Sewage treatment plants around the world are beginning to put value on waste, turning it into a marketable resource.
in Washington is the largest facility of its kind in the world and is among the leaders in the effort.
On an average day, 1.4 billion liters of raw sewage flow into the plant, delivered from around the city through 2,000 kilometers of underground sewer pipes and pumping stations, an amount that could fill the nearby sports stadium.
The waste is loaded with nitrogen and other nutrients.
General Manager makes sure the discharge doesn’t pollute the river on which two million people in the region depend for their drinking water.
By law, Blue Plains can dump only a small percentage of those nutrients into the Potomac River.
“We know that people buy nutrients all the time," Hawkins says. "So the question is how can we take things out of the water that we’re treating here and re-use it for the resource that it is?”
A massive $4 billion environmental program is under way at Blue Plains.
Among the three projects, two are mandated by the government, including one that will cut in half the amount of nitrogen and other waste nutrients discharged into the Potomac River.
The other is an to prevent accidental sewage overflow from its network of ageing pipes.
Engineer Chris Peot heads the solid waste program at Blue Plains, which is working on making better use of the mud-like sludge components of the wastewater stream.
He says by 2012 the four huge digesters now under construction will cook the sludge.
“The microbes in the digesters are methanogens and they help break down the organic matter and convert it into methane which can be collected and burned in a turbine which turns and creates electricity.”
The process will make enough methane gas to supply about one-third of the treatment plant’s electric power needs, a great savings given that Blue Plains is the city’s biggest electricity user.
The other half of the digested wastewater bio-solids will be sold as a nutrient-rich soil additive.
“If we blend it and make it look like a top soil we can market it to the public," Peot says. "It can certainly be a source of revenue, a source of good clean soils for restoration projects, for reducing run-off for tree planting.”
Other sewage treatment plants in the United States and other developed countries have adopted this by-product technology, or are considering doing so. The idea is also generating interest in developing countries.
Amit Pramanik is an environmental engineer with the . In a recent trip to Ghana, West Africa, he visited Kumasi, the nation’s second largest city, where only 10 percent of the residents are connected to a central sewer system.
Pramanik says the under construction will help reduce waste that now flows largely into open pits or landfills. He says project managers hope it will also generate useful and commercially valuable by-products such as nutrient-rich soil additives, bio-diesel fuel and methane gas.
“Can you recover that gas and can you use that either for heating or cooking and so on?" he says. "Can you grow food crops with this? Can you recover the nitrogen and phosphorus and increase agricultural yields?”
What’s attractive to the local community, Pramanik says, is the payback.
He says the model could be adopted anywhere that waste can be marketed as a profitable community resource. “So if you can get the community involved from the beginning and see that the community is benefiting from it, and the community sees that, they will take ownership.”
Pramanik says these new green factories make good sense for the local economy, for public health and for the environment.
George Hawkins at the Washington Water and Sewer Authority agrees, however he and other waste water managers in the United are faced with many challenges to put such new green factories in place. First, he says, their current system of pipes and pumping stations is old and requires on-going maintenance. “In most cities the system was put in at the turn of the century of the last century when cities were being formed. And, he adds, the fact is that we need a lot of revenue from our rate-payers to bring it back up to date.”
Hawkins predicts those rates will increase by double-digits annually for years to come.
Not only is this costly, but secondly operators must also comply with strict environmental rules. Under the Clean Water Act, passed 40 years ago and widely credited with protecting public health and the environment, industries are required to limit the waste that can go into the waterways.