spurred rising world market prices on phosphorus which is increasingly subject to export restrictions.
In the past decades a significant change in composition of urban organic waste products has occurred in many first world countries, due to cleaner technologies as well as outsourcing of heavy industries. Thus, the heavy metal content of dry matter in sludge from Denmark (Zn, Pb, Cd, Hg) has decreased by a factor 3e5 since 1972 (Anon, 2006). Reviews of organic contaminants in sewage sludge indicate that agricultural recycling is not constrained by concentrations found in contemporary sludge (Clarke and Smith, 2011; Eriksen et al., 2009; Smith, 2009). A recent European Community regulation on Chemicals (EPCEU, 2006) will limit the use of environmentally undesirable chemicals in Europe in the future, and therefore the quality of the urban waste products may be expected to improve further.
It has been shown that it is technically possible to design integrated ecological waste management systems (Magid et al., 2006) based on known components that may be operated at or close to the cost level of the current conventional sanitation systems. Instead of merely delivering composites of urban waste containing numerous undesirable compounds (e.g. heavy metals and xenobiotics in sewage sludge), systems may be developed that can deliver source separated fertilizer of high quality (e.g. human urine, and degassed or composted organic waste including fecal materials or latrine) and limiting the