Martina Schäfer, Noara Kebir, Daniel Philipp (editors) - TU Berlin

PROCEEDINGS Conference MPDES 2011
Hydrothermal carbonization as innovative technology in sustainable sanitation in
Tanzania
Engineers Without Borders (Germany) / Project “Carbonization as Sanitation” (CaSa)
Ariane Krause
Pettenkoferstr. 7, 10247 Berlin, Germany
ariane.krause@ingenieure-ohne-grenzen.org
Abstract
The need for sustainable systems is apparent as climate
change and other adverse anthropogenic activities continue
to negatively affect the soil fertility in Africa. One of the
indicators of the loss of soil fertility is the continuous
decrease in soil organic matter, which is the major building
block of a fertile soil. This is mainly attributed to the
inappropriate practice of human-beings of taking more
substances from the ecosystem than the amount replaced.
As the soil fertility is increasingly lost, food insecurity, due
to dropped productivity of the soil, is becoming a critical
issue in many areas of Africa. Tanzania is not any different
in this respect. On the other hand, most people in rural
areas of Africa still lack possibilities to cover their daily
energy needs in a more sustainable way and many people
mainly rely on firewood. This, in turn, has an adverse
impact on the climate and the soil, causing a local viscous
circle of poor soil and productivity conditions. Moreover,
the sanitation coverage of those areas is very low and there
is a need for appropriate sanitation systems. Therefore, the
aim of this project is, to conduct research on the possibility
of establishing a self-sustaining system for the rural areas
of Kagera, Tanzania, to address the three basic issues:
sanitation, energy supply and soil fertility. The system
consists of a small-scale biogas digester, a urine diverting
dehydrating toilet (UDDT) and an adaptive hydrothermal
carbonization (HTC) unit. Biogas is produced from crop
residues and other domestic organic waste. The
fermentation residues and the dehydrated fecal matter from
the UDDT is then treated with HTC. The carbonised and
sanitized residue is then applied as soil amendment to
improve the soil fertility as manifested by the Terra Preta in
the Amazon. This holistic approach is a new development
in ecological sanitation. Therefore, a comprehensive
sustainability assessment including environmental,
economic and socio-cultural issues will be conducted.
Keywords: Hydrothermal carbonization, biochar, Closing-
Loops, Terra Preta, sustainable sanitation, soil amelioration,
development of adaptive technologies
Problems, background and project challenges
Kagera is one of the poorest regions in Tanzania located
in the northwestern part of the country near Lake Victoria.
Most of the people in this area live with their family in
small houses on subsistence farming. More than 97% of
the rural households still use firewood for cooking. This
predominant use of wood fuel causes deforestation
resulting in big scale soil erosion. Moreover, the region is
dominated by a tropical climate with year round elevated
temperature and torrential rains during two rainy seasons.
Under this climate the soil organic matter is lost easily
due to faster microbial decomposition and nutrients are
susceptible to leaching due to the heavy rain. As a result,
the soil in the region is poor lacking humus, an essential
part of a fertile soil. It is characterised by a low water and
nutrient retention capacity, low cation exchange capacity,
high siltation sensitivity, poor texture and hardening. This
results in very low crop yield, which, in turn, results in
malnutrition leaving the people susceptible to diseases.
On the other hand, due to lack of appropriate sanitation
systems, human excreta are often disposed in the
landscapes or in shallow holes in the ground (“pit
latrines”). This further pollutes the environment and
exposes the people to many diseases. However, with an
appropriate management, the human excreta can be safely
recycled to improve the soil quality while at the same time
addressing the sanitation problem. The energy need of the
people can also be met with small scale biogas plants.
The aim of this project is, therefore, to develop an
appropriate innovative sanitation system by optimising,
adapting, and linking existing processes, specifically: (1)
anaerobic fermentation of domestic waste and crop
residues in small-scale biogas digester 1 , (2) carbonization
and sanitation of fermentation residues and feces under
hydrothermal carbonization (HTC), (3) composting and
(4) application of the carbonised materials to agricultural
plots to improve soil quality (see figure 1 for the flow
diagram).
The benefit of this innovative system is manifold:
� Promotes effective and efficient use of resources to
protect the environment through the supply of biogas
as a substitute for firewood (in particular as an
activity against deforestation) and progressive
recycling of nutrients contained in human excreta to
close agricultural nutrient cycles.
� Improves living conditions of the people in the target
region, insuring long-term food security through
improved soil fertility and thus productivity, better
sanitation conditions and sustainable resource-saving
energy supply.
� Improves soil texture by improving humus conditions
like in the “Terra Preta” 2 as an activity against soil
erosion, soil degradation and desertification.
� Reduces greenhouse gas emissions and facilitates
mediumterm sequestration of carbon into the soil and
improves adaptation to climate change through
improved nutrient and water retention capacity of the
soil.
1 Project Biogas Support for Tanzania - “BiogaST” - of
Engineers without borders (EWB) and the Tanzanian nongovernmental
organisation MAVUNO Project.
2 That is a very fertile and black soil with high carbon and
nutrient content, as practised by the Incas in South America a
long time ago.
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