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Material balance and diet in bioregenerative life support systems: Connection with coefficient of closure
Advances in Space Research 35 (2005) 1563–1569 www.elsevier.com/locate/asr
Material balance and diet in bioregenerative life support systems: Connection with coefficient of closure N.S. Manukovsky, V.S. Kovalev *, L.A. Somova, Yu.L. Gurevich, M.G. Sadovsky Institute of Biophysics, Siberian Branch of Russian Academy of Sciences, Academgorodok, 660036 Krasnoyarsk, Russian Federation Received 16 July 2004; received in revised form 25 December 2004; accepted 5 January 2005
Abstract Bioregenerative life support systems (BLSS) with different coefficients of closure are considered. The 66.2% coefficient of closure achieved in ‘‘BIOS-3’’ facility experiments has been taken as a base value. The increase in coefficient of closure up to 72.6–93.0% is planned due to use of soil-like substrate (SLS) and concentrating of urine. Food values were estimated both in a base variant (‘‘BIOS-3’’), and with increases in the coefficient of closure. It is shown that food requirements will be more fully satisfied by internal crop production with an increase in the coefficient of closure of the BLSS. Changes of massflow rates on an Ôinput–outputÕ and inside BLSS are considered. Equations of synthesis and degradation of organic substances in BLSS were examined using a stoichiometric model. The paper shows that at incomplete closure of BLSS containing SLS there is a problem of nitrogen balancing. To compensate for the removal of nitrogen from the system in urine and feces, it is necessary to introduce food and a nitrogen-containing additive. Ó 2005 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Bioregenerative life support system; Coefficient of closure; Diet; Soil-like substrate
1. Introduction 1.1. ‘‘BIOS-3’’ as a test system for modelling the matter turnover in BLSS The results of experiments in the ‘‘BIOS-3’’ BLSS carried out in 1977 are well documented, but there is still much to be learnt from further analysis of them. Such analysis is important, since ‘‘BIOS-3’’ should provide a framework test system for the development of a new generation of BLSS facilities. Obviously, an increase of coefficient of closure will be one improvement sought in new BLSSs. The mass exchange chart published by Trubachev et al. (1979a) does not show distinctive elements of the ‘‘BIOS-3’’ experiments. For example, one should determine in greater details the human mass flow *
Corresponding author. Tel.: +7 3912 494101; fax: +7 3912 433400. E-mail address: [email protected] (V.S. Kovalev).
rates and the composition of the diet provided to the ‘‘BIOS-3’’ crew with respect to stored and recycled food. To study ‘‘BIOS-3’’ as a test system, one must reexamine the observed experimental conditions. Simultaneously, one must develop approaches which can increase the coefficient of closure in the forthcoming experiments. An attempt was made to increase the coefficient of closure during the third stage of the original experiments in 1979. To do that, the inedible crop biomass was recycled using physical–chemical oxidation. This oxidation released toxic gases, in particular, nitric oxide (Okladnikov et al., 1979). An alternative approach would use biological oxidation of the inedible biomass. One method to utilize inedible biomass involves a soillike substrate (SLS) (Manukovsky et al., 1996). This was tested in a physical model of BLSS (Tikhomirov et al., 2003a). A model of matter turnover in BLSS with inclusion of SLS was also developed (Manukovsky et al., 1997). This modeling assumed complete closure of
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material turnover (recycling), but there is interest in examining incomplete closure scenarios as well. It should be stressed that the model had no immediate connection to a specific BLSS. Such approach does not allow estimating the advantages and disadvantages of SLS use in BLSS. Therefore, a preliminary calculation of matter turnover in ‘‘BIOS-3’’ with implementation of a SLS biological oxidation recycling system was carried out (Manukovsky and Kovalev, 2003). The aim of the present paper is to project and analyze matter turnover in ‘‘BIOS-3’’ facility in conditions of increased coefficient of closure, through the utilization of inedible plant biomass, urine and feces.
2. Methodological prerequisites 2.1. Matter flow chart and turnover characteristics in ‘‘BIOS-3’’ The chart and peculiarities of the matter turnover observed during the first stage of the ‘‘BIOS-3’’ experiment were chosen as the starting point (Trubachev et al., 1979a). Some matter flows were combined, and imbalances were eliminated, for to simplify the analysis. The crew included three persons. Plants were cultivated in aeroponic culture. Wastes were removed from BLSS (Fig. 1). The crew consumed 1007 g/day of food from stored supplies consisting of 727 g of lyophilized food materials and 280 g of grains. In addition, the crew was supplied with 16.6 g of sodium chloride and 192.8 g of the household materials (means of disinfection and hygiene). The average weight of one member of crew was equal to 67.2 kg. The plant crops were supplied with 3278 g of water and 293 g of nutrients. Water and gas exchange between the crew and plants occurred inside the BLSS. The coefficient of closure – R was determined according to the formula R ¼ ð1 m=MÞ 100;
ð1Þ
where m is the demand of BLSS (g/day), and M is a demand of the crew (g/day). The value m = 4787.4 g was the total of the flows of materials into the BLSS, namely: household materials (192.8 g), food from stores (1007 g), sodium chloride (16.6 g), nutrients (293 g) and water for plant growing (3278 g). The same amount of substances (4787.4 g) was eliminated with wastes. The daily demand M = 14159.4 g of the crew consisted of food from stores (1007 g), of food produced in phytotron (2141 g), of sodium chloride (16.6 g), of watering (8777 g), of oxygen (2025 g) and of the household materials (192.8 g). Substituting the values of m and M into the Eq. (1), one has R = 66.2%. It should be stressed, that the design shown in Fig. 1 is ideal, since it represents a steady-state of mass exchange. In reality, total crew weight decreased by
2.2 kg during the first stage of the experiment. Matter exchange between plants and the crew was balanced, with respect to carbon dioxide, while the oxygen exchange was not balanced (Trubachev et al., 1979a). The value of the consumption of food from stores (1007 g/day) and that one from phytotron (2141 g/day) did not provide adequate supply of food to the crew (Fig. 1). The data shown above make the supply of food from the phytotron equal to 70.9% of the crew diet. One should keep in mind that 2141 g is a measure of wet biomass. Water content in the stored food was lower. Calculated supply of the crew with proteins fats and carbohydrates from the phytotron was equal to 28.7%, 29.2%, and 33.4%, respectively (Trubachev et al., 1979b). Thus, the actual supply of food (counting on ash free matter) from the phytotron was equal to 30.4% of the crew diet. A preplanned daily consumption of proteins, fats and carbohydrates by the three-person crew was equal to 230, 230 and 1150 g, respectively (Gitelson and Okladnikov, 1979). With the importation of an additional 128 g/day of animal protein into crewÕs diet that makes 55.7% of total protein content. At the first stage of the experiment, the planned addition of animal protein met the constraint of 55% content of an animal protein in the total protein consumption by a crew (Chemical Composition. . ., 1987). Wheat, onion, carrot, radish, beet (edible root and leaves), cabbage, dill and chufa constituted the plant crops grown in ‘‘BIOS-3’’. Each species was supposed to contribute a yield of plant protein (Gitelson and Okladnikov, 1979). The greatest protein yield was produced by wheat and chufa, 67.2% and 22.1%, respectively. Supposing the 28.7% level of the supply of a crew with plant protein of the normal daily consumption of 230 g of total protein, daily plant protein consumption equals 66.0 g/day. Keeping in mind the amino acid composition of edible parts of plants (Trubachev et al., 1979b), the content of essential amino acids in the plant proteins was calculated (Table 1). Biological value of proteins was estimated using amino acid scale of FAO/WHO (Table 1). This scale shows the content of essential amino acids in ‘‘ideal’’ protein. The score of each essential amino acid in such an ‘‘ideal’’ protein was assumed to be equal to 100%. The scores (S) of the essential amino acids in natural proteins were calculated according to this formula (Skurikhin and Nechaev, 1991): S ¼ 100 ðAmino acid; mg=g of natural protein =the same amino acid; mg=g of ideal proteinÞ: The scores of all essential amino acids were less than 100%, except the combination of phenylalanine and tyrosine (Table 1). Plant protein deficiencies could be counteracted by the addition of animal protein. The
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Fig. 1. The scheme of mass flow rates during the first stage of the experiment in ‘‘BIOS-3’’, 1977. The values of mass flow rates are given in g/day.
Table 1 Characteristics of plant protein observed during the first stage of ‘‘BIOS-3’’ experiment, and the calculated value of the mixture of plant and animal proteins Essential amino acid
Lysine Threonine Valine Methionine + cysteine Leucine Isoleucine Phenylalanine + tyrosine
Amino acid content (mg/g)
Scores of essential amino acids (%)
In plant protein
In the mixture of plant and animal protein
In ideal protein
In plant protein
In the mixture of plant and animal protein
24.69 30.74 38.88 13.31 28.30 65.86 76.02
70.27 40.76 52.32 21.52 39.22 77.68 79.60
55 40 50 35 40 70 60
44.89 76.86 77.76 38.02 70.75 94.08 126.69
127.77 101.89 104.63 61.47 98.05 110.97 132.66
amino acid content of animal proteins supplied to the crew during the first stage of ‘‘BIOS-3’’ experiment was not published. The crew may scheduled to get 230–66 = 164 g/day of animal proteins from the stores. One can suppose, then that the crew received 164 g/day of beef. The scores of all essential amino acids in beef are higher than 100% (Chemical Composition. . .,
1987), thus one should consider the latter to be of full value. The content of amino acids (milligrams per gram of protein) was calculated for the mixture of plant and animal proteins. The scores of the mixture are higher in comparison to that of just plant protein. The sulfurcontaining pool of methionine + cysteine still was a constraint (Table 1). Thus, the additional supply of full
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value animal protein fails to compensate for the shortage of sulfur-containing amino acids in the mixture. This fact demonstrates the importance of careful selection of plant species for BLSS with respect to the sulfurcontaining amino acids capacity in protein of edible biomass. 2.2. Stoichiometry of human metabolism and synthesis vs. degradation of plant organic matter The stoichiometric model of human metabolism was used through the following equation: 1 ½proteins þ X1 ½fats þ X2 ½carbohydrates þ X3 ½fiber þ X4 ½nucleic acids þ X5 ½O2 ¼ X6 ½CO2 þ X7 ½H2 O þ X8 ½urine þ X9 ½feces þ X10 ½‘miscellaneous’; ð2Þ where X1–X10 are the stoichiometric coefficients. As against previous models (Waleh et al., 1991; Belianin et al., 1980) ÔmiscellaneousÕ substances (Huttenbach and Binot, 1991; Poughon et al., 1997) and nucleic acids are taken into account. Both published data (Belianin et al., 1980) and our calculations yield the substances formulae (Table 2). The initial data for calculations were taken from the literature (Calloway, 1975; Kustov and Tiunov, 1969; Life Support. . ., 1994, Ovchinnikov, 1987). Elemental compositions of urine and feces were computed with the help of stoichiometric model. The ÔmiscellaneousÕ compartment was divided into two parts: the former is volatile ones, and the latter is the solid materials. Synthesis vs. degradation of plant biomass is described with the equation: 1 ½CO2 þ Y1 ½H2 O þ Y2 ½NH3 þ Y3 ½HNO3 þ Y4 ½H2 SO4 þ Y5 ½H3 PO4 ¼ 1 ½CHONSPbiomass þ Y6 ½O2 :
ð3Þ
In comparison with previous work (Tikhomirov et al., 2003b) in the equation phosphorus is taken into account.
2.3. The possibility to increase the coefficient of closure through the utilization of plant wastes To design the configuration of BLSS with increased coefficient of closure we used the same characteristics of the crew, as they were observed in the prototype, ‘‘BIOS-3’’ (Trubachev et al., 1979a). The consumed dry food mass was equal to 1503.4 g/day for the crew. Water content in urine and feces was assumed to be equal to 95% (Sinyak et al., 1994), and 83% (Kozyrevska et al., 1967), respectively. Meat from beef was assumed to be the stored food. Chemical compounds contained in beef have been determined according to the biochemical composition of that latter (Chemical Composition. . ., 1987). The formula was based on the assumption that casein constitutes the protein and triolein constitutes the fats in beef. The elemental composition of human excretions provided the estimations of the mass of stored food consumption, and the compensating component. The total mass of food and compensating component was balanced with the mass of dry matter, daily eliminated from the BLSS. Human excretions were balanced by stored food, with respect to carbon turnover. It should be kept in mind that the excretions contain less carbon than beef. The mass fraction of carbon in organic matter of urine is equal to 0.23; it is 0.48 in dry feces, and equals 0.65 in beef. Balancing with respect to carbon results in decrease of the mass of food obtained from stored food, in comparison to the mass of human excretions. To equalize the intake–export flows of the BLSS, a compensating component was introduced into the calculations. That latter was included in the nutrients provided from the stored materials and supplied into the soil-like substrate (Fig. 2). The respiratory coefficient of SLS was taken as 0.85. This means that the substrate consumed 1 mol of oxygen per 0.85 mol of the produced carbon dioxide. Plant assimilation coefficient was taken to equal 0.86; the coefficient shows that 1 mol of produced oxygen required the consumption of 0.86 mol of carbon dioxide. The phytotron area was estimated from the following rela-
Table 2 Elemental composition of organic substances in the man massflow model Substances
Elemental composition of organic substances C
H
O
N
S
P
Proteins Fats Carbohydrates Nucleic acids Urine Feces Volatile part of ÔmiscellaneousÕ substances Solid stuff in ÔmiscellaneousÕ substances Food from stocks (beef)
1 1 1 1 1 1 1 1 1
1.588172 1.824826 1.654523 1.105263 3.244168 1.626703 5.153602 1.901873 1.719328
0.310670 0.105248 0.834166 0.736842 1.064297 0.616996 0.172313 0.396507 0.196823
0.253248
0.005042
0.005146
0.394737 1.355657 0.092085 0.300934 0.158695 0.112895
0.026593 0.001328 0.000845 0.002030 0.002248
0.105263 0.0323 0.008124 0.002206 0.002294
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Fig. 2. The scheme of mass flow rates in ‘‘BIOS-3’’ with soil-like substrate (SLS). The values of mass flow rates are given in g/day. VMS – volatile ÔmiscellaneousÕ substances.
tion: 1 m2 of SLS yields 19.35 g/day of edible plant biomass.
3. Calculation results 3.1. A mass flow rates for BLSS The projected phytotron area is 77.7 m2. Plant wastes (2646.3 g/day) are transferred into the module for preoxidation and to support production of oyster mushroom. These wastes produce a spent mushroom compost (2451.4 g/day of wet biomass) and 150 g/day of mushroom fruit bodies. The spent mushroom compost is transferred into the SLS. A part of the wet plant wastes is transferred into the SLS upon a harvesting; this part is equal to 4457.0 g/day. From BLSS 3288 g of urine, 472 g of feces and 116 g of water are removed daily, similar to the prototype. Both the crew, and the SLS produce carbon dioxide daily equalling 2451 and 3193.3 g, respectively. Total discharge of carbon dioxide into the
atmosphere is balanced by the consumption of that latter by plants. Plants produce 4950.4 g of oxygen, daily. The oxygen is used by the crew, by SLS, and by the module of recycling with the rates of 2025, 2737.4 and 188 g per day, respectively. The water supply for the crewÕs domestic needs is provided by the phytotron, as was done in ‘‘BIOS-3’’. Volatile ÔmiscellaneousÕ substances are produced by crew with a rate 3.9 g/day. Solid stuff of ÔmiscellaneousÕ substances is directed to the module with a rate 31.1 g/day together with waste water. 3.2. Balancing of chemical elements in BLSS The proposed pattern differs from the prototype in increased raw food mass obtained from the phytotron up to 6051.0 g/day. It makes 93.8% of the total food mass. As a result, the import of lyophilized stored food mass goes down to 93.9 g/day. The amount of carbon removed from BLSS with feces and urine is 59.0 g/day. The calculated dry weight of feces and urine is equal to 242 g/day. The carbon mass (59.0 g) is contained in
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93.9 g of beef from imported food stores. Projected compensating component mass is equal to 89.9 g/day. This component contains nitrogen, oxygen, hydrogen, and minerals. In particular, to compensate the discharge of elements with the eliminated urine and feces, one must supply the system with 35.2 g of nitrogen, 47.8 g of oxygen, 2.9 g of hydrogen, 1.5 g of sulfur and 2.4 g of phosphorus daily through the compensating component. The removal of salt elements in urine and feces is compensated through the addition into the SLS of 41.6 g of salts, daily. Fig. 2 shows the joint flux of salts and compensating component with the diurnal discharge of 131.5 g. Coefficient of closure of ‘‘BIOS-3’’ facility with the implemented SLS calculated according to the formula (1) is equal to 72.6%.
Maintenance of the precise import–export balance of various individual elements is another problem in implementation of the projected design. Previously, it was mentioned that one must bring a balancing compensating component into the system, conjointly with the alimentary supply. The component must be free of carbon, but bring nitrogen, oxygen, hydrogen, sulfur and phosphorus into the system. Yet, it is not clear what stuff could fulfill that need. The stream of volatile ÔmiscellaneousÕ substances (VMS) is rather small: 3.9 g/day (Fig. 2). Nevertheless, utilization of VMS is an actual problem. Utilization of VMS is supposed to be carried out in the module of recycling of waste products. 4.2. The possibilities to increase the coefficient of closure through the urine and faeces utilization
4. Discussion 4.1. The recycling of plant wastes is the intermediate step towards a complete closure of mass flows in BLSS Production of plant unit was calculated with the results of a two year experiment with a closed BLSS model (Tikhomirov et al., 2003b). Two species of plants only (wheat and radish) were involved in the experiment. Obviously, the plant unit of any real BLSS must involve several plant species. The inclusion of more species into the plant unit will change the estimated production, assimilation and edible mass coefficient. In the future, one should determine the pattern of the plant community with respect to meeting more fully the dietary needs of the crew. Also, the production, energy value of edible phytomass and other features of the candidate species should be determined experimentally, with respect to the growth of the species on the SLS. Utilization of plant wastes allows increase of the coefficient of closure from 66.2% to 72.6%. The recycling of plant wastes is therefore an intermediate step towards a complete closure of mass flows in BLSS. Meanwhile, the increase of coefficient may follow in some difficulties. In the prototype there was an opportunity to improve the quality of intrasystem food due to additives of animal food from stocks (Table 1). At increase in coefficient of closure this opportunity decreases. The projected design does not meet the desired protein supply from animal food (Chemical Composition. . ., 1987). The diet becomes mainly vegetarian. Hence, requirements to a choice of plants–candidates for BLSS increase. Suitability of a vegetarian diet remains a subject of discussion (Konyshev, 1987). It is possible to produce animal food within a BLSS. There are numerous problems which this would raise: producing enough forage for the animals, the need for additional volume in the BLSS, the development of special facilities for animals, and additional sanitary requirements are among them.
To increase the coefficient of closure, it is necessary to reduce the value of m (the needs of the BLSS, formula (1)). A configuration of BLSS involving the use of plant wastes (Fig. 2) reduces the value of m to 3876 g/day. Following are the substances removed from BLSS each day: 116 g of water, 472 g of feces, and 3288 g of urine. Urine accounts for 84.8% of the total removed mass. An increase of coefficient of closure (R) could be achieved due to water recovery from urine. A method for concentrating urine is the simplest way to achieve that. Suppose, the concentrated mass of urine is equal to 400 g. Then BLSS must be supplied with 192.8 g of household materials, 93.9 g of food, 16.6 g of salt, 131.5 g of nutrients for plants, and 553.2 g of water, daily. Hence, urine concentration would result in the reduction of daily water input from 3441.2 to 553.2 g/day, yielding a coefficient of closure equal to 93.0%. Feces utilization may be the next step in further improving the coefficient of closure. The value of m may become as small as 516 g/day, due to reduction of food supply accompanied with the reduction in required imports of water supply of 161.4 g/day. These improvements increase R to 96.4%. Complete urine utilization may result in further increase in R, but this will require more experiments. As the urine and feces utilization is realized, the remaining challenge will be to reduce or eliminate the required import of household materials (192.8 g/day). These materials include hygiene and disinfection materials. Nomenclature and chemical composition of the materials were not documented (Trubachev et al., 1979a). Consequently, no idea arises towards the list of substances of total weight of 192.8 g to be removed from BLSS daily.
5. Conclusion Coefficient of closure at the first stage of the ‘‘BIOS-3’’ experiment was equal to 66.2%. This means that two-
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thirds of the needs of the crew were provided by the life support materials regenerated in the BLSS. It should be noticed, that water regeneration alone contributes most of the coefficient of closure. Food provision to the crew equalled 30.4%. A high-grade diet was provided only with the import of outside foods. Our study indicates that if the BLSS can achieve the utilization of plant wastes due to use of SLS, this would result in the increase of the coefficient of closure to 72.6%. Thus a quota of food, produced in a phytotron, makes 93.8% of the total food mass. Simultaneous utilization of plant wastes and concentrating of urine will give increase in coefficient of closure up to 93%. The challenge of finding ways to produce animal food would then become important for BLSS. As complete closure is approached the balancing the import/export of chemical compounds can become a problem.
References Belianin, V.N., Sidko, F.Ya., Trenkenshoe, A.P. Energy of Microalgae. Nauka, Novosibirsk, 1980 (in Russian). Calloway, D.H. Basic data for planning life-support systems. In: Gazenko, O.G., Calvin, M. (Eds.), Foundations of Space Biology and Medicine, vol. 3. Nauka, Moscow, pp. 13–34, 1975 (in Russian). Chemical Composition of Food, Book 2, Agropromizdat, Moscow, 1987 (in Russian). Gitelson, I.I., Okladnikov, Yu.N. Experimental plan and original characteristics of manÕs unit. In: Lisovsky, G.M. (Ed.), Closed System: Man – Higher Plants. Nauka, Novosibirsk, pp. 25–37, 1979 (in Russian). Huttenbach, R.C., Binot, R.A. ESA PSS-03-406: life support and habitability manual, in: Guyenne, T-D., Hunt, J.J. (Eds.), Proceedings of the 4th European Symposium on Space Environmental Control Systems. vol. 1, pp. 133–144, 1991. Konyshev, V.A. Current state of old conception (vegetarianism). Problems of Nutrition 6, 10–17, 1987 (in Russian). Kozyrevska, G.I., Koloskova, Yu.S., Sitnikova, N.N., et al. Waterbearing wastes as a source for basic alimentary of autotrophic organisms. In: Nichiporovich, A.A., Lisovsky, G.M. (Eds.), Problems in Closed Ecological Systems Implementation. Nauka, Moscow, pp. 166–170, 1967 (in Russian). Kustov, V.V., Tiunov, L.A. Toxicology of volatile human substances and their significance in formation of an artificial atmosphere of the hermetically sealed rooms, in: Problems of Space Biology, vol. 11. Nauka, Moscow, 1969 (in Russian).
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Life Support and Habitability. Sulzman, F., Genin, A.M. (Eds.), vol. 2. Nauka, Moscow, 1994 (in Russian). Manukovsky, N.S., Kovalev, V.S. Massflow estimation in ‘‘BIOS-3’’ facility with the incorporation of soil-like substrate, in: Volova, T.G. (Ed.), Essays in Ecological Biophysics. Novosibirsk, pp. 267– 278, 2003 (in Russian). Manukovsky, N.S., Kovalev, V.S., Rygalov, V.Ye., et al. Waste bioregeneration in life support CES: development of soil organic substrate. Adv. Space Res. 20, 1827–1832, 1997. Manukovsky, N.S., Kovalev, V.S., Zolotukhin, I.G. et al., Biotransformation of biomass in closed cycle. SAE Technical Paper Series 961417. Monterey, USA, 1996. Okladnikov, Yu.N., Vlasova, N.V., Kasaeva, G.E., et al. ManÕs chain in experiments (medical, physiological and hygiene studies). In: Lisovsky, G.M. (Ed.), Closed System: Man – Higher Plants. Nauka, Novosibirsk, pp. 82–99, 1979 (in Russian). Ovchinnikov, Yu.A. Bioorganic Chemistry. Education, Moscow, 1987 (in Russian). Poughon, L., Dussap, C.G., Gros, J.B. Preliminary study and simulation of the Melissa loop including a higher plants compartment, in: Guyenne, T.-D. (Ed.), Proceedings of the 6th European Symposium on Space Environmental Control Systems. vol. 2, pp. 879–886, 1997. Sinyak, Yu.E., Gaidadymov, V.B., Skuratov, V.M., et al. Water supply of crews. In: Sulzman, F., Genin, A.M. (Eds.), Life Support and Habitability, vol. 2. Nauka, Moscow, 1994 (in Russian). Skurikhin, I.M., Nechaev, A.P. All you want to know about food. ChemistÕs View. Higher School, Moscow, 1991 (in Russian). Tikhomirov, A.A., Ushakova, S.A., Manukovsky, N.S., et al. Synthesis of biomass and utilization of plant wastes in a physical model of biological life support system. Acta Astronautica 53, 249–257, 2003a. Tikhomirov, A.A., Ushakova, S.A., Manukovsky, N.S., et al. Mass exchange in an experimental new-generation life support system model based on biological regeneration of environment. Adv. Space Res. 31, 1711–1720, 2003b. Trubachev, I.N., Okladnikov, Yu.N., Gribovska, I.V., et al. Outer and interchain massflow of system. In: Lisovsky, G.M. (Ed.), Closed System: Man – Higher Plants. Nauka, Novosibirsk, pp. 130–150, 1979a (in Russian). Trubachev, I.N., Gribovska, I.V., Barashkov, V.A., et al. Biochemical and mineral composition of plants produced in BLSS, and the provision of food demand of a crew. In: Lisovsky, G.M. (Ed.), Closed System: Man – Higher Plants. Nauka, Novosibirsk, pp. 62– 81, 1979b (in Russian). Waleh, A., Kanevsky, V., Nguyen, T.K. et al. Impact of diet on the design of waste processors in CELSS, in: Guyenne, T.-D., Hunt, J.J. (Eds.), Proceedings of the 4th European Symposium on Space Environmental Control Systems, vol. 2, pp. 817–821, 1991.
Material balance and diet in bioregenerative life support systems: Connection with coefficient of closure N.S. Manukovsky, V.S. Kovalev *, L.A. Somova, Yu.L. Gurevich, M.G. Sadovsky Institute of Biophysics, Siberian Branch of Russian Academy of Sciences, Academgorodok, 660036 Krasnoyarsk, Russian Federation Received 16 July 2004; received in revised form 25 December 2004; accepted 5 January 2005
Abstract Bioregenerative life support systems (BLSS) with different coefficients of closure are considered. The 66.2% coefficient of closure achieved in ‘‘BIOS-3’’ facility experiments has been taken as a base value. The increase in coefficient of closure up to 72.6–93.0% is planned due to use of soil-like substrate (SLS) and concentrating of urine. Food values were estimated both in a base variant (‘‘BIOS-3’’), and with increases in the coefficient of closure. It is shown that food requirements will be more fully satisfied by internal crop production with an increase in the coefficient of closure of the BLSS. Changes of massflow rates on an Ôinput–outputÕ and inside BLSS are considered. Equations of synthesis and degradation of organic substances in BLSS were examined using a stoichiometric model. The paper shows that at incomplete closure of BLSS containing SLS there is a problem of nitrogen balancing. To compensate for the removal of nitrogen from the system in urine and feces, it is necessary to introduce food and a nitrogen-containing additive. Ó 2005 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Bioregenerative life support system; Coefficient of closure; Diet; Soil-like substrate
1. Introduction 1.1. ‘‘BIOS-3’’ as a test system for modelling the matter turnover in BLSS The results of experiments in the ‘‘BIOS-3’’ BLSS carried out in 1977 are well documented, but there is still much to be learnt from further analysis of them. Such analysis is important, since ‘‘BIOS-3’’ should provide a framework test system for the development of a new generation of BLSS facilities. Obviously, an increase of coefficient of closure will be one improvement sought in new BLSSs. The mass exchange chart published by Trubachev et al. (1979a) does not show distinctive elements of the ‘‘BIOS-3’’ experiments. For example, one should determine in greater details the human mass flow *
Corresponding author. Tel.: +7 3912 494101; fax: +7 3912 433400. E-mail address: [email protected] (V.S. Kovalev).
rates and the composition of the diet provided to the ‘‘BIOS-3’’ crew with respect to stored and recycled food. To study ‘‘BIOS-3’’ as a test system, one must reexamine the observed experimental conditions. Simultaneously, one must develop approaches which can increase the coefficient of closure in the forthcoming experiments. An attempt was made to increase the coefficient of closure during the third stage of the original experiments in 1979. To do that, the inedible crop biomass was recycled using physical–chemical oxidation. This oxidation released toxic gases, in particular, nitric oxide (Okladnikov et al., 1979). An alternative approach would use biological oxidation of the inedible biomass. One method to utilize inedible biomass involves a soillike substrate (SLS) (Manukovsky et al., 1996). This was tested in a physical model of BLSS (Tikhomirov et al., 2003a). A model of matter turnover in BLSS with inclusion of SLS was also developed (Manukovsky et al., 1997). This modeling assumed complete closure of
0273-1177/$30 Ó 2005 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2005.01.002
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material turnover (recycling), but there is interest in examining incomplete closure scenarios as well. It should be stressed that the model had no immediate connection to a specific BLSS. Such approach does not allow estimating the advantages and disadvantages of SLS use in BLSS. Therefore, a preliminary calculation of matter turnover in ‘‘BIOS-3’’ with implementation of a SLS biological oxidation recycling system was carried out (Manukovsky and Kovalev, 2003). The aim of the present paper is to project and analyze matter turnover in ‘‘BIOS-3’’ facility in conditions of increased coefficient of closure, through the utilization of inedible plant biomass, urine and feces.
2. Methodological prerequisites 2.1. Matter flow chart and turnover characteristics in ‘‘BIOS-3’’ The chart and peculiarities of the matter turnover observed during the first stage of the ‘‘BIOS-3’’ experiment were chosen as the starting point (Trubachev et al., 1979a). Some matter flows were combined, and imbalances were eliminated, for to simplify the analysis. The crew included three persons. Plants were cultivated in aeroponic culture. Wastes were removed from BLSS (Fig. 1). The crew consumed 1007 g/day of food from stored supplies consisting of 727 g of lyophilized food materials and 280 g of grains. In addition, the crew was supplied with 16.6 g of sodium chloride and 192.8 g of the household materials (means of disinfection and hygiene). The average weight of one member of crew was equal to 67.2 kg. The plant crops were supplied with 3278 g of water and 293 g of nutrients. Water and gas exchange between the crew and plants occurred inside the BLSS. The coefficient of closure – R was determined according to the formula R ¼ ð1 m=MÞ 100;
ð1Þ
where m is the demand of BLSS (g/day), and M is a demand of the crew (g/day). The value m = 4787.4 g was the total of the flows of materials into the BLSS, namely: household materials (192.8 g), food from stores (1007 g), sodium chloride (16.6 g), nutrients (293 g) and water for plant growing (3278 g). The same amount of substances (4787.4 g) was eliminated with wastes. The daily demand M = 14159.4 g of the crew consisted of food from stores (1007 g), of food produced in phytotron (2141 g), of sodium chloride (16.6 g), of watering (8777 g), of oxygen (2025 g) and of the household materials (192.8 g). Substituting the values of m and M into the Eq. (1), one has R = 66.2%. It should be stressed, that the design shown in Fig. 1 is ideal, since it represents a steady-state of mass exchange. In reality, total crew weight decreased by
2.2 kg during the first stage of the experiment. Matter exchange between plants and the crew was balanced, with respect to carbon dioxide, while the oxygen exchange was not balanced (Trubachev et al., 1979a). The value of the consumption of food from stores (1007 g/day) and that one from phytotron (2141 g/day) did not provide adequate supply of food to the crew (Fig. 1). The data shown above make the supply of food from the phytotron equal to 70.9% of the crew diet. One should keep in mind that 2141 g is a measure of wet biomass. Water content in the stored food was lower. Calculated supply of the crew with proteins fats and carbohydrates from the phytotron was equal to 28.7%, 29.2%, and 33.4%, respectively (Trubachev et al., 1979b). Thus, the actual supply of food (counting on ash free matter) from the phytotron was equal to 30.4% of the crew diet. A preplanned daily consumption of proteins, fats and carbohydrates by the three-person crew was equal to 230, 230 and 1150 g, respectively (Gitelson and Okladnikov, 1979). With the importation of an additional 128 g/day of animal protein into crewÕs diet that makes 55.7% of total protein content. At the first stage of the experiment, the planned addition of animal protein met the constraint of 55% content of an animal protein in the total protein consumption by a crew (Chemical Composition. . ., 1987). Wheat, onion, carrot, radish, beet (edible root and leaves), cabbage, dill and chufa constituted the plant crops grown in ‘‘BIOS-3’’. Each species was supposed to contribute a yield of plant protein (Gitelson and Okladnikov, 1979). The greatest protein yield was produced by wheat and chufa, 67.2% and 22.1%, respectively. Supposing the 28.7% level of the supply of a crew with plant protein of the normal daily consumption of 230 g of total protein, daily plant protein consumption equals 66.0 g/day. Keeping in mind the amino acid composition of edible parts of plants (Trubachev et al., 1979b), the content of essential amino acids in the plant proteins was calculated (Table 1). Biological value of proteins was estimated using amino acid scale of FAO/WHO (Table 1). This scale shows the content of essential amino acids in ‘‘ideal’’ protein. The score of each essential amino acid in such an ‘‘ideal’’ protein was assumed to be equal to 100%. The scores (S) of the essential amino acids in natural proteins were calculated according to this formula (Skurikhin and Nechaev, 1991): S ¼ 100 ðAmino acid; mg=g of natural protein =the same amino acid; mg=g of ideal proteinÞ: The scores of all essential amino acids were less than 100%, except the combination of phenylalanine and tyrosine (Table 1). Plant protein deficiencies could be counteracted by the addition of animal protein. The
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Fig. 1. The scheme of mass flow rates during the first stage of the experiment in ‘‘BIOS-3’’, 1977. The values of mass flow rates are given in g/day.
Table 1 Characteristics of plant protein observed during the first stage of ‘‘BIOS-3’’ experiment, and the calculated value of the mixture of plant and animal proteins Essential amino acid
Lysine Threonine Valine Methionine + cysteine Leucine Isoleucine Phenylalanine + tyrosine
Amino acid content (mg/g)
Scores of essential amino acids (%)
In plant protein
In the mixture of plant and animal protein
In ideal protein
In plant protein
In the mixture of plant and animal protein
24.69 30.74 38.88 13.31 28.30 65.86 76.02
70.27 40.76 52.32 21.52 39.22 77.68 79.60
55 40 50 35 40 70 60
44.89 76.86 77.76 38.02 70.75 94.08 126.69
127.77 101.89 104.63 61.47 98.05 110.97 132.66
amino acid content of animal proteins supplied to the crew during the first stage of ‘‘BIOS-3’’ experiment was not published. The crew may scheduled to get 230–66 = 164 g/day of animal proteins from the stores. One can suppose, then that the crew received 164 g/day of beef. The scores of all essential amino acids in beef are higher than 100% (Chemical Composition. . .,
1987), thus one should consider the latter to be of full value. The content of amino acids (milligrams per gram of protein) was calculated for the mixture of plant and animal proteins. The scores of the mixture are higher in comparison to that of just plant protein. The sulfurcontaining pool of methionine + cysteine still was a constraint (Table 1). Thus, the additional supply of full
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value animal protein fails to compensate for the shortage of sulfur-containing amino acids in the mixture. This fact demonstrates the importance of careful selection of plant species for BLSS with respect to the sulfurcontaining amino acids capacity in protein of edible biomass. 2.2. Stoichiometry of human metabolism and synthesis vs. degradation of plant organic matter The stoichiometric model of human metabolism was used through the following equation: 1 ½proteins þ X1 ½fats þ X2 ½carbohydrates þ X3 ½fiber þ X4 ½nucleic acids þ X5 ½O2 ¼ X6 ½CO2 þ X7 ½H2 O þ X8 ½urine þ X9 ½feces þ X10 ½‘miscellaneous’; ð2Þ where X1–X10 are the stoichiometric coefficients. As against previous models (Waleh et al., 1991; Belianin et al., 1980) ÔmiscellaneousÕ substances (Huttenbach and Binot, 1991; Poughon et al., 1997) and nucleic acids are taken into account. Both published data (Belianin et al., 1980) and our calculations yield the substances formulae (Table 2). The initial data for calculations were taken from the literature (Calloway, 1975; Kustov and Tiunov, 1969; Life Support. . ., 1994, Ovchinnikov, 1987). Elemental compositions of urine and feces were computed with the help of stoichiometric model. The ÔmiscellaneousÕ compartment was divided into two parts: the former is volatile ones, and the latter is the solid materials. Synthesis vs. degradation of plant biomass is described with the equation: 1 ½CO2 þ Y1 ½H2 O þ Y2 ½NH3 þ Y3 ½HNO3 þ Y4 ½H2 SO4 þ Y5 ½H3 PO4 ¼ 1 ½CHONSPbiomass þ Y6 ½O2 :
ð3Þ
In comparison with previous work (Tikhomirov et al., 2003b) in the equation phosphorus is taken into account.
2.3. The possibility to increase the coefficient of closure through the utilization of plant wastes To design the configuration of BLSS with increased coefficient of closure we used the same characteristics of the crew, as they were observed in the prototype, ‘‘BIOS-3’’ (Trubachev et al., 1979a). The consumed dry food mass was equal to 1503.4 g/day for the crew. Water content in urine and feces was assumed to be equal to 95% (Sinyak et al., 1994), and 83% (Kozyrevska et al., 1967), respectively. Meat from beef was assumed to be the stored food. Chemical compounds contained in beef have been determined according to the biochemical composition of that latter (Chemical Composition. . ., 1987). The formula was based on the assumption that casein constitutes the protein and triolein constitutes the fats in beef. The elemental composition of human excretions provided the estimations of the mass of stored food consumption, and the compensating component. The total mass of food and compensating component was balanced with the mass of dry matter, daily eliminated from the BLSS. Human excretions were balanced by stored food, with respect to carbon turnover. It should be kept in mind that the excretions contain less carbon than beef. The mass fraction of carbon in organic matter of urine is equal to 0.23; it is 0.48 in dry feces, and equals 0.65 in beef. Balancing with respect to carbon results in decrease of the mass of food obtained from stored food, in comparison to the mass of human excretions. To equalize the intake–export flows of the BLSS, a compensating component was introduced into the calculations. That latter was included in the nutrients provided from the stored materials and supplied into the soil-like substrate (Fig. 2). The respiratory coefficient of SLS was taken as 0.85. This means that the substrate consumed 1 mol of oxygen per 0.85 mol of the produced carbon dioxide. Plant assimilation coefficient was taken to equal 0.86; the coefficient shows that 1 mol of produced oxygen required the consumption of 0.86 mol of carbon dioxide. The phytotron area was estimated from the following rela-
Table 2 Elemental composition of organic substances in the man massflow model Substances
Elemental composition of organic substances C
H
O
N
S
P
Proteins Fats Carbohydrates Nucleic acids Urine Feces Volatile part of ÔmiscellaneousÕ substances Solid stuff in ÔmiscellaneousÕ substances Food from stocks (beef)
1 1 1 1 1 1 1 1 1
1.588172 1.824826 1.654523 1.105263 3.244168 1.626703 5.153602 1.901873 1.719328
0.310670 0.105248 0.834166 0.736842 1.064297 0.616996 0.172313 0.396507 0.196823
0.253248
0.005042
0.005146
0.394737 1.355657 0.092085 0.300934 0.158695 0.112895
0.026593 0.001328 0.000845 0.002030 0.002248
0.105263 0.0323 0.008124 0.002206 0.002294
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Fig. 2. The scheme of mass flow rates in ‘‘BIOS-3’’ with soil-like substrate (SLS). The values of mass flow rates are given in g/day. VMS – volatile ÔmiscellaneousÕ substances.
tion: 1 m2 of SLS yields 19.35 g/day of edible plant biomass.
3. Calculation results 3.1. A mass flow rates for BLSS The projected phytotron area is 77.7 m2. Plant wastes (2646.3 g/day) are transferred into the module for preoxidation and to support production of oyster mushroom. These wastes produce a spent mushroom compost (2451.4 g/day of wet biomass) and 150 g/day of mushroom fruit bodies. The spent mushroom compost is transferred into the SLS. A part of the wet plant wastes is transferred into the SLS upon a harvesting; this part is equal to 4457.0 g/day. From BLSS 3288 g of urine, 472 g of feces and 116 g of water are removed daily, similar to the prototype. Both the crew, and the SLS produce carbon dioxide daily equalling 2451 and 3193.3 g, respectively. Total discharge of carbon dioxide into the
atmosphere is balanced by the consumption of that latter by plants. Plants produce 4950.4 g of oxygen, daily. The oxygen is used by the crew, by SLS, and by the module of recycling with the rates of 2025, 2737.4 and 188 g per day, respectively. The water supply for the crewÕs domestic needs is provided by the phytotron, as was done in ‘‘BIOS-3’’. Volatile ÔmiscellaneousÕ substances are produced by crew with a rate 3.9 g/day. Solid stuff of ÔmiscellaneousÕ substances is directed to the module with a rate 31.1 g/day together with waste water. 3.2. Balancing of chemical elements in BLSS The proposed pattern differs from the prototype in increased raw food mass obtained from the phytotron up to 6051.0 g/day. It makes 93.8% of the total food mass. As a result, the import of lyophilized stored food mass goes down to 93.9 g/day. The amount of carbon removed from BLSS with feces and urine is 59.0 g/day. The calculated dry weight of feces and urine is equal to 242 g/day. The carbon mass (59.0 g) is contained in
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93.9 g of beef from imported food stores. Projected compensating component mass is equal to 89.9 g/day. This component contains nitrogen, oxygen, hydrogen, and minerals. In particular, to compensate the discharge of elements with the eliminated urine and feces, one must supply the system with 35.2 g of nitrogen, 47.8 g of oxygen, 2.9 g of hydrogen, 1.5 g of sulfur and 2.4 g of phosphorus daily through the compensating component. The removal of salt elements in urine and feces is compensated through the addition into the SLS of 41.6 g of salts, daily. Fig. 2 shows the joint flux of salts and compensating component with the diurnal discharge of 131.5 g. Coefficient of closure of ‘‘BIOS-3’’ facility with the implemented SLS calculated according to the formula (1) is equal to 72.6%.
Maintenance of the precise import–export balance of various individual elements is another problem in implementation of the projected design. Previously, it was mentioned that one must bring a balancing compensating component into the system, conjointly with the alimentary supply. The component must be free of carbon, but bring nitrogen, oxygen, hydrogen, sulfur and phosphorus into the system. Yet, it is not clear what stuff could fulfill that need. The stream of volatile ÔmiscellaneousÕ substances (VMS) is rather small: 3.9 g/day (Fig. 2). Nevertheless, utilization of VMS is an actual problem. Utilization of VMS is supposed to be carried out in the module of recycling of waste products. 4.2. The possibilities to increase the coefficient of closure through the urine and faeces utilization
4. Discussion 4.1. The recycling of plant wastes is the intermediate step towards a complete closure of mass flows in BLSS Production of plant unit was calculated with the results of a two year experiment with a closed BLSS model (Tikhomirov et al., 2003b). Two species of plants only (wheat and radish) were involved in the experiment. Obviously, the plant unit of any real BLSS must involve several plant species. The inclusion of more species into the plant unit will change the estimated production, assimilation and edible mass coefficient. In the future, one should determine the pattern of the plant community with respect to meeting more fully the dietary needs of the crew. Also, the production, energy value of edible phytomass and other features of the candidate species should be determined experimentally, with respect to the growth of the species on the SLS. Utilization of plant wastes allows increase of the coefficient of closure from 66.2% to 72.6%. The recycling of plant wastes is therefore an intermediate step towards a complete closure of mass flows in BLSS. Meanwhile, the increase of coefficient may follow in some difficulties. In the prototype there was an opportunity to improve the quality of intrasystem food due to additives of animal food from stocks (Table 1). At increase in coefficient of closure this opportunity decreases. The projected design does not meet the desired protein supply from animal food (Chemical Composition. . ., 1987). The diet becomes mainly vegetarian. Hence, requirements to a choice of plants–candidates for BLSS increase. Suitability of a vegetarian diet remains a subject of discussion (Konyshev, 1987). It is possible to produce animal food within a BLSS. There are numerous problems which this would raise: producing enough forage for the animals, the need for additional volume in the BLSS, the development of special facilities for animals, and additional sanitary requirements are among them.
To increase the coefficient of closure, it is necessary to reduce the value of m (the needs of the BLSS, formula (1)). A configuration of BLSS involving the use of plant wastes (Fig. 2) reduces the value of m to 3876 g/day. Following are the substances removed from BLSS each day: 116 g of water, 472 g of feces, and 3288 g of urine. Urine accounts for 84.8% of the total removed mass. An increase of coefficient of closure (R) could be achieved due to water recovery from urine. A method for concentrating urine is the simplest way to achieve that. Suppose, the concentrated mass of urine is equal to 400 g. Then BLSS must be supplied with 192.8 g of household materials, 93.9 g of food, 16.6 g of salt, 131.5 g of nutrients for plants, and 553.2 g of water, daily. Hence, urine concentration would result in the reduction of daily water input from 3441.2 to 553.2 g/day, yielding a coefficient of closure equal to 93.0%. Feces utilization may be the next step in further improving the coefficient of closure. The value of m may become as small as 516 g/day, due to reduction of food supply accompanied with the reduction in required imports of water supply of 161.4 g/day. These improvements increase R to 96.4%. Complete urine utilization may result in further increase in R, but this will require more experiments. As the urine and feces utilization is realized, the remaining challenge will be to reduce or eliminate the required import of household materials (192.8 g/day). These materials include hygiene and disinfection materials. Nomenclature and chemical composition of the materials were not documented (Trubachev et al., 1979a). Consequently, no idea arises towards the list of substances of total weight of 192.8 g to be removed from BLSS daily.
5. Conclusion Coefficient of closure at the first stage of the ‘‘BIOS-3’’ experiment was equal to 66.2%. This means that two-
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thirds of the needs of the crew were provided by the life support materials regenerated in the BLSS. It should be noticed, that water regeneration alone contributes most of the coefficient of closure. Food provision to the crew equalled 30.4%. A high-grade diet was provided only with the import of outside foods. Our study indicates that if the BLSS can achieve the utilization of plant wastes due to use of SLS, this would result in the increase of the coefficient of closure to 72.6%. Thus a quota of food, produced in a phytotron, makes 93.8% of the total food mass. Simultaneous utilization of plant wastes and concentrating of urine will give increase in coefficient of closure up to 93%. The challenge of finding ways to produce animal food would then become important for BLSS. As complete closure is approached the balancing the import/export of chemical compounds can become a problem.
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Life Support and Habitability. Sulzman, F., Genin, A.M. (Eds.), vol. 2. Nauka, Moscow, 1994 (in Russian). Manukovsky, N.S., Kovalev, V.S. Massflow estimation in ‘‘BIOS-3’’ facility with the incorporation of soil-like substrate, in: Volova, T.G. (Ed.), Essays in Ecological Biophysics. Novosibirsk, pp. 267– 278, 2003 (in Russian). Manukovsky, N.S., Kovalev, V.S., Rygalov, V.Ye., et al. Waste bioregeneration in life support CES: development of soil organic substrate. Adv. Space Res. 20, 1827–1832, 1997. Manukovsky, N.S., Kovalev, V.S., Zolotukhin, I.G. et al., Biotransformation of biomass in closed cycle. SAE Technical Paper Series 961417. Monterey, USA, 1996. Okladnikov, Yu.N., Vlasova, N.V., Kasaeva, G.E., et al. ManÕs chain in experiments (medical, physiological and hygiene studies). In: Lisovsky, G.M. (Ed.), Closed System: Man – Higher Plants. Nauka, Novosibirsk, pp. 82–99, 1979 (in Russian). Ovchinnikov, Yu.A. Bioorganic Chemistry. Education, Moscow, 1987 (in Russian). Poughon, L., Dussap, C.G., Gros, J.B. Preliminary study and simulation of the Melissa loop including a higher plants compartment, in: Guyenne, T.-D. (Ed.), Proceedings of the 6th European Symposium on Space Environmental Control Systems. vol. 2, pp. 879–886, 1997. Sinyak, Yu.E., Gaidadymov, V.B., Skuratov, V.M., et al. Water supply of crews. In: Sulzman, F., Genin, A.M. (Eds.), Life Support and Habitability, vol. 2. Nauka, Moscow, 1994 (in Russian). Skurikhin, I.M., Nechaev, A.P. All you want to know about food. ChemistÕs View. Higher School, Moscow, 1991 (in Russian). Tikhomirov, A.A., Ushakova, S.A., Manukovsky, N.S., et al. Synthesis of biomass and utilization of plant wastes in a physical model of biological life support system. Acta Astronautica 53, 249–257, 2003a. Tikhomirov, A.A., Ushakova, S.A., Manukovsky, N.S., et al. Mass exchange in an experimental new-generation life support system model based on biological regeneration of environment. Adv. Space Res. 31, 1711–1720, 2003b. Trubachev, I.N., Okladnikov, Yu.N., Gribovska, I.V., et al. Outer and interchain massflow of system. In: Lisovsky, G.M. (Ed.), Closed System: Man – Higher Plants. Nauka, Novosibirsk, pp. 130–150, 1979a (in Russian). Trubachev, I.N., Gribovska, I.V., Barashkov, V.A., et al. Biochemical and mineral composition of plants produced in BLSS, and the provision of food demand of a crew. In: Lisovsky, G.M. (Ed.), Closed System: Man – Higher Plants. Nauka, Novosibirsk, pp. 62– 81, 1979b (in Russian). Waleh, A., Kanevsky, V., Nguyen, T.K. et al. Impact of diet on the design of waste processors in CELSS, in: Guyenne, T.-D., Hunt, J.J. (Eds.), Proceedings of the 4th European Symposium on Space Environmental Control Systems, vol. 2, pp. 817–821, 1991.