November 1, 2009
Summary
The project converts the blackwater, or human excreta, from one student household
into biogas and fertilizers, which are safe for food production. Compared to
conventional sewage treatment and food production, this system reduces resource
depletion, pollution and greenhouse gas emissions.
Quote
Let us abandon all consumption and pollution. Let us just eat and excrete.
Actors
Residents of Droevendaalsesteeg 87, 93, and 99, Wageningen, the Netherlands
Designed and operated by Kealan Gell
Some equipment donated by Dr. Gatze Lettinga
Support and inspiration from countless people and organizations, especially the
Community Composting Network, UK
Description
Urine is collected in a unisex odor-proof urine collection vessel, as shown in Figure 1.
Urea is hydrolyzed in the collection vessel. Seawater, a source of magnesium ions, is
added at a 1:4 volumetric ratio of seawater to urine (Figure 2). Mixing and settling,
each for 15 minutes followed by decanting, produces 0.10 mm diameter struvite
crystals, which are air-dried, shown in Figures 3 and 4. Struvite (12% P by mass) has
a similar effectiveness, plant availability and P content to triple super phosphate (19%
P by mass).
Feces are collected in a dry toilet, covered with sawdust or paper to eliminate odor as
shown in Figure 5. Feces are then mixed with paper and ground food waste,
pasteurized at 70 C for 1 hour, and digested to produce biogas and safe liquid
fertilizer, which includes stable organic matter. Digester is show in Figure 6.
Currently electricity is used for heating the digester and pasteurizer, however in the
future, biogas will be used. Biogas is currently used for cooking, Figure 7. The liquid
fertilizer, Figure 8, is applied in the garden.
Fertilizer products contain very low levels of pathogens, metals, hormones and
pharmaceuticals. Tests have been done to ensure compliance with Dutch soil
regulations, EU animal byproducts regulations and Dutch fertilizer regulations.
An evaluation of this system should consider the alternative impacts of conventional
sewage treatment and fertilizer production, including drinking water treatment and
delivery, sewage transportation network, energy used for carbon and nutrient removal
and loss, and phosphate fertilizer mining, depletion of P, processing and
transportation, as well as overall self sufficiency, resilience and pollution.
Figure 1. Urine collection vessel
Figure 2. Before (left) and after (right) sea water addition
Figure 3. Drying struvite crystals
Figure 4. Microscopic photos of struvite crystals
Figure 5. Dry toilet with saw-dust
Figure 6. Anaerobic digester with insulation and heater
Figure 7. Biogas cooking
Figure 8. Digestate, liquid mineralized fertilizer
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