Linking energy-sanitation-agriculture: Intersectional resource management in smallholder households in Tanzania
Graphical abstract
Introduction
In many regions of the world, including sub-Saharan Africa (SSA), biomass is the most significant energy carrier for domestic cooking (Parikka, 2004). In this context, “bioenergy” refers to the technical recovery of energy from biomass resources, such as firewood, organic waste, energy plants, etc. (Kaltschmitt et al., 2009). To avoid exhausting natural resources, it is necessary to manage biomass resources effectively, both in its collection, and its efficient use. The former is realised through sustainable resource management techniques, such as forestry management. The latter is achieved largely through employing well-designed technology, such as those for cooking. The simplest and most prominent application of bioenergy is likely to be the three-stone fire. There are, however, more environmentally friendly, technologically sophisticated bioenergy alternatives available that have been designed with the aim of reducing, or substituting, the use of firewood. These include improved cooking stoves (ICS), which use firewood or organic waste materials with a low moisture content, such as sawdust, maize cobs, rice husks, coffee husks, etc. ICSs are employed to provide heat for cooking in both households and institutions (Jetter and Kariher, 2009, Mukunda et al., 2010). So-called microgasifier stoves are a particularly technologically advanced example of ICS (Roth, 2011). After cooking with a microgasifier stove, a mix of ash and char particles with a significant carbon (C) content is produced as a by-product (McLaughlin et al., 2009). Referred to as ‘biochar,’ it can be used as an additive for compost (Kammann et al., 2015) and thus as a soil amendment (Lehmann and Joseph, 2015), after the principles of the genesis of Terra Preta soils (Glaser and Birk, 2012). Organic matter with comparatively higher moisture content, meanwhile, such as cow dung, kitchen waste, harvest residues, etc., can be anaerobically fermented in small-scale biogas digesters (Tumwesige et al., 2011, Vögeli et al., 2014). The residue of biogas production, biogas slurry (also called bio-slurry or digestate), is particularly rich in nutrients and is a suitable fertilizer in organic farming (Möller and Müller, 2012). To sum up, depending on the availability of the respective fuel resources, bioenergy technologies can (i) substitute firewood as the main energy carrier, which reduces pressure on forest resources, and (ii) provide residues, which can in turn be used to recover nutrients and C for agriculture.
Bioenergy can also be applied to sanitation processes in order to destroy or deactivate pathogens from human excreta (Krause et al., 2015). Preventing the transmission of disease when managing human excreta (i.e. urine and faeces) is an essential element of ecological sanitation (EcoSan) and needs to take place at as early a stage as possible during the process (WHO, 2006). For this reason, thermal sanitation must take place directly after the faeces, which have the highest pathogen content, have been collected in a urine-diverting dry toilet (UDDT) or composting toilet, and before the matter is composted. Thermal sanitation follows the time-temperature relationship to deactivate pathogens as described by Feachem et al. (1983), and is realised in practice via pasteurisation (Krause et al., 2015), co-pelletising with subsequent gasification (Englund et al., 2016), or direct incineration (Niwagaba et al., 2009). Further approaches for sanitation include drying (Richert et al., 2010), composting (Ogwang et al., 2012), or lacto-acid fermentation (Factura et al., 2010). Sanitising urine, in contrast, is relatively easy and safe. The World Health Organisation recommends simply storing it, which leads to a rise in pH that inactivates pathogens (WHO, 2006). Once sanitation has been completed, human excreta constitutes a valuable resource of nitrogen (N), phosphorus (P), potassium, and micronutrients. Against this background, within the framework of EcoSan, human excreta is no longer regarded as ‘waste’ but rather as a resource. To sum up, EcoSan is an alternative to conventional ‘one-way’ or ‘end-of-pipe’ sanitation systems which aims to (i) prevent environmental pollution, especially that of aquatic ecosystems, and (ii) recycle resources, including the nutrients in human excreta and wastewater (Esrey et al., 2001, Winblad et al., 2004).
The prime source of energy in Tanzania (TZ) is wood, either utilised directly as firewood, or in the form of processed charcoal (Msuya et al., 2011). When looking at farming households in rural TZ, meanwhile, we find a variety of different biomasses used as cooking fuels, though firewood still clearly dominates (Grimsby et al., 2016). Furthermore, while septic systems are most common in peri-urban and urban areas, pit latrines are the most common sanitation system in rural areas (Chaggu, 2004, Cheruiyot and Muhandiki, 2014). The widespread installation of pit latrines from the 1940s, largely through ‘development cooperation’, has led to the abandonment of locally adapted recycling practices (Rugalema et al., 1994). This means that those nutrients removed from the soil by crops are no longer fully recycled back into the agricultural soils. The result of this is that depletion of nutrients and soil organic matter (SOM) is, alongside erosion, a major threat to smallholder farming in SSA (Markwei et al., 2008, Montanarella et al., 2016). As mentioned above, residues from bioenergy and EcoSan are a potential resources to recover C for restoring SOM and nutrients, thereby filling the fertiliser gap.
To the best of knowledge, there have been as yet no integrated resource studies carried out that combine an analysis of both applied cooking and sanitation technologies in relation to smallholder households in SSA. It is the aim of the present work to develop a model that enables an assessment of the added benefits intersectional resource management could bring to a model region in north-western TZ. The study was conducted on a micro-level, i.e. on a household level, and is presented with three specific projects as case studies. The objective was to compare locally available cooking and sanitation technologies in regards to (i) resource consumption, (ii) potential for resource recovery for use in agriculture (i.e. ash, biochar, biogas, slurry, and human excreta, as well as the nutrients and C contained therein), and (iii) environmental emissions. In order to meet this objective, we identified, quantified, visualised, and evaluated technology-specific material flows within the anthroposphere of a smallholder farming system in TZ. Negative effects on the ecosystem were assessed using global warming potential (GWP) and eutrophication potential (EP). It is our aim through this study to (i) advance the practical application of bioenergy and EcoSan technologies in SSA, and (ii) promote the recycling of resources through established methods, including agroecology, composting, integrated plant nutrient management, and Terra-Preta practices.
We identified our underlying research questions as follows: (Q1) How do locally available bioenergy alternative, such as rocket stoves, microgasifiers, and biogas systems, compare to more widespread technologies, such as three-stone fires and charcoal burners, in terms of input, output, and potential recycling flows? (Q2) How does a locally available EcoSan facility, namely a UDDT with or without additional thermal treatment of faeces, compare to both septic tank systems with flush toilets, and the current practice of favouring pit latrines in terms of input, output, and potential recycling flows?
Section snippets
Study area & case studies
This study was carried out in Karagwe, one of eight districts in Kagera region, north-west TZ (lat. 01°33′ S; long. 31°07′ E; alt. 1500–1600 m.a.s.l.). Kagera forms part of the Lake Victoria basin, close the East African Rift Zone. Local soil is vitric Andosol (Krause et al., 2016), and there are two rainy seasons, from March to May and October to November. Precipitation varies between 500 and 2000 mm year− 1, and mean temperatures range from 20 to 28 °C (Tanzania, 2012). The regional economy is
Results and discussion
The following chapter contains (i) a presentation of selected results from the MFA, checked for plausibility and briefly discussed in relation to relevant factors, (ii) a synthesis of results from MES and MSS from an integrated perspective, and (iii) a brief discussion of the applied methodology.
Conclusions
By adopting an integrated perspective on cooking and sanitation in smallholder households in TZ, the following conclusions with respect to the research objectives can be drawn:
- •
ICSs and the biogas system reduce the demand of firewood in smallholder households. The resulting reduced resource consumption can consequently ease pressure on local forest resources.
- •
Capturing residues from sanitation systems contributes to the recycling of nutrients, whilst recycling of residues from energy systems
Funding
This work was supported through a PhD-scholarship by the Hans Böckler Foundation (391240) for Ariane Krause.
- A
Abbreviation part of the analysed scenarios indicating the integrated use in agriculture
- AES
Agroecosystem
- BiogaST
Project “Biogas Support for Tanzania”
- C
Carbon
- CAMARTEC
Centre for Agricultural Mechanisation and Rural Technology
- CaSa
Project “Carbonization and Sanitation”
- CHEMA
Programme for Community Habitat Environmental Management (project partner)
- DM
Dry matter
- E
Abbreviation part of the analysed
Abbreviations
Acknowledgements
We would like to express our sincere thanks to the teams of the case study projects, the MAVUNO staff, Agnes Naluwagga (CREEC), Franziska Meinzinger (TU Hamburg-Harburg), Jakob Lederer (TU Wien), Matthew Reid (Princeton University), Nelson Nbyanyima (CREEC), and Nolbert Muhumuza (Avemu Biomass Ltd.), who all kindly shared available data with us and supported the modelling. Special thanks to Fabian Schmid, who contributed to the design of the energy model as student assistant. He also
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