Design and establishment of a large-scale controlled ecological life-support system integrated experimental platform.

A Controlled Ecological Life-Support System (CELSS) can meet the demands of food, oxygen, and water for human, as well as providing psychological benefits during deep space exploration by the continuous materials regeneration. Many key techniques of the platform are needed to explore before applying to the extraterrestrial planets. In this study, a large-scale CELSS integrated experimental platform was designed and constructed to meet the basic life-support material demands of six crew members (max). The platform was composed of four kinds of cabins including Crew Cabin (CC), Plant Cabin (PC), Life-Support Cabin (LSC), Resource Recycling Cabin (RRC) and affiliated facilities. Eight cabins were involved in the platform, i.e., CCs I and II, PCs I, II, III and IV, LSC, and RRC. The platform involved 15 subsystems and covered a plant culture area of 206.6 m2 (a max extensible area of 260 m2) and a total volume of 1340 m3. The joint debuggings and the 4-subject 180-day CELSS integration experiment were carried out successfully. The material closures were 55% (on average) for food (70.8% in highly efficient production period), 100% for atmospheric regeneration, 100% for water regeneration, and 87.7% for recycled solid waste in the 4-subject 180-day integration experiment. It verified that the indicators of the platform meet the technical requirements and realize food regeneration, air regeneration and water regeneration through the integration of physico-chemical technique and biological technique for the long-term survivals of six crew members in the closed cabins.

Operation overview of a biological waste treatment system during the 4-crew 180-day integrated experiment in the controlled ecological life support system (CELSS).

Waste management and treatment is vital to health care and material circulation, especially in the Controlled Ecological Life Support System (CELSS) with finite resources for long-duration manned space missions. A closed ecological-cycle integrated 4-crew 180-day experiment platform was established to investigate the key technologies such as effective cultivation of higher plant, water treatment and recycling, waste management and treatment. In this study, generated waste during the integrated experiment was classified as renewable and non-renewable waste. The renewable waste including all crew feces and part of inedible plant biomass were treated in a biological system where the aerobic composting technology was utilized. The performance in relation to degradation effect, phytotoxicity and nutrient evaluation was examined during the continuous 180 days. The long-term operation results displayed that 96.26 kg feces and 74.4 kg wheat straw were treated, and 90.6 kg compost product was discharged in nine batches. The microbial community variation was analyzed and Firmicutes, Actinobacteria and Proteobacteria enriched in the compost. The phytotoxicity of compost was examined by seed germination index (GI) and GI of Chinese cabbage ranged from 88% to 132% for all batches. Compared to grown in vermiculite only, the lettuce yield increased 19% when grown in a mixture of vermiculite and processed compost. The summary of this work will be helpful to facilitate future applications of aerobic composting technology as the bio-based waste treatment technology in CELSS.

Wheat Cultivation and Nutrient Control for the 180-day CELSS Integrated Experiment.

This research aimed to select the well-adapted wheat cultivar and to explore an optimum nutrient control pattern for wheat cultivation in the 180-day integrated experiment of controlled ecological life support system (CELSS). In the experiment, six wheat cultivars from different areas of China were preselected and cultivated in four separate recirculating hydroponic systems (HySy), nutrients in which could be controlled and recycled according the values of pH, electrical conductivity (EC) and dissolved oxygen (DO). Wheat covered an area of 111.3 m2 and had been planted in 17 batches with a 15-day time interval to realize stable regeneration of oxygen, water and food during the 180-day duration in the closed cabin. The results indicated that different cultivars displayed different adaptabilities to the controlled environment. Wt04 had a stronger adaptability with the highest yield (12.82 g DM m-2 d-1) and edible radiation use efficiency (RUE) (0.28 g DM mol-1) whereas Wt06 adapted this environment poorly because of its excessive vegetative growth. For the morphological characters, wheat plants tended to dwarf in the CELSS environment compared with the field. An innovative controlling pattern was established for nutrient supplement. Through the real-time monitoring of pH, EC and DO of the nutrient solution and the periodical detection of the contents of nutrient elements, the nutrient solution could be controlled and recycled continuously without being renewed under a suitable state for wheat plants growth during the 180-day integrated experiment.

Deactivation Kinetics of Polyethylenimine-based Adsorbents Used for the Capture of Low Concentration CO2.

CO2 emission is generally regarded as the major contributor to global climate change, and polyethylenimine (PEI)-based CO2 adsorbents are promising materials for the capture of low concentration CO2. This paper deals with the deactivation kinetics of PEI-based CO2 adsorbents used for the capture of low concentration CO2. EA and TG analyses demonstrated that thermal degradation and O2-induced deactivation of the adsorbents occurred simultaneously under air exposure conditions. It was found by N2 exposure experiments at the temperature of 50-80 °C that the thermal degradation of PEI-based adsorbents followed a first-order reaction model with an activation energy of 80.98 kJ/mol and a pre-exponential factor of 6.055 × 108 (h-1). The parallel reaction model was employed to distinguish the O2-induced deactivation from the thermal degradation of the adsorbents through air exposure experiments within 50-80 °C. The O2-induced deactivation exhibited a second-order reaction with an activation energy of 74.47 kJ/mol and a pre-exponential factor of 6.321 × 106 (%-1·h-1). The results of simulating the overall deactivation of the adsorbents by the parallel reaction kinetic model were well consistent with those of the experiments, proving that the parallel reaction model was feasible for the description of the deactivation of PEI-based adsorbents.

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.

A modified MBR system with post advanced purification for domestic water supply system in 180-day CELSS: Construction, pollutant removal and water allocation.

Water supply was vital to people's life, especially inside Controlled Ecological Life Support System (CELSS) for long-term space exploration. A platform of 4-person-180-day integrated experiment inside a CELSS including 6 cabins called 'SPACEnter' was established in Shenzhen, China. Based on this platform, a Membrane Bio-Reactor (MBR) system configuring post advanced purification, including I-MBR, II-MBR, nanofiltration (NF), reverse osmosis (RO), ion-exchange (IE), polyiodide disinfection (PI) and mineralization (MC) stages, used as a Domestic Water Supply System (DWSS) to guarantee crew's daily life was constructed. The performance of DWSS to treat the real plant cabin's condensate water was examined during continuously 180-day experiment. The long-term operation results showed that, though the influent pollutant load changed as the experiment processing, the system exhibited stable performance on pollutants removal with average effluent TOC＜0.5 mg/L, NH4+-N＜0.02 mg/L, NO3--N＜0.25 mg/L, NO2--N＜0.001 mg/L, and displayed good capacity for controlling the trace metal ions and microorganism. The effluent through such modified MBR system was sufficiently allocated as hygiene water and potable water, and the average value was 39.69 and 10.93 L/d, respectively. The consumption of the modified MBR process was within the designed allowable scope. The outcomes of this study will be helpful for facilitating future applications of MBR as bio-based water supply technology in the CELSS.

Aromatic hydrocarbons in a controlled ecological life support system during a 4-person-180-day integrated experiment.

Indoor air quality is vital to the health and comfort of people who live inside a controlled ecological life support system (CELSS) built for long-term space explorations. Here we measured aromatic hydrocarbons to assess their sources and health risks during a 4-person-180-day integrated experiment inside a CELSS with four cabins for growing crops, vegetables and fruits and other two cabins for working, accommodations and resources management. During the experiment, the average concentrations of benzene, ethylbenzene, m,p-xylenes and o-xylene were found to decrease exponentially from 7.91±3.72, 37.2±35.2, 100.8±111.7 and 46.8±44.1µg/m3 to 0.39±0.34, 1.4±0.5, 2.8±0.7 and 2.1±0.9µg/m3, with half-lives of 25.3, 44.8, 44.7 and 69.3days, respectively. Toluene to benzene ratios indicated emission from construction materials or furniture to be a dominant source for toluene, and concentrations of toluene fluctuated during the experiment largely due to the changing sorption by growing plants. The cancer and no-cancer risks based on exposure pattern of the crews were insignificant in the end of the experiment. This study also suggested that using low-emitting materials/furniture, growing plants and purifying air actively would all help to lower hazardous air pollutants inside CELSS. Broadly, the results would benefit not only the development of safe and comfort life support systems for space exploration but also the understanding of interactions between human and the total environment in closed systems.

Non-methane hydrocarbons in a controlled ecological life support system.

Non-methane hydrocarbons (NMHCs) are vital to people's health and plants' growth, especially inside a controlled ecological life support system (CELSS) built for long-term space explorations. In this study, we measured 54 kinds of NMHCs to study their changing trends in concentration levels during a 4-person-180-day integrated experiment inside a CELSS with four cabins for plants growing and other two cabins for human daily activities and resources management. During the experiment, the total mixing ratio of measured NMHCs was 423 ± 283 ppbv at the first day and it approached 2961 ± 323 ppbv ultimately. Ethane and propane were the most abundant alkanes and their mixing ratios kept growing from 27.5 ± 19.4 and 31.0 ± 33.6 ppbv to 2423 ± 449 ppbv and 290 ± 10 ppbv in the end. For alkenes, ethylene and isoprene presented continuously fluctuating states during the experimental period with average mixing ratios of 30.4 ± 19.3 ppbv, 7.4 ± 5.8 ppbv. For aromatic hydrocarbons, the total mixing ratios of benzene, toluene, ethylbenzene and xylenes declined from 48.0 ± 44 ppbv initially to 3.8 ± 1.1 ppbv ultimately. Biomass burning, sewage treatment, construction materials and plants all contributed to NMHCs inside CELSS. In conclusion, the results demonstrate the changing trends of NMHCs in a long-term closed ecological environment's atmosphere which provides valuable information for both the atmosphere management of CELSS and the exploration of interactions between humans and the total environment.

Simultaneous Online Measurement of H2O and CO2 in the Humid CO2 Adsorption/Desorption Process.

A dew point meter (DP) and an infrared (IR) CO2 analyzer were assembled in a humid CO2 adsorption/desorption system in series for simultaneous online measurements of H2O and CO2, respectively. The humidifier, by using surface-flushing on a saturated brine solution was self-made for the generation of humid air flow. It was found that by this method it became relatively easy to obtain a low H2O content in air flow and that its fluctuation could be reduced compared to the bubbling method. Water calibration for the DP-IR detector is necessary to be conducted for minimizing the measurement error of H2O. It demonstrated that the relative error (RA) for simultaneous online measurements H2O and CO2 in the desorption process is lower than 0.1%. The high RA in the adsorption of H2O is attributed to H2O adsorption on the transfer pipe and amplification of the measurement error. The high accuracy of simultaneous online measurements of H2O and CO2 is promising for investigating their co-adsorption/desorption behaviors, especially for direct CO2 capture from ambient air.

Measurement and ANN prediction of pH-dependent solubility of nitrogen-heterocyclic compounds.

Based on the solubility of 25 nitrogen-heterocyclic compounds (NHCs) measured by saturation shake-flask method, artificial neural network (ANN) was employed to the study of the quantitative relationship between the structure and pH-dependent solubility of NHCs. With genetic algorithm-multivariate linear regression (GA-MLR) approach, five out of the 1497 molecular descriptors computed by Dragon software were selected to describe the molecular structures of NHCs. Using the five selected molecular descriptors as well as pH and the partial charge on the nitrogen atom of NHCs (QN) as inputs of ANN, a quantitative structure-property relationship (QSPR) model without using Henderson-Hasselbalch (HH) equation was successfully developed to predict the aqueous solubility of NHCs in different pH water solutions. The prediction model performed well on the 25 model NHCs with an absolute average relative deviation (AARD) of 5.9%, while HH approach gave an AARD of 36.9% for the same model NHCs. It was found that QN played a very important role in the description of NHCs and, with QN, ANN became a potential tool for the prediction of pH-dependent solubility of NHCs.

Direct electron transfer from electrode to electrochemically active bacteria in a bioelectrochemical dechlorination system.

Pentachlorophenol (PCP) was dechlorinated by electrochemically active bacteria using an electrode as the direct electron donor. Dechlorination efficiency and coulombic efficiency (CE) were investigated. When hydrogen evolution reaction was eliminated by controlling the potential, both dechlorination efficiency and CE increase as the potential decreases, which implied the dechlorination was stimulated by electric current rather than hydrogen gas. Further investigation of the cyclic voltammetry characterization of the medium revealed nearly no redox mediator secreted by the bacteria. Moreover, the comparison of dechlorination experiments carried out with filtered and unfiltered medium provided convincible evidence that the dominating electron transfer mechanism for the dechlorination is direct electron transfer. Additionally, 454 pyrosequencing technique was employed to gain a comprehensive understanding of the biocathodic microbial community. The results showed Proteobacteria, Bacteroidetes and Firmicutes were the three predominant groups. This paper demonstrated the direct electron transfer mechanism could be involved in PCP dechlorination with a biocathode.