Nitrogen holding property of the composts in an aerobic mesophilic composting reactor for sanitary disposal of human feces

Aerobic composting is a method for sanitary disposal of human feces as has been used in bio-toilet systems. As the composting products can be utilized as fertilizer, it would be favorable if the composting condition could be well controlled for holding fecal nitrogen as far as possible in the composts. In this study, batch experiments were conducted using a closed aerobic composting reactor with sawdust as the bulky matrix to simulate the condition of a bio-toilet for sanitary disposal of human feces. Attention was paid to the characteristics of nitrogen transformation. Under a controlled condition of temperature at 35 °C, moisture content at 60%, and continuous air supply, merely 31.4% fecal nitrogen loss was observed in a two-week composting period. The nitrogen loss was found to occur mainly in the 0-4 day (2-3 day better) with quick depletion of inorganic nitrogen and changed organic nitrogen content. The fecal NH₄-N which was the main component of the inorganic nitrogen (>;90%) decreased quickly in the 0-4 day, gradually decreased in the following days, and finally disappeared. A mass balance between the exhausted NH₃ gas and the fecal NH₄-N content in the 0-4 day indicated that the conversion of ammonium into gaseous ammonia was the main reason for nitrogen loss. without an automatically controlled heating system, mesophilic composting could be considered to increased fecal nitrogen loss, keep less organic nitrogen content in the composts for worse fertilizer utilization.