Terra Preta Toilets

Urine diversion terra preta toilets are dry terra preta sanitation (TPS) systems based on urine diversion, lacto-fermentation, the addition of charcoal and vermicomposting to produce lasting and highly fertile soils with properties similar to the terra preta soils (GENSCH 2010 b).

Pre-Columbian native populations generated terra preta soils, literally “black earth”, by incorporating large amounts of charred residues (charcoal) either produced intentionally or as a by-product from human activity into the soil together with nutrient-rich material (GLASER 2006). Nutrient-rich material was used to be human and animal manure (rich in P and N), waste including mammal and fish bones (rich in P and Ca), ash residues of incomplete combustions (rich in Ca, Mg, K, P and charcoal) or plant biomass (e.g. kitchen wastes, compost, algae etc.) (GLASER 2006). It is the addition of charcoal resulting in high contents of black carbon, which gives these soils their black appearance and their unique properties.

Due to its polycyclic aromatic structure, black carbon is chemically and microbiologically stable and persists in the environment over centuries (GLASER et al. 2001). Over the time, it gets partly oxidised and carboxylic groups are produced on the edges of the black carbon backbones (GLASER et al. 2001). The carboxylic groups act as a trap for nutrients in the soil preventing them from being washed out. The nutrients entrapped in the micro pores and cracks in charcoal provide not only necessary elements for plant growth, but also food and a safe housing for the protection form gazing protozoa to beneficial bacteria (O'GRADY & RUSCH 2007).

As the backbones of the black carbon remain stable, terra preta has a large potential as a long-term carbon sink: a hectare of meter-deep terra preta can contain 250 tons of carbon as opposed to 100 tones in unimproved soils (GLASER et al. 2001; LEHMANN et al. 2006; GUENTHER 2007).

Many years of research have helped to better understand terra preta soils since they have been discovered. Today, the production of terra preta soils by the co-composting of charcoal is an emerging and promising concept to improve long-term fertility of arid soils and contribute to carbon sequestration from the atmosphere. Terra Preta Sanitation (TPS) is the name of the concept, which aims to use this technology for a safe and recycling-oriented treatment of wastes.

To date, TPS has been scientifically established for kitchen and garden wastes, human faeces and human urine. As a toilet system, TPS could be applied to Urine Diversion Toilets (UDDTs), arborloos, fossa alternas or any other kind of composting toilet. The terra preta toilets are based on a three-step process of collection (including urine diversion), lacto-fermentation and vermicomposting. The products are fertile compost (terra preta) and liquid fertiliser (sanitised urine containing stable nitrogen). The separate collection of urine can be done in a UDDT, arborloo with extra urine collection or any other adapted composting toilet. The terra preta toilets consist thus of basically four elements: A toilet superstructure, which provides shelter for the user and the toilet itself; a urine diversion seat or slab; a urine collection chamber (e.g. a jerry can) and a faeces collection chamber (bucket; vault; etc.).

Toilet superstructure

Any toilet should have a superstructure for two main reasons. First, a toilet should be a place of privacy and give the impression to be safe and cosy. Second the toilet housing has a important effect on the functioning because it protects the toilet from heavy rain, sunshine, wild animals or vandalism and influences the ventilation system, which is crucial for the control of odour and fly breading. 

Terra preta toilets process both faeces and urine in an anaerobic process in which no gas and thus no odour is produced. This makes them particularly interesting for larger scale and indoor application (in urban area) (OTTERPOHL 2009; GENSCH 2010 a; FACTURA et al. 2010). Consequently, there is no need for a special ventilation of the collections chamber and ventilation of the toilet can be limited to the circulation of fresh air in the cabinet or the indoor toilet room.

Collection of Urine

The urine can be collected in any container which is air and liquid-tight and can safely be connected to the urine diversion toilet seat or slab. A connection tube generally is introduced into the bottom of the container, so as a minimum of air can enter the tank. About half a litre (for a 20 L jerrican) of the microbial mix (liquid mix of lacto-fermenting bacteria and Bacillus subtilis, see below) should be added to the urine container prior the collection (GENSCH 2010 b).

The microbial mix prevents the bacterial urease process, that hydrolyses urea into ammonia (NH3) and carbon dioxide (CO2) (RECKIN 2010) what is usually happening when urine is conventionally stored (GENSCH 2010 b). As NH3 and CO2 are volatile, these elements are quickly lost to atmosphere, resulting in bad odour and pollution (NH3 can cause acidification and eutrophication when it settles again with the rain, while CO2 is a greenhouse gas). As the bacterial urease process is prevented, no volatile ammonia is produced, resulting in almost no odour, a reduced loss of nitrogen into the atmosphere and the conversion of N in the urine, leading to higher fertilisation potential (RECKIN 2010; GENSCH 2010 b).

Collection of Faeces

Almost any sealable bucket can be used as a faeces collection chamber. The most important feature of the faeces collection chamber is its air-tightness to make sure that there are anaerobic conditions for lacto-fermentation. The most simple collection chamber is a bucket, placed under a toilet seat. Thus, not only the collection chamber / bucket, should be airtight, but the toilet seat or squatting hole needs to be sealable. After each defecation, a charcoal mix needs to be added to cover the faeces. Charcoal removes the bad odour of the faeces (OTTERPOHL n.y. b) and provides stable organic matter for the terra preta soil production. Sliced-cut wood is used as a bulking agent and to raise the C/N ratio in order to create a substrate, which will be accepted by the earthworms (FACTURA et al. 2010).

To initiate the lacto-fermentation process in the faeces collection chamber/bucket, a few dashes of a lacto-bacilli (Lactobacillus spec.) containing microbial mix can be added after each use (GENSCH 2010). In this case, it is important, that after each use, the toilet seat is sealed again, even thought the system still works with some remaining air (OTTERPOHL 2009). It is also possible to use a bucket for one or two weeks, and then replace it with a new, empty one. The microorganisms are added then to the full bucket, before it is sealed and left aside for the lacto-fermentation process to happen (FACTURA et al. 2010). For an optimal conversion, minimum 4 weeks of lacto-fermentation (both of faeces and urine) are recommended before vermicomposting (OTTERPOHL n.y. b; FACTURA et al 2010). However, faeces can be stored that way over longer periods without the formation of odours or nocuous gases (OTTERPOHL n.y. b).

Charcoal Mix

Terra preta toilets only function properly if the charcoal mix and the microbial mix are regularly added and processed together with the excreta. The mix should contain charcoal (black carbon), stone dust, finely cut wood (or another bulking agent to raise the C/N ratio necessary for vermicomposting) and some limestone or volcanic soil (FACTURA et al. 2010; GENSCH 2010). It can be prepared in advance regarding the local available material and stored beside the toilet to be used after each defecation.

Microbial Mix

The effective mixture of microorganisms needed for the lacto-fermenting process is available commercially (e.g. effective microorganisms, EM). But these mixtures are often expensive and spoil after some weeks as they are manipulated for commercialisation. The easiest way to obtain an effective microbial mix is probably to take an inoculum from Sauerkraut (pickled sour cabbage) liquid (OTTERPOHL 2009; FACTURA et al. 2010).

Dr. Reckin, a German researcher, which is involved in TPS development, has developed a microbe mixture similar to EM, containing a mixture of five microbes namely: Bacillus subtilis, Bacillus mesentericus, Geobacillus stearothermophilus, Azotobacter croococcum and Lactobacillus sp., respectively. This mixture is specifically designed to prepare for vermicomposting and thus may be better suited than commercial effective microorganism or Sauerkraut liquor. Bacillus subtilis is not a lacto-fermentation bacterium per se, and it is probably the combination of lacto-fermentation with some other processes together with the addition of some thin wood particles that is leading to a better compost quality (FACTURA et al 2010).

Dr. Reckin’s mixture is available with him, at the Technical University Hamburg-Harburg (TUHH, Institute of Wastewater Management and Protection, aww, Germany) or from the Xavier University Sustainable Sanitation Center (Philippines).

Vermicomposting

After lacto-fermentation of the faeces, these need to be vermicomposted to produced transform the carbon and nutrients into humic acids, clay-humus complexes and other elements, which form the fertile terra preta compost. Vermicomposting is an aerobic decomposition process involving the combined action of earthworms and microorganisms. Both, faeces and urine can be vermicomposted, even though the nitrogen and phosphorus rich lacto-fermented urine can also be used directly as liquid fertiliser after lacto-fermentation. The initial addition of the finely cut wood and the Bacillus subtilis to the microbial mix allows the vermicomposting of faeces without any additional bio-waste (kitchen or garden waste). The final product is nutrient-rich vermi-cast (cast of the earthworms) with properties similar to terra preta (see TPS factsheet).

Urine can also be composted on its own by adding a little bit of the microbial mix and mixing with a finely sliced wood source (80%), ground charcoal power (10%) and existing soil (10%) (GENSCH 2010 a). This mix should then be covered with some dry leaves and left beside under regular watering. After about one month (tropical conditions), the heap will convert into a humus-like fertile material with no significant N, P and K losses (GENSCH 2010 a).

TPS is, even though rediscovered from ancient cultures, a rather new technology and still some research is needed for exact estimation of pathogen removal. However, lacto-fermentation is used throughout the world in industry to preserve foods (pathogenic microorganisms are killed when acidity rises) and vermicomposting is a rather well established treatment of kitchen and garden wastes. A recent publication indicates that faecal indicator bacteria are reduced by over 99 %, confirming this assumption (FACTURA et al. 2010).

Terra preta toilets are an interesting option for the adaption of UDDT (urine diversion dry toilets): Not only because the combined process of anaerobic lacto-fermentation and aerobic vermicomposting prevents the emission of ammonia to the atmosphere and loss from urine, but also because the process is expected to hygienise faeces faster and more lasting than simple dehydration (e.g. for helminth eggs). The effect on other more persistent pathogens in faeces like helminth ova (Ascaris lumbricoides) still requires further research.

The costs of terra preta toilets depend on the type of urine diversion or composting toilets it taken as collection units (e.g. UDDT, arborloo, fossa alterna, etc.). As every toilet construction the effective costs depend strongly on the local context, climate and availability of material and work. Terra Preta Toilets could be constructed as a high-tech alternative to conventional sanitation systems in multi-story houses as well as at the household level. The most basic terra preta toilet does not require more than a sealable bucket for faeces; a urinal; the microbial mix; the charcoal mix and space for vermicomposting. Thus there is a high potential for low-cost solutions even though a well-established urine diversion toilet (which is also convenient for woman, children and elderly people) should be considered as the minimal standard for long-term solutions.

Operation and maintenance efforts for terra preta toilets are not very high but crucial for a good functioning of the system. The main task to be done are: checking for air-tightness of the faeces and urine chamber, rinsing urine pipes from deposits (precipitates from the urine); the maintenance of the lacto-fermentation (e.g. addition of charcoal and microbial mix); changing of containers and proceeding of vermicomposting; reuse of products in the garden.

The microbial mix can be kept at the household level and continuously fed and cultivated. Generally the bacteria can be duplicated every 2 days, but they should be fed at least once a week with some water, a sugar source (blended bananas, sugar can juice etc.) and sterilised milk (GENSCH 2010 b). Sugar content in the solution should be around 3 to 5 % (GENSCH 2010 b). The entire solution should be cooked for sterilisation and cooled down before added (GENSCH 2010 b). Bottles, containing the microbial mix have o be clearly labelled and kept away from children.

The lacto-fermentation process should be maintained at least for one month (up to six month, OTERRPOHL n.y. a; FACTURA et al. 2010) in a completely close container before transferring the products to the vermicomposting step or to use the urine. Vermicomposting should be done for three to six month (OTERRPOHL n.y. a; FACTURA et al. 2010).