrical tank. Carbon dioxide produced in the treatment process is fed to the euglena, which uses it in photosynthesis. For the algae, household sewage is rich in nutrition.

While the experiment involves developing jet fuel, the company has already grown food and cosmetics products made from euglena.

With a global goal of the airline industry to stop increasing CO2 emissions from 2020, biojet fuel may be a solution, as it does not add to emissions. As the plant life grows, it absorbs CO2, discharging it only when it is burned as fuel, with no net increase in the atmosphere.

In Yokohama, southwest of Tokyo, Euglena is building a pilot plant to manufacture biojet fuel by distilling oil contained in euglena. The pilot of phase of the joint project with All Nippon Airways and engineering company Chiyoda will start in 2018, with commercial operations targeted for 2020.

If the plant proves viable, it could mean that a jet fuel plant can be built wherever there is a sewage plant.

It could also pave the way for manufacturing euglena in an arid climate, such as deserts, according to Euglena Director Akihiko Nagata. He said euglena jet fuel has the potential to hark the way toward an era when fossil-based fuel sources may no longer be the main ones.

There are also moves afoot nationwide to generate power by using sewage, with the first biomass power plant to go online in Toyohashi, Aichi Prefecture, in October.

Developed by JFE Engineering, the plant will collect sewage sludge, human excreta and food waste, and have them coagulate in a tank to produce biogas. Using this gas, the plant will generates 24,000 kilowatt-hour per day, enough to meet the energy needs of 2,400 households. The residue will also be made into fuel through a process of carbonization.

"It will be able to process every form of biomass that remains unused in the region," a JFE Engineering executive said.

In Japan, local governments operate wastewater treatment facilities, spending tax money to do so. But biogas power generation turns this waste into fuel, and the electricity generated could bring in steady revenues through a feed-in tariff system that ensures it is purchased at fixed prices.

Nikkei staff writer Yuji Ohira and Nikkei senior editor Masaya Maeno contributed to this story.