Assessment of a prototype of composting toilet : field scale study assessing the design, performance and potential of the prototype.

Inglés. Common problems with composting toilets are the appearance of odors, the control of themoisture content and the heat and energy demand. The objective of this study is to assess theperformance of an innovative design of a composting toilet that targets to improve the performancefor cold climate especially. Solar energy is utilized to optimize ventilation and provide temperature forbetter composting and evaporation control.The system was conceptualized by Petter Jenssen, Petter Heyerdahl and Jon Fredrik Hanssen andwas built by Jørgen Kjørven in Grua, Lunner municipality, Norway. The installation consist ofsolar air collector, gravel bed and composting chamber. The solar collector transforms the solarradiation to heat. The heat is transported by air that is sucked through the system by an exhaustfan. The gravel bed function as heat storage. The target of the design is to transport heat to thecomposting chamber to facilitate the degradation, evaporation and sanitization of the compost.The system was optimized along with this study and modifications are described and assessed.The assessment is based on measurement of air temperature, light intensity, air flow, evaporationvisual observations, and an interview with the users. The results are analyzed in terms of air andheat flow within the system, incoming solar radiation and heat storage capacity. Furthermore, thepotential of the toilet system design is discussed and improvements suggested.The performance of the system was correlated to airflow velocity and improved when airleakages and heat losses were reduced. The mean temperatures in the composting chamberduring the period with the most optimal performance of the system were 10°C higher than themean ambient temperatures. The temperatures in the solar collector reached up to 80°C.Comparison of the airflow at the inlet and outlet of the system showed that the air path was notsealed properly and when the leakages were sealed the airflow velocity was increased. The heatflow estimations in the system identified that only 20-25% of the solar energy was utilized andthat during daytime the energy is transferred from the solar collector to the composting chamber.The energy flow in the system is as follows: energy is gained by the air in the solar collector, inthe gravel bed this energy is transferred to the rocks, some of the residual energy is used to warmthe compost chamber and some is lost with the exhaust air.3The results suggest that the present design will have beneficial effect on the composting processbut the future development of the prototype theoretically have the potential to sanitize thecompost in the warm months and to prolong the time without freezing in the cold months.

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