Content uploaded by Torben Anker Lenau
Author content
All content in this area was uploaded by Torben Anker Lenau on Nov 29, 2017
Content may be subject to copyright.
Lenau, T. & Hesselberg, T. (2015) Dry sanitation concepts with inspiration from nature, Journal of
Water, Sanitation and Hygiene for Development, vol.5 is.2, p.330-335, doi: 10.2166/washdev.2015.178
1
Dry sanitation concepts with inspiration from nature
Torben Lenau
Department of Mechanical Engineering, Technical University of Denmark,
Building 426B, DK2800 Lyngby, Denmark,
Phone: +45 4525 4811
lenau@dtu.dk
www.polynet.dk/lenau
Thomas Hesselberg
Department of Zoology, University of Oxford,
Oxford OX1 3PS, United Kingdom
thomas.hesselberg@zoo.ox.ac.uk
Abstract:
Poor sanitation is a major problem for health and water resources in many developing
countries. Inexpensive but also attractive toilets could be a way to fight these problems.
However radical new ideas are needed to identify innovative solutions. Such novel ideas
might be found by using systematic design methods that search nature for animals and
plants that solve similar problems. The paper describes how 4 conceptual sanitation
solutions for dry toilets solving problems with smell, cleaning and flies can be made in
collaboration between a design engineer and a biologist using biomimetic design
methods. The solutions have the potential to offer significant improvements compared
to conventional non-water based sanitation.
Keywords:
Biomimetic design, dry toilets, cleaning, flies, smell
Lenau, T. & Hesselberg, T. (2015) Dry sanitation concepts with inspiration from nature, Journal of
Water, Sanitation and Hygiene for Development, vol.5 is.2, p.330-335, doi: 10.2166/washdev.2015.178
2
Introduction
The motivation for focussing the present study on sanitation is the fact that it is a global
challenge with huge potential to improve life for many people. It is furthermore a
commercial market area that is still very open in many parts of the world making
radically new solutions more realistic. Sanitation is a major global problem since about
2.5 billion people lack improved sanitation and do not have access to toilets (WHO
2014). Diseases related to bad water, sanitation and hygiene habits cause the death of
about 2.4 million people every year (Prüss-Üstün et al 2008). The solution is better
sanitation that can be achieved using either water based or dry toilets, which are both
safer solutions than traditional open pit holes, defecation in waterways or in the open.
Water based toilets are used in most of the rich countries but suffer from three
problems: Water is a scarce resource in many areas, large investments in sewers are
required and wastewater is often not treated properly. Dry toilets are attractive
alternatives from both an economic and hygienic point of view. They require only a
minimum of infrastructure and waste materials can be kept separated when handled
right. This makes waste treatment much more straightforward. A basic understanding of
the sanitation area was achieved through a literature survey (Winblad et al. 2004; Kar et
al. 2008; Tilley et al. 2008) and contact to key players within the sanitation area. The
volume of urine and faeces that need to be transported to a disposal site are manageable
compared to other transport tasks like garbage and daily goods. The average yearly
faeces and urine production rates per person found in the literature are approximately 47
kg for faeces and 440 kg for urine (Almeida et al. 1999; Del Porto and Steinfeld 2000;
Zavala and Funamizu 2006). However, a number of basic problems are not solved
properly for dry toilets including smell, cleaning and flies. Therefore they are often
regarded as less attractive compared to the water based alternatives, especially for the
large groups of people in developing countries that gradually become wealthier.
Lenau, T. & Hesselberg, T. (2015) Dry sanitation concepts with inspiration from nature, Journal of
Water, Sanitation and Hygiene for Development, vol.5 is.2, p.330-335, doi: 10.2166/washdev.2015.178
3
Methods
Ideas to new innovative solutions can potentially be found using biomimetic design
where inspiration is found in nature. The basic approach used here followed the iterative
procedure described by Lenau et al. (2010). Three specific dry toilet problems were
generalised and keywords formulated to allow a search for analogies within the
biological domain as shown in table 1.
In order to focus the search, the keywords were first used to browse general biology
books and making observations in zoological and botanical gardens. This was followed
by searches in the online literature databases Asknature.org, ISI Web of Science and
Google Scholar and in cited literature within identified articles. Search terms covered
the keywords, relevant synonyms and antonyms.
Each of the found biological phenomena were analysed and the functionality of the
basic biological mechanisms were described and generalised as technical principles.
These principles were used to generate design ideas and develop conceptual product
solutions.
Results
Results include identification of relevant biological analogical phenomena and the
conceptual design of bio-inspired solutions.
Biological analogies
A large number of biological analogies (phenomena) were identified as shown in table 1
and 21 of the search results were considered relevant.
Lenau, T. & Hesselberg, T. (2015) Dry sanitation concepts with inspiration from nature, Journal of
Water, Sanitation and Hygiene for Development, vol.5 is.2, p.330-335, doi: 10.2166/washdev.2015.178
4
The smell problem
One of the main challenges for a wider embracement of dry toilets is the strong odour
emanating from faeces and urine. The smell is caused by the interaction and relative
intensities of a wide range of volatile compounds, arising from the breakdown of
organic matter by primarily aerobic bacteria (Sweeten 1986). One way of handling the
smell is the terra preta principle, which works by maintaining an anaerobic environment
by mixing the faeces with charcoal and adding lacto bacteria in an airtight container.
The terra preta method was developed following a recent re-discovery of the practices
of ancient South American civilisations (Factura et al. 2010). Another possible way to
reduce smell is the feacal sac principle: Bird nestlings make small parcels by wrapping
portions of the faeces in a biologically degradable membrane that can be flown away in
order to increase nest sanitation and reduce predation (Weatherhead 1984; Guigueno
and Sealy 2012).
The cleaning problem
Another problem with dry toilets is how to keep them clean without rinsing them with
large volumes of water. This might be solved using the animal eyeball cleaning
principle using an intermediate removable substance (the tear film) that adheres to dirt
particles (Walls 1942; Braun and Fitt 2003; Jones et al. 2008).
The fly problem
Flies are attracted to both food and faeces and can, in addition to being a general
nuisance, constitute a serious health risk by transmitting diseases. The pitcher plant
attracts flies using volatile substances, including 2-phenylethanol (Chapman et al. 1998;
Di Giusto et al. 2010) and prevents them escaping ones trapped using a special slippery
surface (Gaume et al. 2004). Platelet shaped wax crystals form a sponge-like layer with
Lenau, T. & Hesselberg, T. (2015) Dry sanitation concepts with inspiration from nature, Journal of
Water, Sanitation and Hygiene for Development, vol.5 is.2, p.330-335, doi: 10.2166/washdev.2015.178
5
a pore size of about 1.5 µm, which generate a mechanical stable surface with a
roughness that is too high for the hairy pads found on insect feet to adhere to, while
simultaneously being too low for the insect claws to work efficiently on as shown in
figure 1 (Scholz et al. 2010).
Bioinspired solutions
The technical principles are used as input to the creative part of the design process. We
propose conceptual solutions for 4 principles.
Avoiding smell using the Terra Preta principle
An anaerobic environment is expected to be maintained if an airtight container is used
as shown in figure 2a. This only requires an airtight lid that closes the entrance to the
toilet container when it is not used. In use the lid needs to be opened, but this will only
be for a short period of time. Charcoal, stone dust and lacto bacteria could be stored in
separate containers behind the toilet similar to the water tank in conventional toilets.
The right doses of these materials could then be added into the toilet when ‘flushing’
after using the toilet.
Reducing smell and cleaning problems using the nestling fecal sac principle
Similar to the way nestlings encapsulate their droppings in thin dry membranes a toilet
solution might use a biodegradable plastic bag that covers the toilet bowl and is closed
and sealed after use. It might be possible to automate the process by using a mechanism
driven by the opening and closing of the lid (figure 2b). When the lid is opened a new
bag could be spanned over the toilet bowl and when the lid is closed the bag could be
sealed and removed into a collection chamber. Slightly modified conventional garbage
bags with build in closing wires could be used.
Lenau, T. & Hesselberg, T. (2015) Dry sanitation concepts with inspiration from nature, Journal of
Water, Sanitation and Hygiene for Development, vol.5 is.2, p.330-335, doi: 10.2166/washdev.2015.178
6
Toilet cleaning using the eyeball cleaning principle.
A solution based on the blinking eyeball cleaning principle could use an intermediate
substance to collect the excrements. Two sliding cover plates could form the barrier
between the bowl and the collection chamber. To avoid that the cover plates gets dirty
and to collect liquid substances it is proposed to cover them with a thin layer of gravel.
Gravel and excrements will slide into the collection chamber when the cover plates are
opened. After closing the cover plates a mechanism could spread new gravel onto the
cover plates similar to the eyelid blinking. The potential solution is illustrated in figure
2c.
Avoiding flies using the pitcher plant principle
A trap using the pitcher plant principle could lure the flies into a chamber from where
they cannot escape and will eventually drown. This solution could be placed as an
external object attached to the wall or hanging from the ceiling. The trap could be made
as a vertical cylinder that is closed at both ends and provided with holes at the top just
big enough to allow the entrance of flies as shown in figure 2d. The inside of the
cylinder could be covered with a micro-structured surface that hinders the flies to attach
to it. The bottom part of the cylinder could be detachable to allow it to be filled with a
liquid with a smell that attracts the flies while being acceptable to humans.
Discussion
A relevant question is if the extra work in applying a formalised design method is worth
the effort. Design researchers normally justify such work by looking at the results and
assessing if they are better than reference solutions (Shah et al 2003). The new solutions
should be more innovative and useful to the users.
Lenau, T. & Hesselberg, T. (2015) Dry sanitation concepts with inspiration from nature, Journal of
Water, Sanitation and Hygiene for Development, vol.5 is.2, p.330-335, doi: 10.2166/washdev.2015.178
7
The novelty aspect of the terra preta solution is the chemical reaction used within the
toilet to reduce smell and decompose the waste products, i.e. a decentralised waste
treatment that eliminates the need for costly infrastructure. The novelty aspect of the
nestling solution and the blinking eyelid solution is the reduced need for cleaning
caused by the use of membranes and gravel. The advantage compared to a water based
toilet is the avoidance of flush water and sewer infrastructure. However, the
disadvantage is that the nestling solution requires plastic bags and the blinking eyelid
solution needs gravel or sand. The novelty aspects of the pitcher plant fly trap are the
slippery surface and the closed container. One potential advantage compared to ordinary
flypaper is the closed container that hides the dead flies and functions as a multiuse
product that can be emptied and used many times.
All potential solutions represent improvements regarding both novelty and usefulness.
The work suggests and illustrates how biomimetic design work can be done with
success and presents suggestions for how to overcome a number of difficulties in the
design work of new sanitation solutions. A procedural model for biomimetic search and
design has been demonstrated by applying it to suggest solutions to some of the basic
problems with dry toilets. Thinking in terms of biological analogies produced a large
number of relevant ideas.
Conclusion
The sanitation problems in developing countries has been addressed and is proposed
solved using dry toilets where urine and faeces are handled separately. However, such
separation toilets are potentially less attractive due to poor handling of a number of
problems. We examine three of those problems: smell, cleaning, and contamination
from flies by using a biomimetic design approach. A large number of analogical
solution principles were identified by searching in nature. Conceptual designs were
Lenau, T. & Hesselberg, T. (2015) Dry sanitation concepts with inspiration from nature, Journal of
Water, Sanitation and Hygiene for Development, vol.5 is.2, p.330-335, doi: 10.2166/washdev.2015.178
8
made using four of the principles thus proposing possible solutions. The solutions are
feasible and would most likely not have been arrived at if biological inspiration and
biomimetic design procedures had not been employed during the design process.
Acknowledgements
We are indebted to Christina Okai Mejborn for valuable discussions and experiences
from carrying out a workshop on new toilet solutions. Tomas Benzon made the
illustration for which we are very grateful. TH would like to thank Wolfson College for
providing travel funds.
References
Almeida, M.C., Butler, D. and Friedler, E. 1999 At-source domestic wastewater quality,
Urban Water 1, 49-55
Braun, R. J., & Fitt, D. 2003. To minimise shear stress and to avoid solid to solid
contact between the eyelid and the eye surface, the latter is covered by a thin
tear film. Math Med Biol 20, 1-28.
Chapman, J.W., Knapp, J. J., Howse, P.E., & Goulson, D. 1998. An evaluation of Z-9-
tricosene and food odours for attracting house flies, Musca domestica, to baited
targets in deep-pit poultry units. Entomol Exp Appl 89, 183-192.
Del Porto, D. and Steinfeld, C. 2000. The Composting Toilet System Book. Center for
Ecological Pollution Prevention.
Di Giusto, B., Bessière, J.-M., Guéroult, M., Lim, L. B.L., Marshall D.J., Hossaert-
McKey, M., & Gaume, L. 2010. Flower-scent mimicry masks a deadly trap in
the carnivorous plant Nepenthes rafflesiana. J Ecol 98, 845-856.
Factura, H., Bettendorf, T., Buzie, C., Pieplow, H., Reckin, J., & Otterpohl, R. 2010.
Terra Preta sanitation: re-discovered from an ancient Amazonian civilisation –
integrating sanitation, bio-waste management and agriculture. Waste Science &
Technology 6110, 2673-2679.
Gaume, L., Perret, P., Gorb, E., Gorb, S., Labat, J.-J., & Rowe, N. 2004. How do plant
waxes cause flies to slide? Experimental tests of wax-based trapping
Lenau, T. & Hesselberg, T. (2015) Dry sanitation concepts with inspiration from nature, Journal of
Water, Sanitation and Hygiene for Development, vol.5 is.2, p.330-335, doi: 10.2166/washdev.2015.178
9
mechanisms in three pitfall carnivorous plants. Arthropod Struct Dev 33, 103-
111.
Guigueno, M.F. & Sealy, S.G. 2012. Nest sanitation in passerine birds: implications for
egg rejection in hosts of brood parasites. J Ornithol 153, 35-52.
Jones, M.B., Please, C.P., McElwain, D.L.S., Fulford, G.R., Roberts, A.B., & Collins,
M.J. 2008. Dynamics of tear film deposition and draining. Math Med Biol 22,
265-288.
Kar, K., & Chambers, R. 2008. Handbook on Community-Led Total Sanitation,
University of Sussex, Brighton, UK,
http://www.communityledtotalsanitation.org [as of 14/11/2014]
Lenau, T., Dentel, A., Ingvarsdóttir, Þ., & Guðlaugsson, T. 2010. Engineering Design of
an Adaptive Leg Prosthesis Using Biological Principles. Design 2010
Conference, Dubrovnik, Croatia, 331-340.
Prüss-Üstün A., Bos R., Gore F., Bartram J. 2008. Safer water, better health: costs,
benefits and sustainability of interventions to protect and promote health.
Geneva: World Health Organization. www.who.int as of 14/11/2014.
Scholz, I., Bückins, M., Dolge, L., Erlinghagen, T., Weth, A., Hischen, F., Mayer, J.,
Hoffmann, S., Riederer, M., Riedel, M., & Baumgartner, W. 2010. Slippery
surfaces of pitcher plants: Nepenthes wax crystals minimize insect attachment
via microscopic surface roughness. J Exp Biol 213, 1115-1125.
Shah J.J. and Vargas-Hernandez, N. 2003. Metrics for measuring ideation effectiveness,
Design Stud 24, 111–134
Sweeten, J.M. 1986. Odor measurement and control for the swine industry - Recent
developments. J Environ Health 50, 282-286.
Tilley, E., Lüthi, C., Morel, A., Zurbrügg, C., & Tenleib, R.S. 2008. Compendium of
Sanitation Systems and Technologies, Eawag, Dübendorf, Switzerland.
www.wsscc.org [as of 14/11/2014]
Walls, G.L. 1942. The Vertebrate eye and its adaptive radiation. New York: Haftner
Publishing Company
Weatherhead, P.J. 1984. Fecal sac removal by tree swallows: the cost of cleanliness.
Condor 86,187–191.
WHO (2014) Progress on Drinking Water and Sanitation – 2014 update,
http://www.wssinfo.org/ [as of 16/2-2015]
Lenau, T. & Hesselberg, T. (2015) Dry sanitation concepts with inspiration from nature, Journal of
Water, Sanitation and Hygiene for Development, vol.5 is.2, p.330-335, doi: 10.2166/washdev.2015.178
10
Winblad, U., & Simpson-Hébert, M. 2004. Ecological Sanitation, Stockholm
Environment Institute, Stockholm, www.ecosanres.org/publications.htm [as of
14/11/2014]
Zavala, M.A. and Funamizu, N. 2006 Design and operation of the bio-toilet system,
Water Sci Technol 53, 55–61.
Lenau, T. & Hesselberg, T. (2015) Dry sanitation concepts with inspiration from nature, Journal of
Water, Sanitation and Hygiene for Development, vol.5 is.2, p.330-335, doi: 10.2166/washdev.2015.178
11
Table 1. Search criteria and selected results
1. Problems
– specific
2. Challenges –
generalized
3. Keywords
() marks the number
of hits in
Asknature.org as of
14/11/2014
4. Phenomena (selected)
Normal case = Asknature
Italics = biologist input, brainstorm and
literature
Bold= selected
Smell
- Remove smell
- Hide smell
- Contain/camouflage smell
- Reverse: enhance smell
Smell (22), Odor (51)
Odor eliminator (51)
Remove smell (58)
Hide (34),
camouflage (44) or
Enhance (80) smell
Milkweed protect against predators using
chemicals
Many animals include pheromones in faeces to
signal reproductive status.
Smell in faeces comes from bacteria so use of
antibacterial substances?
Terra preta
Cats burying their faeces
Leaf cutter ants water management
Dessert insects water extraction
Removal of faeces from bird nestlings
Hygiene,
Toilet cleaning
- Cleaning surroundings
- Cleaning oneself
- Avoid getting dirty
Clean (29)
Cleaning (46)
Washing (5)
Self-cleaning (28)
Avoid dirt (97)
Soil does not adhere to earthworms
Gnawers keep soil out of mouth
Lotus flower, Cicada wings
Eye lid in horses wipes the eye.
Gecko eye cleaning
Lotus effect/insect wings. How do dung beetles
and maggots stay clean?
Contamination
from flies
- Keep flies away
- Contamination from direct
contact
- Reverse: pollination
- Reverse: attract flies
- Catch / kill flies
Repel flies (53)
Contamination (16)
Infection (34)
Attract flies (64)
Fly predation (75)
Natural fly control
(419)
Flies find food using their olfactory system
Blowfly feet taste food
Giraffe has repelling skin secretions
Catnip repels insects
Smell attracts flies
Herbs in starling nests keep fleas away
Flies are prey for lizards, spiders etc..
Picher plant
Lenau, T. & Hesselberg, T. (2015) Dry sanitation concepts with inspiration from nature, Journal of
Water, Sanitation and Hygiene for Development, vol.5 is.2, p.330-335, doi: 10.2166/washdev.2015.178
12
Figure 1. Left: The eyelid cleaning mechanism. Right: Non-adhesive behavior of the
inside plant surface to insect feet (based on Scholz et al., 2010).
Lenau, T. & Hesselberg, T. (2015) Dry sanitation concepts with inspiration from nature, Journal of
Water, Sanitation and Hygiene for Development, vol.5 is.2, p.330-335, doi: 10.2166/washdev.2015.178
13
Figure 2. Sketches of conceptual solutions for dry toilets: a) The terra preta toilet, b)
The bird nestling toilet, c) The eyeball cleaning toilet, d) The pitcher plant fly trap.