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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.