Ecological Sanitation (also: EcoSan, Sustainable Sanitation, Alternative Sanitation) is a sanitation approach which aims at collecting the different waste streams separately at source and treating them individually with the objective of recovering valuable nutrients and reusing the clarified water.
Ecological sanitation technologies are based on the following three fundamental aspects[1]:
- pollution prevention rather than pollution control
- sanitize human excreta
- use the safe products of sanitized human excreta for agricultural purposes
Introduction
The reuse of wastewater in agriculture is increasing both in developing and industrialized countries. The main drivers are[2]:
- increasing water scarcity and degradation of water quality resulting from improper wastewater disposal
- population growth and related increased food demand
- acceptance of wastewater (and the containing nutrients) as a resource
- the Millenium Development Goals (MDGs), and more specially the MDGs focusing on environamental sustainability and the elimination of poverty and hunger.
In developing countries, over 780 million people still lack access to improved sources of drinking water and 2.5 billion people have no access to improved sanitation[3]. They urgently need access to affordable infrastructures and sustainable sanitation solutions.
In the Western World, the sanitation industry – challenged by its aging infrastructure and new pressures such as climate change or increasing regulatory requirements – is at a turning point and needs reengineering[4]. In fact, conventional centralized wastewater treatment systems eliminate nutrients and can therefore be characterized as “end-of-pipe” solutions.
No Mix technology
No Mix toilets are used to separate urine from feces directly at source. The benefits of using such separation toilets are manifold:
- they save up to 80% of the water used for toilet flushing (this represents 30% of the average daily water use of a Western European)[5]
- urine is collected as a concentrated nutrient solution free of pathogens. In fact, urine contributes to less than 1% of the composition of municipal wastewater whilst adding more than 50% of the phosphorus and more than 75% of the nitrogen load[6].
A difference is made between dry and wet types of toilets. The wet type mixes feces with water for transport. Urine is flushed with or without water. The dry type on the other hand is operated without the use of flushing water. Urine and feces are diverted to separate storage tanks. Examples of more simple separation toilets are squatting pans or seat risers with urine diversion.
Yellow Water (urine)
The major proportion of the nutrients is excreted with human urine. It contains most of the macronutrients and smaller amounts of the micronutrients in plant available forms. Urine is a nitrogen-rich liquid fertilizer with N concentrations of 3 to 7 grams per liter of urine. An adult produces between 0.8 and 1.5 liters of urine per day.
The use of human urine in plant production represents low health risks if there is no of little feacal cross-contamination. Pharmaceutical residues and hormones are excreted with urine. However, the risk of negative impacts on plants or human beings is thought to be negligible. The risk of using human urine as a fertilizer is far lower than the risk associated with using sewage sludge or farmyard manure for example. Storage is a simple, efficient and cheap method for treating collected urine. More complex treatment methods include technologies such as reverse osmosis, ion exchange, freeze/thaw, stripping/adsorption, nitrification, nanofiltration, ozonation or struvite precipitation.
During storage, urine sludge is generated as a result of the degradation of urea to ammonium. The sludge is composed of phosphate, magnesium, calcium and ammonium precipitates. It can be mixed with the supernatant and used with the rest of the urine.
Field trials have shown that yields of urine-fertilized crops did not differ from mineral fertilized crops.
Brown Water (feces)
Although feces contain lower nutrients than urine, the concentration of phosphorus and potassium is high. Feces also contain organic matter, which improves the water-holding and buffering capacity as well as the structure of soils.
Contrary to urine, feces contains large amounts of pathogens. Therefore, safe handling and treatment of feces are crucial in order to minimize disease transmission. The risk of odors, flies and number of potential pathogens in the feces can be reduced by adding ash after each defecation in a dry system. This is referred to as primary treatment. Secondary treatment takes place when the collection period is completed. The various options include composting, digestion, storage, chemical treatment and incineration.
Greywater
Greywater is essentially all wastewater except toilet wastes (toilet wastewater is called “blackwater”). It is sometimes referred to as washwater as it contains water from sinks, showers, tubs and washing machines. Greywater can directly be used as irrigation water by introducing it into the topsoil. Untreated greywater should not come in contact with edible parts of crops.
Examples
Further reading
References
- ↑ Sida/Esrey S. et al. (1998): Ecological Sanitation. http://www.ecosanres.org/pdf_files/Ecological_Sanitation.pdf (Access 2013-12-30)
- ↑ WHO (2006): Guidelines for the safe use of wastewater, excreta and greywater. Volume 2 - Wastewater use in agriculture. http://whqlibdoc.who.int/publications/2006/9241546832_eng.pdf (Access 2013-12-30)
- ↑ UNICEF, WHO (2012): Progress on drinking water and sanitation: 2012 update. http://whqlibdoc.who.int/publications/2012/9789280646320_eng_full_text.pdf (Access 2013-12-30)
- ↑ Mitchell et al. (2011): Effectively managing the transition towards restorative futures in the sewage industry: A phosphorus case study. In: Water Sensitive Cities, p.83-96. http://water-alliance.org/storage/content/Restorative%20Futures%20-%20Mitchell.pdf (Access 2013-12-30)
- ↑ Larsen et al. (2001): Re-engineering the toilet for sustainable wastewater management. Environ Sci Technol 35:192A-7A
- ↑ Larsen and Gujer (1996): Separate management of anthropogenic nutrient solutions (human urine). Water Sci Technol 34:87-94.
