Environmental consequences of adopting source separated sanitation system : first and third world perspectives

Abstract

Urine constitutes only about 1% of domestic sewage but contains major fractions of nutrients (90% N, 50% p and 55% K) and chemicals like pharmaceutical residues and estrogens (95%) excreted from the human body. Agricultural food crop yield in many countries is decreasing because of nutrient mining and human undernourishment is 20% or higher in 41 countries. The annual human excretion of nutrients only in urine is more than the average fertilizer application rates in 22 countries. Urine, thus, can serve as a "free" but locally available nutrient source. Urine diverting toilets (UDTs) can be used to separate urine at the source. Coordinated and simultaneous intervention on water sanitation and agriculture could be the most effective and economical means of increasing agricultural yield and reducing water pollution, poverty and hunger in these countries. The human excreted estrogens are recognized endocrine disrupting chemicals (EDCs) and are considered about hundred to thousand times more estrogenic than known EDCs like bisphenol A. The effects can vary from cancer to sex reversals at levels as low as parts per trillion in sensitive organisms. To remove 99% of estrogenicity in discharged waters from source separated urine would require approximately 12 kWh/p-y whereas it would require 23 kWh/p-y to achieve the same removal from bulk wastewater by adding advanced oxidation processes to existing municipal wastewater treatment plants. From an energy standpoint it makes sense to practice source separation and treatment of urine to limit estrogen discharges into the environment. By employing UDT, a typical family in the US could realize a saving of $101/y and a decrease of 100 kg green house gas emissions. A social acceptability study conducted in Hawaii showed that 82% of respondents were willing to use UDTs and more than 60% were willing to pay extra while only 22% knew that such systems existed. With a public education program, it is possible that most people would be willing to adopt UDTs and human waste recycling with incurred societal benefits of reduced water and fertilizer use, reduced greenhouse gas emissions, and collection of EDCs at the source to prevent their entry into waterways.