Different forms of dehydration toilets have been in used in many parts of the world. However, all use the same basic principle of dehydration. Dehydration toilets are mostly used in Vietnam, Mexico, China, El Salvador, Ecuador, Yemen, South Africa and India. Double-Vault dehydrating toilets as shown in figure 13, which consist of two alternately used vaults constructed above the ground, have been widely used in Northern Vietnam since 1954, and adapted models were implemented in Mexico, Central America and Sweden (Esrey et al., 1998). In this toilet, urine is diverted to a collection tank or soak pit under the toilet vault or outside the toilet and faeces drop into one of the two vaults located below the toilet’s seat. When one vault is full, it is sealed and another vault is used. Dry materials like ash or soil or a mixture of sawdust/lime or soil/lime are added after the defecation. The added dry material assists the desiccation process and raises the pH, which aids in pathogen reduction.

Central American and Mexican version of Vietnamese double-vault toilets have been successfully applied in urban areas of El Salvador and Mexico (Moe et al., 2001 and 2003). These toilets are usually attached to the house, sometimes even placed inside the house. The double-vault toilet as shown in figure 9 is built in a bathroom of a modern, high standard house in the city of Cuernavaca, Mexico. A urine diverting mobile toilet bowl is placed just above the opening of one of the two chambers located below the bathroom. When the first vault is full, it is sealed and the bowl is moved to the opening of another empty vault. The vaults are accessible from outside the house.

Figure 13: Vietnamese double-Vault Dehydrating toilet (left) and double-vault toilet with solar heater (right) (Source: Esrey et al., 1998)

The double-vault toilet without urine diversion has been used in a dry region of Ecuador. The vault is covered with a lid made up of a wooden frame covered with thin galvanised iron painted black in order to absorb the sun's radiation and increase the vault temperature and rate of dehydration (figure 13 right). Sawdust or ash is added after every defecation as in the urine diversion system.

The single-vault dehydrating toilet uses a passive solar panel to increase the chamber temperature and rate of dehydration. The addition of dry materials after defecation is required as in the double-vault dehydrating toilet. In this system, the faecal materials that are accumulated below the toilet’s seat are shift to the rear of the chamber with a hoe or rake. There are also systems, which have been equipped with a pusher to shift the faecal materials to the rear of the vault (figure 14). After some months, the dry materials which are collected at the rear of the chamber are shovelled into a sack and stored outside the toilet until reuse.

Figure 14: Single-vault toilet equipped with a pusher (Source: Esrey et al., 1998)

German Technical Co-operation (GTZ) with the company Otterwasser has implemented some dehydrating toilets in Mali, West Africa (see figure 15).

Figure 15: Dehydration toilet in Male, West Africa

Dehydration toilet is very beneficial for regions of warm climate. However, also in Sweden there are a number of dehydration toilets on the market for many years (Del Porto and Steinfeld, 1999). WM Ekologen system, for example, is based on urine diversion and dehydration. This system has been used in indoor bathrooms.

By now tens of thousands of urine diversion ecosan toilets have been built in China (Xianghong and Jiang, 2003; Jiang, 2000). Ash, soil and lime are added after the use of the toilet. The urine-diversion squatting pan and mechanical ash dispensers are provided in the systems (figure 16). Many of the toilets are built inside the dwelling, and often upstairs.

Figure 16: Squatting pan urine diverting toilet with double-vault from China

The main principles for good functioning of dehydration toilets are:

• it should be built above the ground to avoid entering and contamination of groundwater;

• urine diversion is beneficial;

• two vaults system with alternative usage is advantageous;

• vault should be heated with solar by covering each chamber with black lids;

• wash water has to be kept out;

• post-composting after collecting the dehydrated faecal materials can be required.