Environ Sci Pollut Res (2015) 22:7020–7024 DOI 10.1007/s11356-014-3743-5
RESEARCH ARTICLE
Study on the kinetic characteristics of trace harmful gases for a two-person-30-day integrated CELSS test Shuangsheng Guo & Weidang Ai & Jinxue Fei & Guoxin Xu & Gu Zeng & Yunze Shen
Received: 15 July 2014 / Accepted: 17 October 2014 / Published online: 9 December 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract A two-person-30-day controlled ecological life support system (CELSS) integrated test was carried out, and more than 30 kinds of trace harmful gases including formaldehyde, benzene, and ammonia were measured and analyzed dynamically. The results showed that the kinds and quantities of the trace harmful gases presented a continuously fluctuating state during the experimental period, but none of them exceed the spacecraft maximum allowable concentration (SMAC). The results of the Pre-Test (with two persons without plants for 3 days) and the Test (with two persons and four kinds of plants for 30 days) showed that there are some notable differences for the compositions of the trace harmful gases; the volatile organic compounds (VOCs) such as toluene, hexane, and acetamide were searched out in the Pre-Test, but were not found in the Test. Moreover, the concentrations of the trace harmful gases such as acetic benzene, formaldehyde, and ammonia decreased greatly in the Test more than those in the Pre-Test, which means that the plants can purify these gases efficiently. In addition, the VOCs such as carbon monoxide, cyclopentane, and dichloroethylene were checked out in the Test but none in the Pre-Test, which indicates that these materials might be from the crew’s metabolites or those devices in the platform. Additionally, the ethylene released specially by plants accumulated in the later period and its concentration reached nearly ten times of 0.05 mg m−3 (maximum allowed concentration for plant growth, which must have promoted the later withering of plants). We hoped that Responsible editor: Philippe Garrigues S. Guo (*) : W. Ai National Key laboratory of Human Factors Engineering, China Astronaut Research and Training Center, Beijing 100094, China e-mail:
[email protected] J. Fei : G. Xu : G. Zeng : Y. Shen China Astronaut Research and Training Center, Beijing 100094, China
the work can play a referring function for controlling VOCs effectively so that future more CELSS integrating tests can be implemented smoothly with more crew, longer period, and higher closure. Keywords CELSS . Integrating test . Trace harmful gases . Formaldehyde . Dynamic features
Introduction To establish the controlled ecological life support system (CELSS) is a fundamental guarantee for solving the longterm manned space life support puzzle in the future (Ohya et al. 1984; Sirko et al. 1994; Guo et al. 2008a; Cohen et al. 2013), and it will face many challenges, such as long-term running, high efficiency, high stability, and automation, in which a lot of gaseous contaminants will be released from devices, metabolites of crew, plants, animals, and microorganisms separately. Emphatically, all of these contaminants must be monitored and cleaned out effectively; otherwise, they will probably arouse harmful effects on the equipment, operation, and crew’s physical and psychological health, etc. (Nalette et al. 2006; Yates et al. 2006; Macatangay et al. 2009). Generally, the researchers have referred to the spacecraft maximum allowable concentration (SMAC) as the relevant harmful gases standards of CELSS (Lane et al. 2003). The Chinese Astronaut Research and Training Center has developed a CELSS platform and conducted an experiment with a crew of two persons for a 30-day duration in the end of 2012, with the purpose of establishing a gas–water closed-cycle ecosystem (Guo et al. 2008b, 2014a, b). Meanwhile, the trace gaseous contaminants and their dynamic patterns were monitored continuously. The main results are reported as follows.
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Experimental conditions and methods Basic experimental conditions The research was carried out in the CELSS integrating experimental platform (CIEF). The facility includes a plant cabin and a crew cabin, and the gas exchange between them was adjusted by two circulation fans with opposite ventilating ways. In addition, an activated carbon air-cleaning facility was installed outside the crew cabin, and the air from the crew cabin was treated and then returned through a closed pipeline. In the beginning, a two-person-3-day CELSS integrated pre-test (Pre-Test for short) without plants was conducted, and then a two-person-30-day CELSS integrated test (Test for short) with plants was carried out soon. The air-cleaning facility worked at all times both in the Pre-Test and the Test. For both of the Pre-Test and the Test, all of the conditions and states such as the number of crew, crew’s working and resting pattern, working load, and on–off modes of experimental devices are all uniform, except for with or without plants which consisted of four types of vegetable plants and totally occupied a 36.0 m2 cultivated area. The four cultivated vegetable plants are Lactuca sativa L. var. Dasusheng, Lactuca sativa L. var. Youmaicai, Gynura bicolor DC, and Cichorium endivia L., separately (Guo et al. 2014a, b). Gas sample measurement methods
Results and discussion Basic characteristics of trace harmful gases The analyzed results showed that the kinds and concentrations of trace contaminants within the plant cabin and the crew cabin were nearly the same for both the Pre-Test and the Test; this is for the reason that the air within the plant cabin and the crew cabin were continuously circulated to each other. Therefore, all those measured data came from the crew cabin, and the data from the plant cabin were not showed here. Totally, there are 35 kinds of trace harmful gases to be found out for both the Pre-Test and the Test; among them are eight major gaseous contaminants, i.e., (1) ammonia, (2) carbon monoxide, (3) formaldehyde, (4) hydrogen sulfide, (5) benzene, (6) ethylbenzene, (7) ortho-xylene, and (8) 1,3dimethylbenzene, and each concentration did not exceed the
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The gas samples were obtained by utilizing a sample pump and a tube outside both the plant cabin and the crew cabin, and the gathered sample’s volume was 5.0 L every time; the gascollecting site was 2.0 m apart from the ground, and 1.5 m from the top of the platform. From the beginning of the experiment until the end, gas-collecting frequency was once per day for the Pre-Test and once per 3 days for the Test, and gases were collected within the plant cabin and the crew cabin,
respectively. The collected samples were stored at a cool and dark container, and then detected and analyzed in time. The trace harmful gases consist of five kinds; they are (1) ammonia (NH3), (2) hydrogen sulfide (H2S), (3) carbon monoxide (CO), (4) ethylene (C2H4), and (5) volatile organic compounds (VOCs) separately. The relevant detection methods are as follows: VOCs were analyzed using gas chromatography–mass spectrometry, consulting the EPA TO-14 method (EPA/625-96/010b, 1999), calibration gas was American TO-14; carbon monoxide and ethylene, using Agilent 7890 gas chromatograph (GB/T8984-2008, GB/ T14677–1993); ammonia and hydrogen sulfide, using the “indophenol blue method” and “polyvinyl alcohol sulfate absorption-methylene blue colorimetry” GB Chemical Analysis Method (GB/T18204.25-2000, GB11742-89), respectively; and the calibration gas was provided by the Chinese National Institute of Standard Substance.
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Fig. 1 The total amount of volatile organic compounds during the Pre-Test and the Test (left is for the Pre-Test and right for the Test)
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Environ Sci Pollut Res (2015) 22:7020–7024 ammonia
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Fig. 2 Dynamic characteristics of eight major contaminants during the Pre-Test and the Test (left is for the Pre-Test and right for the Test)
SMAC all along. The remaining 27 kinds of VOCs were, respectively, (1) chloroform fluoride, (2) dichloromethane, (3) chloroform, (4) tetrachloromethane, (5) dichlorotetrafluoroethane, (6) butane, (7) cyclopentane, (8) methyl cyclopentene, (9) hexane, (10) hexamethylene, (11) methanol, (12) methanol ethylbenzene, (13) ethanol, (14) ethanethiol, (15) heptanol, (16) theaspirone, (17) ethylene (produced by plants), (18) dichloroethylene, (19) trichloroethylene fluorine, (20) cyclopentene, (21) pinene, (22) methyl acetate, (23) heptyl acid, (24) methylbenzene, (25) acetamide, (26) dimethyl disulfide, and (27) carane, etc. The total concentration range of the VOCs in the Pre-Test was 2.757~ 6.451 mg m − 3 , and that in the Test was 2.032 ~ 4.645 mg m−3. This result is similar to the data of 0.3~ 4.3 mg m−3 from NASA’s four-person-90-day Moon–Mars life support integrated test (Lane et al. 2003), which is far lower than the SMAC (25 mg m−3, Fig. 1). Therefore, it is showed that they can meet the environmental medicine requirement of manned spacecraft. In addition, it can be seen from Fig. 1 that during the PreTest, the total concentration of the VOCs increased nearly 1.4 times, but during the Test, their concentrations kept almost constant without distinct fluctuation. The results show that the cultivated vegetable plants in the plant cabin of the CIEF exert better purifying effect on the VOCs.
Fig. 3 Showing the normally growing lettuce plants and withered lettuce plants
Dynamic characteristics of eight major contaminants During both the Pre-test and the Test, the dynamic characteristics of eight major contaminants were showed in Fig. 2. As shown in Fig. 2, the ammonia concentration in the PreTest was in the range of 0.226~0.360 mg m−3, while its early concentration in the Test was at the level of 0.128 mg m−3; afterwards, it gradually declined and reached 0.079 mg m−3 until the 10th day, and from the 13th day onward, the presence of ammonia almost could not be monitored. Secondly, the concentration of formaldehyde in the Pre-Test was in the range of 0.048~0.089 mg m−3 which presented a slightly increasing trend; during the Test, the concentration ranged at 0.020~ 0.030 mg m−3 which fell slightly, and always kept at lower level. Moreover, ethylbenzene in the Pre-Test on the first day was not detected, and by the third day, its concentration reached 0.1 mg m−3, but in the Test, it reached 0.098 mg m−3 at the beginning and remained at 0.010 mg m−3 henceforth. Likewise, ortho-xylene, 1,2-dimethylbenzene, ortho-xylene, and 1,3-dimethylbenzene had similar changing trends during both the Pre-Test and the Test. The results showed that lettuce and other leafy vegetables have stronger capacity of purifying the contaminant gases such as ammonia, formaldehyde, ethylbenzene, ortho-xylene, 1,2-dimethylbenzene, ortho-xylene, and 1,3-dimethylbenzene, etc.
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Fig. 4 Variation trend of ethylene during the Test (the result of the Pre-Test is not showed)
In addition, benzene was not detected in the Pre-Test; however, it went up to 0.050 mg m−3 at the start of the Test, and did not decline at middle and later stage. Hydrogen sulfide was not detected in the Pre-Test; during the Test, hydrogen sulfide came forth but remained at a very low level of 0.020 mg m−3. This result indicates that there almost were no benzene and hydrogen sulfide gases released by this system. Carbon monoxide was not found in the Pre-Test, but by the early and middle phase of the Test, it reached 1.0 mg m−3, declined slightly later, and kept at the level of about 0.6 mg m−3 hereafter. This indicates that the carbon monoxide should come from both the plant cabin and the crew cabin or some devices inside them. The result is not consistent with that from the famous BIOS-3. Their result indicates that the plants have good purification performance for CO. There were more than ten kinds of plant species in the BIOS-3, including wheat, carrots, beets, radish, turnip, cabbage, cucumbers, onions, chufa, and sorrel (tomatoes and potatoes were also grown, but their yield was very low) (Eckart 1994; Gitelson
et al. 2003; Nelson et al. 2013). Different plants may possess different purification effect on trace contaminant gases; therefore, the CO-purifying effect of plants should be explored further. The dynamics of ethylene Ethylene is a gaseous hormone that was produced by plants, specially, and promotes the maturity and senescence of plants. Generally speaking, ethylene concentration in an artificial environment should not be more than 0.05 mg m−3 for plant cultivation (Wang and Gu 2003). In the experimental research, the ethylene purification treatment by means of adsorption or decomposition was not carried out. This time, there was no ethylene detected in the Pre-Test due to the absence of plant within the cabin, but in the Test, ethylene concentration climbed from early 0.008 to 0.490 mg m−3; it increased by 61 times and approached 10 times of 0.05 mg m−3 (the maximum allowed concentration for plant growth). At the late stage of the Test, it could be
Fig. 5 Dynamic change of other VOCs in the Pre-Test and the Test (left is for the Pre-Test, right is for the Test. Note: during the Test, methylbenzene and methanol was not detected)
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obviously seen that some of plant leaves got wrinkled, yellowing, and withered, which is likely to be associated with the quite high ethylene concentration (Figs. 3 and 4). Dynamic characteristics of other VOCs In other more than 20 trace harmful gases, formaldehyde concentration in the Pre-Test was 0.101~0.211 mg m−3; in 3 days, it went up gradually, but it was not detected in the Test all the while. Chloroform fluoride in the Pre-Test was 1.744 mg m−3, and increased to 2.242 mg m−3 gradually by the end of 3 days; at the start of the Test, its concentration was 0.194 mg m −3 , but by the 30th day, it declined to 0.155 mg m−3, keeping a slightly declining concentration. Methanol was not detected in the Pre-Test on the first day, and on the third day, it reached 0.294 mg m−3, which have not been detected in the Test. In addition, the concentrations of some VOCs such as 2-butane, tetrachloromethane, and 3carane in the Pre-Test kept an uplifted trend, but they all showed a substantial decline in the Test. This can be explained that the salad vegetables such as leafy lettuce have better purification ability for many kinds of these trace contaminants (Fig. 5). Additionally, some volatile organic compounds, such as dichlorotetrafluoroethane, cyclopentane, heptanol, theaspirone, pinene, dichloroethylene, trichloroethylene fluorine, and dimethyl disulfide were not detected in the Pre-Test, but turned up in the Test with lower concentrations. These VOCs gases might be released from the cabin bodies, human metabolism, skin secretion, and/or experimental devices, which remains to be detected further. Besides, the data from NASA’s four-person-90-day integration test of the Moon– Mars proposed that methylcyclosiloxane gas was detected from the unknown sources (Lane et al. 2003). Nevertheless, the trace gas was not detected in our tests.
Conclusion The kinetic characteristics and regularity of the trace harmful gases of the two-person-3-day pre-test and the two-person-30day formal test are introduced, and its changing principles and mechanisms are illustrated too. The experimental results show that all the trace harmful gases inside this system are much less than the spacecraft maximum allowed criterion concentration, which means that this test platform can well purge a lot of trace gases contaminants. The leafy vegetables, such as lettuce, possess a good purification effect for ammonia, formaldehyde, ethylbenzene, dimethylbenzene, and methanol. Meanwhile, it is found out that the system can release some
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of other volatile organic compounds such as carbon monoxide, heptanol, and dichloroethylene, etc. that might come from module board insulation materials, sealing ring, human respiration of skin, plant and microorganism metabolism, or some equipment inside the plant cabin and the crew cabin which deserve to be searched further. Future research should focus on trace contaminants monitoring and eliminating the pollution effects on crew, devices, and whole CELSS platform, so as to provide insurance for the large CELSS integration test with more crew, longer duration, and higher material closure. Acknowledgments This work was supported by the Chinese Manned Space Engineering Advance Research Projects (No. 2010SY5404001).
References Cohen MM, Matossian R, Mancinelli R, Flynn M (2013) Water Walls Life Support Architecture. 43rd International Conference on Environmental Systems July 14–18, 2013, Vail, CO, American Institute of Aeronautics and Astronautics, AIAA-2013-3517 Eckart P (ed) (1994) Spaceflight life support and biospherics. Herbert Utz Publishers, Munich Gitelson II, Lisovsky GM, McElroy R (2003) Man-made closed ecological systems. CRC Press, Boca Raton Guo S, Tang Y, Gao F, Ai W, Qin L (2008a) Effects of low pressure and hypoxia on the growth and development of wheat. Acta Astronaut 63:1081–1085 Guo S, Tang Y, Zhu J et al (2008b) Development of a CELSS experimental facility. Adv Space Res 41(5):725–729 Guo S, Ai W, Tang Y et al (2014a) Study on O2 generation and CO2 absorption capability of four co-cultured salad plants in an enclosed system. Adv Space Res 53(2014):1551–1556 Guo S, Dong W, Ai W et al (2014b) Study on regulating technique of material flow for 2-person and 30-day integrated CELSS. Acta Astronaut 100:140–146 Lane HW, Sauer RL, Feeback DL (eds) (2003) NASA experiments in closed-environment living. Advanced human life support enclosed system. Published for the American Astronautical Society by Univelt, Incorporated Macatangay AV, Perry JL, Belcher PL, Johnson SA (2009) Status of the International Space Station (ISS) trace contaminant control system. SAE Technical Paper Series 2009-01-2353 Nalette T, Papale W, Smith F, Perry J (2006) Development Status of Amine-based, Combined Humidity, CO2 and Trace Contaminant Control System for CEV. SAE Technical Paper Series 2006-01-2192 Nelson M, Dempster WF, Allen JP (2013) Key ecological challenges for closed systems facilities. Adv Space Res 52:86–96 Ohya H, Oshima T, Nitta K (1984) Survey of CELSS concepts and preliminary research in Japan. Adv Space Res 4(12):271–277 Sirko RJ, Smith GC, Hamlin LA, Tazawa R (1994) Lunar base CELSS design and analysis. Adv Space Res 14(11):105–112 Wang Z, Gu Y (eds) (2003) Plant physiology. Science and Technology Literature Press, Beijing Yates SF, Tonev T, Lupton S (2006) Trace contaminant removal from air via photocatalytic oxidation. SAE Technical Paper Series 2006-012127
