Nitrogen-retaining property of compost in an aerobic thermophilic composting reactor for the sanitary disposal of human feces |
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Authors: | Fan Bai and Xiaochang Wang |
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Institution: | (1) Nature Conservation and Plant Ecology Group, Wageningen University, P.O. Box 47, 6700 AA Wageningen, The Netherlands; |
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Abstract: | Aerobic composting is a method for the sanitary disposal of human feces as is used in bio-toilet systems. As the products
of composting can be utilized as a fertilizer, it would be beneficial if the composting conditions could be more precisely
controlled for the retention of fecal nitrogen as long as possible in the compost. In this study, batch experiments were conducted
using a closed aerobic thermophilic composting reactor with sawdust as the bulk matrix to simulate the condition of a bio-toilet
for the sanitary disposal of human feces. Attention was paid to the characteristics of nitrogen transformation. Under the
controlled conditions of temperature at 60°C, moisture content at 60%,anda continuous air supply, more than 70% fecal organic
removal was obtained, while merely 17% fecal nitrogen loss was observed over a two-week composting period. The nitrogen loss
was found to occur mainly in the first 24 h with the rapid depletion of inorganic nitrogen but with an almost unchanged organic
nitrogen content. The fecal NH4-N which was the main component of the inorganic nitrogen ( > 90%) decreased rapidly in the first day, decreased at a slower
rate over the following days, and finally disappeared entirely. The depletion of NH4-N was accompanied by the accumulation of NH3 gas in the ammonia absorber connected to the reactor. A mass balance between the exhausted NH3 gas and the fecal NH4-N content in the first 24 hours indicated that the conversion of ammonium into gaseous ammonia was the main reason for nitrogen
loss. Thermophilic composting could be considered as a way to keep a high organic nitrogen content in the compost for better
utilization as a fertilizer. |
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