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Getting rid of household waste water from sinks, toilets, baths and the like is a growing problem around the world. In modern cities, such water finds its way into municipal sewage treatment plants, where processing yields huge amounts of sewage sludge. But instead of disposing of this sludge as waste, people are realizing that it can be a valuable source of renewable energy.     

     So rather than simply dumping the sludge or using it for cement filler and other applications, there is a growing movement to utilize the material as biomass, to produce hydrogen gas for fuel cell vehicles, as a source of heat to generate electricity, and to make fertilizer and fuel pellets.

Hydrogen power

Fukuoka is the largest city in the Kyushu region in southern Japan, with a population of 1.5 million. It is also home to the world's first serious effort to commercialize hydrogen derived from sewage sludge.

 

     Mitsubishi Kakoki and Kyushu University are collaborating with the city as part of the Fukuoka Hydrogen Town project to establish a means of generating hydrogen from sewage sludge and supply it for fuel cell vehicles.

     To process sewage sludge, waste water from homes and the like travels through sewer pipes to reach a sewage treatment plant, where it is collected and treated. This waste water contains human waste and other solid material, so the first step is to separate out the water component and decompose the organic materials using microorganisms. Sewage sludge consists of the original solid material plus the remains of the microorganisms used in the treatment process.

     Currently, most of this sewage sludge is incinerated or otherwise disposed of at great expense.     

     But Fukuoka is interested in the beneficial uses of this sludge. It uses a process to heat and break down the sludge to generate biogas containing large amounts of methane. It then processes this biogas using a special facility that extracts only methane, and reacts this with steam at high temperature to make 99.999% pure hydrogen, exceeding international quality standards.

     The water treatment facility in Fukuoka where this is taking place is also equipped with a hydrogen station for fuel cell vehicles. It's estimated that up to 2 million fuel cell vehicles could be plying the roads in 2025 in Japan, and based on that prediction, the city calculates it can turn a profit on such fueling stations in a decade.

     Fukuoka has a history of reusing resources. It lacks a so-called Class A river system, which is the designation for systems deemed important for the national economy and people's lives, so in 1978, a dry year, it was forced to impose restrictions on water use for 287 consecutive days. The city was the first in Japan to reuse processed waste water for toilets, and to this day it has more facilities for supplying this kind of recycled water than any other city in Japan. The citywide ethos for the reuse of resources helps explain why it is now tackling the conversion of sewage sludge into hydrogen.

 
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