More than two million people worldwide die each year from diseases carried in contaminated water. A United Nations report, released this month, says that's because more than one-third of the world's population lacks access to adequate sanitation. Cutting that number in half is one of the U.N. Millennium Development Goals, and it's one of the main topics of the 3rd World Water Forum which began Friday in Kyoto, Japan.
Water rushes over the top of a clarifying tank at the Blue Plains wastewater treatment plant in Washington D.C. Wastewater from more than two million people in the Washington area collects in twenty of these house-sized tanks, where solid matter settles to the bottom. Removing the solids from the water is called primary treatment.
Chief Engineer Mike Marcotte says this simple first step makes the biggest improvement in water quality. "The water that comes off of this is, substantially the solids have been pretty well removed, the heavy solids, so you have a shot at disinfecting this," he says. "And depending on the stream that's getting your waste, this may pass for good in some locations."
Mr. Marcotte says disinfecting water from one of these $20 million clarifying tanks could provide basic sanitation needs for a city of up to 100,000 people.
At the Blue Plains plant, water goes through two more steps. Secondary and tertiary treatment take out most of the amounts of polluting chemicals in the water. Finally, the treated water is disinfected with chlorine and discharged into the Potomac River.
Removing these polluting chemicals can run into the hundreds of millions of dollars. In the developing world, environmental engineering professor Donald Harleman says money is best spent on primary treatment, not on those later steps that are aimed at protecting the environment. "Those are secondary benefits that are not crucial to the protection of the population from disease," he says.
Experts say there are other reasons besides cost why a plant like Blue Plains might not be appropriate in the developing world. The equipment requires electricity, which, in many parts of the world, can be hard to come by. And in countries where education is lacking, it may be hard to find highly-trained workers to run the plant.
But Geraldo Galvis of the Pan-American Health Organization, a branch of the World Health Organization, says developing-world cities have something that many sprawling developed countries don't land. "If you go to a city in a developing country, you may have a lot of area around the city which is not necessarily densely populated," he says. "So you can use technology that requires more land. And you can use technology that requires less amount of equipment, and less amount of highly trained operators."
Environmental engineer Edward Winant of the National Small Flows Clearinghouse, which provides information on waste water treatment, says one low-cost technology is a waste lagoon. "In a lagoon, you're going to have a lot of land, you're not going to have a lot of expense, and you're not going to need a lot of technical know-how," he says.
That's because a lagoon is just a five to 10-acre pond where waste water from up to 50,000 people can be collected. Mr. Winant says in many ways it can treat wastewater to nearly the same standard as a mechanical plant, like Blue Plains. But the water will still be rich in some fertilizers. Mr. Winant says an Indian reservation in the U.S. state of Wisconsin has used a lagoon successfully for about 20 years.
Clearinghouse environmental engineer Andrew Lake says a more aesthetically pleasing approach is a constructed wetland. "To look at it, you might not recognize it as a constructed wetland," he says.
Mr. Lake says aquatic plants and bacteria growing in a bed of gravel treat the wastewater. "It's a natural type of system," he says. "It's one that people like to look at. It kind of sits in with the scenery."
Mr. Lake says although constructed wetlands and lagoons are effective, their use is limited to cities of under 50,000 people with land to spare. But he says any improvements in sanitation, whether using these methods or basic mechanical plants, would provide substantial benefits in public health.