Water Systems of Biosphere 2

by William F. Dempster, Director of SystemsEngineering, Space Biosphere Venture
Abstract

Biosphere 2 is a large closed ecological system including five wilder- ness biomes, an intensive agriculture, and human habitat. Water is completely recycled for all uses including potable, hygiene, and irrigation, as well as within natural analogue freshwater streams and natural analogue marine areas. The organization of these water systems is described.

Introduction

Biosphere 2 at once integrates the capability to support several human inhabitants for indefinite periods of time with the broader scope of maintaining natural ecosystem analogues on a substantial scale within the same enclosure. The total footprint of the airtight area is 12,700 square meters with a combined volume of 180,000 cubic meters. Biosphere 2 is extensively described in many aspects in several other publications. (1,2,3,4,5).

The wilderness biomes, rainforest, savannah, ocean, marsh, desert all include significant bodies of water in addition to moisture in soils and water vapor in air. The intensive agriculture biome also maintains rice paddies with water several inches deep.

Overall Water Systems Cycles and Operation

The overall freshwater system is schematically diagrammed in Fig. 1. The critical recycling step is condensation from the atmosphere as represented at the top of the diagram. Water vapor enters the atmosphere by evaporation and transpiration throughout all biomes, both from planted areas and from the exposed surface of water bodies. Relative humidity is generally high, typically in the 60% -90% range and not infrequently up to 100% when temperatures are falling.

Figure 1

 

Condensation occurs within each biome at two different locations: a) on the cooling coils of the air handlers, and b) on the airtight glazing of Biosphere 2.
The air handlers recirculate air within each biome to control space temperature and humidity. They do so utilizing both hot and cold water circulated inside closed loop piping systems supplied by energy sources outside of the Biosphere 2 airtight enclosure. Condensate forms on the air handler cooling coils and is collected in trays from which it is pumped to collection tanks. In the diagram, the collection tanks are represented as cylindrical tanks labeled “condensate”. The overhead boxes labeled “condensate” represent both the collection on air handler cooling coils and on the airtight envelope.

The glazing of Biosphere 2 is in direct contact with both inside and outside air. In cold weather, the latter imparts enough cooling to the glass to cause condensate to form on the inside surface. This condensate drains to the lower edge of the glass and is collected in a series of plastic extruded troughs. The network of troughs form a tributary system to the bottom edge of the glazing/space frame from where drain pipes subsequently deliver the water to the same condensate tanks.

Some areas of the glazing/ space frame envelope are horizontal and condensed water does not run to one edge but collects and drips off. This condition is represented by the dashed lines descending from the “condensate” boxes to the individual biomes in the diagram. During cold weather, which at the Biosphere 2 site would typically include November through February, this pathway of condensate return can be a significant part of the “rainfall” delivered to the biomes.

Distribution Of Collected Condensate

Once collected, the condensate water is available for distribution. The dominant use by volume is for rainwater in the wilderness areas and irrigation of the agricultural systems. This is illustrated as delivery to the “Utility Water” and “Rainwater” tanks in the diagram from which further delivery is shown to each biome. Another use is to a misting system on the mountaintop in the rainforest for creating a fog analogous to natural rainforest high altitude fogs. Overflow from the condensate storage goes to the very large (880,000 liter capacity) “Primary Storage and Supply” tank shown near the bottom of the diagram.

The other condensate use of major importance is for potable water. Condensate is passed through two-stage filtration to 0.1 micron and ultraviolet sterilization to potable water holding tanks. Potable water is distributed to the human habitat for drinking, cooking and hygienic uses as well as drinking water for the domesticated animals.

In the wilderness, all of the biomes except the ocean receive direct rainfall from overhead sprinklers mounted in the spaceframe. In addition, there are extensive drip irrigation networks to pockets that are not reached by the overhead sprinklers or need special watering schedules. Release of water through sprinklers or the drip network is controlled by programmable timers or by manual action. The biome manager determines the watering schedule by exercising judgment based on regular observations of each biome. The schedule may have large variations due to planned events such as dormancy of an entire biome, for example.

In the intensive agriculture biome, crop irrigation is separately con- trolled according to the need of each of the 18 plots. Common faucets and garden hoses are also used for special areas and planter boxes requiring individual watering. The water level in rice paddies is constant at an overflow pipe that drains into a sump. A pump then maintains constant circulation from the sump to the paddy and back to the overflow. A float valve maintains the water level in the sump to make up for evapotranspiration losses from the paddy.

Habitat Uses And Waste Return

Potable water derived from condensate supplies all hygiene, drinking, cooking, shop, and analytical laboratory outlets in the habitat. The analytical laboratory also has a reverse osmosis/deionization system which produces 18 megaohm of water for washing glassware and other analytical purposes. The six toilets are all served with water from the “Utility Water” supply. The domestic animal pens are also washed with utility water .

There are three separate sets of anaerobic holding tanks for receiving waste water from different sources. Each set has three individual tanks that are used in rotation in batch operation, which allows a few days of anaerobic digestion prior to release to marsh treatment. Toilet, hygiene, and kitchen wastewaters drain together to the human waste anaerobic holding tanks. Waste water from the animal pens drain to animal waste holding tanks, and waste from the analytical laboratory and machine shop drain to the lab / shop holding tanks.

The analytical laboratory uses very little wet reagent chemistry I and is not a source of pollutants into the water supply. Analytical procedures are almost entirely based on gas chromatography, mass spectroscopy, ion chromatography, and atomic absorbtion spectrophotometry which avoid the need for significant quantities of reagent wastes. Small amounts of reagent wastes from exceptional and infrequent analytical needs can be stored indefinitely in a few bottles. Some small amounts of acids and bases are used but neutralize each other before release. Acids have a slight dominance and the imbalance is neutralized by NaOH. The amounts of salt created are negligibly small in the total water system.

Effluent from the anaerobic holding tanks is further treated in marsh treatment beds following methods developed at NASA Stennis Space Center by Wolverton (6). There are two treatment beds, one devoted to wastewaters of human origin and one treating the combined effluents from the animal pens, laboratory, and machine shop. Water discharged from the marsh treatments returns to the utility water tanks and is again available for toilet water, animal pen washing or agriculture.

Subsoil Drainage Return

As diagrammed, subsoil drainage occurs from all but the marine biomes. This water is collected and made available again to the biomes via the rain or irrigation systems. Overflow returns to the primary storage tank.

Marine Systems

The marine biomes, saltwater marsh and ocean, together contain more than five million liters of saltwater. Volumetrically, they constitute the largest water system in Biosphere 2. The ocean holds nearly four million liters in a basin up to 7.6 meters deep x 19 meters wide x 45 meters long. The saltwater marsh has varying salinity through five zones progressing from the most saline adjacent to the ocean to the least saline furthest from the ocean. The salinity gradient is created by intrusion of freshwater into the least saline zone counteracting tidal influx entering the most saline zone. The “tide” is pumped from the ocean and propagates upward throughout the five zones similar to the propagation of natural ocean tide up a river delta. The effect of receding tide is created by allowing the marsh to partially drain back to the ocean again.

Pumped recirculation of water is maintained in the ocean and all five marsh zones to assist continuous redistribution of nutrients and waterborne exchanges. There is also a vacuum operated system of wave generation. Seawater is alternately raised by vacuum and released in a chamber to create the sudden movement necessary to generate waves.

Excessive nutrient levels that would be created in the ocean from marsh discharge are mitigated by a system of algae scrubbers. Algae scrubbers are shallow trays with growing algae, over which seawater is made to flow. The algae extracts nutrients from the water by growing and so protects the delicate coral reef from nutrient excesses.

The uppermost saltwater marsh zone is adjacent to a freshwater marsh which has a small overflow into the saltwater marsh. This, plus rainwater, combine to give a surplus of freshwater entering the saltwater marsh system over the amount removed by evapotranspiration. The excess is removed by a flash evaporative distiller shown in the lower right side of the diagram. In this unit, fresh water is extracted from salt water by boiling in a vacuum at low temperature. The heat energy required is supplied by hot water circulated in closed loop piping from energy sources outside of Biosphere 2.

Freshwater Streams

Natural analogue freshwater bodies exist in the rainforest, savannah, and desert of Biosphere 2. The rainforest mountain holds a pond that overflows in a waterfall down to a winding creek at ground level. Similarly, a stream of 43 meters length x 1 -2 meters wide runs through the northern half of the savannah. A variety of aquatic organisms, including fish, inhabit these streams, which are continuously flowing due to recirculating pumps. In the desert, there is also a pond plus a seasonally wet and dry lakebed.

 

References

REFERENCES

1. Allen, J., Biosphere 2: The Human Experiment, Viking/Penguin, NY,1991, 156pp.

2. Allen, I., Nelson,M., Space Biospheres, Synergetic Press, London/Tucson, 1986. Revised Ed., 1989.

3. Dempster, W. F., Biosphere n: Technical Overview of a Manned Closed Ec0logical System. SAE Technical Paper 891599, 19th Intersociety Conference On Environmental Systems, 1989.

4. Dempster, W.F., Biosphere n: Closed Ecological Systems Engineering. Engineering, Construction, and Operations in Space n. Proceedings of Space 90, Subsection 4.2: Life Supporl Systems, pp. 1206-1215, American Society of Civil Engineers, Apri11990.

5. Nelson, M., Allen, I., Dempster, W., Biosphere 2: A Prototype Project for a Permanent and Evolving Life System for a Mars Base, COSPAR XXVI11 Plenary Meeting, June 1990, Paper Identification No. MF 1.4.6.

6. Wolverton, B. C., Aquatic Plant/Microbial Filters for Treating Septic Tank Effluent, pp. 173-178 in: Constructed Wetlands for Wastewater Treatment, Donald A. Hammer, Lewis Publishers, 1989. Proceedings from the First International Conference on Constructed Wetlands for Wastewater Treatment, Chattanooga, Tennessee, June 1988.