Human excreta as a resource in agriculture – Evaluating the fertilizer potential of different composting and fermentation-derived products

Abstract

Acknowledging the resources in human excreta provides new options to address future challenges for fertilizer availability and nutrient management in a sustainable way. In dry on-site sanitation systems, the high nutrient concentration and low volume of the waste provides an opportunity for low-tech recycling, while the product can be a valuable input to the local agro-ecological system. However, successful recycling requires balanced fertilization with a low environmental impact. The aim of this study was therefore, to evaluate and compare the nutritional content and fertilizer potential of different organic amendments derived from human excreta. Nine amendments were obtained previously by treating human excreta from a dry toilet through composting or fermentation at 7°C, 20°C or 38°C, followed by a secondary vermicomposting. We evaluated the fertilizer potential of the amendments by conducting a soil incubation study to determine nitrogen and phosphorus mineralization, and by a pot experiment with barley. For all amendments, the nitrogen mineralization was slow and the available nitrogen determined the yield. The treatment method had a significant effect on the availability of nitrogen and the amendments obtained by active composting at 38°C had significantly higher levels of total and mineral nitrogen than those composted/fermented at 7°C and 20°C. These amendments also led to the highest barley yields, which were equivalent to a mineral nitrogen fertilization of 30 to 60 kg N ha−1. These findings contribute towards better agronomic value quantification of products from on-site dry sanitation systems and the effect of treatment method on the availability of nitrogen.