Fertiliser derived from human urine : novel media for alkaline urine dehydration

Abstract: Every year, each human excretes approximately 4 kg of nitrogen, 1 kg of potassium and 0.3 kg of phosphorus through their urine. In conventional wastewater treatment, these nutrients are usually not recovered for agricultural production, although they can enhance plant growth. Dehydration technologies decrease the volume of source-separated urine and increase its nutrient density, facilitating the use of the dried product as fertiliser. This study investigated the suitability of various alkaline dehydration media for urine dehydration. Magnesium oxide and calcium hydroxide were used as alkalising agents, and biochar and wheat bran acted as co-substrates. Pure magnesium oxide and mixtures between magnesium oxide, biochar, wheat bran and calcium hydroxide were subjected to an average dehydration temperature of 48.3 °C (SD 2.8 °C) during the dehydration process. In this dehydration setup, all dehydration media reduced the mass of urine by > 90 % and dehydration rates of > 19 kg m-2 d-1 were observed. Magnesium oxide showed an N-recovery of 66.8 % (±1.2), while the other four dehydration media showed an N-recovery rate of > 74.5 %. A large amount of the ammonia that could not be recovered was plausibly lost due to ammonia stripping, as > 30 % of the urea in the urine used for this experiment was already hydrolysed. These promising dehydration and N-recovery rates contribute to the research on new on-site dehydration systems that sustainably produce fertiliser out of human urine.