Key ecological challenges for closed systems facilities

Closed ecological systems are desirable for a number of purposes. In space life support systems, material closure allows precious life-supporting resources to be kept inside and recycled. Closure in small biospheric systems facilitates detailed measurement of global ecological processes and biogeochemical cycles. Closed testbeds facilitate research topics which require isolation from the outside (e.g. genetically modified organisms; radioisotopes) so their ecological interactions and fluxes can be studied separate from interactions with the outside environment. But to achieve and maintain closure entails solving complex ecological challenges. These challenges include being able to handle faster cycling rates and accentuated daily and seasonal fluxes of critical life elements such as carbon dioxide, oxygen, water, macro- and mico-nutrients. The problems of achieving sustainability in closed systems for life support include how to handle atmospheric dynamics including trace gases, producing a complete human diet, recycling nutrients and maintaining soil fertility, the maintenance of healthy air and water and preventing the loss of critical elements from active circulation. In biospheric facilities, the challenge is also to produce analogues to natural biomes and ecosystems, studying processes of self-organization and adaptation in systems that allow specification or determination of state variables and cycles which may be followed through all interactions from atmosphere to soils. Other challenges include the dynamics and genetics of small populations, the psychological challenges for small isolated human groups and backup technologies and strategic options which may be necessary to ensure long-term operation of closed ecological systems.     

The legacy of Biosphere 2 for the study of biospherics and closed ecological systems.

The unprecedented challenges of creating Biosphere 2, the world's first laboratory for biospherics, the study of global ecology and long-term closed ecological system dynamics, led to breakthrough developments in many fields, and a deeper understanding of the opportunities and difficulties of material closure. This paper will review accomplishments and challenges, citing some of the key research findings and publications that have resulted from the experiments in Biosphere 2. Engineering accomplishments included development of a technique for variable volume to deal with pressure differences between the facility and outside environment, developing methods of atmospheric leak detection and sealing, while achieving new standards of closure, with an annual atmospheric leakrate of less than 10%, or less than 300 ppm per day. This degree of closure permitted detailed tracking of carbon dioxide, oxygen, and trace gases such as nitrous oxide and ethylene over the seasonal variability of two years. Full closure also necessitated developing new approaches and technologies for complete air, water, and wastewater recycle and reuse within the facility. The development of a soil-based highly productive agricultural system was a first in closed ecological systems, and much was learned about managing a wide variety of crops using non-chemical means of pest and disease control. Closed ecological systems have different temporal biogeochemical cycling and ranges of atmospheric components because of their smaller reservoirs of air, water and soil, and higher concentration of biomass, and Biosphere 2 provided detailed examination and modeling of these accelerated cycles over a period of closure which measured in years. Medical research inside Biosphere 2 included the effects on humans of lowered oxygen: the discovery that human productivity can be maintained with good health with lowered atmospheric oxygen levels could lead to major economies on the design of space stations and planetary/lunar settlements. The improved health resulting from the calorie-restricted but nutrient dense Biosphere 2 diet was the first such scientifically controlled experiment with humans. The success of Biosphere 2 in creating a diversity of terrestrial and marine environments, from rainforest to coral reef, allowed detailed studies with comprehensive measurements such that the dynamics of these complex biomic systems are now better understood. The coral reef ecosystem, the largest artificial reef ever built, catalyzed methods of study now being applied to planetary coral reef systems. Restoration ecology advanced through the creation and study of the dynamics of adaptation and self-organization of the biomes in Biosphere 2. The international interest that Biosphere 2 generated has given new impetus to the public recognition of the sciences of biospheres (biospherics), biomes and closed ecological life systems. The facility, although no longer a materially-closed ecological system, is being used as an educational facility by Columbia University as an introduction to the study of the biosphere and complex system ecology and for carbon dioxide impacts utilizing the complex ecosystems created in Biosphere '.The many lessons learned from Biosphere 2 are being used by its key team of creators in their design and operation of a laboratory-sized closed ecological system, the Laboratory Biosphere, in operation as of March 2002, and for the design of a Mars on Earth(TM) prototype life support system for manned missions to Mars and Mars surface habitats. Biosphere 2 is an important foundation for future advances in biospherics and closed ecological system research.     

The water cycle in closed ecological systems: Perspectives from the Biosphere 2 and Laboratory Biosphere systems

To achieve sustainable, healthy closed ecological systems requires solutions to challenges of closing the water cycle – recycling wastewater/irrigation water/soil medium leachate and evaporated water and supplying water of required quality as needed for different needs within the facility. Engineering Biosphere 2, the first multi-biome closed ecological system within a total airtight footprint of 12,700 m² with a combined volume of 200,000 m³ with a total water capacity of some 6 × 10⁶ L of water was especially challenging because it included human inhabitants, their agricultural and technical systems, as well as five analogue ecosystems ranging from rainforest to desert, freshwater ecologies to saltwater systems like mangrove and mini-ocean coral reef ecosystems. By contrast, the Laboratory Biosphere – a small (40 m³ volume) soil-based plant growth facility with a footprint of 15 m² – is a very simplified system, but with similar challenges re salinity management and provision of water quality suitable for plant growth. In Biosphere 2, water needs included supplying potable water for people and domestic animals, irrigation water for a wide variety of food crops, and recycling and recovering soil nutrients from wastewater. In the wilderness biomes, providing adequately low salinity freshwater terrestrial ecosystems and maintaining appropriate salinity and pH in aquatic/marine ecosystems were challenges. The largest reservoirs in Biosphere 2 were the ocean/marsh with some 4 × 10⁶ L, soil with 1 to 2 × 10⁶ l, primary storage tank with 0 to 8 × 10⁵ L and storage tanks for condensate and soil leachate collection and mixing tanks with a capacity of 1.6 × 10⁵ L to supply irrigation for farm and wilderness ecosystems. Other reservoirs were far smaller – humidity in the atmosphere (2 × 10³ L), streams in the rainforest and savannah, and seasonal pools in the desert were orders of magnitude smaller (8 × 10⁴ L). Key technologies included condensation from humidity in the air handlers and from the glass space frame to produce high quality freshwater, wastewater treatment with constructed wetlands and desalination through reverse osmosis and flash evaporation were key to recycling water with appropriate quality throughout the Biosphere 2 facility. Wastewater from all human uses and the domestic animals in Biosphere 2 was treated and recycled through a series of constructed wetlands, which had hydraulic loading of 0.9–1.1 m³ day⁻¹ (240–290 gal d⁻¹). Plant production in the wetland treatment system produced 1210 kg dry weight of emergent and floating aquatic plant wetland which was used as fodder for the domestic animals while remaining nutrients/water was reused as part of the agricultural irrigation supply. There were pools of water with recycling times of days to weeks and others with far longer cycling times within Biosphere 2. By contrast, the Laboratory Biosphere with a total water reservoir of less than 500 L has far quicker cycling rapidity: for example, atmospheric residence time for water vapor was 5–20 min in the Laboratory Biosphere vs. 1–4 h in Biosphere 2, as compared with 9 days in the Earth’s biosphere. Just as in Biosphere 2, humidity in the Laboratory Biosphere amounts to a very small reservoir of water. The amount of water passing through the air in the course of a 12-h operational day is two orders of magnitude greater than the amount stored in the air. Thus, evaporation and condensation collection are vital parts of the recycle system just as in Biosphere 2. The water cycle and sustainable water recycling in closed ecological systems presents problems requiring further research – such as how to control buildup of salinity in materially closed ecosystems and effective ways to retain nutrients in optimal quantity and useable form for plant growth. These issues are common to all closed ecological systems of whatever size, including planet Earth’s biosphere and are relevant to a global environment facing increasing water shortages while maintaining water quality for human and ecosystem health. Modular biospheres offer a test bed where technical methods of resolving these problems can be tested for feasibility.     

Biosphere 2 Test Module: a ground-based sunlight-driven prototype of a closed ecological life support system.

Constructed in 1986, the Biosphere 2 Test Module has been used since the end of that year for closed ecological systems experiments. It is the largest closed ecological facility ever built, with a sealed variable volume of some 480 cubic meters. It is built with a skin of steel spaceframes with double-laminated glass panels admitting about 65 percent Photosynthetically Active Radiation (PAR). The floor is of welded steel and there is an underground atmospheric connection via an air duct to a variable volume chamber ("lung") permitting expansion and contraction of the Test Module's air volume caused by changes in temperature and barometric pressure, which causes a slight positive pressure from inside the closed system to the outside thereby insuring that the very small leakage rate is outward. Several series of closed ecological system investigations have been carried out in this facility. One series of experiments investigated the dynamics of higher plants and associated soils with the atmosphere under varying light and temperature conditions. Another series of experiments included one human in the closed system for three, five and twenty-one days. During these experiments the Test Module had subsystems which completely recycled its water and atmosphere; all the human dietary needs were produced within the facility, and all wastes were recycled using a marsh plant/microbe system. Other experiments have examined the capability of individual component systems used, such as the soil bed reactors, to eliminate experimentally introduced trace gases. Analytic systems developed for these experiments include continuous monitors of eleven atmospheric gases in addition to the complete gas chromatography mass spectrometry (GCMS) examinations of potable, waste system and irrigation water quality.     

Current concepts and future directions of CELSS.

Studies of bioregenerative life support systems for use in space indicate that they are scientifically feasible. Preliminary data suggest that they would provide cost- and weight-saving benefits for low Earth orbit, long duration space platforms. Concepts of such systems include the use of higher plants and/or micro-algae as sources of food, potable water and oxygen, and as sinks for carbon dioxide and metabolic wastes. Recycling of materials within the system will require processing of food organism and crew wastes using microbiological and/or physical chemical techniques. The dynamics of material flow within the system will require monitoring, control, stabilization and maintenance imposed by computers. Future phases of study will continue investigations of higher plant and algal physiology, environmental responses, and control; flight experiments for testing responses of organisms to weightlessness and increased radiation levels; and development of ground-based facilities for the study of recycling within a bioregenerative life support system.     

A combined modeling and experimental approach for achieving a simplified closed ecosystem.

In CELSS both biological and physico-chemical processes have to be used to support the main needs of the crews and to minimize the re-supply of food and air from Earth. The basic idea is to create a complete food chain (an artificial ecosystem), beginning from the crew, with its wastes, and returning to the crew to supply it with food and air. Two main other steps of this food chain are a waste treatment process and a biomass production including higher plants. We set up the connection of these key modules, which we called ECLAS (Ecosysteme Clos Artificiel Simplifie). A growth chamber containing higher plants is connected to a continuous supercritical water oxidation reactor, that converts the harvested biomass into carbon dioxide and enables the photosynthesis of the canopy. To achieve a stable coupling through optimized regulations between the modules, we programmed a modular numerical simulation of the system, in order to assess the involved fluxes and to constrain the last degrees of freedom of the experimental system already built. Simulation results and the first experimental results are here compared.     

Regenerative life support systems--why do we need them?

Human exploration of the solar system will include missions lasting years at a time. Such missions mandate extensive regeneration of life support consumables with efficient utilization of local planetary resources. As mission durations extend beyond one or two years, regenerable human life support systems which supply food and recycle air, water, and wastes become feasible; resupply of large volumes and masses of food, water, and atmospheric gases become unrealistic. Additionally, reduced dependency on resupply or self sufficiency can be an added benefit to human crews in hostile environments far from the security of Earth. Comparisons of resupply and regeneration will be discussed along with possible scenarios for developing and implementing human life support systems on the Moon and Mars.     

Possible nutrient limiting factor in long term operation of closed aquatic ecosystem

To investigate nutrient limitation effect on the community metabolism of closed aquatic ecosystem and possible nutrient limiting factors in the experimental food chains, depletion of inorganic chemicals including carbon, nitrogen and phosphorous was tested. A closed aquatic ecosystem lab module consisting of Chlorella pyrenoidosa and Chlamydomonas reinhardtii, Daphnia magna and associated unidentified microbes was established. Closed ecological systems receive no carbon dioxide; therefore, we presumed carbon as a first limiting factor. The results showed that the algae population in the nutrient saturated group was statistically higher than that in the nutrient limited groups, and that the chlorophyll a content of algae in the phosphorus limited group was the highest among the limited groups. However, the nitrogen limited group supported the most Daphnia, followed by the carbon limited group, the nutrient saturated group and the phosphorus limited group. Redundancy analysis showed that the total phosphorus contents were correlated significantly with the population of algae, and that the amount of soluble carbohydrate as feedback of nutrient depletion was correlated with the number of Daphnia. Thus, these findings suggest that phosphorus is the limiting factor in the operation of closed aquatic ecosystem. The results presented herein have important indications for the future construction of long term closed ecological system.     

Basic design concept of Closed Ecology Experiment Facilities.

In order to study the relationship between the physiological metabolism of living things and the environmental factors such as the atmospheric contents and so on within the closed ecosystem, Closed Ecology Experiment Facilities (CEEF) were designed and now under construction based on the following concepts: (1) Individual sealed chambers (called modules) for the plant cultivation, animal breeding, human habitation and microbial waste treatment are to be constructed independently to be able to study the metabolic effects of each living thing on the environmental factors within closed ecosystem. (2) A chamber for the microbial waste treatment are to be replaced with two systems; wet oxidation reactors and chemical nitrogen fixation reactors. (3) Atmospheric control systems are to be independently attached to each module for stabilizing atmospheric contents in each module. (4) Any construction materials having the possibility to absorb oxygen and carbon dioxide are to be prohibited to use in each module for sustaining material balance. (5) Facilities have to be developed so that the closed plant and animal experiments can be done independently, as well as integrated experiments with plants and animals through exchanging foods, carbon dioxide, oxygen, condensed water and nutrient solution.     

Plants + soil/wetland microbes: Food crop systems that also clean air and water

The limitations that will govern bioregenerative life support applications in space, especially volume and weight, make multi-purpose systems advantageous. This paper outlines two systems which utilize plants and associated microbial communities of root or growth medium to both produce food crops and clean air and water. Underlying these approaches are the large numbers and metabolic diversity of microbes associated with roots and found in either soil or other suitable growth media. Biogeochemical cycles have microbial links and the ability of microbes to metabolize virtually all trace gases, whether of technogenic or biogenic origin, has long been established. Wetland plants and the rootzone microbes of wetland soils/media also been extensively researched for their ability to purify wastewaters of a great number of potential water pollutants, from nutrients like N and P, to heavy metals and a range of complex industrial pollutants. There is a growing body of research on the ability of higher plants to purify air and water. Associated benefits of these approaches is that by utilizing natural ecological processes, the cleansing of air and water can be done with little or no energy inputs. Soil and rootzone microorganisms respond to changing pollutant types by an increase of the types of organisms with the capacity to use these compounds. Thus living systems have an adaptive capacity as long as the starting populations are sufficiently diverse. Tightly sealed environments, from office buildings to spacecraft, can have hundreds or even thousands of potential air pollutants, depending on the materials and equipment enclosed. Human waste products carry a plethora of microbes which are readily used in the process of converting its organic load to forms that can be utilized by green plants. Having endogenous means of responding to changing air and water quality conditions represents safety factors as these systems operate without the need for human intervention. We review this research and the ability of systems using these mechanisms to also produce food or other useful crops. Concerns about possible pathogens in soils and wastewater are discussed along with some methods to prevent contact, disease transmission and to pre-screen and decrease risks. The psychological benefits of having systems utilizing green plants are becoming more widely recognized. Some recent applications extending the benefits of plants and microbes to solve new environmental problems are presented. For space applications, we discuss the use of in situ space resources and ways of making these systems compact and light-weight.     

Theoretical and practical considerations for staggered production of crops in a BLSS.

A functional Bioregenerative Life Support System (BLSS) will generate oxygen, remove excess carbon dioxide, purify water, and produce food on a continuous basis for long periods of operation. In order to minimize fluctuations in gas exchange, water purification, and yield that are inherent in batch systems, staggered planting and harvesting of the crop is desirable. A 418-d test of staggered production of potato cv. Norland (26-d harvest cycles) using nutrients recovered from inedible biomass was recently completed at Kennedy Space Center. The results indicate that staggered production can be sustained without detrimental effects on life support functions in a CELSS. System yields of H2O, O2 and food were higher in staggered than batch plantings. Plants growing in staggered production or batch production on "aged" solution initiated tubers earlier, and were shorter than plants grown on "fresh" solution. This morphological response required an increase in planting density to maintain full canopy coverage. Plants grown in staggered production used available light more efficiently than the batch planting due to increased sidelighting.     

Advantages of using subsurface flow constructed wetlands for wastewater treatment in space applications: ground-based Mars Base prototype.

Research and design of subsurface flow wetland wastewater treatment systems for a ground-based experimental prototype Mars Base facility has been carried out, using a subsurface flow approach. These systems have distinct advantages in planetary exploration scenarios: they are odorless, relatively low-labor and low-energy, assist in purification of water and recycling of atmospheric CO2, and will support some food crops. An area of 6-8 m2 may be sufficient for integration of wetland wastewater treatment with a prototype Mars Base supporting 4-5 people. Discharge water from the wetland system will be used as irrigation water for the agricultural crop area, thus ensuring complete recycling and utilization of nutrients. Since the primary requirements for wetland treatment systems are warm temperatures and lighting, such bioregenerative systems may be integrated into early Mars base habitats, since waste heat from the lights may be used for temperature maintenance in the human living environment. "Wastewater gardens (TM)" can be modified for space habitats to lower space and mass requirements. Many of its construction requirements can eventually be met with use of in-situ materials, such as gravel from the Mars surface. Because the technology requires little machinery and no chemicals, and relies more on natural ecological mechanisms (microbial and plant metabolism), maintenance requirements are minimized, and systems can be expected to have long operating lifetimes. Research needs include suitability of Martian soil and gravel for wetland systems, system sealing and liner options in a Mars Base, and wetland water quality efficiency under varying temperature and light regimes.     

Biomass recycle as a means to improve the energy efficiency of CELSS algal culture systems.

Algal cultures can be very rapid and efficient means to generate biomass and regenerate the atmosphere for closed environmental life support systems. However, as in the case of most higher plants, a significant fraction of the biomass produced by most algae cannot be directly converted to a useful food product by standard food technology procedures. This waste biomass will serve as an energy drain on the overall system unless it can be efficiently recycled without a significant loss of its energy content. We report experiments in which cultures of the algae Scenedesmus obliquus were grown in the light and at the expense of an added carbon source, which either replaced or supplemented the actinic light. As part of these experiments we tested hydrolyzed waste biomass from these same algae to determine whether the algae themselves could be made part of the biological recycling process. Results indicate that hydrolyzed algal (and plant) biomass can serve as carbon and energy sources for the growth of these algae, suggesting that the efficiency of the closed system could be significantly improved using this recycling process.     

BLSS: A contribution to future life support

For extended duration missions in space the supply of basic life-supporting ingredients represents a formidable logistics problem. Storage volume and launch weight of water, oxygen and food in a conventional non-regenerable life support system are directly proportional to the crew size and the length of the mission. In view of spacecraft payload limitations this will require that the carbon, or food, recycling loop, the third and final part in the life support system, be closed to further reduce logistics cost. This will be practical only if advanced life support systems can be developed in which metabolic waste products are regenerated and food is produced.

Biological Life Support Systems (BLSS) satisfy the space station environmental control functions and close the food cycle. A Biological Life Support System has to be a balanced ecological system, biotechnical in nature and consisting of some combination of human beings, animals, plants and microorganisms integrated with mechanical and physico-chemical hardware.

Numerous scientific space experiments have been delineated in recent years, the results of which are applicable to the support of BLSS concepts. Furthermore ecological life support systems have become subject to intensified studies and experiments both in the U.S. and the U.S.S.R. The Japanese have also conducted detailed preliminary studies.

Dornier System has in recent years undertaken an effort to define requirements and concepts and to analyse the feasibility of BLSS for space applications. Analyses of the BLSS energy-mass relation have been performed, and the possibilities to influence it to achieve advantages for the BLSS (compared with physico-chemical systems) have been determined. The major problem areas which need immediate attention have been defined, and a programme for the development of BLSS has been proposed.     

Earth applications of closed ecological systems: relevance to the development of sustainability in our global biosphere.

The parallels between the challenges facing bioregenerative life support in artificial closed ecological systems and those in our global biosphere are striking. At the scale of the current global technosphere and expanding human population, it is increasingly obvious that the biosphere can no longer safely buffer and absorb technogenic and anthropogenic pollutants. The loss of biodiversity, reliance on non-renewable natural resources, and conversion of once wild ecosystems for human use with attendant desertification/soil erosion, has led to a shift of consciousness and the widespread call for sustainability of human activities. For researchers working on bioregenerative life support in closed systems, the small volumes and faster cycling times than in the Earth's biosphere make it starkly clear that systems must be designed to ensure renewal of water and atmosphere, nutrient recycling, production of healthy food, and safe environmental methods of maintaining technical systems. The development of technical systems that can be fully integrated and supportive of living systems is a harbinger of new perspectives as well as technologies in the global environment. In addition, closed system bioregenerative life support offers opportunities for public education and consciousness changing of how to live with our global biosphere.     

Atmosphere behavior in gas-closed mouse-algal systems: An experimental and modelling study

Concepts of biologically-based regenerative life support systems anticipate the use of photosynthetic organisms for air revitalization. However, mismatches in the rates of production and uptake of oxygen or carbon dioxide between the crew and the plants will lead to an accumulation or depletion of these gases beyond tolerable limits. One method for correcting these atmospheric changes is to use physicochemical devices. This would conflict with the constraint of minimal size and weight imposed upon the successful development of a competitive bioregenerative system. An alternate control strategy is based upon reducing the gas exchange mismatch by manipulation of those environmental parameters known to affect plant or algae gas exchange ratios. We have initiated a research program using a dual approach of mathematical modelling and laboratory experimentation aimed at examining the gas exchange characteristics of artificial animal/plant systems closed to the ambient atmosphere. Our goal is to develop control techniques and management strategies for maintaining the atmospheric levels of carbon dioxide and oxygen at physiological levels. A mathematical model simulating the atmospheric behavior in these systems has been developed and an experimental gas-closed system has been constructed. These will be described and preliminary results will be presented.     

二氧化碳甲烷化在载人航天器再生式环控生保系统中的应用

二氧化碳甲烷化（Sabatier反应）是载人航天再生式环控生保系统中空气质量管理的关键技术,也是焦炉气甲烷化和煤制天然气甲烷化流程中最后一级反应器主要进行的化学反应.化工行业中的二氧化碳甲烷化,尤其是针对高纯度二氧化碳的甲烷化技术,与载人航天用Sabatier技术既有共同点又存在差异.通过对Sabatier技术工艺、催化剂和关键设计的总结,对比分析应用于两个不同领域的二氧化碳甲烷化技术在工艺流程、催化剂和反应器方面的差异,借鉴工业二氧化碳甲烷化技术经验,提出载人航天用Sabatier技术可能的优化方向.      

Biomonitoring and risk assessment on earth and during exploratory missions using AquaHab

Bioregenerative closed ecological life support systems (CELSS) will be necessary in the exploration context revitalizing atmosphere, waste water and producing food for the human CELSS mates. During these long-term space travels and stays far away from Earth in an hostile environment as well as far for example from any hospital and surgery potential, it will be necessary to know much more about chemical and drug contamination in the special sense and by human’s themselves in detail.     

中国微藻航空煤油制备潜能及CO2减排

综合考虑中国各地温度变化、水资源和CO₂的供给能力等因素,分析了中国适合微拟球藻规模化养殖的地区;根据2013年沿海地区燃煤发电排放CO₂量,结合蓬莱地区微拟球藻规模化养殖的实际数据,预测了中国微藻的年产量潜力及在现有技术水平下利用这些微藻原料可制备航空煤油的潜力;并采用全生命周期模型GREET计算了微藻航空煤油相比传统石油基航空煤油在全生命周期内中可减少CO₂的排放量。结果表明:目前中国具有每年8894万t的微藻养殖潜力,这些微藻共可制备航空煤油1917万t;与传统航煤相比,制备1 t微藻航空煤油在全生命周期内相比传统航空煤油可降低CO₂排放2.28 t。