| 
|
Seth Wilkinson and Alison Flynn enjoy explaining their unusual toilet to visitors. With its trim tapered tank and unique two-button flush knob (one is pushed and one is pulled), it could pass for one of the new dual-flush toilets. But lift the lid and the key difference is apparent: inside, a small drained basin is cast like a shelf in the front of the toilet bowl, so that urine is caught and flushed with a tablespoon of water to a tank. Solids are flushed away via a standard 1.2-gallon flush to a conventional septic system.
This urine-diverting toilet, the Ekologen DS by Wost-Man of Sweden, is only one of a handful in North America, but they are far more common in Scandinavia, Mexico, China, and Germany. In some installations, such as in multi-unit buildings, the urine drains to tanks inground or under the building that are periodically pumped. Others drain directly to onsite evapotranspiration trenches, sometimes lined. In some instances, the pumped urine is applied to animal fodder crops.
Wilkinson and Flynn live in Orleans, MA, on Cape Cod, a region grappling with nitrogen pollution affecting lakes, seashores, and groundwater. With the blessing of their local health agent, they chose the urine-diverting toilet to reduce their environmental impact. Urine drains to a 250-gallon in-ground tank. A float switch turns on a light when it's full, about once a year. Flynn hoses the urine-water mixture on piles of composting leaves and well-mulched gardens. It has no major odor, she reports.
Growing Away Pollution
As federal regulations increasingly require tertiary treatment, and regulators work to mandate expensive advanced denitrification systems—most with powered aeration to convert nitrogen to ammonia gas that is vented away—some are asking if there might be a better way to manage nitrogen. After all, they reason, it's a valuable fertilizer when applied to crops and landscapes, and only a pollutant when discharged to surface and ground waters.
Porcelain urine-diverting toilets were developed in Sweden in the past decade in response to nutrient pollution and eutrophication evident in that country's many lakes and along the Baltic and Atlantic coastlines. Large "dead zones" of eutrophication are also apparent in the sea. The Swedes isolated the source of the nutrients: urine—from humans as well as farms. Several authorities and research institutions investigated and proved the viability of diverting this nitrogen source and using it in place of farm fertilizer—another source of nitrogen pollution via runoff.
Human urine accounts for about 90% of nitrogen in human excreta. What points to opportunities is that urine is usually pathogen-free in a healthy population (feces are the main source of potential pathogens). In essence, we flush away free pathogen-free urea fertilizer in the form of urine. (The amount of nutrient value is determined by how much protein one eats.)
A Resource in the Wrong Place
Every day in the US, Americans excrete about 90 million gallons
of urine. Most of it is flushed away. That day's urine contains
an estimated 7 million pounds of nutrients in the form of
nitrogen. By some estimates, that's enough nitrogen to fertilize
up to 31,962 acres of corn in one year. And one year of US
urine could fertilize 11.5 million acres of corn. Instead,
manufactured and animal-derived urea fertilizer is imported—sometimes
at great cost.
When we flush urine to septic systems, it can leach into ground and surface waters—often with much of the nitrogen intact.
In lakes and other surface waters, aquatic plants and algae consume the nitrogen, resulting in a great bloom of growth. When this growth dies and decomposes, it pulls oxygen from the water—or eutrophies—which can suffocate fish and other aquatic life. Underground, nitrogen can seep into drinking water, posing a potential health hazard. At the same time this is happening, farmers worldwide purchase tons of nitrogen fertilizer, much of it from industrial fertilizer factories that produce it with imported energy.
Urine-diverting toilets are still rare in the US and not yet listed in plumbing codes. Another method to divert urine is waterless and low-water urinals, which are working their way into codes. (However, since these are designed for males, this only addresses half of the nitrogen load.)
Health-Risk Parameters
Beneficial use of urine, which we might term "nutrient reclamation," differs from land application of septage and treated sludge. Urine offers low-pathogen risk, high-nutrient content, and the ability to drain itself away. Combined septage and sewer sludge potentially contains disease-causing organisms carried by the feces and household chemicals. By not mixing urine with these sources of potential health risks, we isolate the high-value constituent—nitrogen—and put it to use.
Safe methods for using urine to nourish plants are now well
documented, particularly in Sweden, where several research
institutions and Stockholm's water authority studied the sociology,
bacteriology, and viability of collecting urine and using
it to fertilize grain crops.
According to sanitation researcher Caroline Schönning of the Swedish Institute of Infectious Disease Control, humans rarely excrete disease-causing organisms, or pathogens, in urine. Also, most pathogens die when they leave their hosts, either immediately or shortly thereafter. The only significant urine-transmitted diseases are leptospirosis (usually transmitted by infected animals), schistosomiasis, and salmonella. The first two are rare—usually found only in tropical aquatic environments—and the last is typically inactivated shortly after excretion.
The more likely health risk is urine contaminated by feces that were misplaced in a urine-diverting toilet.
Ways to inactivate pathogens include time (waiting them out), composting; heat; and adding high-alkaline additives, such as lime and wood ash. Following are some general guidelines for use:
- For deactivation of most pathogens that may be present, especially if urine from outside of one's household has been collected to fertilize food crops, store urine for six months before use. This period can be shortened if the ambient temperature is higher, such as 65°F. For lowest risk usage, apply it to crops that do not touch the earth, such as orchard fruit, vines, and berry bushes. Or use it only for crops that will be cooked or fed to animals. When in doubt, it should not be used.
- For personal and household urine used for growing food, Schönning deems it an acceptable health risk to harvest raw-eaten crops one month after urine-fertilization.
- Urine is best worked into the soil or applied under the soil to reduce exposure, allow soil organisms to deactivate pathogens, and preserve its nutrient value.
Onsite Possibilities
Collecting urine for farm fertilizer may be on the very far
horizon for the regulated mainstream in the US, but we can
thank the Swedes for pointing the way.
Denitrification with urine diversion can be an easy way to complement existing septic systems without installing expensive biofilters. To treat urine for plant use, it must be oxidized to a nitrate form that plants can use. Or it can be diluted and mixed into well-aerated soil, where the soil's aerobic microbes complete the oxidation (nitrification) process.
Methods for Managing Diverting Urine
- Drain urine to planted graywater system beds. For planted systems, urine's nitrogen is a good addition to graywater, which is a lot of water and a little carbon (BOD) but nearly no nutrients. Direct this combination to a planted evapotranspiration bed. This can take the form of a lined or unlined trench no deeper than 2 feet and filled with .75-inch to 3-inch gravel. These beds can double as landscape features. • Constructed wetlands created to treat only graywater often suffer for lack of nitrogen. Because the wetland environment is more anaerobic than aerobic, nitrogen in a wetland is largely lost to the atmosphere, providing cheap denitrification.
- Drain urine to a tank that is periodically pumped like a septic system. The collected urine can be contained, tested for pathogens, and applied to high well-draining forests, tree farms, or pasture lands. Or it can be discharged to a tertiary treatment plant.
- Municipal composting facilities that handle woody landscape waste and shredded paper often have a nitrogen deficit. Urine provides a low-risk nitrogen match.
Urine can be slightly acidic and salty. It should not be distributed with drip-irrigation tubing unless it is diluted; otherwise emitters might clog.
The world needs all the nutrients we are flushing away each day in our urine. Given the high cost of onsite denitrification systems and the far-reaching costs of using manufactured fertilizers, utilizing this valuable and usually pathogen-free resource deserves more consideration.
Diverting and using urine may seem on the "lunatic fringe" now, but the benefits are so great that it will be a common-sense practice in the future.
CAROL STIENFELD is the author of Liquid
Gold: The Lore & Logic of Using Urine to Grow Plants
(Ecowaters Books), from which parts of this article are excerpted.
OW
- September/October 2005
|
