SAFE NUTRIENT RECOVERY OF HUMAN URINE AS A CROP FERTILIZER: Capture of the free ammonium nitrogen during alkaline urine dehydration

Abstract

The symbiosis between agriculture and sanitation has long been one of the hot topics for environmentalists. Human urine contains all of the essential nutrients needed for plant growth and can potentially be used as a balanced fertilizer. One of the technologies used to produce such fertilizer is alkaline urine dehydration. The objective of this thesis was to examine whether free ammonium nitrogen lost during alkaline urine dehydration can be captured by struvite precipitation. Qualitative methods were used to examine the recovery rate of urine nutrients (primarily N), through continuous additions of alkalized urine to three different dehydration media (MgO, Mg(OH)2, Ca(OH)2) and subsequent drying at 40 °C. The urine samples (before and after drying) were analyzed, and recovery rates and fertilizer value of the end products were assessed. The study showed that all three drying media managed to recover almost all the nutrients, thus creating a high-value dry fertilizer. While the free ammonium N may have been captured as magnesium ammonium phosphate, the results were inconclusive because the urine contained very little ammonium (about 2% of the total N), which was less than the standard deviation of the analytical methods used to measure the N content of urine and the end-products. This thesis also provides recommendations for future research by describing which further adjustments to the experimental setup are needed for quantifying the rate of free ammonium nitrogen capture from fresh human urine.