Most Americans flush the toilet without thinking twice about where the contents end up, but a handful of companies are paying close attention to what goes down the drain. They argue it should be seen as a resource rather than waste.
Dealing with human waste is a tricky business. The wet material typically has to be treated at a sewage plant, dried and turned into a biosolid, then either hauled away to a landfill or turned into mulch and reused as fertilizer.
According to the U.S. Geological Survey, wastewater treatment plants generate about 7 million dry tons of biosolids per year. The conventional methods of dealing with this waste are expensive and energy-intensive. Landfills are also filling up, and sludge that's turned into fertilizer may still contain chemicals that are potentially harmful to humans and the environment.
Now, some companies are saying this method of dealing with waste is just plain wasteful.
That's where sewage-to-energy comes in. Industry estimates show that if all biosolids in the United States were converted into biomass energy, they would produce 7 million to 7.6 million megawatts of power. By way of comparison, the current installed capacity of wind power in the United States is around 43,000 MW.
By essentially recycling the waste as electricity or converting it to biodiesel fuel, rather than putting it in a landfill, converting sewage into energy also reduces greenhouse gas emissions. The global warming effect of methane produced by decaying landfills is about 20 times more powerful than that of carbon dioxide. The waste conversion process avoids these emissions by capturing the gas and turning it into a product.
"There are truly not many options for dealing with sewage, but [municipalities] need to address it somehow," said Dennis Wherrell, CEO of Earth, Wind & Fire Technologies. So why not turn dirty waste into clean energy?
Wherrell's Florida-based company is one of just a few in the world with the technology to run sludge-to-energy operations on a consistent basis. There is still some distance to go before these companies are fully commercialized, but progress is being made. "This is not a pipe dream on a drawing board for us," said Wherrell.
Finding the money in sludge
Since the year began, Earth, Wind & Fire has started writing up contracts and engineering plans at over 50 sites around the world, most of which are in the United States, said Wherrell. The company is focused on establishing its new technology in Tennessee, Alabama and Florida, but is already in the process of manufacturing the third unit of a project being sent to Belgium.
Traditional waste disposal is not cheap. For instance, Pasco County, Fla. -- where Earth, Wind & Fire recently struck up discussions on a new project -- pays $800,000 per year to deal with its sludge. Daytona Beach spends $500,000, and Orlando spends an amount in the millions, said Wherrell.
Eager to pay less, municipalities are turning to other sewage options. Another major sell for his company, said Wherrel, is that cities and homeowners won't pay a dime for one of his plants. Earth, Wind & Fire will cover all capital expenditures and earn them back by selling the biodiesel or electricity that's produced in the treatment process.
The company's income stream starts with taking the waste and microwaving it. The process uses pellets of dried human sludge and carbon-based landfill material, runs an electrical current through it, captures the vapor that's produced and then condenses it into a No. 2 diesel fuel.
The drop-in biodiesel burns cleaner than traditional diesel-biofuel mixtures and contains less particulates, said Wherrell. Apart from a test facility in Germany and a functioning unit in China, the practice is not being used anywhere else in the world, he added.
A second process involves sublimation, turning a substance from a solid into a gas without it first becoming a liquid. This creates methane gas that's captured and burned to spin generators that feed electricity to the grid. Justifying one of these systems requires a significant amount of sludge to begin with. It takes 30 tons of dry waste to produce enough methane to generate 1.2 MW of electricity.
Earth, Wind & Fire markets its diesel "Microfuel Refinery" and sublimation process as solutions to inefficient waste management and U.S. dependence on foreign oil. But the practices may also have other advantages -- they're closed-loop systems that don't produce any harmful byproducts, and help reduce carbon dioxide levels by recycling waste that would otherwise emit methane into the air from a landfill.
Getting steam and the fizz for soft drinks
But Earth, Wind & Fire isn't the only sewage hero around.
A company based out of Cork, Ireland, called AquaCritox has also made significant progress. It already has one sewage-to-energy demonstration plant in operation and three others in construction. According to John O'Regan, CEO and founder of SCFI Group, the parent company of AquaCritox, his company uses a novel process to manage waste, first developed by the U.S. military -- it creates supercritical water.
AquaCritox's technology takes in raw sewage and brings the temperature and pressure above 700 degrees Fahrenheit and 221 bar (3,000 psi). In these conditions, it enters a supercritical condition or "fourth phase" that completely destroys organic material, producing only carbon dioxide, which O'Regan says can be used in the soft drink industry or to create dry ice.
The steam generated by the process is then used to drive turbines for power generation. "We can generate 1 megawatt-hour of electricity from 1 ton of digested sewage sludge solids," said O'Regan. "We can actually say that we're energy positive."
AquaCritox can also treat wet waste, rather than the pre-processed semi-solid matter used by its competitors. The problem with using solids, says O'Regan, is that is that it takes more energy to evaporate the water than can be recovered once the waste is treated.
"That's hugely significant, because the energy input to evaporate water in sewage sludge and other wet waste is more than 50 percent of the total energy input into any of the terminal technologies in existence," said O'Regan. The mechanical dewatering process is also a big part of the cost of dealing with sewage and has a sizable carbon footprint attached to it, he said.
"That means our technology is significantly more energy-efficient [than our competitors']," he added.
If you ask Wherrell of Earth, Wind & Fire, however, he'd say his company beats AquaCritox in the "simplicity" of its technique. And although it requires a dry material, the company can take care of the drying process on site, he said, which will save municipalities from doing it, and paying for it.
When O'Regan was asked about Earth, Wind & Fire, he said he'd heard of its existence, but couldn't say much else about it.
Putting the bugs in
"Really, you're looking at a new industry," said Alan Rozich, chairman of the board of PMC BioTech, a company that uses strictly biological processes to convert sewage into energy. Much is still uncertain when it comes to how different types of technologies will be deployed and who the players are, said Rozich. "This is the Wild West right now."
PMC Biotech is currently developing two projects in the Caribbean that will produce both renewable energy and fertilizer.
Rozich says that his company's method of turning waste into energy has an advantage over others, because it's cheap and doesn't require the energy necessary to heat up and change the state of the material. The most frugal and efficient way to make energy, he says, is to let microorganisms do the work. Microbes turn the sludgy feedstock into methane, and break down the organic material to nitrogen and phosphorus, which can be used as fertilizer.
The process takes 10 to 15 days, said Rozich. But the conversion rate from sewage to energy is more than 90 percent, which produces biodiesel or biomethane that can be used for electricity, and a high-grade fertilizer that doesn't have the same environmental and health concerns attached to it as the fertilizer that comes from conventional sewage treatment.
Rozich added that the energy released by this natural process is greater than the energy put into the system. For other companies, that energy balance isn't there, he said, which means they're producing more greenhouse gas emissions than they're taking care of.
O'Regan insists his supercritical water process is energy-positive, however. He also said the anaerobic digester method used by PMC BioTech doesn't offer a full service, because the microbes need to feed on dewatered sludge, rather than raw sewage, so it doesn't save cities from having to process the waste. Plus, the fertilizer business is not a profit-making operation, O'Regan said.
But, he added, the broader pursuit of turning sewage into a resource is worthy, and indeed necessary. Society can't afford to be wasteful, even when it comes to waste. "If we're going to create waste, we should turn around and use every component of it," he said. "We can, and we should do so."