Water management in a controlled ecological life support system during a 4-person-180-day integrated experiment: Configuration and performance

Water management subsystem (WMS) is a major component of the controlled ecological life support system (CELSS). For guaranteeing the water requirement of crop growth and crewmember's daily life, a WMS was established in a 4 person 180-day integrated experiment (carried out in Shenzhen, China, 2016) to maintain a closed cycle with a total water amount of ~23 m3. The design and operation of the WMS was summarized as follows: (1) Collection and allocation of condensate water. About 917 L/d condensate water (>98% was from plants' evapotranspiration) was collected, and ~866 L/d of which was reused as plant nutrient solution after ultraviolet (UV) disinfection, and 50.6 L/d was used as the raw water for the domestic water supply module (DWS). (2) Domestic water supply. The condensate water from the plant cabin was purified through the DWS, a modified membrane bioreactor (MBR) system, and then provided hygiene and potable water to 4 crewmembers with different water quality standards. (3) Wastewater recovery. 51.4 L/d wastewater from urination and personal hygiene were treated together via a biological wastewater treatment process to complete the conversion of nitrogen and organic matters, and then recycled to plant nutrient solution. (4) Nutrient solution recycling. In the overall water cycle process, the plant nutrient solution was continuously self-circulated and the water quality of which was maintained at a relatively stable level with total organic carbon of 20–30 mg/L and NH4+-N < 1.0 mg/L. The 180-day continuous operation demonstrated that a 100% water closure was achieved. Based on the results of this study, an upgraded water cycle system for larger-scale and longer-term CELSS has been proposed.