All conventional wastewater treatment systems usually deprive agriculture, and hence food production, of the valuable nutrients contained in human excreta, since the design of these systems is based on the aspect of disposal. In households, resources are converted into wastes. When the systems we have designed fail to reconvert the waste back into resources, they don’t meet the important criteria of sustainable sanitation (Esrey, 2000). Thus, the future sanitation designs must aim for the production of fertiliser and soil conditioner for agriculture rather than waste for disposal (Otterpohl, 1999). Nutrients and organic matter in human excreta are considered resources, food for a healthy ecology of beneficial soil organisms that eventually produce food or other benefits for people. One person can produce as much fertiliser as necessary for the food needed for one person (Niemcynowicz, 1997). Therefore, the new approach should be designed in such a way that it could reconvert the waste we produce into resources free of pathogens in reasonable costs without polluting aquatic Environment.

Figure 6: Material flows in resource management sanitation (Source: Otterpohl et al., 1997)

Figure 6 illustrates a possible scenario for closing the nutrients cycles and simul­taneously preserving fresh water from pollution. This scenario can be achieved with the application of resource management sanitation, base on ecological principal. There are numerous advantages of resource management sanitation compared to conventional sanitation (Werner et al., 2002; Otterpohl, 2001; Esrey et al., 1998). The major advantages of them are :

• reuse of human excreta as fertiliser and soil conditioner; water and energy;

• preservation of fresh water from pollution as well as low water consumption;

• preference for modular, decentralised partial-flow systems;

• design according to the place, Environment and economical condition of the people;

• hygienically safe;

• preservation of soil fertility;

• food security;

• low cost (ecological, economical and health cost);

• reliable.

Resource management sanitation bases on the concept of source control. High levels of nutrient recovery are possible with the concept of source control in household (Otterpohl et al., 1999; Henze et al., 1997; Esrey et al., 1998). The technologies to realise source control have already been developed (Otterpohl, 2001; Esrey et al., 1998). Sorting toilet is a suitable technology to separate the urine and faeces at source (see figure 7). Usually, the toilet has two bowls, the front one for urine and the rear one for faeces. Each bowl has its own outlet from where the respective flow is piped out. The flush for the urine bowl needs little water (0.2 l per flush) or no water at all, a mechanical device closes the urine pipe when users stand up whereas flushing water for faeces bowl can be adjusted to the required amount (about 4 to 6 l per flush). However, in the present system separate collection is efficient only when men sit down while urination. Recently, there is a new development in Norway for separating urine even when men stand up while urination.

Figure 7: Sorting toilet(Source: Ruediger)

Figure 8: Vacuum toilet(Source: Ruediger)

Vacuum toilets as shown in figure 8 has been used in aeroplanes and ships for many years and is increasingly used in trains and flats for water saving. It uses 1 l water per flush and is independent of gravity. The black water is transported by air and pressure differential (vacuum) instead of water and gravity to bio-gas plant. Water is used only for rinsing the bowl, not for transporting the faeces. Limited vertical lifts and long horizontal transportation of the black water are possible. Noise is a concern with vacuum toilets but modern units are not much louder than flushing toilets and give only a short noise.

Composting / dehydrating toilet needs 0.2 l water per flush, only for cleaning the toilet seat. There are also urine diversion composting or dehydration toilets (figure 9). These low-flush and non-flush toilets save not only water, but also produce low diluted or dry faecal material that is easier to manage than highly diluted faecal wastewater as in conventional systems.

Figure 9: Double-vault toilet with urine diversion (Source: Esrey et al., 1998)