Optimisation of a low-cost urine treatment system for resource recovery

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Today, over 800 million people are estimated to be chronically undernourished and 2.5 billion live without basic sanitation facilities (FAO, IFAD and WFP, 2014; UN Water, 2014). Current sanitation challenges require new alternatives to conventional sewerage systems. Among them, the reuse of source-separated urine could help mitigate poverty and malnutrition by providing an in-country supply of fertiliser.

Historically urine has been applied as a fertiliser to a variety of crops in numerous countries including Japan, Yemen and Sweden (Schönning, 2001). Scientific research as well as development projects have studied and demonstrated the efficiency of urine reuse in agriculture (Richert et al., 2010). Lately, research has focused on nutrient recovery from urine as struvite (Wilsenach et al., 2007). However, studies on the recovery of urea from urine are scarce although urea constitutes the main source of nitrogen in urine. Therefore this study aims to provide an understanding of the potential for nutrient recovery from urine as urea and recommendations of practices based on experimental work.

Sponsored by WaterAid UK, this project aimed to test a new low-cost solution for urine management in developing countries based on the production of urea using solar powered evaporation for use as a fertiliser. This study investigated the performance of urine evaporation in producing urea, leading to recommendations on the design and broader application of the system and on its viability as a business model. As concluding remarks, the project assessed the relevance of the proposed system in the production of urine derived-urea for agricultural purposes in developing countries.

Preliminary analyses of urine chemical composition were carried out in order to compare the results with the literature review. Five samples of one-litre urine were evaporated using an experimental set-up under different conditions. In particular, the influence of pasteurisation and the design characteristics of the prototype (surface area and height of the light) on the chemical composition of the final product and its stability were considered. The results suggest that pasteurisation of urine impacts the initial chemical characteristics and crystallisation process. Ventilation and temperature were also identified as a parameter of major impact on the speed of crystallisation of urine. With a view to a possible implementation, the mass of recovered urea crystals, around 13 g of dry product per litre of urine, appears as a limitation to this technique.

Although the recovery of urea by solar pasteurisation and evaporation requires little maintenance and low-cost materials, and is particularly adapted for developing countries, our work showed that urine evaporation is a slow process producing limited amounts of urea. In addition, the end product appeared very unstable as it easily absorbs atmospheric moisture. Our findings suggest that the implementation of the current system is not viable. Further research is specifically required to optimise the process in terms of yield and quality/stability of the final product.