Sewage Treatment Simulation in an Eco-Machine Prototype. P. Ganeshan, S. Greene, M. Walsh, D. Blersch, P. Kangas Dept. Biological Resources Engineering, University of Maryland, College Park, Maryland. ABSTRACT
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P. Ganeshan, S. Greene, M. Walsh, D. Blersch, P. Kangas
Dept. Biological Resources Engineering, University of Maryland, College Park, Maryland
Wastewater treatment performance of an ecomachine was tested during Fall 2003. The ecomachine was housed in the Mars Society’s prototype greenhouse located on the University of Maryland campus. The purpose of the system is to serve as a test bed of life support system technology development for the society’s simulated Mars habitat in Utah. The ecomachine is a sequential treatment system composed of a recirculating trickling filter and a series of three aquatic hyacinth tanks. Total volume of the system is 210 gal and the retention time was scaled to be 21 days. The system was loaded with a simulated sewage made from a slurry of commercial dog food mixed in water. Measurements were made of temperature, dissolved oxygen, chemical oxygen demand, nitrogen compounds and phosphate. The ecomachine was effective at reducing chemical oxygen demand from more than 3500 mg/l in the simulated sewage to less than 500 mg/l in the water hyacinth tanks. In terms of nutrients, phosphate was reduced and nitrification occurred along the length of the ecomachine. These data will be utilized to improve performance of future ecomachine designs.
MATERIALS & METHODS
The Mars Greenhab living machine consists of three basic parts and systems (wastewater, trickling filter and vegetation tanks) that are combined to make a complete unit as shown in Figure 1. The purpose of the Greenhab living machine is to improve water quality.
RESULTS AND DISCUSSION: COD
Figure 2: Results of simple dilution model, simulated with STELLA, showing the expected COD concentration over time in the living machine assuming absolutely no COD removal by the living machine.
Figure 3:COD levels in input sewage, trickling filter and vegetation tanks over time.
Figure 7: Total inorganic nitrogen concentration in living machine components.
The Greenhab Project was started in 2001 by the Mars Society to explore life support technologies suitable for proposed long-term, manned space missions. The Mars Society is an organization of people interested in the exploration and settlement of the planet Mars. Human space missions require large amounts of consumables (food, water and air). A closed ecological life support system maximizes use of power from biological organisms and the sun to accomplish the recycling of human gaseous, liquid and solid waste to useful products. These concepts are based upon the ecological relationships that exist between organisms, recognizing that one organism’s waste is another organism’s food source.
A greenhouse was installed at the University of Maryland to house a living machine – a biologically-based technology suitable for multiple life support functions. The greenhouse was constructed from steel-reinforced PVC pipe (frame) and translucent polythylene sheeting (exterior) as a cylindrical module that can be combined with additional segments as required. The living machine itself is a series of bioreactor tanks, ideally composed of multiple high-diversity ecosystems, which enable the conversion and uptake of nutrients and other pollutants. Living machines have been shown to adequately and efficiently treat wastewater to acceptable levels (Todd and Josephson, 1996).
In this study, a living machine prototype was exposed to simulated sewage over a period of 5 weeks, during which time nutrient and COD dynamics were monitored in the various machine components. In addition, a simple dilution model was developed to provide a basis of comparison for the empirical data.
Figure 4: Phosphate concentrations in living machine input sewage, trickling filter and vegetation tanks.
Stumm, W. and J.J. Morgan. 1970. Aquatic chemistry: an introduction emphasizing chemical equilibria in natural waters. Wiley Interscience, New York.
Sundby, B., C. Gobeil, N. Silverberg, and A. Mucci. 1992. The phosphorus cycle in coastal marine sediments. Limnology and Oceanography. 376(6):1129-1145.
Todd, J. and B. Josephson. 1996. The design of living technologies for waste treatment. Ecological Engineering. 6: 109-136.
Figure 5: Example of spatial patterns in dissolved phosphate concentration in living machine components.
Figure 6: Example of spatial patterns in dissolved oxygen concentration in living machine components.
• The drop in phosphate concentration from sewage to trickling filter (Figure 5)can most likely be explained by incorporation of phosphate into iron oxyhydroxide compounds due to oxidation of iron as the sewage moved to the more aerobic trickling filter (Sundby et al. 1992).
• The decrease in dissolved oxygen (Figure 6) from trickling filter to vegetation tanks is probably too small to explain the coincident increase in dissolved phosphorus (P).
• The increase in P concentration from trickling filter to vegetation tanks could be explained by changes in pH, as a small increase in pH can create large increases in dissolved P due to desorption from particles (Stumm and Morgan 1970). Future monitoring efforts should include pH
• To effectively remove P from wastewater, it must be ensured that P remains bound in sediments, which requires relatively constant redox conditions and pH.
A student collects data from vegetation tanks inside the Greenhab greenhouse.
Figure 8: Percent composition of Total Inorganic Nitrogen in living machine components.
Vegetation tanks and trickling filter inside the Greenhab greenhouse.
Greenhab greenhouse segment
at the University of Maryland.