This document discusses a proposal for greywater reuse on Duke University's campus. It would involve collecting greywater from residential housing sources like sinks, showers, and washing machines. The greywater would undergo treatment including bar screening, microfiltration, and UV disinfection. The treated greywater would then be used to irrigate golf courses and highway medians on campus in accordance with North Carolina regulations. The system has the potential benefits of conserving water and providing a learning opportunity for students while meeting regulatory requirements for greywater reuse.

1. Greywater Reuse on Duke’s
Campus
Natalya Polishchuk
Liwei Zhang
Changheng Yang
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2. Outline
Introduction
Sources
Treatment
Use Plan
Conclusion
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3. Introduction
What is greywater?
 Urban wastewater that
includes
 Baths, showers,
 Hand basins, washing
machines,
 Dishwashers and
kitchen sinks,
 But excludes streams
from toilets
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http://green.harvard.edu/theresource/new-construction/design-element/water-efficiency/images/greywater-system_000.gif

4. Introduction
UN: 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
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http://ndn3.newsweek.com/media/62/071219_NewDrought_wide-horizontal.jpg

5. Introduction
Duke used 566.4 million gallons in 2007
 Residential 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: 1 1
http://www.duke.edu/web/ESC/campus_initiatives/water/conservation.html

6. Sources
Residential Housing at Duke:
 Sinks
 Showers (hair collectors added)
 Washing machines (lint filters installed)
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7. Sources
Characteristics of the grey water
Particle Total
BOD COD TOC TSS
size coliforms
Mean 20 86 49 29 286 5.26
Standard
deviation 6 23 13 34 142 0.80
Unit: BOD, COD, TOC and TSS (mg L−1), Particle size (μm), Total coliforms ((log10CFU100 mL−1))
(Winward et al. 2008) 1 1

8. North Carolina Regulations
5 mg/L TSS Storage: 5 day
monthly, 10 mg/L detention pond plus
TSS daily irrigation pond for
Max fecal coliform overflow
1/100 mL *Hydraulic loading
Treatment in <1.75”/week
duplicate 100’ vegetative buffer
Back-up power to nearest dwelling
source
No COD or BOD limit in North Carolina
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9. Treatment
Raw grey water
Bar screen
Equalization tank
Physical
Treatment
Disinfection
Reuse 1 1

10. Treatment
Physical treatment methods and performances
TSS Turbidity COD BOD
Reference Processes
In Out In Out In Out In Out
Sand filter+
Ward (2000) Membrane+ - - 18 0 65 18 23 8
Disinfection
Screening+
CMHC Sedimentation+
(2002) 67 21 82 26 - - - -
Multi-media
filter+Ozonation
Gerba et al. Cartridge filter 19 8 21 7 - - - -
(1995)
UF membrane 35 18 - - 280 130 195 86
Sostar-Turk
et al. (2005) NF membrane 28 1 0 30 1 226 15 - -
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11. Treatment
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
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12. Treatment
Bar screen
 Coarse particles,
 Body hairs and
 Large-size items
 Vegetable leaves
 Eggshell pieces, etc)
http://www.chishun.com.tw/image/barscreen.jpg
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13. Treatment
Typical design parameters:
(Tchobanoglous et al, 2002)
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14. Treatment
Microfiltration membrane
 Stainless metal membrane is used.
Basic characteristics are in the following table:
Metal membrane characteristics summary (Kim et al, 2007)
Parameters Values
Nominal pore 0.5μm
radius (ri)
Filter 0.222m
length (L)
Membrane 0.32m2
area (Am)
Membrane 1.04×1010 m–1
resistance (Rm) 1 1

15. Treatment
Impact of fouling on the permeate flux
Following expression is applied to calculate the permeate
flux when fouling is considered (Wiesner and Bottero,
2007):
∆P
J= (1)
µ[ Rm (t ) + Rc × c (t )]
δ
Assume the resistance of the membrane (Rm(t)) does not change with
time, then
Rm(t)=const=1.04×1010 1/m. dp=286×10-6m
△P=operation pressure=100kPa εc=0.4
μ=viscosity of water=10-3kg.m/s 180(1 − ε c ) 2
Rc = = 1.238 × 1010 m −2
Rc=resistance of the cake, d pε c3
2
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16. Treatment
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:
105 Pa
J=
kg
−3 −1 −2 29 × 10−3 kg ×m −3 (2)
10 [1.04 ×10 m + 1.238 × 10 m ×J ×
10 10
−3
×]
t
m ×s 1.01× 10 kg ×m
3
Final expression:
0.00704 × (−2.08 ×106 + 2383.28 × 761690 + t )
J= (3)
t 1 1

17. Treatment
The curve of permeate flux vs. time:
Critical Point:(1688 hours , 4.81×10-3 m3/m2s)
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18. Treatment
Particle removal efficiency of the membrane
Removal Efficiency, %
100
90
80
70
60
50
40
30
20
10
0
d≥ 15μm 13μm 10μm 8μm 5μm 2μm
Particle size
1 (Kim et al, 2007) 1

19. Treatment
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 = 0.855C + 0.035C = 89%
C
Meet North Carolina
∵TSS in influent=29mg/L, regulations (5 mg/L TSS
monthly, 10 mg/L TSS daily)
∴TSS in effluent=3.19 mg/L
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20. Treatment
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
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21. Treatment
The particle removal rate of the filter be calculated as
(Wiesner M. 2009):
Final result:
 3α ηT 
removal rate=1-n/n0= 1 − exp  − 2 ×(1 − ε ) ×d ×L ÷ , where
 c 
α is the affinity of the adsorbed particles to the filter media, εis
the porosity of the media, ηT
is the collector efficiency, 1 1
dc is the diameter of the collector and L is the media depth.

22. Treatment
Collector efficiency (ηT) can be
evaluated with the use of the
expression developed
by Rajagopalan and Tien (1976):
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23. Treatment
Particle removal efficiency of the membrane and
the sand filter:
removal Removal rate Removal rate
particle rate (membrane) (sand filter)
diameter
D=286μm (Dmean) >97% 100%
D=13μm (D10) 95% 99.8%
D=2μm 35% 46.4%
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. 1 1

24. Treatment
Microfiltration cost
Estimated between $400-800 (Keystone Filter Division)
Sand filtration cost
Estimated between $400-600 (Doheny’s water ware
house)
http://www.thomasnet.com/catalognavigator.html?
cov=NA&what=microfiltration+membrane+price&heading=51 1 1
170967&cid=141076&CNID=&cnurl=http%3A%2F http://www.waterwarehouse.com/Pool-Filters.html?gclid=
%2Fkyfltr.thomasnet.com%2FCategory%2Ffine-sediment-

25. Treatment
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.
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26. Disinfection
The advantage of UV
 Cheaper than chlorine according to the EPA.
 Does not create harmful chlorinated hydrocarbons
 Salt concentration is higher in recycled water,
which can damage plants, especially in sprinkler
irrigation.
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27. Disinfection
1 1
Lu, G., C. Li, et al. (2008).

28. Option: RO
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/m 2
(FILMTEC Membranes product information,
2009). Therefore, total price of the RO membrane
is $10,636.
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29. Use Plan
North Carolina grey water reuse regulation:
 Allowed  Not Allowed:
Golf courses Parks, Toilets
Cemeteries Residences, Fountains
Highway medians Construction Sites
http://www.dataflowsys.com/services/images/scada- http://www.roadstothefuture.com/Western_Freeway.jpg
applications/golf-course-irrigation.jpg 1 1

30. Use Plan
Duke uses reclaimed water from North Durham
Water Reclamation Facility to water select plants
 Advantages of grey water:
Available water during droughts, when more reclaimed
water must be sent to the lake
Less energy use
Less trucking water
Learning opportunity for students
Good publicity
Duke University, (April 25, 2008). Sustainability: What is Duke doing to conserve water?. Retrieved April 12, 2009, f
Duke Sustainability Web site: http://www.duke.edu/web/ESC/campus_initiatives/water/conservation.html
1 1

31. Conclusions
Source: on-campus residences
Treatment:
 Bar screen
 microfiltration membrane
 UV disinfection
Uses:
 golf course irrigation
 street median irrigation
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32. Thank You
Questions?
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33. References
Li 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,
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USA

34. 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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35. 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.
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