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Resources, Conservation and Recycling 62 (2012) 64– 70

Contents lists available at SciVerse ScienceDirect

Resources, Conservation and Recycling

journa l h o me pag e: www.elsev ier .com/ locate / resconrec

nfluence of operating conditions on direct nanofiltration of greywaters:pplication to laundry water recycling aboard ships

ulie Guilbauda, Anthony Masséa,∗, Yves Andrèsb, Franc ois Combec, Pascal Jaouena

LUNAM Université, Université de Nantes, CNRS, GEPEA UMR 6144, 37 Bd de l’Université, BP 406, 44602 Saint-Nazaire, FranceLUNAM Université, EMN, CNRS, GEPEA UMR 6144, 4 rue Alfred Kastler La Chanterie, BP 20722, 44307 Nantes, Cedex 3, FranceSTX Europe, STX France Cruise SA, Avenue Antoine Bourdelle, BP 90180, 44613 Saint-Nazaire, France

r t i c l e i n f o

rticle history:eceived 29 August 2011eceived in revised form 2 February 2012ccepted 2 February 2012

eywords:reywaterecycling

a b s t r a c t

The present study completes a previous work dedicated to the feasibility to implement, on-board ship,a direct nanofiltration process in order to treat laundry greywaters and recycle 80% to the inlets of thewashing machines (Guilbaud et al., 2010). At present, the study investigates the influence of nanofiltrationoperating conditions on Chemical Oxygen Demand (COD) rejection rates and permeates fluxes. Thus, thepH and temperature of greywater as well as transmembrane pressure have been fixed to 7 or 9, 25 or 40 ◦Cand 35 or 40 bar, respectively. AFC80 membranes show different COD rejection rates whereas permeatefluxes are quasi similar when the same greywater (pH 7) is nanofiltered at 35 bar and 25 ◦C. Amongst all

ater reuseruise shipanofiltration

the tested operating conditions, the nanofiltration of greywater (pH 7) on AFC80 membrane, at 35 barand 25 ◦C, allows to obtain the highest COD rejection rate (around 93% at VRF5). The best permeate flux(85.5 L/h/m2 at VRF5) has been obtained at 40 bar and 40 ◦C. An increase of temperature or pressure above25 ◦C and 35 bar respectively leads to a drop of COD rejection rates. The pH should be maintained at avalue of 7, the initial pH of raw greywater, in order to allow a good COD rejection rate. An economicevaluation of greywater nanofiltration has been investigated.

. Introduction

Aboard ships, greywaters generally refer to wastewaters com-ng from sinks, baths, laundry and galleys. These effluents contain a

ide variety of pollutants such as bacteria, suspended solids, met-ls, detergents, oil and grease, food particles, hairs, lint, medicalnd dental wastes. Greywaters are one of the largest liquid flowsn-board cruise ships with a wide range of pollutant forms (soluble,olid, biodegradable, non-biodegradable) and concentrations.

A cruise ship of 3000 passengers can daily generate 340–960 m3

f greywater (The Ocean Conservancy, 2002). A Choi’s article, fromew York Times journal (March 25th 2007), points out an explosionf cruise ship market during the last years (12 millions of cruise lineassengers in 2006 compared to 500,000 in 1970), which inducesn increase of produced greywaters. An increase of the number ofruise ship travels is also expected in the coming years (Johnson,002; Lois et al., 2004).

Discharge of waste stream generated by cruise ships is governed

y international regulations as well as national laws. From an inter-ational point of view, the reference document for the preventionf marine pollution is the MARPOL (MARine POLlution) convention

∗ Corresponding author. Tel.: +33 0 2 40 17 26 15; fax: +33 0 2 40 17 26 18.E-mail address: anthony.masse@univ-nantes.fr (A. Massé).

921-3449/$ – see front matter © 2012 Elsevier B.V. All rights reserved.oi:10.1016/j.resconrec.2012.02.001

© 2012 Elsevier B.V. All rights reserved.

which is implemented by the International Maritime Organization(IMO).

As the present trend is to reinforce existing discharge stan-dards, companies have developed several types of strategies andimplemented a waste management: (i) Minimization of generatedwaste quantity (use of low-flow devices, vacuum collection andwaste concentration systems for example) and reduction of theharmfulness for the environment (use of “green detergents” forexample). (ii) Development of systems able to treat wastewaterspreferentially on-board. Thus, the strategies consist in prevent-ing or controlling pollution. Compared to land-based systems, forgreywater treatment, other requirements add to on board systemssuch as lightness, footprint, maintainability, shock and vibrationtolerance, noise minimization and electromagnetic compatibility.

Some Advanced Wastewater Treatment Systems (AWTSs) havebeen developed by operators in order to meet discharge stan-dards and respect regulations. Treatments include chemical andmechanical treatments, activated oxidation, reverse osmosis filtra-tion, bio-reactor/filtration.

Membranes are the most implemented AWTS on-board com-mercial passenger vessels (EPA, 2006a–c). For 2007, according to

Alaska Department of Environmental Conservation, amongst 18large commercial passenger vessels (250 or more passengers) thatdischarged greywaters in Alaska, all were equipped with mem-branes.

servat

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ttblmb

uctfMMf2qAmfhbufmlaaaombbfie

a

Greywater was generated by washing 5 kg (5 T-shirts, 8 handtowels, 4 dish towels, 1 tablecloth, 10 napkins) of dry and dirty linenat 60 ◦C for 3 h. The linen is always dirtied by the same 10 persons,

J. Guilbaud et al. / Resources, Con

Some authors studied the use of porous membranes for greywa-er treatment (Ahmad and El-Dessouky, 2008; Raney et al., 2002).ack et al. (1999) implemented a process for greywater recyclingoming from dishwashers, showers and clothes washers. Ultra-ltration membranes (Molecular Weight Cut Off ranged from 5o 500 kDa) generated a permeate which fed a storage tank oras used for subsequent rinse washing cycle. The authors men-

ion a 50% reduction of used water quantity and 30% of detergentequirement compared to conventional residential and commercialashers.

Brown (2001) registered a patent concerning an integrated dis-harge system for oily and non-oily liquid waste generated aboardhips. The system combined ultrafiltration membranes and thermalncineration;

Nemser and Cragg (2001) implemented a dioxole-coated mem-rane module with a low surface energy which would allow foulingeduction. The authors mention the usefulness of implementat-ng micro and ultrafiltration membranes for greywater treatmentn-board ship.

Chesner and Melrose (2001) patented a mobile floating waterreatment aboard vessels applied to ballast waters, greywater,lackwater and dredge waters. The in situ multistage treatmentf waters includes a pre-treatment consisting of collection, flowqualization and solid removal followed by a second stage whichncludes an ultrafiltration or microfiltration membrane system. Theystem was preferably equipped with either polymeric low pres-ure or vacuum-driven hollow fibre membrane. Some backpulses orackwashes were periodically applied onboard to clean the mem-rane.

Markle and Jones (2007) developed a patented wastewaterreatment system for marine and land-based applications. This sys-em allowed treatment of greywater different from or similar tolackwater. After passing through screening and house polyethy-

ene filter sleeves, greywater alone passed through ultrafiltrationembrane and advanced oxidation zone. Treated greywaters could

e reused as technical waters.Nevertheless, the quality of water produced by direct micro or

ltrafiltration membranes of greywaters does not seem to be suffi-ient to consider greywater recycling. Thus, several works mentionhe addition of a biological treatment to the porous membranesor such applications (Kim et al., 2009; Paris and Schlapp, 2010;

erz et al., 2007; Jefferson et al., 2000; Buchheister et al., 2006).embrane bioreactors (MBR) are largely studied and widespread

or black water treatment (Spérandio et al., 2005; Massé et al.,006) but not much for greywater treatment. However, we canuote several MBR implementations on-board ships. The Hollandmerica Veendam vessel has been equipped with an aerobic sub-erged MBR to treat ship greywaters (accommodation, laundry,

ood pulper and galley wastewater) mixed with sewage. The systemas a daily treatment capacity equal to 700 m3. An external mem-rane bioreactor working with a high cell density, up to 30 g/L, andltrafiltration membrane with a molecular weight cut-off rangedrom 50 to 200 kDa has been developed by Heine et al. (2001) for

arine installations. Hussain et al. (2002) depict a submerged hol-ow fibre membrane bioreactor designed to treat on-board blacknd greywaters. An international patent was registered by Prattnd Baker (2002) concerning the treatment of waste water (blacknd grey water) in marine vessels. A submerged MBR was devel-ped by Higgins et al. (2006) for an automatic onboard treatment ofarine sewage or greywater. The permeate was discharged over-

oard. On board Queen Mary II ship, greywaters have been treatedy an external membrane bioreactor equipped with Pleiade® ultra-

ltration modules (Judd, 2006). Island Princess vessel has also beenquipped with MBR for greywater treatment.

From literature review, it appears that black waters are oftendded to greywater in view of biological treatment. Nevertheless,

ion and Recycling 62 (2012) 64– 70 65

after MBR, a final treatment is sometimes required to respect dis-charge standards and recycle greywater.

Unlike to micro or ultrafiltration process, reverse osmosis allowsto provide high water quality for direct water recycling but lowerpermeate flux (Bellona and Drewes, 2007). Reverse osmosis systemoperating at low pressure, lower than 5 bar, has been experimentedon Holland America Oosterdam ship. A production of 650 m3 perday could be ensured by this system. A greywater pre-treatmentis generally used before reverse osmosis feeding in order to avoidinlet fouling of spiral wound module (Sostar-Turk et al., 2005). Thisaspect should be taken into account for the economic balance of anintegrated process.

Thus, on the basis of a literature review and previous works ledin our laboratory (Paugam et al., 2004; Trébouet et al., 1999, 2001;Gaucher et al., 2002a,b), it appears that nanofiltration technologycould be a good compromise between ultrafiltration and reverseosmosis to direct greywater recycling (Ramon et al., 2004). Further-more, tubular membranes could be interesting to avoid a greywaterpre-treatment before module feeding (Arnal et al., 2008; Avlonitiset al., 2008; Fersi and Dhahbi, 2008; Trébouet et al., 1999). From aprevious study (Guilbaud et al., 2010) nanofiltration on the AFC80membrane (ITT industry), at 35 bar and 25 ◦C, could be efficient fororganic matter rejection (reverse osmosis is not necessary) as wellas for recycling 80% of greywater. At volume reduction factor equalto 5, Chemical Oxygen Demand (COD) of generated permeate waslower than 100 mg/L and the permeate flux equal to 49 L/h/m2. Per-meate from greywater nanofiltration could be used for subsequentwashing cycle. On-board ship, nanofiltration operating conditionssuch as greywater pH and temperature or working pressure couldnot be perfectly controlled. So, the present work studies the robust-ness of nanofiltration process faced with changing of operatingconditions. Concerning the present paper, the robustness has beenevaluated according to two criteria:

1. COD rejection rate and concentration in permeate. The limitof COD concentration in permeate has been fixed to 100 mg/L.Compared to potable water which traditionally feeds washingmachines, exceeding this value could lead to an accumulationof organic pollution in recirculation loop; the cleanness of linencould not be ensured.

2. Permeate flux. The permeation flux should be as high as possible.Indeed, high permeate flux will allow to reduce nanofiltrationtime for a given membrane surface area or will reduce the unitfootprint (reduction of membrane surface area).

2. Materials and methods

2.1. Greywater synthesis

In this study, contrary to other authors that have used syn-thetic greywater, it has been chosen to produce real greywaterresulting from clothes washing (Jefferson et al., 2001; Fenner andKomvuschara, 2005; Diaper et al., 2008; Winward et al., 2008;Hourlier et al., 2010a,b). The methodology adopted in the presentstudy allowed to produce real greywater with physico-chemicalcharacteristics close to the ones on-board ships.

then washed with a Haier® washing machine (HW-C1460TVE-Fmodel) operating at 1000 rotations per minute. Washing productswere similar to those classically encountered on-board ships andsystematically the same for each washing machine.

66 J. Guilbaud et al. / Resources, Conservation and Recycling 62 (2012) 64– 70

Permeate

Module

Volumetric pump

Feed tank

Retent ate

2

wpw

V

Vo

p

1l

3

3

3

otA

np

7ttFma

t

1o

0

20

40

60

80

54321

Volumic Reduction Factor

Per

mea

te f

lux (

L/h

/m²)

Fig. 2. Nanofiltration of greywater on different AFC80 membranes (concentration

a practical point of view, it will be possible to recycle more than

Fig. 1. Scheme of nanofiltration pilot plant.

.2. Experimental set-up

A new greywater was generated before each experiment. Grey-aters were concentrated by batch nanofiltration, i.e. withoutermeate recycling into feed tank. Volumic Reduction Factor (VRF)as calculated according to Eq. (1):

RF = V0

Vf(1)

0 is the initial volume in the feed tank and Vf is the final volumef retentate in the feed tank

Tangential nanofiltration is carried out on Microlab 40 pilotlant (Fig. 1) equipped with an AFC80 membrane.

Surface membrane area is equal to 0.0327 m2 (diameter:2.7 mm, length: 820 mm). Circulation velocity inside membrane

umen is equal to 2.5 m/s (Reynolds criterion is equal to 13,190).

. Results

.1. Reproducibility of results and preliminary experiments

.1.1. Reproducibility of resultsIn the present work, the reproducibility of performances

btained on the AFC80 membrane was evaluated. So, three nanofil-ration experiments were carried out at 35 bar and 25 ◦C, with threeFC80 membranes from different sets.

Fig. 2 shows the average permeate flux obtained from the threeanofiltration experiments during the concentration process; theermeate is not recirculated into feed tank of membrane module.

The permeate flux decreases by 28% from VRF1 to VRF2 and by% from VRF2 to VRF5. At the end of concentration step (VRF5)he permeation flux is equal to 47.3 L/h/m2. For each dot of graph,he minimal and maximal values of permeate flux are specified.ew deviations appear between permeate flux values of the 3embranes. Thus, the change of membrane set does not induce

significant change on permeate flux.The reproducibility on Chemical Oxygen Demand (COD) rejec-

ion and produced water quality have been also studied (Fig. 3).The average COD concentration of greywater is equal to

350 mg/L. No high deviation of COD concentration has beenbserved between experiments. The adopted methodology for

mode, 25 ◦C, 35 bar, VRF 1–5; 3 experiments for each cases).

greywater production seems to allow a good repeatability of waterquality.

Nevertheless, the quality of produced permeates changes froman experiment to the other (Fig. 3). The average COD concentra-tion of permeates produced (i) from 3 AFC80 membranes comingfrom 3 different sets, or (ii) from the same AFC80 membrane(nanofiltration trials have been repeated 3 times) is equal to 85 and123 mg/L respectively; 94% and 91% for COD rejection rate respec-tively. Furthermore, deviation of permeate COD concentration isvery high for nanofiltrations with the different AFC80 membranes,contrary to experiments with the same membrane. Thus, AFC80have different COD rejection rate whereas the initial water andgreywater permeabilities are similar. The pore size distributioncould be different from a membrane to another. The results showthe importance of operating with the same set of membranes inorder to compare performances in changing of operating condi-tions.

It is worth to note that suspended solid, carbon organicmatter and micro-organisms are almost completely retained bymembrane. On average 92% of salts are retained (results notshown).

3.1.2. Preliminary experimentsThe aim of the present work is to investigate the feasibility

to recycle a minimum of 80% of greywater. In batch nanofiltra-tion, it would correspond to a Volumic Reduction Factor equalto 5. Nevertheless, it is interesting to evaluate the feasibility tonanofilter at VRF higher than 5; higher quantity of recycled watercould be required periodically with a nanofiltration process initiallydesigned to recycle 80% of greywater. Thus, greywater (pH equalto 7) has been nanofiltered (40 ◦C, 40 bar) on AFC80 membraneup to VRF8 (Fig. 4). These operating conditions (pH, temperature,pressure) allowed to obtain the highest permeate flux (see the sub-sequent sections of the present paper).

At VRF equal to 8, the permeate flux is equal to 81 L/h/m2, whichis close to the permeate flux corresponding to VRF5. The perme-ate flux value is in the range of permeate flux for nanofiltrationunits (Bourseau et al., 2009; Walha et al., 2011). Thus, the hydraulicyields of nanofiltration remain convenient at VRF8; 87.5% of treatedgreywater can be recycled. For these operating conditions, thepolarization concentration does not seem to be important. So, from

80% of greywater without significant drop of permeate flux. Fig. 4shows that from a greywater COD equal to 1029 mg/L, it is possibleto obtain a permeate COD concentration equal to 124 mg/L. Thus,the COD rejection rate is equal to 88%.

J. Guilbaud et al. / Resources, Conservation and Recycling 62 (2012) 64– 70 67

0

400

800

1200

1600

Grey water

Conce

ntr

atio

n (

mg/L

)

0

40

80

120

160

Permeate

(a) (b)

Fig. 3. Greywater (a) and permeate (b) COD concentration from 3 different set (�) or same ( ) AFC80 membrane (for the last case, the experiments have been repeated 3times).

0

20

40

60

80

100

120

1 3 5 7 9

Per

mea

te f

lux

(L

/h/m

²)

0

400

800

1200

CO

D (

mg

/L)

(a) (b)

d per

3

fpw3fbr

it

F)

Volumic Reduction Factor

Fig. 4. Permeate flux (a) and COD concentration (b) for greywater (�) an

.2. Influence of pH

On average, the pH of produced greywater on shipboard rangesrom 7 to 9. In order to evaluate the influence of pH on processerformance (permeate flux and COD rejection rate), greywatersith pH equal to 7 then 9 have been nanofiltered at 25 ◦C and

5 bar up to VRF5 (Fig. 5). The same membrane has been usedor both experiments. Greywater COD concentration was close foroth experiments: 1416 mg/L and 1267 mg/L for pH 7 and pH 9espectively (results not shown).

At the end of concentration step (VRF5), the permeate fluxs equal to 51 L/h/m2 and 34 L/h/m2 for pH 7 and pH 9 respec-ively: an increase of pH induces a drop of hydraulic nanofiltration

0

20

40

60

80

100

1 2 3 4 5

Per

mea

te f

lux

(L

/h/m

²)

Volumi c Reduction Fac tor

(a)

ig. 5. Permeate flux (a) and COD permeate concentration (b) obtained during the nanofi pH 7; 25 ◦C; 35 bar, (�) pH 9; 25 ◦C; 35 bar.

meate ( ) during the nanofiltration at 40 ◦C and 40 bar (pHgreywater = 7).

performances. From VRF2, the difference between permeate fluxesat pH 7 and 9 increases with an increase of VRF.

The permeate COD is equal to 98 mg/L and 115 mg/L for thenanofiltration at pH 7 and pH 9 respectively. Consequently, CODrejection rate is equal to 93% and 91% for the nanofiltration at pH 7and pH 9 respectively.

pH influences the dissociation of the functional groups of amembrane. So, a change of pH can modify the membrane sur-face charge and then the adsorption of compounds as well as cakelayer structure. The value of the contact angle of membranes is

also dependent of pH. So, as previously observed on nanofiltrationmembranes (Jarusutthirak et al., 2007; Kaya et al., 2010) the pH ofsolution to be filtered acts on rejection rates and permeate fluxes.

0

20

40

60

80

100

120

140

160

Co

nce

ntr

atio

n (

mg

/L) (b)

Permeate

ltration at different conditions: (�) pH 7; 40 ◦C; 35 bar, ( ) pH 7; 25 ◦C; 40 bar, (

6 servat

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3

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8 J. Guilbaud et al. / Resources, Con

So, the pH of greywater should be kept at a value equal to 7, inrder to gain in productivity and permeate quality.

.3. Influence of temperature

Greywaters are generated by washing linen at 60 ◦C. This tem-erature exceeds the maximum tolerated temperature of AFC80embrane, which is equal to 40 ◦C. So, the influence of tempera-

ure (25 ◦C and 40 ◦C) on process performances (permeate flux andOD rejection rate) has been evaluated at 35 bar up to VRF5 whenhe pH of greywater is equal to 7 (Fig. 5). The same membrane haseen used for all nanofiltration experiments. The greywater CODas close for both experiments: 1416 mg/L and 1536 mg/L for 25 ◦C

nd 40 ◦C experiments respectively (results not shown).At the end of the concentration step (VRF5), the permeate flux

s equal to 51 L/h/m2 and 74 L/h/m2 for 25 and 40 ◦C respectively. temperature increase from 25 ◦C to 40 ◦C, which corresponds to

viscosity drop equal to 36%, induces a permeate flux increaseanged from 46 to 56% depending on VRF value. It can be con-luded that the viscosity change does not completely explain thehange in permeate flux as described by Darcy law. So, in addition toariations in greywater viscosity, the temperature has probably annfluence on the interactions between membrane and suspensiono be nanofiltered; surface properties of membrane and greywaterompounds are probably modified due to a variation of operatingemperature.

The permeate COD is equal to 98 mg/L and 142 mg/L for theanofiltration at 25 and 40 ◦C respectively. Consequently, CODejection rate is equal to 93% and 91% for the nanofiltration at 25 ◦Cnd 40 ◦C respectively. Concerning the present study, we have fixedhe COD limit concentration to 100 mgCOD/L with the aim to allowermeate recycling. Exceeding this value could induce a deteriora-ion of linen cleanness for the subsequent washings. Consequently,n spite of good hydraulic performances, nanofiltration at 40 ◦C and5 bar does not allow to consider a direct recycling of permeate dueo the mediocre quality of permeate.

.4. Influence of pressure

Some nanofiltration membranes behave like porous mem-ranes, i.e. micro- or ultrafiltration or dense membranes, i.e. reversesmosis. In the latter case, an increase of operating pressure gener-lly induces an increase of rejection rates. Nevertheless, accordingo the manufacturer’s data, the maximal operating pressure forFC80 is equal to 40 bar. Thus, the greywaters generated for theresent study have been nanofiltered with the same AFC80 mem-rane at 35 bar, first experiment, and 40 bar, second experimentFig. 5).

At the end of concentration step at VRF5, the permeate flux isqual to 51 L/h/m2 and 60 L/h/m2 for nanofiltration at 35 bar and0 bar respectively.

The raw greywater COD is close between both experi-ents: 1416 mgCOD/L and 1392 mgCOD/L before 35 bar and 40 bar

xperiments, respectively (results not shown). Nevertheless, theermeate COD is equal to 98 mg/L and 143 mg/L for the nanofil-ration (pH 7, T = 25 ◦C) at 35 bar and 40 bar respectively. Thus, theejection rate is slightly higher for the lowest pressure (93% against0% for 35 bar and 40 bar respectively) showing that AFC80 behaves

ike a porous rather than dense membrane. Consequently, for theargeted application, it is not pertinent to nanofiltrate at a pressurexceeding 35 bar.

.5. Economic analysis

The goal of the present study is to identify the best operatingonditions to be applied during the greywater nanofiltration on

ion and Recycling 62 (2012) 64– 70

AFC80 membrane in order to recycle 80% of greywaters to the inletof the washing machines.

Amongst all the tested operating conditions of pH, temperatureand pressure, the best quality of permeate has been obtained duringthe greywater nanofiltration (VRF5) on the AFC80 membrane at35 bar and 25 ◦C (pH 7); the permeate COD was equal to 98 mg/Lfor a permeate flux equal to 51 L/h/m2. The quality of the permeate,which is close to the quality of a household tap water should allowits recycling at the inlet of washing machines.

However, is it necessary to produce the best quality of per-meate although the permeate flux is the lowest or is it sufficientto feed the inlets washing machines with a lower quality of per-meate (124 mgCOD/L) such as the one coming from the greywaternanofiltration at 40 bar, 40 ◦C but with a higher permeate flux(85.5 L/h/m2)? A higher permeate flux means a lower membranesurface for a given production capacity, which induces a reductionof membrane cost. Future experiments consisting in linen washingwith nanofiltered greywater at 40 bar, 40 ◦C will allow to know ifcleanness of washed clothes is guaranteed on the long term.

An economic analysis of these two options: greywater nanofil-tration at 35 bar, 25 ◦C and 40 bar, 40 ◦C has been led, on anindustrial membrane unit able to daily recycle 80% of 65 m3 grey-water during 200 days a year (daily production classically found oncruise ships with 1600 passengers – personal communication withSTX Europe Company). In order to estimate the water productioncost of the nanofiltration unit, capital and operating costs (mem-brane replacement, chemicals, maintenance, and electricity) havebeen calculated (Fig. 6).

A daily greywater nanofiltration has been assumed during20 h30′ followed by a 2-h unit cleaning. The configuration of theunit was previously described by Guilbaud et al. (2010). On the basisof permeate fluxes obtained during the present study, at laboratoryscale, 50 m2 of membrane are needed for greywater nanofiltrationat 35 bar, 25 ◦C versus 30 m2 at 40 bar and 40 ◦C; almost 20 mod-ules (B1-ITT-PCI) should be required for the first case and 12 for thesecond case. No more than 2 modules in series have been placed ineach branch of nanofiltration in order to be in turbulent flow insidemembrane lumen. Thus, the nanofiltration unit operating at 35 barand 25 ◦C will consist of 10 branches of 2 modules in series and6 branches of 2 modules in series for the nanofiltration at 40 barand 40 ◦C. According to the option, a centrifugal pump generating apressure of 2 bar will feed a high-pressure-volumetric-pump whichmust deliver 10 m3/h of greywater at 38 bar or 6 m3/h at 43 bar atthe inlet of the branches in order to operate at a mean pressure of35 bar or 40 bar respectively. For a flow rate equal to 1 m3/h at themembrane module inlet, a pressure drop inside membrane modulewas assumed equal to 3–4 bars (data from manufacturer).

The configuration unit and the capital cost have been agreedby a French membrane consulting engineering firm. Capital costincludes the tanks, pumps, pipes and valves, instruments and con-trols, membranes and modules (Humeau et al., 2011; Denis et al.,2009). The annual payments (ACC) to be made by the borrowerin order to recover the capital plus interest have been calculatedaccording to the uniform series capital recovery method (Eq. (2)):

ACC = P

[(i)(1 + i)n

(1 + i)n − 1

](2)

P is the principal, i the interest rate equal to 4%, n the time life ofunit taken equal to 20 years (Banat and Jwaied, 2008; Sethi andWiesner, 2000).

The annual electricity consumption has been evaluated assum-

ing an electricity cost equal to 0.1 D kWh−1 (figures from Eurostatreport, 2011). The pump yield has been taken to 80% for thehigh pressure volumetric pump and 70% for the centrifugal pump(Liikanen et al., 2006).

J. Guilbaud et al. / Resources, Conservation and Recycling 62 (2012) 64– 70 69

filtrat

c

me

rfu

A

F2

iabbtp

w2

4atowuNab

Ticgd

tti

Fig. 6. Total costs and distribution for greywater nano

The maintenance cost has been estimated equal to 2% of capitalost on a yearly basis (Atikol and Aybar, 2005).

Whatever the unit, nanofiltration at 35 bar, 25 ◦C or 40 bar, 40 ◦C,anpower has been estimated equal to 2 h per day at an hourly cost

qual to 20 D h−1 (figures from Eurostat report, 2011).A uniform amount of money will be placed in a fund in order to

eplace the membranes after 3 years of use (n). The annual paymentor membrane replacement (AMR) has been calculated by using aniform series sinking fund method (Eq. (3)):

MR = F

[(i)

(1 + i)n − 1

](3)

is the future amount of money and i is the interest rate equal to%.

Two cleanings a day will be operated: an acid and alkaline clean-ng. A chemicals cost was assumed equal to 3 D kg−1. Before, afternd between chemical cleanings, the water rinsing of unit wille operated. The volumes of cleaning and rinsing solutions wille equal to the dead volume of unit plus the volume of storageank. The permeate of greywater nanofiltration will be used for thereparation of rinsing and cleaning solutions.

Thus, the distribution of costs during the nanofiltration of grey-ater is gathered in Fig. 6 for both operating conditions: 35 bar,

5 ◦C and 40 bar, 40 ◦C.The production cost of nanofiltered greywater is the lowest at

0 bar and 40 ◦C and equal to 4.2 D m−3 comparatively to 5.5 D m−3

t 35 bar and 25 ◦C. This total cost seems expensive compared tohe cost of water production by seawater reverse osmosis unitsr evaporator, on ship board, estimated around 2–3 D m−3. So, itould be more interesting from an economical point of view, tose distilled water to feed the inlet washing machine on board.evertheless, the recycled greywater by nanofiltration will induce

drop of greywater volume to be treated with blackwater on shipoard and probably a drop of wastewater treatment cost.

The cost distribution between both options is relatively similar.he chemicals represent the main part of the total cost. Indeed, anmportant volume of chemicals/water must be prepared in order tolean and rinse the nanofiltration unit. For instance, in the case of areywater nanofiltration at 40 bar and 40 ◦C, 18 kg of chemicals isaily needed, as well as 4.5 m3 of water.

The annual capital cost counts for approximately 25 and 27% ofhe total cost assuming an amortization period equal to 20 years, i.e.he estimated lifetime unit. A reduction of amortization period willnduce an increase of this expense item. This point is to be noted

ion operating at 40 bar, 40 ◦C (a) and 35 bar, 25 ◦C (b).

because a lot of shipowners will prefer to pay off the unit beforethe end of its lifetime.

Manpower counts for 14–19% of total specific cost, whereaselectricity is close to 9–10%.

Thus, the choice to operate at 40 bar, 40 ◦C or 35 bar, 25 ◦Cdepends on the criteria of selection: technical or economical.Indeed, a lower quality of recycled water will be obtained at 40 bar,40 ◦C but the water production cost will be lower. At present, thewater which feeds the inlet washing machines on ship board comesfrom seawater reverse osmosis units or evaporators. The qualityof this water is obviously better than permeate of nanofiltrationbut further experiments need to be performed in order to evaluatethe cleanness of linen after several washing cycles with greywaternanofiltered at 40 bar and 40 ◦C. Indeed, the quality of producedwater at 35 bar and 25 ◦C is close to the household tap water andcould allow water recycling. But, the water which comes from grey-water nanofiltration at 40 bar and 40 ◦C could be also sufficient fora linen washing.

4. Conclusion

The present work investigates the search of optimal operatingconditions for the recycling of greywater by nanofiltration. The pro-cess should allow the recycling of 80% of a produced permeate withCOD concentration lower than 100 mg/L.

The study investigates the influence of 3 operating parameters,pH, temperature and pressure on nanofiltration performance. Thesame AFC80 membrane was used in order to allow comparison ofthe results and more specifically, COD rejection rate.

Amongst all the tested operating conditions, nanofiltration onthe AFC80 membrane, at 35 bar and 25 ◦C induces the best qualityof permeate. An increase of temperature or pressure decreases theCOD rejection rate. The results show that more than 80% of recyclingcould be reached. The pH should be maintained at a value of 7 inorder to allow a good COD rejection rate. Greywater nanofiltrationat 40 bar and 40 ◦C induces the highest permeate flux.

Whatever the nanofiltration conditions, 35 bar, 25 ◦C or 40 bar,40 ◦C, the total water production cost will range between 4 and6 D m−3 with the lower price for the second option.

Acknowledgement

This research has been realized within the framework ofCYCLEAUX program (France) approved by the Competitivenesscluster EMC2.

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