Storage of human urine:: acidification as a method to inhibit decomposition of urea

One strategy to increase the recycling ratio of nutrients from wastewater to agriculture is to handle urine separately and use it as a fertiliser in agriculture. Potential drawbacks to urine handling systems are the risk of ammonia evaporation and the relatively large volumes to be handled. The amount of urine solution could be reduced by using drying techniques if ammonia evaporation could be avoided. The objective of this project was to study how different acids could be used to prevent the decomposition of urea into ammonia during storage. The project was performed in two phases. The initial phase was conducted with one time dosage of urine in bottles of 0.5 l each to evaluate the effect of different storage conditions and to estimate suitable amounts of acids to be added. The second phase was conducted with multi-time dosages of urine, simulating the continuous addition of urine found in full-scale systems, in plastic cans of 10 l each. The results show that a one-time dosage of 60 meq sulphuric or acetic acid per litre undiluted urine at the beginning of the storage period could inhibit the decomposition of urea during more than 100 days of storage in cans with multi-time dosages of urine. (C) 1999 Elsevier Science B.V. All rights reserved.