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| F-MARS Wastewater Treatment System |
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Conceptual Design version 1.0 - May 2, 2000 |
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Introduction |
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The Maryland subgroup of the Mars Society's Life Support Technical Task Force (TTF) has been considering various options for the Flashline Arctic Research Station (F-MARS) wastewater treatment system. In keeping with the TTF's mission statement, conceptualization of the project has focused on a biological waste treatment system incorporating some complex ecology to allow possible expansion for other life support functions. Figure 1 presents one preliminary concept. It is a relatively standard design for a wastewater treatment system utilizing different biological unit processes to support various functions in the overall treatment process. The concept presented here represents a living machine-a mechanism that, by design, combines biological and ecological processes with electro-mechanical functions. |
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This is a concept design only. The detailed engineering is yet to come. Among other things, this engineering is dependent on the influent wastewater. Once this determination is made specifications and engineering may commence. Plant choices will follow from the nature of the influent wastewater, engineering design, and quality of effluent water desired. The accompanying design drawing and discussion that follows is meant to elicit comments from the community as to the concepts presented. |
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Some of the emails previous to this have expressed interest in Living Technologies and John Todd's work. We are familiar with Living Technologies, John Todd's work, and Living Machines in general. The design presented is based upon a working system designed by one of us (JI-H and see below). Emails have also expressed concern over plant materials. Although this is very important to the final design and function of the system, we are only presenting the flow design and general system components at this time. Once these have been discussed by the group and with a detailed description of the influent waste-stream along with the effluent quality needed, we can move to the next step. |
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The effort of the design team thus far is grounded in a review of the extensive literature regarding wastewater treatment and recycling options for closed systems (Blersch, et al., in press). This literature review is an on-going effort for which the team continues to solicit contributions. For the attached design, a related bench-scale system has been tested (Biermann et al., 1999), and other graduate-level research in ecologically-engineered wastewater treatment systems at the University of Maryland has contributed to the conceptualization. |
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Of particular importance to this effort are working systems that may serve as models for the design of the F-MARS wastewater treatment system. The attached diagram is a second generation conceptual layout of a commercial system currently in use-the Second Nature™ System, designed and manufactured by NatureWorks™, Inc., with initial design work from the University of Maryland group. This system is a household-sized, greenhouse-enclosed living machine that treats and recirculates wastewater from a rural community center in northern Virginia. The system has been successfully operated for nearly a year, and is currently under study for improved performance. |
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| Figure 1 |
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Description of System |
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All water and toilet waste generated within the F-MARS habitat is to be collected in the anaerobic digester for treatment of the complex organics. Biochemical oxygen demand (BOD) would be significantly reduced by anaerobic bacteria in this stage. Some control and stream separation may be necessary for laboratory and some kitchen waste, or the digester might have multiple chambers, depending upon design constraints. The anaerobic digester will have a flexible bladder for its top and be airtight. Methane generated in this tank might be captured for use within the habitat. In addition to gas generation, most solids would settle out here. Solids production will be low with a crew of only six, and might be minimized even further by maintaining the anaerobic digester at an optimum temperature of 35° C. However, periodic disposal of the solids (i.e. once per year) might be necessary. |
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Water exiting the anaerobic tank will be pumped to the top of the trickling filter via an airlift pump in a screened filter vault. An airlift pump is a simpler way to move fluid than most other pumps, as it requires little power and low maintenance. Airlifted effluent trickles over the filter media and is thereby aerated. The aerobic microorganisms that colonize the media utilize the energy and carbon found in the waste stream, thus reducing BOD and COD. Additionally, the aerobic environment will induce nitrification by the attached bacteria. The trickling filter might be designed as a waterfall for aesthetic purposes and thus contribute to the "livability" of the habitat. The effluent leaving this filter will be relatively clean with a significant amount of the nitrogen and carbon compounds removed. The trickling filter media will be a lightweight recycled plastic. Effluent from the trickling filter will flow via gravity into the next unit process. |
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The constructed wetlands will do the final polishing. Wetlands provide a complex environment for both nitrifying and denitrifying microorganisms. The biota found in the wetlands convert organic nitrogen, nitrates, and ammonia coming from the trickling filter to plant and microbial biomass and nitrogen gas. The effluent from the wetland will be recycled back through the trickling filter two times per volume of flow from the anaerobic digester. In this way another nitrification-denitrification cycle will occur to further reduce the ammonia coming through the wetland to acceptable levels. The wetlands will also act as a filter for any suspended solids that have made it through the trickling filter. Thus the water ending up in clean water storage will have been treated to advanced standards and be acceptable for recycling for reuse. Possible innovations in the design of these wetlands will include considerations of poikilohydric design, i.e., design of a wetland that is functional under various moisture regimes. The wetlands could also serve double duty in agricultural production as well. |
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If the reuse is for potable applications, then it will first pass through an ozonator for disinfection. These applications might include showers, edible produce hydroponics, laundry, and toilet flushes. Toilet flush water might be sterilized for aesthetic reasons. In fact, the water passing through the ozonator should be suitable for drinking, although some additional sterilization may be required. Water to be used for non-potable applications such as irrigation of ornamental plants (a good source of fresh air) would not need to run through a sterilization cycle. |
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All these sources would then be returned to the Anaerobic Digester and the cycle begins again. |
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Conclusion |
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This is a minimal design concept for a wastewater treatment system suitable for the F-MARS. Certainly other unit processes might be substituted and added to increase the overall functionality and to support other life support dimensions, such as additional aerobic tanks for hydroponic or aquacultural production. The concept presented here represents a platform upon which development of a multi-dimensional closed life support system might be based. The TTF looks forward to input and contributions from those involved in other successful designs, such as the Pike's Peak recirculating system (Parker), the Biostar-A system (Kok 1998), and the continuing NASA efforts in bioregenerative life support (Johnson 1990). The effort pursued here is considered a recent contribution to the large field of bioregenerative life support technology that has been growing since the beginning of the manned space program. |
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References |
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Blersch, D.M., Biermann, E., Kangas, P. In Press. Preliminary design considerations for the M.A.R.S. wastewater treatment system: Phyico-chemical or living machine? Proceedings of the Second International Convention of the Mars Society, August 12-15, 1999 University of Colorado, Boulder. |
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Biermann, E., Streb, C., Jessup, B., May, P., Schaafsma, J., and Kangas, P. 1999. The development of an ecological engineering design seminar. Annals of Earth v.17 n.1. |
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Johnson, A. 1990. The BioHome: A spinoff of space technology. In Biological Life Support Systems, M. Nelson, G. Soffen eds. Synergetic Press. |
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Parker, L. A water reuse system for Pike's Peak, Colorado. Master's Thesis, University of Colorado. |
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Kok, T. 1999. Biostar-A: A first-year report-Living with a home scale biological life support system. Proceedings: 1998 Third International Conference on Life Support and Biosphere Science, Orlando, Florida. |
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