"48 Natal Street is a family home... . [Its example] shows that almost any home, even a 100-year-old Edwardian inner-city house, can be converted for dry sanitation, greywater recycling and rainwater harvesting."

• Background
• Dry sanitation system
  • Design
  • Issues in implementation
  • Composting of fecal matter
• Greywater recycling
  • Greywater and context
  • Three main issues
• Rainwater harvesting
• Conclusions
  • Urine diversion
  • Greywater recycling
  • General
• Endnotes
• References
• Author information

Background

(Back to top)
48 Natal Street is an Edwardian home situated in the tough, densely populated inner city of Johannesburg, South Africa. It serves as a family home for two adults and an 11-year-old child, as well as a tenant renting the garden cottage.

For the past 3-1/2 years, the household has been using dry sanitation (i.e., dehydrating, urine diversion toilet) as well as composting, grey water recycling and rainwater harvesting. These measures have resulted in considerable water saving. According to the Johannesburg Water Services Provider, the average Johannesburg household uses 30 kiloliters (kl; 7,925 U.S. liquid gallon [gal]) of water per month. In affluent suburbs with large gardens, this average increases to 50 kl (13,209 gal). Water consumption at 48 Natal Street, on the other hand, has been reduced from a monthly average of 26 kl (6,868 gal) to 18 kl (4,755 gal). This represents a water saving of 30%.

Dry sanitation system

Design

(Back to top)
The dry sanitation system chosen by the household is a low-cost, owner-built, single chamber dehydrating urine diversion system with external composting. The pedestal toilet is cast in concrete from a mould imported into South Africa from Mexico. The design facilitates the separation of urine and feces, while having the appearance of a conventional toilet.

Urine flows from the front of the pedestal (a urinal) down a pipe into a 25-liter (6.6 gal) container. A shallow chamber (approximately 600 mm X 600 mm [23.6 in X 23.6 in]) under the toilet contains a 30-liter (7.9 gal) bucket into which the feces fall. After defecation, two cupfuls of dry soil are sprinkled down the toilet. This thin layer of dry soil prevents smell and facilitates the drying of the feces.

In South Africa, at least 8 liters (2.1 gal) of water is used every time a conventional toilet is flushed. Dry sanitation presents an obvious water saving, and the daily experiences at 48 Natal Street over the past 3-1/2 years show that it is a viable alternative to waterborne sewage.

Issues in implementation

(Back to top)
However, given the urban 'flush-and-forget' culture created by waterborne sewage, dry sanitation is widely viewed as inferior, distasteful and/or unacceptable to city dwellers. The main issues to be dealt with in overcoming this aversion are:

• smell
• personal safety and convenience
• aesthetics
• temporary versus permanent systems
• household involvement
• cost, and
• aversion to handling feces and urine.

Smell

The household finds that the urine diversion system doesn't smell. This is especially important as the system is not merely inside the house, but in the main bedroom's en-suite bathroom. That unpleasant odors do not occur, is dependent on the fecal matter remaining dry.

Personal safety and convenience

In the high crime, inner city area of Johannesburg an outside toilet will present personal safety issues for the household. Also, having an outside toilet is inconvenient and lacks privacy. Experience at 48 Natal Street shows that the urine diversion system functions well inside the home which means security and privacy remain intact.

Aesthetics

Link to Figs 1 & 1a, ~38K

The urine diversion pedestal in use at 48 Natal Street looks at first glance like an ordinary flush pedestal. It doesn't have a home-made, second rate appearance. From an aesthetic point of view, it fits in well with the rest of the bathroom.

A temporary versus a permanent system

Not all dry sanitation systems are suitable for use in the average city home. From a space and design point of view, a typical bathroom requires a toilet pedestal to remain fixed in its original position. This makes such designs as, for instance, a double-pit composting toilet unsuitable since the pedestal needs to be repositioned over the second pit once the first pit is full. The system at 48 Natal Street works well with a fixed pedestal because its design enables easy periodic removal of materials for composting.

Household involvement

Link to Figure 2, ~ 33K

The system requires some involvement from the household. Once a week, the urine is emptied into an on-site composter, which contains the garden waste. This results in a balanced carbon:nitrate ratio, which promotes rapid decomposition into a rich compost..Once every three weeks, the feces is also added to a second on-site composter, where it is co-composted with the kitchen waste.

Cost of the system

Cost is an important issue in developing countries where most households cannot afford expensive technologies. The household of 48 Natal Street spent approximately R250.00 (USD 45) to convert their flush toilet to the urine diversion system currently in use.

Aversion to handling of human wastes

Individuals may have an aversion to handling feces and urine and therefore find a urine diversion system unacceptable. In some instances, cultural issues come to play. However, in developing countries the cost of conventional services (in-house water with flush toilets) can be prohibitive for people on low incomes. If individuals have an aversion to handling their own fecal matter then they must pay someone else to do so. They cannot expect someone else to handle their feces for free if they themselves will not handle it. What is sometimes referred to as "feco-phobia" may be overcome where cost concerns take precedence.

In the case of 48 Natal Street, the household does not have an aversion to adding urine and feces to their compost since no direct contact with these wastes is ever required. Further, the household composts feces safely and responsibly in line with current research findings and therefore sees no danger in it.

Composting of fecal matter

(Back to top)
At 48 Natal Street, feces from the toilet, together with the organic waste from the kitchen are composted on-site, in a process comprising four phases (1):
1. mesophilic phase
2. thermophilic phase
3. cooling phase
4. curing phase.

For the safe composting of feces, the second (thermophilic) and fourth phases (curing) are the most important. During the thermophilic phase, the temperature of the compost should rise to 60 degrees Celsius [140 degrees Fahrenheit] , preferably no higher than 65 degrees C [149 degrees F]. The heat kills off harmful pathogens found in human feces. The size of the composter at 48 Natal Street (1 m X 1 m [3.3 f X 3.3 f]) is necessary to facilitate this rise in temperature. The curing phase of the compost at 48 Natal Street lasts for at least a year. This long period provides another safety net for the destruction of harmful organisms.

People may assume that the placement of a large composter in a small inner-city garden is an issue because it will surely smell. At 48 Natal Street, however, the composter is situated at the front door of the home. The household reports that there is no smell, nor do visitors realize that it contains fecal matter.

Link to Figure 3, ~ 35K

Keeping the composting process aerobic further helps to prevent smell. Towards this end, the compost is turned on a regular basis. Also, covering the top of the compost with a thin layer of soil prevents smell from decaying organic matter, especially decaying tropical fruit, another regular component of the household's compost.

Greywater recycling

(Back to top)
At 48 Natal Street, greywater from the bath, shower, kitchen sink and washing machine is recycled on-site.

Greywater and context

(Back to top)
To lay down the law or even suggest guidelines regarding greywater recycling is a challenge, because greywater recycling is context-specific. Multiple factors particular to any one greywater site (e.g. existing soil conditions, climate, quality of greywater, the recycling system, even family habits) work hand-in-hand towards achieving any particular result. For the practitioner, greywater information and guidelines abound. While these are useful to highlight issues of concern, it has been the experience at 48 Natal Street that information should be evaluated, applied and modified in line with actual site-specific circumstances.

Three main issues

(Back to top)
A review of available greywater literature indicates three dominant issues:

• the recycling system
• effects of greywater on soil
• risks to human health.

The recycling system

Link to Figs. 4 & 5, ~ 60K

At 48 Natal Street, the household waste water pipes lead into a subterranean sump (a 50 liter [13.2 gal] bucket). As it fills up, a float switch automatically turns on a small submersible pump. The greywater is pumped from the sump down a garden hose and sprayed onto the garden. Because the water is not stored but is sprayed on the garden right away, the process is kept aerobic.

Water from the kitchen sink is filtered, through a standard kitchen sink filter and then by a swimming pool filter in the sump, to prevent solid kitchen waste blocking the system. The 2nd filter needs cleaning approximately once a week.

This system presents several advantages. It is easy to run and doesn't require high input from the household. Also, the greywater isn't stored but is used immediately. Greywater stored for more than 24 hours become anaerobic, takes on an unpleasant odor, presents a health hazard and is to be avoided. A further advantage of immediate use is that surface spraying via garden hose allows for the greywater to be easily applied to garden areas where irrigation is most needed. The household also reports that blockages occur infrequently.

The system has some disadvantages in that some vigilance is needed to avoid the pump burning out in event of a blockage.

The household's experience is that surface spraying does not adversely affect most ornamental plants, but that the leaves of some vegetables such as tomato plants cannot tolerate greywater. As the quality of greywater and recycling systems differ from site to site, it is suggested that greywater users experiment to ascertain which plants in their own garden react adversely to greywater.

Effect of greywater on soil

Two soil samples from 48 Natal Street were analyzed by Central Analytical Laboratories (South Africa) (CAL). Sample 1 ("fresh water soil") served as control sample and was taken from an area not irrigated or in contact with greywater. Sample 2 ("greywater soil") was taken from an area almost exclusively irrigated with greywater. The samples were tested for pH, phosphorus, potassium, calcium, magnesium, sodium, calcium/magnesium ratio, magnesium/potassium ratio and boron.

Numerous factors will have a bearing on the effect of greywater on soil. These may include the characteristics of soil prior to recycling, period of recycling, area irrigated, volume of greywater used, rainfall, detergents used, and the pH of soil and municipal water supply.

• Detergents
  • A review of the literature reveals an emphasis on cautioning against sodium and boron build-ups in soil from high-strength detergents. In the light of these stern warnings, 48 Natal Street has done worst-case-scenario recycling: The cleaners and washing powders used to date are high-strength, containing both of these elements. Further, the soil samples were taken at the end of the dry winter season before the arrival of the summer rains, making leaching of excess sodium and boron unlikely. The greywater soil sample collected contained sodium and boron, but levels of both fell within accepted norms. Thus, the sodium and boron build-up repeatedly cautioned against in the literature has, rather surprisingly, not occurred.
• pH
  • CAL suggests that the ideal pH for soil is between 5.8 and 6.8. Both on-site soil samples fell within this range. Also, the pH of the soil from both the control and the greywater soil samples was almost the same, suggesting that in 3-1/2 years of greywater recycling the soil pH had not changed.
• Concentration of salts
  • The greywater soil shows a low resistance (high electrical conductivity), indicating high levels of salts other than sodium. CAL suggests that the most probable source of these salts is urine which was poured over this patch of soil shortly before the sample was taken.
• Magnesium and potassium
  • Both the greywater soil and the fresh water soil contain low concentrations of potassium and magnesium, nutrients required for normal plant growth. According to CAL this shortage cannot be linked to greywater recycling.
• Fat build-up in soil
  • An accumulation of fats in soil from kitchen sink water is harmful as it makes soil hydrophobic.
    Although the collected soil samples were not tested for fat content, the household believes that it is unlikely that fats have accumulated in soil at 48 Natal Street. Firstly, CAL points out that dishwashing liquid and detergents are designed to break down fat into smaller molecules (that are no longer fats). Secondly, the household refrains from pouring liquid fats down the sink; they are disposed of into the composter.

Health risks

The greywater literature widely reports that there is no recorded case of anyone falling ill as a result of household recycling of greywater.

The only study on this issue located by the author is one referred to in a paper by Glen Marshall (1996). Marshall mentions a 1992 study by the Los Angeles Office of Water Reclamation. Unfortunately a copy of the original study could not be obtained. From Marshall's paper it appears that eight greywater re-use systems were monitored for one year in the City of Los Angeles. The conclusion was that greywater didn't pose a significant health risk. No disease organisms were present either in areas irrigated with greywater or in stored grey water. The study further concluded that this indicated either an entirely healthy test population, which would be highly unlikely, or a mechanism for deactivation of pathogens.

Enquiries to the South African Medical Research Council and The National Institute for Communicable Disease (South Africa) proved fruitless as these organizations had nothing to add. However, the consensus is apparently that, on the face of it, household greywater recycling doesn't pose enough of a health risk to warrant expensive research. Further, the conditions existing in an aerobic greywater system do not allow for any surviving harmful organisms to multiply sufficiently to pose a threat to human health. The experience at 48 Natal Street reflects this conventional wisdom: No member of the family has fallen ill as a result of greywater.

Link to Figure 6, ~ 36K

Based on the available evidence, then, it seems only reasonable to conclude that the health risks associated with responsible greywater recycling (particularly aerobic greywater) are negligible.

On the whole, greywater literature reflects a general "rather-safe-than-sorry"' approach, particularly where vegetable crops and surface spraying are concerned. The University of Massachusetts Extension Service online fact sheet "Recycling greywater for Home Gardens" (Barker and English 2000) is a typical example, suggesting that it is unlikely that disease can be transferred from greywater to vegetables and back to humans. Nevertheless these guidelines recommend that vegetables should not be watered with greywater -- to be on the safe side. They further suggest that sub-surface irrigation should be used, as greywater might pose a health hazard for humans who come into direct contact with it.

At 48 Natal Street, vegetables have been watered with greywater, including surface irrigation, for 3-1/2 years with no apparent ill effect on the household. Due mainly to the hot climate, greywater doesn't pool or cause run-off; nor is it stored long enough to become anaerobic. Finally, the sprayer used for surface irrigation is highly visible and people simply avoid being sprayed by keeping out of its way.

Rainwater harvesting

(Back to top)
Johannesburg is a summer rainfall area with a moderate annual rainfall of 715 mm (~28 in). During the wet season, rainwater runoff is collected through down pipes into two water tanks with a collective capacity of 1.2 m3 (317 gal). This water supplements the grey water garden irrigation and is used mainly on sensitive plants, planters or other areas where confined irrigation is required.

For the inner city home, rainwater harvesting capacity is limited due to lack of space. 48 Natal Street cannot accommodate large enough rainwater tanks to see the winter months through. During this very dry period, tanks often run dry and some municipal water must be used for irrigation.

Conclusions

(Back to top)
Urine diversion

The build-up of salts from urine in the greywater soil sample collected from the household suggests that high concentrations of urine should not be added to any one patch of soil. Rather, urine should be poured into a garden waste composter or led into a soakaway. (Urine can be used as garden fertilizer when it is spread around, or else concentrated in areas with vegetation able to absorb the nitrates.) Also, it is suggested that compost from 48 Natal Street be analyzed to determine whether it reflects research findings on the safe composting of feces.

Greywater recycling

(Back to top)
Despite three and a half years of greywater recycling and using high-strength detergents, no sodium or boron build-up has occurred in the greywater soil. Several questions arise. In a household recycling context, is it at all likely that such a build-up will occur? If so, within what period? Further soil analysis involving existing household greywater sites using high-strength detergents should be done to find answers to these and other questions.

With regard to greywater health issues, the state of research is such that it is left to individuals to make up their own minds as to what is "safe" and what not. Practitioners have to find their own comfort zone on the "neurosis vs recklessness" continuum. This is especially true in countries such as South Africa, where there is no legislation giving direction in this regard.

On the whole, a review of available greywater literature reflects a mix of research, opinion, and varying levels of anxiety concerning health risks. Since greywater and its use is context-specific, it is suggested that the greywater practitioner should supplement research with hands-on experience, and allow common sense to prevail.

General

(Back to top)
Technical issues aside, the successful use of urine diversion and greywater recycling depends on user acceptance. It should be a household choice with the necessary information available to the family.

In an urban setting, water saving systems need to fit busy urban lifestyles; they should not be time-consuming to run and maintain. At 48 Natal Street the urine diversion and greywater systems substantially fulfill these requirements; both need minimal involvement from the household. Also, systems need to be aesthetically pleasing and free of offensive smells -- especially in confined urban spaces where smelly composters, toilets and foul-smelling stored greywater cannot be hidden or banished to far-flung corners, away from the main house. Again, experiences at 48 Natal Street show that both dry sanitation and greywater systems can be designed to avoid such odors, making them suitable for urban settings. And, a good choice of rainwater harvesting tank can even add to the aesthetics of a small garden.

Finally, 48 Natal Street is a family home as opposed to a 'project' or a show house not actually lived in. It shows that systems often associated with rural homes or New Age Green fringe cultures are suitable for use by the average family. It also shows that almost any home, even a 100-year-old Edwardian inner-city house can be converted for dry sanitation, greywater recycling and rainwater harvesting.

End notes

(Back to top)
1. For more information see Chapter 3: Four Stages of Compost in Jenkins (1999). [return to text]

References

(Back to top)
Jenkins, Joseph C. 1999. The humanure handbook: A guide to composting human manure. Grove City, PA: Jenkins Publishing. Online: http://www.weblife.org/humanure/

Marshall, Glen. 1996. Greywater re-use: Hardware, health, environment and the law. Paper delivered at the sixth International Permaculture Conference and Convergence, Perth & Bridgetown, Western Australia, September 27 to October 7, 1996. Online: http://www.rosneath.com.au/ipc6/ch08/marshall/index.html

Barker, Allen V. and Jean E. English. 2000. Recycling gray water for home gardens. Amherst, MA: Univ. of Massachusetts Cooperative Extension Service. Online: http://umassgreeninfo.org/fact_sheets/plant_culture/gray_water_for_gardens.html