Pretreating Stored Human Urine for Solar Evaporation by Low-Technology Ammonia Stripping

Abstract

In order to avoid the loss of ammonia during solar drying of stored urine, low-tech stripping is suggested as a pretreatment process for ammonia recovery. The mass transfer of ammonia from stored urine with an initial pH of about 9 was tested in a simple closed vessel operated at 72°C, 74°C and 85°C. The specific urine/gas interface was 16.97 m -1 . For ammonia absorption, a beaker with sulfuric acid was positioned in the gas phase of the container. After keeping the stored urine for 73 h at 85°C, the concentration of free ammonia (NH 3 ) was reduced by more than 99%, and the pH of the stored urine decreased to 6.4 due to ammonia volatilization. Total ammonia (NH3+ NH 4 + ) concentration was reduced by only 83% in the same period. At lower temperatures, the process was slower. Required treatment time can be reduced when specific gas/liquid interface is increased. Because it is known that water can be heated in solar boxes to temperatures above 90 °C , this simple stripping apparatus is feasible to be operated with solar energy in remote areas with suitable climatic conditions where no electric power is available. As the area demand for solar “low-tech stripping” is less than 1 m 2 per capita, this process can be looked at as a suitable pretreatment of stored urine prior to solar evaporation.