Blackwater sanitization with urea in Sweden : sanitization effect and environmental impact

Abstract: The increasing global population is placing pressure on the water resources and nutrients needed for food production, while increasing the amount of waste generated and the environmental contamination. Technical solutions and changes in the social perception of the environmental problems are needed to address these problems. The blackwater (wastewater from toilets only) represents the major proportion of the plant nutrients found in household wastewater (about 90 % of the phosphorous and nitrogen from the total effluent) and thus they should be recycled in order to close the nutrients loop in the environment. The aim of this research was to analyze the possible use of blackwater as fertilizer in agriculture by comparing three different scenarios: conventional wastewater treatment, separate storage with addition of urea 1 % and separate storage with addition of urea 0.5 % and heat from different sources. The methodology included a system analysis to evaluate the environmental impact of the treatments, considering primary energy use, electricity use and global warming potential. Furthermore, a sanitation part was carried out in the laboratory as a pilot study by monitoring of indicator organisms over time in blackwater treated with 1 % urea. The urea added in situ is degraded into ammonium, which has a sanitization effect due partly to the increment of the pH that consequently inactivates the pathogens. The results showed that the urea treatment was better than the conventional wastewater treatment both from environmental and sanitation perspective. The indicator organisms studied in the lab showed good inactivation rates. The importance of this research relies on the possibility to minimize waste and environmental pollution, close the nutrients cycles by an efficient use of the available resources and, at the same time, decrease the demand of chemical fertilizers by the agricultural sector. In addition, an adequate sanitation process is ensured to reduce the hygienic risks associated.