Feasibility and annual performance of zero-energy ecological toilet in cold regions

Abstract

Toilet Revolution has been implemented and many kinds of sanitary toilets, such as three-boxed, water flushing and anaerobic fermentation, have been spread to achieve on-site harmless treatment of feces and improve living standard of farmers in Chinese rural areas. However, in northwestern of China, the ambient temperature is often below 0℃ and pipes are easily broken by frozen in winter, which leads to the inability of on-site harmless feces treatment. Furthermore, with the improvement of living standard of farmers, the toilet has become an important place for bathing and above prevalent toilets are out of date. Therefore, a zero-energy ecological toilet was designed to meet various users’ needs, integrating photovoltaic, solar heater and thermostatic anaerobic digester into a unit. Subsequently, theoretical model was built to simulate the winter performances of the zero-energy ecological toilet and an experimental prototype was developed to discover practical performances throughout the year in Lanzhou City, Gansu Province. The novel zero-energy ecological toilet runs independently and reliably with the energy yields by itself, even encountering the lowest ambient temperature of −14.5 °C, the indoor temperature is still 6.1 °C above the frozen point. It can provide users with 240.8 kW·h of electricity and 1853.8 kW·h of heat throughout the year, and can generate 305.3 m³ of biogas. Its annual income is 2603.3 yuan, with an investment payback period of 4.1 years. It can save 1266.5 kg of standard coal and reduce carbon dioxide emissions by 3320.8 kg throughout the year, which can provide new ways and ideas for rural Toilet Revolution.