Dry toilet

Schematic of a dry toilet (user interface)

A dry toilet is a toilet that operates without flushwater. The dry toilet may be a raised pedestal on which the user can sit, or a squat pan over which the user squats. In both cases, excreta (both urine and faeces) fall through through a drop hole.^[1] The excreta can either become mixed at the point of dropping (the more common scenario) or stay separated (the scenario in a toilet with urine diversion which is not as common).

Strictly speaking, a dry toilet refers only to the device that the user squats over or sits on. In practice, however, it is often used to denote a variety of technologies and in particular combinations of technologies, namely the user interface plus the storage or treatment unit below it. For this reason, a person who speaks about a "dry toilet" could mean one of four toilet technologies:

1. Composting toilet (in most cases without urine diversion but can also be with urine diversion)
2. Urine-diverting dry toilet (UDDT) - with urine diversion, as the name implies; this type of toilet is also called by many people ecosan toilet, although this is not recommended as ecosan is not limited to this type of toilet
3. Arborloo - which is similar to a pit latrine but has a much shallower pit and is designed for making compost in the pit
4. Pit latrine (always without urine diversion)

When speaking about a pit latrine with another person, one should therefore always clarify which type of toilet they actually mean. Probably the most common use of the term "dry toilet" is for a composting toilet.

Calling a pit latrine a dry toilet is not recommended because:

• Some pit latrines use water for flushing - these are called pour-flush pit latrines.
• As urine and faeces are mixed, the pit content is actually quite wet (even though urine does infiltrate in the ground unless clogging as occurred)
• Users of pit latrines may use water for anal cleansing which is added to the pit and makes the pit content wetter. Sometimes they even discard greywater (from showering) into the same pit.

Uses

Dry toilets, or more generally speaking "dry excreta management systems" are useful in all areas and may be especially suitable in situations where water flushed toilets or sewer-based sanitation systems and their required infrastructure are not feasible:^[2]

Dry toilets are used for three main reasons

1. To save water - when there is either water scarcity, water is costly (such as in arid or semi-arid climates) or because the user wants to save water for environmental reasons
2. To prevent pollution of water - dry toilets do not mix excreta with water and do not pollute groundwater (except for pit latrines which may pollute groundwater)
3. To enable safe reuse of the excreta (or the faecal sludge in the case of pit latrines) in gardening or agriculture, after it has undergone further treatment by either drying or composting

Locations

Dry toilets are used in developed countries, e.g. many Scandinavian countries (Sweden, Finland, Norway) for summer houses and national parks. They are more widely used in developing countries in situations where flush toilets connected to septic tanks or sewer systems are not feasible or not desired due to resource limitations, poverty, for environmental reasons or other reasons. Sewerage infrastructure costs can be prohibitive in instances of unfavourable terrain, sprawling settlement patterns or poverty (in the case of developing countries).

Debates around dry toilets

Some people strongly believe that dry toilets (and "dry sanitation") are the more sustainable way for sanitation, whereas others argue that a generalisation is not possible and all the different sanitation systems have their place for all the different contexts. Dry toilets - or "dry sanitation systems" - can lead to reduced water consumption, the recovery of valuable resources from domestic wastewater, reduced eutrophication, and reduced toxicity of agricultural soils. They therefore offer potential benefits in areas with low water availability, limited access to synthetic fertilizers, surface water bodies impacted by eutrophication, and agricultural lands affected by heavy metals.^[3] However, these advantages need to be evaluated for each case and weighed against the potential disadvantages related to the loss of economy of scale.

The use of dry toilets in urban settings has some significant social and technical disadvantages (as was demonstrated in a large scale urban dry toilet system in Erdos Eco-City in Inner Mongolia Autonomous Region of China).^[4] These disadvantages should be weighed against their benefits, including the amount of water that they can save relative to other options in each location. For example, water savings from toilets might be insignificant compared to possible water savings in agricultural practices. Finally, the sanitation system selected needs to have not only legal acceptability but support at the local policy level amongst the various government departments affected.^[3]

References

External links

• Sustainable Sanitation Alliance

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