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A team proposal (with Liwei Zhang, Changheng Yang) analyzing the potential of reusing water on Duke University campus.
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Greywater Reuse on Duke’s Campus
Natalya Polishchuk
Liwei Zhang
Changheng Yang
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Outline
Introduction
Sources
Treatment
Use Plan
Conclusion
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Introduction
What is greywater?Urban wastewater that
includes Baths, showers, Hand basins, washing
machines, Dishwashers and
kitchen sinks, But excludes streams
from toilets
http://green.harvard.edu/theresource/new-construction/design-element/water-efficiency/images/greywater-system_000.gif
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IntroductionUN: Good grade water should not be used for
purposes that can be served with a lower
grade unless there is a surplus
Water is becoming more scarce
Serious drought in the Southeast in 2007
http://ndn3.newsweek.com/media/62/071219_NewDrought_wide-horizontal.jpg
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Introduction
Duke used 566.4 million gallons in 2007Residential housing (11%) Reused water (estimate: 40 % of residential housing) 68,300 gpd or 47 gpm
Duke University, (April 25, 2008). Sustainability: What is Duke doing to conserve water?. Retrieved April 12, 2009, from Duke Sustainability Web site: http://www.duke.edu/web/ESC/campus_initiatives/water/conservation.html
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Sources
Residential Housing at Duke:SinksShowers (hair collectors added)Washing machines (lint filters installed)
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Sources
Characteristics of the grey water
BOD COD TOC TSS Particlesize
Total coliforms
Mean 20 86 49 29 286 5.26
Standarddeviation 6 23 13 34 142 0.80
(Winward et al. 2008)
Unit: BOD, COD, TOC and TSS (mg L−1), Particle size (μm), Total coliforms ((log10CFU100 mL−1))
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North Carolina Regulations
5 mg/L TSS monthly, 10 mg/L TSS daily
Max fecal coliform 1/100 mL
Treatment in duplicate
Back-up power source
Storage: 5 day detention pond plus irrigation pond for overflow
*Hydraulic loading <1.75”/week
100’ vegetative buffer to nearest dwelling
No COD or BOD limit in North Carolina
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Treatment
Reuse
Bar screen
Physical Treatment
Disinfection
Raw grey water
Equalization tank
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Physical treatment methods and performances
Reference ProcessesTSS Turbidity COD BOD
In Out In Out In Out In Out
Ward (2000)
Sand filter+Membrane+Disinfection
- - 18 0 65 18 23 8
CMHC (2002)
Screening+
Sedimentation+
Multi-media filter+Ozonation
67 21 82 26 - - - -
Gerba et al. (1995)
Cartridge filter 19 8 21 7 - - - -
Sostar-Turk et al.
(2005)
UF membrane 35 18 - - 280 130 195 86
NF membrane 28 0 30 1 226 15 - -
Treatment
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Membrane filtration advantages: Easy to operate Moderate cost Removal rate meets regulations
No biological treatment processes. No COD or BOD limit in North Carolina
The disinfection process is needed To meet fecal coliform limit in North Carolina
Treatment
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Bar screen
Coarse particles,
Body hairs and
Large-size items
Vegetable leaves
Eggshell pieces, etc)
Treatment
http://www.chishun.com.tw/image/barscreen.jpg
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Typical design parameters:
Treatment
(Tchobanoglous et al, 2002)
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Treatment
Microfiltration membrane Stainless metal membrane is used.
Basic characteristics are in the following table:
Parameters Values
Nominal pore
radius (ri)
0.5μm
Filter
length (L)
0.222m
Membrane
area (Am)
0.32m2
Membrane
resistance (Rm)1.04×1010 m–1
Metal membrane characteristics summary (Kim et al, 2007)
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Treatment
Following expression is applied to calculate the permeate flux when fouling is considered (Wiesner and Bottero, 2007):
Assume the resistance of the membrane (Rm(t)) does not change with time, then
Rm(t)=const=1.04×1010 1/m.
△P=operation pressure=100kPa
μ=viscosity of water=10-3kg.m/s
Rc=resistance of the cake,
dp=286×10-6m
εc=0.4
(1)
Impact of fouling on the permeate flux
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Assume δc(t) = J × C × t/ρ,
J is the permeate flux (m3/(m2.s))
C is the mass concentration of particles (29×10-3kg/m3),
ρ is the density of particles (1.01×103 kg/m3).
Put all values of parameters into expression (1), we have:
Final expression:
(3)
Treatment
(2)
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The curve of permeate flux vs. time:
Critical Point:(1688 hours , 4.81×10-3 m3/m2s)
Treatment
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Treatment
(Kim et al, 2007)
0
1020
3040
5060
7080
90100
d≥ 15μm 13μm 10μm 8μm 5μm 2μm
Particle size
Removal Efficiency, %
Particle removal efficiency of the membrane
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Characteristics of the grey water: D mean=286μm, D 10=13μm
Removal amount of particles (C be the concentration of TSS in influent )
(D>13μm) is C×90%×95%=0.855C
(D<13μm) is C×10%×35%=0.035C
(worst case: assume the removal efficiency of particles with Dp=2μm can represent the overall removal efficiency of particles (D<13μm) ).
Total Removal Efficiency
∵TSS in influent=29mg/L,
∴TSS in effluent=3.19 mg/L
Meet North Carolina regulations (5 mg/L TSS
monthly, 10 mg/L TSS daily)
Treatment
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Comparison: Microfiltration membrane vs. Traditional sand filter
Key Design Parameters:
Parameters Value
Flow rate (m3/s) 2.99×10-3
Bulk velocity (m/s) 6.67×10-3
Filter plan area (m2) 0.45
Depth of filter media (m) 0.762
Sand grain diameter (mm) 0.6
Porosity of filter bed 0.4
Treatment
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The particle removal rate of the filter be calculated as (Wiesner M. 2009):
Final result:removal rate=1-n/n0= , where
α is the affinity of the adsorbed particles to the filter media, εis the porosity of the media, ηT is the collector efficiency, dc is the diameter of the collector and L is the media depth.
Treatment
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Collector efficiency (ηT) can be
evaluated with the use of the
expression developed
by Rajagopalan and Tien (1976):
Treatment
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Particle removal efficiency of the membrane and
the sand filter: Removal rate (membrane)
Removal rate (sand filter)
D=286μm (Dmean) >97% 100%
D=13μm (D10) 95% 99.8%
D=2μm 35% 46.4%
removal rateparticle
diameter
The table shows that the particle removal efficiency of the sand filter is a little higher than the microfiltration membrane. Therefore, the sand filter can also work well in the filtration process.
Treatment
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Treatment
Microfiltration cost
Estimated between $400-800 (Keystone Filter Division)
Sand filtration cost
Estimated between $400-600 (Doheny’s water ware
house)
http://www.waterwarehouse.com/Pool-Filters.html?gclid= CN_P0NTjhJoCFRpN5QodHTJUFg
http://www.thomasnet.com/catalognavigator.html?cov=NA&what=microfiltration+membrane+price&heading=51170967&cid=141076&CNID=&cnurl=http%3A%2F%2Fkyfltr.thomasnet.com%2FCategory%2Ffine-sediment-filtration-5-micron-particles
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However, compared with the membrane, a sand filter requires a higher frequency of backflushing.
Typical backflushing frequency of sand filters when treating surface water:
Rapid sand filter (widely used in potable water supply facilities; pressure-driven filtration process)—48-72 hours (Salvato et al, 2003) (1688 hrs- MF at Duke)
Therefore, microfiltration membrane is still a better choice.
Treatment
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Disinfection
The advantage of UVCheaper than chlorine according to the EPA.Does not create harmful chlorinated hydrocarbonsSalt concentration is higher in recycled water,
which can damage plants, especially in sprinkler irrigation.
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Disinfection
Lu, G., C. Li, et al. (2008).
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The membrane has good total ion removal rate (>80%) (Yoon and Lueptow. 2005)
However, the cost will be definitely high, due to a large membrane area (344m2) is needed.
Commercial price of RO membrane: $30.92/m2
(FILMTEC Membranes product information, 2009). Therefore, total price of the RO membrane is $10,636.
Option: RO
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Use Plan
AllowedGolf coursesCemeteriesHighway medians
Not Allowed:Parks, ToiletsResidences, Fountains Construction Sites
http://www.roadstothefuture.com/Western_Freeway.jpghttp://www.dataflowsys.com/services/images/scada-applications/golf-course-irrigation.jpg
North Carolina grey water reuse regulation:
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Use Plan
Duke uses reclaimed water from North Durham Water Reclamation Facility to water select plantsAdvantages of grey water:
Available water during droughts, when more reclaimed
water must be sent to the lakeLess energy use Less trucking waterLearning opportunity for studentsGood publicity
Duke University, (April 25, 2008). Sustainability: What is Duke doing to conserve water?. Retrieved April 12, 2009, from Duke Sustainability Web site: http://www.duke.edu/web/ESC/campus_initiatives/water/conservation.html
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Conclusions
Source: on-campus residences
Treatment:Bar screenmicrofiltration membraneUV disinfection
Uses:golf course irrigationstreet median irrigation
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Thank You
Questions?
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ReferencesLi F., Wichmann K., Otterpohl R., 2009. Review of the technological
approaches for grey water treatment and reuses. Science of the Total Environment, 407: 3439–3449
Ward M., 2000. Treatment of domestic greywater using biological and membrane separation techniques. MPhil thesis, Cranfield University, UK.
CMHC (Canada Mortgage and Housing Corporation), 2002. Final assessment of conservation Co-op’s greywater system. Technocal series 02–100, CHMC, Ottawa, Canada.
Gerba C., Straub T., Rose J., et al, 1995. Water quality study of greywater treatment systems. Water Resour J., 18:78–84.
Sostar-Turk S., Petrinic I., Simonic M., 2005. Laundry wastewater treatment using coagulation and membrane filatration. Resour.Conserv. Recycl., 44 (2):185–96.
Tchobanoglous G., Burton F., Stensel D, et al, 2002. Wastewater Engineering: Treatment and Reuse. McGraw-Hill Professional, USA
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References
Duke University, (April 25, 2008). Sustainability: What is Duke doing to conserve water?. Retrieved April 12, 2009, from Duke Sustainability Web site: http://www.duke.edu/web/ESC/campus_initiatives/water/conservation.html Lu, G., C. Li, et al. (2008). "A novel fiber optical device for ultraviolet disinfection of water." Journal of Photochemistry and Photobiology B: Biology 92(1): 42-46.US EPA, (1992). Manual, Guidelines for Water Reuse. Washington, DC: US Agency for International Development.
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References
Kim R., Lee S., Jeong J., et al, 2007. Reuse of greywater and rainwater using fiber filter media and metal membrane. Desalination, 202: 326–332
Wiesner M., Bottero J., et al, 2007. Environmental Nanotechnology: Applications and Impacts of Nanomaterials. McGraw-Hill Professional, USA
Wiesner M. 2009. Class note of course: physical and chemical processes in Environmental Engineering.
Rajagopalan R. and Tien C., 1976. Trajectory analysis of deep-bed filtration with the sphere-in-a-cell porous media model. AIChE J. 2(3): 523-533
Winward. P.G. , Avery M. L., , Stephenson T, and Bruce Jefferson, 2008. Chlorine disinfection of grey water for reuse: Effect of organics and particles. Water Res. 42: 483–491.