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Returning Water to the Bosom of Nature Cleaning Urban Water Using Water as an Energy Source |
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Cleaning Urban Water |
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Sewers beneficial It has been suggested that securing water supplies will be a major issue for humanity in the 21st century. Certainly, there is an abundance of water on the planet; but usable water—that which is drinkable—is unevenly distributed in the extreme. And, if desertification due to global warming and water-quality degradation due to urbanization continue to advance unchecked, by 2025 some 3 billion people, mainly in Asia and Africa, could face severe water shortages. The depletion of water resources is an issue of such acute concern that it ranks alongside the “garbage explosion” and global warming as one of the world’s three major crises. That is how important the use of water is in urban areas, the major centers of water consumption. Sewers are no doubt the most effective means for using water efficiently and preventing water contamination in urban areas. On average, 63.5% of Japan is served by sewers (as of fiscal 2002). Compared with other industrialized countries, this, sadly, is by no means a high figure. But nearly all of Tokyo—about 97%—is served by sewers, and all indications are that the quality of water in its rivers has improved: Beginning late last year and continuing into this, stories have abounded of seals swimming upstream in Tokyo-area rivers, and the discovery of large schools of striped mullet in several rivers also made the news. Sumitomo Heavy Industries, Ltd. (SHI) manufactures and supplies a wide variety of plant and equipment used in sewage treatment plants. Toshio Izuhara, general manager of its Water and Sewage Plant Division, says: “Japanese regulations governing water discharged from sewage treatment plants are very tough, even in comparison to those of other countries, and Tokyo’s rivers have become much cleaner than they once were, that’s for sure.” Sewage treatment involves a combination of two basic processes, one biological and the other chemical and physical, which yield treated water and sludge. The biological treatment entails exploiting natural principles and the technology is pretty much universal, having “not changed much over the past 100 years or so,” says Izuhara. |
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Technological innovation initiatives |
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| At the plant or equipment level, though, technological innovations have been numerous. SHI’s Cascade sludge collector is one example. Machines to collect sludge on the bottoms of settling ponds are traditionally designed to do so via scraper blades, called flights, which are mounted on a traveling chain that circulates around the settling pond. In 2002, SHI announced its Cascade sludge collector, which directly uses the forward and reverse motions of motor to drive the flights. During the collection stroke, a flight moves forward along the bottom of the settling pond to push the sludge to an outlet without leaving any residue behind; during the return stroke, the flight is lifted off the bottom of the pond so as not to stir up any sludge as it traverses back to home position. This mechanism is simpler than that using chain-mounted flights, and it is also substantially lighter. By innovating a system that reduces both weight and friction, SHI’s engineers developed one that also helps conserve energy because it uses less electricity, requiring only about half the primary motive force of conventional sludge collectors. Further, less friction means longer life for replacement parts, and maintenance costs can be reduced to about one-third those of conventional systems. Reducing the cost of public services has become an urgent issue for operating authorities trying to work within recent budget constraints. SHI’s Cascade sludge collector with its lower operating costs is a boon in this situation, with the added advantage that it encourages the installation and upgrading of sewer infrastructure. SHI has also developed the Sumirator UD, which is a vertical shaft aerator for small-scale sewage treatment, and the company has garnered the industry’s top performance record in vertical shaft aerators. By varying the revolutions of a blade, or impellor, that agitates water in a biological reactor, the aerator can control the volume of oxygen (which is essential for the desired biological reaction) entrained into the water. This also means that it allows the efficient removal of nitrogen, a source of eutrophication. The aerator incorporates a function for raising and lowering the impellors discretely shaft-by-shaft, which makes it very easy to set parameters for aeration agitation at the water’s surface and anoxic agitation underwater. One of the Sumirator UD’s salient features is that even under low load immediately after plant startup, when the volume of organics is low, it can easily perform anoxic agitation. General Manager Izuhara says: “Sludge load is quite low when a plant first starts up, which means that too much agitation at the water surface will cause over oxygenation, and sometimes the microorganisms stop working. But because it’s a reaction tank, you can’t stop the agitation because you have to keep the water and sludge from separating. At times like this you can lower the blade and rotate it underwater—you can agitate the slurry without entraining oxygen.” Both of these examples are applications of reduction-gear technology, an area in which SHI holds the worldwide number-one position. SHI has leveraged its total corporate strengths and established a track record in taking on package contracts to operate human-waste and sewage treatment facilities, to manage and purchase the power, fuel, and chemicals used, and even to carry out facility maintenance—all tasks that municipalities and intermunicipal sewage-treatment cooperatives traditionally commissioned separately. Sewage treatment technology was originally developed in North America and Europe, but in the process of rebuilding after World War II, Japan installed water mains and sewage infrastructure in a very short time and amassed a wealth of experience and technical expertise. This experience and know-how will most likely now be used outside Japan as well.
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