Ecological Sanitation (local copy) is at the heart of dry toilets. The idea is that "...urine and faeces are not simply waste products of the human digestion process, but rather are an asset that if properly managed can contribute to better health and food production and reduce pollution."
Dry toilets do two jobs:
Arborloos (local copy) are great family-sized units for sanitation, but when it comes to providing sanitation for a market, larger, more comfortable units are needed. That's where the dry toilet comes in.
My introduction to dry toilets came through the organization Sustainable Organic Integrated Livelihoods (SOIL).
"In Mexico City, experimentation with fermented urine to grow food has shown that leafy vegetables do very well. This includes lettuce, cilantro, parsley, celery, fennel, scented herbs, prickly pear, and chile piquin. Average results were obtained for cauliflower, broccoli, cabbage and root produce (turnips, carrots, beets and onions). Fruiting plants, such as tomatoes, squash, cucumber, peppers and eggplants have not done as well with fermented urine as with other fertilisers." (from Closing the loop in wastewater management and sanitation, p. 43 -- an international symposium)
"If only 30% of India's projected 2021 urban population of 600 million used ecological sanitation it would save at least 3.6 million cubic metres of water per day and stop the production of at least 3.9 million cubic meters of sewage per day. It would produce annually 820,000 tonnes of N nutrient (or at least 400,000 tonnes even allowing for 50% loss through volatility), 99,000 tonnes of P nutrient and 230,000 tonnes of K nutrient." (ibid)