Transcript Document

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
4500
4,000
4000
Input Conc
Trickling Filter
Aquatic Tanks
2,500
2,000
1,500
Vegetation tanks and trickling filter
inside the Greenhab greenhouse.
Greenhab greenhouse segment
at the University of Maryland.
2000
1500
Data Collection
• Five sets of water samples were collected over a five week period
in each component of the living machine:
- Dog food slurry container
- Lower tank of trickling filter
- Third vegetation tank.
• Measurements of DO (mg/L), DO (% saturation) and Temp. (0C)
were taken directly from the three locations.
• Measurements of NO3- (mg/L), NO2- (mg /L), NH4+ (mg/L) and
PO43- (mg/L) were taken from samples and analyzed using standard
methods.
• A HACH DR-2000 spectrophotometer was used to measure
chemical oxygen demand (mg/L COD) from collected samples.
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Time (days)
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Time (days)
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Phosphates
Figure 3:COD levels in input sewage, trickling filter and
vegetation tanks over time.
Contribution to "sewage" TIN by various N species
Dogfood Slurry
Trickling Filter
Vegetation Tanks
250
Percent of TIN
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50
0
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NH4
NO2
NO3
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10%
0%
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Sample Date
Date
Contribution to trickling filter TIN by various N species
Figure 4: Phosphate concentrations in living machine input
sewage, trickling filter and vegetation tanks.
• Phosphate exhibited a consistent spatial pattern.
• Highest concentrations observed in “sewage”
• Lowest concentrations observed in trickling filter
• Intermediate concentrations observed in vegetation tanks
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10
Dogfood
Slurry
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150
Vegetation
Tanks
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0
Trickling
Filter
Figure 5: Example of spatial patterns in
dissolved phosphate concentration in
living machine components.
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•The Mars Society, especially Gary Fisher of the
Philadelphia Chapter.
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Samp le D at e
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Dogfood
Slurry
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Component
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.
• The living machine significantly decreased the COD of
sewage inputs, as compared to zero-treatment model
outputs.
• The living machine has the potential to effectively remove
phosphate, but optimum pH and redox conditions must be
Maintained.
• There was strong evidence that nitrification occurred, and
perhaps evidence of nitrogen removal.
Contribution to vegetation tank TIN by various N species
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• There appeared to be a decline in TIN over time
throughout the living machine.
• This may be due to decreased remineralization of organic
nitrogen in “sewage” as microbial processes slowed due to
decreasing temperatures
• An analysis of organic nitrogen in the living machine would
provide more insight into nitrogen dynamics and permit an
analysis of total nitrogen removal by the living machine.
• Measurements of denitrification would also add to the
analysis.
• The Nutrient Analytical Services Lab (NASL) at the
Chesapeake Biological Laboratory, Solomons, Maryland.
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ACKNOWLEDGEMENTS
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Vegetation
Tanks
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NH4
NO2
NO3
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30%
20%
10%
0%
Trickling
Filter
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CONCLUSIONS
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Figure 7: Total inorganic nitrogen concentration in living machine
components.
Nitrogen
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Date
• The STELLA simulation graph (“no treatment” scenario, Figure 2) shows how the 3800 mg/L input COD increases
over time in the vegetation tanks and trickling filter.
• Actual data (Figure 3) shows substantial COD removal with time in both the trickling filter and vegetation tanks,
especially compared to the “no-treatment” scenario of Figure 2.
• COD levels begin to rise as the system is overloaded with sewage (Figure 3).
Component
A student collects data from vegetation
tanks inside the Greenhab greenhouse.
Input Sewage
Percent of TIN
Vegetation tanks
• Receives 19 L of treated wastewater from trickling filter 2x a day.
• Purpose is to provide additional treatment of wastewater.
• Three individual tanks with water hyacinths (Eichhornia crassipes)
with capacities of ~121 L, 121 L and 378 L respectively.
• The storage/overflow tank has a capacity of ~100L, however
volume is not constant due to evaporation.
• Water circulates continuously through all tanks to provide thorough
mixing within the system.
Trickling Filter
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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.
Trickling Filter
• Composed of two stacked 121 L containers
• Upper container filled with 2” diam. bio-barrrels to facilitate
microbial activity.
• Lower container collects wastewater from upper filter and
recirculates water back to upper container for continuous treatment.
• Residence time is approximately 12 hours, after which ~19 L of
treated wastewater are released to vegetation tanks. Each new
addition of wastewater to the lower reservoir of the trickling filter
forces an equal amount of the treated wastewater to overflow into
the vegetation tanks.
Vegetative Tanks
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Dogfood Slurry
Trickling Filter
Vegetation Tanks
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35
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Waste water
• Dry dog food with an analysis of 21.0% crude protein, 10.0% crude
fat, 4.5% crude fiber, was used as a base to create wastewater.
• Approximately 27.5g dry dog food/L mixture was allowed to
decompose into a slurry in water in 121 L and 208 L covered
containers.
• Approximately 19 L were pumped into the trickling filter twice a day
for five weeks.
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3500
3,000
COD mg/l
COD (mg/L)
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[TN] (mg/L)
4,500
Percent of TIN
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.
Nitrogen (cont.)
Dissolved Oxygen (mg/L)
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 steelreinforced 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).
RESULTS AND DISCUSSION:
COD
[PO43-] (mg/L)
INTRODUCTION
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.
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.
Phosphate (mg/L)
ABSTRACT
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.
NH4
NO2
NO3
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0%
REFERENCES
Stumm, W. and J.J. Morgan. 1970. Aquatic chemistry: an
introduction emphasizing chemical equilibria in natural
waters. Wiley Interscience, New York.
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Sample Date
Figure 8: Percent composition of Total Inorganic Nitrogen
in living machine components.
• Nitrate became an increasingly important
component of TIN in the trickling filter and
vegetation tanks.
• This may be evidence of nitrification
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.