Blersch_2002

PROJECT GREENHAB AT THE UNIVERSITY OF MARYLAND:DEVELOPMENT OF A RESEARCH-SCALE LIFE SUPPORT GREENHOUSE*

David Blersch and Patrick KangasBiological Resources Engineering Department

University of MarylandCollege Park, Maryland 20742

dblersch@wam.umd.edu

ABSTRACT

Project Greenhab is an ongoing research and development initiative to explore life supporttechnologies suitable for the missions at the Mars Society’s remote research stations. Evolvingfrom earlier efforts of the Mars Society’s life support technical task force, the Greenhab projecthas developed a low-cost greenhouse that is an analog of inflatable structures that might be usedin an actual manned mission to Mars. The modular design of the greenhouse has allowed stagingof segments at various locations around the country, providing a platform for various researchinitiatives within the life support context. One such segment, located at the University ofMaryland’s Department of Biological Resources Engineering, has been used for prototypeengineering, education, and R&D. Prototype engineering began with segment installation inJanuary 2002 and is ongoing as mission support for a similar Greenhab segment at the MDRS inUtah. Research continues at the Maryland segment to develop biologically-based wastewaterrecycling system, based on living machine technologies, appropriate for Mars Society fieldsimulation sites. Finally, educational opportunities created around the Maryland segmentincluded a graduate course in ecological engineering, providing a successful model of universitypartnerships with Mars Society research initiatives.

INTRODUCTION

Project Greenhab is a technical task force within the Mars Society that focuses on several lifesupport issues of possible human bases on Mars. Although many volunteers from the U. S. andother countries have participated, one focus of effort has been by a group in the Mid-Atlanticregion. Early work of this group dealt with the design of a greenhouse-based wastewatertreatment system for the simulated Mars habitat on Devon Island in the Canadian Arctic.Alternative designs were surveyed [1] and a specific design was offered in the form of amodified living machine [2]. In 2001 work shifted to applying the living machine design to theMars Desert Research Station (MDRS) in south central Utah.

Several alternatives for wastewater management at the MDRS are being explored but the livingmachine concept has been emphasized. A living machine is a wastewater treatment system thatcombines conventional technological components (plumbing, pumps, etc.) and aquatic * Copyright © 2003 by D. Blersch & P. Kangas, University of MarylandPublished by The Mars Society with permission.

ecosystems that are contained in tanks connected in a flow-through pattern [3, 4]. Bothanaerobic and aerobic tanks are included along with a high diversity of plants, aquaticinvertebrates and microbes. Treatment of wastewater in a living machine occurs by physical-chemical processes (sedimentation, filtration, absorption) and by biological metabolism. This isa form of ecological engineering since constructed ecosystems are employed for a practicalfunction.

The greenhouse-based living machine design is being implemented for the Mars Society’ssimulated Mars habitats. Each system consists of an external greenhouse structure and a livingmachine constructed inside the greenhouse with various water and power interfaces to thehabitat. Gary Fisher of the Mars Society has designed the greenhouses and has supervised theirconstruction [5]. The living machines have been designed and constructed by the coauthors ofthis paper. A first generation system was constructed on the University of Maryland at CollegePark (UMCP) campus as a prototype design. This system was tested at the MDRS in Utah and,based on experience from the test, a second generation design has recently been constructedthere. The purpose of this paper is to describe the first generation system on the UMCP campus.This system is being used both to test design details for implementation at the MDRS and foreducational applications by university students.

THE UNIVERSITY OF MARYLAND MARS GREENHOUSE SYSTEM

The overall concept of the Greenhab greenhouse is a cylindrical structure with a frameworkmade of standard 1" PVC pipe reinforced with steel electrical conduit. To manage cost and toallow reproduction by other interested parties and hobbyists, the greenhouse is constructed withcommercial off-the-shelf products normally available at a local hardware store. The cylindricalshape simulates a possible inflatable greenhouse structure that would be attached to a habitat uniton Mars. To implement the Greenhab greenhouse modularly in a rugged terrestrial setting,however, a segmented rigid-structured greenhouse concept was pursued for modularimplementation. Each segment is a cylinder on its side 8 ft. (2.5 m) long and 13 ft. (4 m) indiameter. Segments may be built and joined together axially as needed to simulate inflatablecylindrical greenhouse concepts (Figure 1). The outer covering of the greenhouse is composedof double-layer corrugated polyethylene sheet, which provides a low-cost translucent exterior.The end caps on the greenhouse are custom-sized translucent tarps that can be removed asnecessary for maintenance work. For the Maryland segment, the entire structure is built on alarge wooden pallet located in the enclosed work area of the Biological Resources EngineeringDepartment on the UMCP campus (Figure 2).

The living machine inside the greenhouse segment consists of three translucent polyethylenetanks connected in series (Figures 3 and 4). The tanks are elevated in such a way that water willflow by gravity from Tank 1 to Tank 3. A sump pump in Tank 3 connected to a flexible hoseand sprayer manifold drives continuous recirculation from Tank 3 to Tank 1. Tank 1 is a 10-gallon (40 L) rectangular tank filled with plastic 1” diameter plastic bioballs to create a tricklingfilter unit process, providing an aerobic environment for communities of attached-growthmicroorganisms. Tanks 2 and 3 are aerobic 30-gallon (120 L) cylindrical tanks. Tank 2 containsfloating-leaved and submerged aquatic plants, dominated by water hyacinths, and Tank 3contains submerged rocks for extra habitat space and a floating rack for terrestrial, potted plants.

A fourth tank, located on a rack below Tank 1, could serve as an anaerobic tank, but it is notplumbed into the system at present. During operation, wastewater would flow into the livingmachine either at the anaerobic tank (i.e., the presently unconnected Tank 4) or at the tricklingfilter. Continuous recirculation of the water from the last tank to the first increases the effectivehydraulic retention time in the system, thus improving the overall treatment process. The UMCPliving machine is currently a closed water loop (i.e. no system outflow, except for evaporation).In field implementation, however, outflow would occur from Tank 3, either as overflow to anunderground drain field, or, following additional filtration and sterilization, to a recycled usesuch as for irrigation of food plants or for toilet flushing.

APPLICATIONS

The primary purpose of the Mars Society greenhouse at UMCP has been to test design featuresfor applications at the simulated habitat field sites. Preliminary work on greenhouse sensors hasbeen conducted [6, 7] and heat and power budgets are currently being studied. Anotheremphasis has been on wastewater treatment performance. Figure 5 shows the results of oneshort-term experiment in the living machine. In this case a pulse addition of partially-digesteddairy wastewater was used to simulate input of human sewage. 1.5 L of wastewater at 13,800mg/l chemical oxygen demand (COD) was added to the system, approximating the organic wasteload of two crewmen per day if averaged over the total volume of the system. COD is a measureof the concentration of organic and other oxidizable compounds in the water, similar tobiological oxygen demand (BOD). After the sewage was added to the system, the system wasallowed to continue recirculating undisturbed for two days. One water sample was collected fromeach tank immediately before sewage addition, one hour after sewage addition, and two daysafter sewage addition. These samples were analyzed with a Hach 2000 spectrophotometer forconcentrations of COD, ammonium, and nitrate. The results of these measurements show thatboth COD (Figure 5a) and ammonium (NH4

+) (Figure 5b) declined during the experiment whilenitrate (NO3

-) (Figure 5c) increased. The opposite pattern of ammonia versus nitrateconcentrations represents nitrification, the microbial metabolic conversion of ammonia to nitrate.As a preliminary characterization of the treatment potential of the living machine, removal rateconstants have been calculated for each of the chemical species assuming a first-orderexponential relationship. All of the patterns shown in Figure 5 demonstrate the oxidation of thewastewater by the ecosystems of the living machine, a dominant process in wastewatertreatment.

In addition to effectively treating wastewater with ecological processes, the UMCP livingmachine has proven to be amazingly robust and resilient to perturbations and intervals with littleor no maintenance. The use of large-diameter plumbing connections prevents the likelihood ofsystem clogging. The mechanical requirements are few: only one low-power recirculation pumpis necessary to keep water flowing through the system. The biological components incorporatedinto the system organize at the ecosystem level: the high level of biological diversity introducedat the start of the system provides countless metabolic pathways for nutrient and organic removaland affords system resiliency from extreme environmental events or disease. In addition to itsreliability, the living machine has been easy to build and maintain. The mechanical componentsof the system were assembled in a day using second hand and available parts, and maintenanceand repair operations have proven to be relatively easy. These characteristics make the living

machine concept a desirable candidate wastewater management technology for operations inremote locations.

Because it is located on a university campus, the UMCP Greenhab greenhouse is also being usedfor educational purposes. For example, research was conducted in the greenhouse by graduatestudents in the ecological engineering course (ENBE 688D) during spring semester 2002. Asone of their course projects, the students designed a water harvesting system that collectedcondensation moisture inside the greenhouse. A small wetland ecosystem was added to thegreenhouse in this experiment to compare plant evapotranspiration versus open waterevaporation as sources of water vapor. Relationships were found with temperature and relativehumidity that can form the basis for future research on water harvesting in greenhouses at thesimulated Mars habitat field sites [8]. In addition to being used as the subject of course researchprojects, the Greenhab greenhouse has been used for tours in undergraduate courses and forrecruitment of incoming freshmen during campus orientation days. All of these applicationsprovide outreach information on the Mars Society to students, thereby advancing the society’seducation mission. Future plans include the offering of an undergraduate course on Biospherics,which will utilize the greenhouse for various engineering design studies, and use of the system asa starting point for an entry by undergraduates to NASA’s Mars greenhouse design competition.

LITERATURE CITED

[1] Blersch, D. M., E. Biermann and P. Kangas. 2000. Preliminary design considerations onbiological treatment alternatives for a simulated Mars base wastewater treatment system. SAETechnical Paper Series 2000-01-2467, Engineering Society for Advancing Mobility, Warrendale,PA.

[2] Blersch, D., E. Biermann, D. Calahan, J. Ives-Halperin, M. Jacobson and P. Kangas. 2001. Aproposed design for wastewater treatment and recycling at the Flashline Mars Arctic ResearchStation utilizing living machine technology. Presented at the 3rd Annual Mars SocietyConference, Toronto, Ontario. Published in: Zubrin, R. and F. Crossman (eds.). 2002. On toMars: Colonizing a New World. Apogee Books, Burlington, Ontario, Canada.

[3] Todd, J. 1991. Ecological engineering, living machines and the visionary landscape. Pp. 335-343. In: Ecological Engineering for Wastewater Treatment, C. Etnier and B. Guterstam (eds.).BokSkogen, Stensurd Folk College, Trosh, Sweden.

[4] Todd, J. and B. Josephson. 1996. The design of living technologies for waste treatment.Ecological Engineering 6:109-136.

[5] Fisher, G. 2002. Project Greenhab: The Origin, Efforts, and Future. Presentation at the 5th

Annual Mars Society Convention, August 8-11, 2002. University of Colorado, Boulder, CO.

[6] Calahan, D. 2002. Greenhab Sensor Net. Presentation at the 5th Annual Mars SocietyConvention, August 8-11, 2002. University of Colorado, Boulder, CO.

[7] Frederick, G. 2002. Data Acquisition Concepts for ET Agriculture. Presentation at the 5th

Annual Mars Society Convention, August 8-11, 2002. University of Colorado, Boulder, CO.

[8] Ballam, D., E. Hanssen, C. Nagoda, K. Phyillaier, M. Pittek, G. Seibel and E. Turner. 2002.An ecological engineered technique for water limited environments. Unpublished course reportin ENBE 688D - Introduction to Ecological Engineering, Biological Resources EngineeringDepartment, University of Maryland, College Park, MD.

FIGURES

Figure 1: Rigid cylindrical segment concept to create a terrestrial greenhouse that mimics the shape and sizeof an inflatable Mars greenhouse.

Figure 2: The Greenhab greenhouse segment at the University of Maryland.

Aerobic/anoxic tanks (30 gal/120L ea.)

Waste flow added

periodically

ProposedAnaerobic tank

Trickling filter (10 gal/40L)w/ bioballs

Continuous low-flow (2.5 gpm/10 lpm) recycle

Sump pump

30

15

24

48

30

85

Floating Rack w/terrestrial vascular plants

Floating aquatic submerged &

emergent plants

Rocks from streambed(suspended in basket)

NOTES:1. All tanks: translucent polyethylene.2. All racks: steel drum holders.3. All dimensions in inches.

Figure 3: Schematic flow diagram of the UMCP Greenhab living machine.

Figure 4: The living machine tanks in the UMCP Greenhab greenhouse.

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

0 1 2

Day

[CO

D]

(mg

/L)

Exponential Decay:

Ct = C0 ekt

kavg = -0.327 day-1

Sewage added:

1.5L @ 13,800 mg/L COD(appx. 2 man day-1)

Figure 5a. UMCP living machine COD concentration vs. time.

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0 1 2

Day

[NH 4

] (m

g/L

)

Sewage added:

1.5L @ 1970 mg/L NH4+

Exponential Decay:

Ct = C0 ekt

kavg = -0.244 day-1

Figure 5b. UMCP living machine ammonia concentration vs. time.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

0 1 2

Day

[NO

3] (m

g/L

)

Sewage added:

1.5L @ 50 mg/L NO3-

Exponential Decay:

Ct = C0 ekt

kavg = 0.395 day-1

Figure 5c. UMCP living machine nitrate concentration vs. time.