Direct use of urine as fertilizer

Abstract

Ecological sanitation or Ecosan is an alternative approach to avoid the disadvantages of conventional water-based sanitation systems. This approach, based on ecosystem functioning and the closure of material flow cycles, includes different sustainable and environmental friendly technologies to provide appropriate sanitation solutions to specific local situations. Perhaps the most relevant aspect of ecological sanitation is that it recognizes human excreta and household water as resources (not as a waste), giving the opportunity for its re-use. This study focused on re-use of human urine as fertilizer and the identification and mitigation of risks of spreading pharmaceutical and hormone residues into the agricultural fields. For that purpose, a case study was performed in Bogotá, Colombia to understand the actual sanitation scenario as well as to identify the limitations and strengths of implemented Ecosan strategies in peri-urban and rural areas of Bogotá. Furthermore, a group of pharmaceuticals frequently used was identified for a small population group. In the search for an analytical tool that was cost effective, and also required low investment in facilities and equipment when compared to other analytical methods, it was decided to test the yeast estrogen screen assay (YES) for analysis of estrogenic compounds in soil and plant material as well as in human urine. The YES assay was a reliable analytical technique for finding estrogenic activity in soil, wheat grains and human urine. However, difficulties were encountered while analyzing estrogenic compounds in some plant tissues. The current research assessed the degradation potential of estrogenic compounds and discovered that estrogens contained in human urine can degrade under both light and dark conditions where exposure to light presented a slightly higher degradation rate. Degradation of 17β-estradiol (βE2) also occurred in the nutrient solution of a hydroponic system. The findings suggest that there is little risk of βE2 accumulation in agricultural fields since it is easily degraded via different pathways (e.g. photodegradation and biodegradation). Consequently, more attention should be paid to persistent compounds such as carbamazepine (CBZ) which was found in the plant leaves and stems. However, concentrations in the edible parts (wheat grains and sunflower seeds) were rather low, and according to the results did not reach concentrations for therapeutic use. Also, Verapamil (VER) which has not been frequently studied as an emergent micropollutant and very little is known about its environmental risk, was found in soils as well as in plants, and - most importantly it occurred in edible parts. Although the concentrations found were very low, there is the need to further investigate the effect and degradation potential of this compound in different environmental systems (e.g. soils and natural water bodies).