|
By Carol Steinfeld
Consider the flows that might be discharged by a two-bedroom house inhabited by a family of two adults and two children every day:
Perhaps five gallons of slightly soapy water from bathroom sinks.
Maybe 19 gallons (10 flushes) of water, paper and excreta from two bathrooms, 16 gallons of which are urine and water.
Thirty gallons of graywater from four daily showers.
Three gallons of greasy washing water and four gallons of rinse from the kitchen sink and dishwater.
Forty gallons of graywater from two loads of laundry in the washing machine.
Each flow has a different biological oxygen demand (BOD), total suspended solids (TSS), nitrogen (N) and an actual or potential fecal coliform count. Some of these constituents and concentrations are easier to treat than others. Some are more dilute, some are more concentrated, even from the same fixture.
The toilet water, or blackwater, by far represents the greatest potential source of fecal coliform and pathogens and certainly nitrogen and phosphorus.
Other flows, such as sink and washing machine graywater, are relatively benign, with minor BOD volumes and fecal coliform to treat.
Yet all of these flows ultimately combine to leave the house in one pipe to a septic system or municipal sewer, where considerable energy, time and money are spent to separate these elements for treatment then disposal or use. As one wastewater treatment plant operator says, “Most of my job is separating solids from water.”
The premise of the decentralized onsite treatment advantage is that flows are kept small, local and separate from effluents that require more technical treatment, such as industrial discharges laden with heavy metals or toxic chemicals.
Yet perhaps we don’t take the decentralized onsite recycling approach far enough: Instead of thinking of flows as building- or site-specific (i.e., the discharge of one building is one flow), we might work up the home’s pipe and tease out the various flows that enter it to allow for a flow-specific treatment approach.
This approach takes the onsite advantage to its ultimate efficiency: treating each dilute or high-strength flow with a modality best suited to its specific constituents and treatment goals. Besides offering treatment efficiencies and possibly cleaner discharges to soils and groundwater, this approach also provides more reuse opportunities for both water and nutrients.
The most obvious and popular example is treating graywater—a relatively low-strength effluent—to irrigate gardens and landscapes.
The tradeoff is more pipes, possibly more hardware, and more complexity. However, this complexity offers advantages for effectiveness and security. In the specific sense, it allows for the security of knowing if one system is not working optimally, the others likely are. In the broader sense, It is nature’s way, just as a robust and resilient ecosystem consists of a diversity of systems working interdependently and locally at a scale appropriate to the site environment, with resource and energy cycles kept tight. In the same way, water and nutrient flows can be more strategically managed to be used onsite to the benefit of the humans, flora and fauna on that site.
In the future, a home’s landscape will likely feature two or more wastewater treatment components disguised as gardens or groves of trees.
The result: Cleaner effluents, fewer potential pollutants, more reuse opportunities, and possibly lower costs overall.
 |
Photo: Edward Steinfeld |
| Engineered landscape features, including shrubbery, can be showcased or simply
blend into the surrounding landscape, such as this backyard at the home of Alison
Flynn and Seth Wilkinson. |
A Menu Of Effluents
To illustrate the advantages of source separation, consider the menu of specific flows from a home and some specific treatment methods.
Blackwater—The highest-strength flow, with the highest nitrogen and phosphorus (mostly from urine), organics, total suspended solids, and potential pathogens in the form of human excretions and toilet paper is toilet effluent or “blackwater.” More than any other domestic wastewater, this flow is the most technical and mostly what comes to mind when one thinks of brown-gray malodorous “wastewater”.
Diverting this flow from the home’s lower-strength flows reduces the pathogen deactivation challenge.
Interestingly, blackwater, with or without urine, has an advantageous carbon-nitrogen ratio and average pH for faster aerobic and anaerobic stabilization.
This flow can be thick, but at about 80% water, it is liquid enough to effectively drain to sewer or septic without a boost from other flows.
Fastest stabilization occurs with aerobic processing. The septic tank in the future might be replaced with aerobic biofilters that dewater blackwater and expose it to air, either passively or mechanically, creating a more finished and dry end-product that is lighter to transport to septage or composting facilities or for use onsite. Today’s so-called composting toilet system technology essentially operates in this way. An in-ground aerobic biofilter system might look like a cage within an aerated tank, much like some of the aerated denitrification systems on the market today. In many states, installing a composting toilet system allows for a reduced-size leachfield, often a significant cost savings that also minimizes disruption of the site and its trees.
 |
Photo: Carol Steinfeld |
| Alison Flynn shows her low-flush toilet designed to
divert urine into a separate tank that in turn drains
to a garden specially engineered for growing away
the plentiful nitrogen in this flow. |
 |
Photo: Waterless Co. |
| Waterless urinals help isolate half the
primary nitrogen stream discharged
from most buildings. |
The result: more quickly stabilized organics and pathogens and an end-product more suited to land application for its lack of heavy metals and household chemicals.
Further possibilities include using micro-flush toilets and dual-flush toilets to further reduce toilet-flushing water.
The Aquatron Separator from Sweden even uses a centrifugal unit to separate solids from the flushing water.
And certainly the blackwater-only approach is most economical for those using holding tanks.
Treatment possibilities include:
- Septic systems
- Reduced-size, advanced septic systems with air diffusers, specialized media, etc.
- Composting toilet systems
- Reduced-size holding tanks
- Methane digesters
Urine and “Yellow water”—Most of the nitrogen and phosphorus in blackwater are in the urine stream alone.
As nitrogen pollution of ground and surface waters emerges as the hot issue for more and more communities, the advantage of isolating its primary source—human urine—is huge.
Urine accounts for as much as 90% of the nitrogen in a household flow. Nitrogen leaves the human body in the form of urea, creatine and other components, mostly as a result of consumed protein unused by the body. (And with today’s high-protein diets, that content is perhaps higher than ever.)
Yet urine is nearly always pathogen free in a healthy population. The most likely exceptions are hepatitis C, leptospirosis, and schistosomiasis; however, Swedish research shows that all are deactivated with a short period of containment, and usually are not measurable hours after excretion.
Urine leaves the human body separately, and that provides opportunities to collect it.
The easiest opportunity, already common in public facilities, is urinals—both waterless and water-flush.
A newcomer to the wastewater field is the urine-diverting toilet. Today’s models are mostly manufactured in Sweden and Mexico, and feature a separate drained compartment cast in the front of the toilet bowl to which urine naturally expresses when the user sits (or aims carefully while standing). These are available as both waterless and flush models.
Separated without water, urine in dry weight has about a 11-2-2 NPK (nitrogen-phosphorus-potassium) value, although this varies widely, depending on the diets of the users.
For the value of flushed urine, add the per-flush volume. The Europeans coined a term for the urine-flushwater mix: “yellow water.”
There are two ways to view the urine advantage: Use and easier disposal.
The yellow water flow is a blend of water and nitrogen-rich urine, an ideal mixture for plants. Therefore a natural opportunity is to use this flow for fertilizing and irrigating landscapes.
 |
Photo: Carol Steinfeld |
| A translucent Lexan overhang helps keep out precipitation that would require expanding
the size of this washwater garden. |
 |
Photo: David Del Porto |
| A vegetated treatment solution can be outdoors or indoors, such as this polishing
marsh in a greenhouse. |
Swedish and Mexican schemes collect urine and diluted urine, and use it to fertilize animal fodder crops, such as alfalfa and barley. Studies show that six months of containment deactivates any pathogens present, most of which are likely due to fecal contamination of the urine.
Human-derived nitrogen is in a nitrite form and must be converted to nitrate (by the nitrification process) to be used by plants. This is best done with an aerobic system or by applying it to aerobic, well-mulched soil with a high carbon content to fix the nitrogen.
For the wastewater system designer, a more feasible approach is to create a garden system to either grow it away or to denitrify it.
To denitrify, or put the nutrients into the air, this flow can be kept separate for denitrification through conventional a denitrification box system or via a small wetland, both of which provide anoxic conditions to denitrify it.
By isolating this flow, which accounts for most of a home’s nitrogen discharge, a smaller nitrogen management solution can be employed in place of a larger one sized for a total flow.
This also allows for addressing nitrogen without major pathogen concerns.
Another advantage: Removing plant matter (biomass) periodically also removes the phosphorus.
 |
Photo: Society for the Protection of New Hampshire Forests |
| Graywater is recycled for irrigating indoor planters at the headquarters of the Society
for the Protection of New Hampshire Forests. Condensate from air conditioners
and dehumidifiers can also be used, helping to take a load off the septic or sewer
system. |
And urine is a relatively low-phosphorus fertilizer, making it ideal for phosphorus-sensitive sites near streams, ponds and lakes. Nitrogen is the primary nutrient for growing leafy greens.
Designers of wastewater systems for day-use only facilities, such as schools, might look at yellow water-only solutions since these facilities often have nitrogen-rich flows without sufficient carbon or graywater to provide the biochemistry necessary to treat it.
Treatment possibilities include:
- Reduced-size denitrification box systems
- Intermittent and trickling sand filters
- Constructed wetlands, both free-flowing and subsurface
- Planted evapotranspiration system for nitrification and use by plants
- Collection and storage for on- or offsite use such as for grass, hayfields, and tree farms, and for composting sites that need a nitrogen boost.
Graywater—Graywater, or water used for washing, is one of the lowest-strength effluents yet represents the highest effluent volume in a home. Property owners increasingly seek to use this effluent for non-potable purposes, especially in water-scarce regions.
Graywater is more than soapy water: Its content of BOD (mostly carbon from soaps and oils) and fecal coliform potentially washed off bodies deserves respect and treatment.
Showers and sinks in bathrooms generate a lot of warm soapy water. Because bathroom fixtures are used to wash human bodies, there can be a fecal coliform presence in bathroom graywater. Hair, skin oils and particles are best filtered from this flow.
Kitchen graywater is deemed blackwater in many states for its potential content of blood, grease and oil, particles, and animal-derived pathogens. Installing a garbage grinder also makes this a blackwater flow and can add to septic system design-flow size in states. Avoiding the grinder, instead using disposal or a composter for food scraps, allows for a smaller flow. To better prepare this flow for use, install a grease and oil interceptor and avoid using a garbage grinder.
Washing machine and dishwater effluent have the lowest pathogen risk unless diapers are washed. Many clothes today are made of recycled plastic and other non-degradeable fibers that can clog soils. A 30-micron filter, such as a Septic Protector, removes this. For easier filter service, install a 120-micron filter and a 30-micron filter in line, so the larger particles do not instantly clog the finer filter.
Phosporus can be present in laundry effluent, as phosphates are used to prevent caking in powdered detergents. If a powder doesn’t claim to be free of phosphates, switch to liquid detergent.
Graywater’s BOD content asks for aerobic processing to provide the biology the breaks this down and prevents clogging of soils. Greases and fibers should be filtered out. Remember that graywater’s BOD is mostly carbon; for fastest breakdown, it needs a nitrogen boost, such as a small amount of urine.
Consider season- and use-specific strategies that change throughout the year: Graywater might be collected during the winter and used throughout the summer. Minnesota sanitarian David Abaz directs his graywater to a greenhouse crops in the spring, an orchard during the summer, and to a deep leachfield during the winter.
Treatment possibilities include:
- Graywater-only leachfield
- Graywater wetlands
- Planted evapotranspiration system
- Recirculated planted system with filtration
- Two-day retention, settling and filtration for drip-irrigation systems
- Intermittent sand filters
- Advanced filtration and disinfection for toilet flushing and hot-cycle clothes washing
- Collection for offsite irrigation use or fire protection
Maintaining It
Do more pipes, more treatment systems, and more complexity mean more likelihood of problems? Because the landscape-integrated systems require mostly gardening tasks to maintain them, their care is less specialized. On the homeowner end, an incentive to maintain and respect them is built in. No one wants to pour toxics or greases down a drain that leads to a beautiful garden.
As is often a conclusion of the onsite wastewater field, centralized management of these decentralized systems offers obvious advantages. The same team of employees who might staff a central treatment plant would instead monitor and troubleshoot a municipality’s onsite systems. Instead of a staff of 10 grade-8 wastewater treatment operators, a mobile management team could consist of 10 grade-2 treatment plant operators—a cost savings. Landscapers and gardeners, who already understand landscape ecology, could services these systems with very little additional training.
At the same time, a homeowner with an overloaded septic system or a town with a topped-out wastewater treatment plant might look to flow-specific strategies as an alternative to costly new systems. Yellow water might be collected from schools and cluster systems for use on hayfields. Graywater systems might be installed in communities. Urinals could be installed in homes and drained to specially engineered gardens—skimming off half of an average home’s nitrogen output.
The potential of growing away wastewater—which sequesters both nitrogen and carbon—and incorporating treatment modalities into landscape features and perhaps even local growth of food, biofuels and building fiber, is a strategy that may one day obviate the terms “pollutants” and “wastewater”.
Carol Steinfeld is author of Liquid Gold: The Lore and Logic of Using Urine to Grow Plants.
OW - January/February 2007 |
