Design of Composting-Type Toilet

Abstract

Based on results of experimental research presented in previous chapters, criteria for the proper design and operation of composting toilet were established. In addition, size of the composting reactor was determined attending the already established criteria and based on results of drying tests conducted in a laboratory-scale drying device designed by us. Design procedure considered the daily water loading, due to contributions of urine and feces, as the main criterion. Organic loading, in terms of feces/sawdust ratio (F/S), resulted to be a non-governing factor for the design, because it was very low. Even though mixing frequency may enhance the biodegradation and drying rates in the composting reactor, the design was conducted regarding no mixing conditions due to the evaluation of its effect on such rates has not been studied yet. However, mixing frequency was considered an important factor for operating the system. The establishment of operation criteria led to the formulation of an operation scheme where three main zones are distinguished: (i) “green zone” where the best composting performance is expected; (ii) “yellow zone” where biodegradation can be conducted but performance is not the most efficient; (iii) other zones where operation of the bio-toilet is not recommended because odor problems and human health risk will develop, high operation cost for concept of excessive mixing may result, or in the worst case, biodegradation of feces will not occur.