Catalysis Today 240 (2015) 3038

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Catalysis Today

j o ur na l ho me page: www.elsev ier .com/ locate /ca t tod

Disinfe 2 pA study mpof micr

Irene Ga InmPilar FernPlataforma Solar de Almera-CIEMAT, P.O. Box 22, 04200 Tabernas, Almera, Spain

a r t i c l e i n f o

Article history:Received 28 JaReceived in reAccepted 13 MAvailable onlin

Keywords:Fusarium solanEscherichia colTiO2 photocatWW treatmenTemperatureDissolved oxy

a b s t r a c t

The enhancement of current technologies used to treat polluted water is one of the most important

1. Introdu

Recentlywater treatusing procetocatalytic attention askill microor

CorresponE-mail add

http://dx.doi.o0920-5861/ nuary 2014vised form 10 March 2014arch 2014e 13 April 2014

iialysist

gen

challenges in water research. The application of physico-chemical treatments could reduce the loadof chemical and biological pollutants present in WW reducing the pressure over water requirements,allowing the reclaim of the treated water. Advanced Oxidation Processes (AOPs) and, in particular, photo-catalysis using titanium dioxide (TiO2) have shown a great potential for chemicals removal as well as forpathogens reduction in water. Moreover, the use of solar Compound Parabolic Collectors (CPC) reactorshas been also shown to be very effective for water treatment purpose by solar photocatalysis. Neverthe-less, the effects of some key parameters in photocatalytic disinfection have not been already investigatedat pilot scale in solar reactors; like dissolved oxygen concentration, water temperature, water matrixcomposition and the type of microorganism. The roles of these parameters in photocatalytic processesare individually known for chemicals degradation, but their relative signicance in water photocatalyticdisinfection has been never studied at pilot scale. The aim of this work was to investigate the inu-ence of these parameters on the disinfection efciency using a solar 60 L-CPC reactor with suspendedTiO2 (100 mg/L). The following variables were experimentally evaluated: injection of air in the reactor(160 L/h); different controlled temperatures (15, 25, 35 and 45 C); two very different models of waterpathogen, Escherichia coli (model of fecal water contamination) and Fusarium solani spores (a highlyphytopathogenic fungus); and the chemical composition of the water comparing urban WW efuents(UWWE) and simulated urban WW efuent (SUWWE). The increase of water temperature (from 15to 45 C) had a benet on the disinfection rate for both pathogens in all the experimental conditionsevaluated. The air injection led to an important enhancement on the inactivation efciency, which wasstronger for F. solani spores, the most resistant microorganisms to TiO2 photocatalysis. The compositionof the water matrix signicantly affected the efciency of the photocatalytic treatment, showing a betterinactivation rate in SUWWE than for UWWE.

2014 Elsevier B.V. All rights reserved.

ction

, big efforts have been done to develop alternativement systems to decontaminate wastewater (WW)sses based in reactive oxygen species (ROS). The pho-treatments which use solar light have gained great

they produce ROS to destroy organic contaminants andganisms in water with very low energy consumption. In

ding author. Tel.: +34 950 387957; fax: +34 950 363015.ress: pilar.fernandez@psa.es (P. Fernndez-Ibnez).

the last decade, a number of articles have demonstrated the capa-bility of solar photocatalysis to decontaminate and disinfect waterpolluted by organic and biological agents [1].

Reuse of treated WW is an alternative resource of water sincefreshwater scarcity and lack of access to safe water is a humansizeable problem today [2]. Wastewater must be treated beforedischarge or for restricted reuse; it may contain industrial and agri-culture chemical pollutants and also a wide range of pathogens, i.e.bacteria, viruses and fungi [3].

Agriculture is probably the most affected eld by fungalpathogens like Fusarium spp. which is especially harmful in inten-sive agriculture [4]. Fusarium has been reported to be highly

rg/10.1016/j.cattod.2014.03.0262014 Elsevier B.V. All rights reserved.ction of urban efuents using solar TiO of signicance of dissolved oxygen, teoorganism and water matrix

rca-Fernndez, Isabel Fernndez-Calderero, Marandez-Ibnez hotocatalysis:erature, type

aculada Polo-Lpez,

I. Garca-Fernndez et al. / Catalysis Today 240 (2015) 3038 31

resistant to chemical and photocatalytic treatments due to itsspores [5,6]. Fusarium spp. have been associated with human dis-seminated infections which recently has increased, particularlyin patients with underlying immunosuppressive conditions, asleukemia, cfrequently whose presother enterbacteria thapresents wi

Advancefor the tradhave some cesses that radicals (Oconductor Twater contapathogens [( < 387 nmgen and in Eqs. (1) andfore a shortadsorbed ovand this is ism and catand their fupermeabilitending in ce

TiO2 + hv

H2O + h+BV

O2(ads) + eBCHoweve

trons are noand inhibitoxygen is aalytic proceacts as a dis

A numbphotocatalytivation in of using TiOE. coli [14]. Staphylococvisiae usinghas also stuFusarium spbe used wiwater [16,1

Water tebut it has nofection. Theas pasteurizature, drastof integrity temperaturis around 28action of soperatures btemperaturknowledge ture of phoexperimenttemperatur

The role of oxygen in metabolic processes is already well known.Oxygen crosses membranes freely and ROS are generated inter-nally due to aerobic metabolism. This increases the oxidative stressinside cells [22]. It has been proven that an increase of dissolved

(DO of SOudie

fecad wawated in ore, ms idisineporcillusying portaraturerimre atE anataly, 35

r.

teria

lar C

solaled 3licateiamly re95% ater h th0 PStic pan)t sedrison). Teng elng syps t

eacto

ater

ulate a syc carc mat in tan W(SpaUWWrninaracs meared wn chancer or AIDS patients [7]. On the other hand, WW isloaded with Escherichia coli, fecal indicator organismence in water indicates possible contamination withic pathogens like Salmonella, Shigella or Yersinia, enterict could cause gastrointestinal diseases that generallyth diarrhea [8].d Oxidation Processes (AOPs) are a good alternativeitional disinfection methods which are limited anddrawbacks. AOPs are based on physicochemical pro-produce powerful oxidizing species, mainly hydroxylH), in situ. Heterogeneous photocatalysis with the semi-iO2 is an AOP that has been used to decontaminateining hazardous pollutants and for disinfection of some9]. TiO2-photocatalysis in water use the UVA radiation) to excite the photocatalyst, that in presence of oxy-contact with the water produces OH (summarized in

(2)). Hydroxyl radicals have a high reactivity and there- half-life. Thus the process will be favored when TiO2 iser (or very close to) the cell wall of the microorganisminduced by different electrical charge of microorgan-alyst [10]. The oxidative action alters cell componentsnctionality, causing a loss of cell integrity, changing they and diffusion of cellular components to the medium,ll death.

eBC + h+BV (1)

OH + H+aq (2)

O2(ads) (3)

r, if oxygen concentration is low in the system, elec-t caught (Eq. (3)) and then e/h+ pairs can recombine

the production of OH. To avoid this, the presence oflways required for proper efciency of the photocat-ss. Moreover, O

2 is also oxidant (ROS) and therefore

infectant causing DNA damage [11].er of articles have demonstrated the capability of TiO2sis for bacteria, viruses, protozoa, prions or fungi inac-water [12,13]. Rincn et al. demonstrated the benets2 for disinfecting distilled and lake water polluted withSeven et al. inactivated E. coli, Pseudomonas aeruginosa,cus aureus, Candida albicans and Saccharomyces cere-

TiO2 with very good results in all cases [15]. Our groupdied the photocatalytic susceptibility of a variety ofp. and have demonstrated that TiO2 photocatalysis canth CPC reactors for eliminating pathogens present in7].mperature has direct effects on disinfection efcacy,t investigated up to date in photocatalytic water disin-

disinfecting effect of high temperatures is well knownation. Thermal increasing beyond the optimal temper-ically reduce the viability of microorganisms due to lossof proteins, enzymes and genetic material. The optimale for the most bacteria is between 35 and 40 C; while itC for the most of the fungus [18]. Moreover, the lethal

lar mild heat over bacteria has been investigated at tem-etween 40 and 52 C [1921]. Given the importance ofe in microbial metabolism and disinfection, up to ourthere is no research done on the effects of tempera-tocatalytic disinfection of water. This contribution willally undertake this aspect at pilot scale with controllede.

oxygentainers[23]. Strate ofgenatethat if resulteTherefcoliforalytic et al. rand Ba(supplthe imtempeto expperatuSUWWphotoc(15, 25reacto

2. Ma

2.1. So

Theules titborosiouter dof highCF = 1 (total wthrougNH-20magnetion, Jacatalysture (C(Fig. 1ba heatia cooliair pumsolar r

2.2. W

Simused asorganiorganiconten

UrbBobar ment. the mowas chpoundmeasuUSA) io) in water induced by proper agitation of batch con-DIS accelerates the disinfecting effect of solar radiation

s by Reed et al. [24] found a 48 times faster inactivationl bacteria in oxygenated water, compared to deoxy-ter [2527]. Furthermore, these authors demonstratedr was bubbled with nitrogen before to solar exposure, itworst inactivation efciency than aired samples [24].oxygen was conrmed as essential to disinfect fecaln batch solar disinfection process. In solar photocat-fection the DO plays also an important role. Rincnted an increased photocatalytic inactivation of E. coli

spp. in water with conditions of oxygenation >8 mg/Loxygen as bubbled pure O2) [28]. This work conrmednce of oxygen even for disinfection in non-controllede conditions at small scale (4 L). The present work aimsentally evaluate this factor but with controlled tem-

pilot scale (60 L). The disinfection of contaminatedd UWWE with Fusarium solani and E. coli using solarsis with TiO2 was evaluated at different temperaturesand 45 C) with and without air injection in the solar

ls and methods

PC pilot plant

r CPC pilot plant used consists of two CPC mirror mod-7 (Fig. 1a). Each CPC mirror module is made up of 10

glass tubes of 1500 mm long, 2.5 mm thick and 50 mmeter (UVA-transmission: 90%). The CPC mirror is madeective anodised aluminum with concentration factortotal reectivity). The ratio of irradiated water (45 L) to(60 L) is 75%, with a CPC of 4.5 m2. Water is recirculatede tubes to a tank by a centrifugal pump (150W, Mod.

PanWorld, USA). Flow was controlled by a Yokogawaow meter (Admag, RXF, Yokogawa Electric Corpora-

at 30 L/min (turbulent ow; Reynolds: 16600) to avoidimentation. Online sensors for pH, DO and tempera-, Spain) acquired the measurements during the testsmperature was controlled at: 15, 25, 35 and 45 C usingectric resistance to increase the water temperature, andstem (Fig. 1c). DO in the water was increased by twohat inject air (160 L/h) at two equidistant points of ther system (Fig. 1a and b).

sources

d urban WW treatment plant efuent (SUWWE) wasnthetic model of WW efuent with 25 mg/L of dissolvedbon (DOC). This water was chosen because it containstter (urea, peptone and meet extract) [29]. The ionichis SUWWE was measured (Table 1).W treatment plant efuent (UWWE) of Almera, El

in), was used as real efuent of a secondary treat-E was freshly collected from the treatment plant in

g of each disinfection assay. Every UWWTE stock usedterized and the average of the inorganic chemical com-sured is shown in Table 1. The concentration of ions wasith a Dionex DX-600 and Dionex DX-120 (California,

romatographs for anions and cations.

32 I. Garca-Fernndez et al. / Catalysis Today 240 (2015) 3038

Fig. 1. Images of collreactor: air inj

2.3. Genera

Spores omeration andescribed eing the cult(15 g/L of Kof incubatiothe spores distilled waconcentratiplate (BrandJapan) and tial concent

Table 1Chemical char

Na+ (mg/L) NH4+ (mg/L)K+ (mg/L) Mg2+ (mg/L)Ca2+ (mg/L) SO42 (mg/LCl (mg/L) NO3 (mg/LPO43 (mg/LpH ConductivityTurbidity (NDOC (mg/L) DIC (mg/L) E. coli (CFU/m

DOC = dissolve

erim of mcid) w of the 60 L-CPC reactor at PSA facilities. Front view of the solar CPC reactor (4.5 m2

ection and DO probe (b), and cooling and heating systems (c).

tion and enumeration of F. solani spores

f F. solani strain (CECT 20232) were used. The enu-

all exp(20 g/Lcitric ad quantication methods used in this work have beenlsewhere [5,16]. Small pieces (1 cm) of agar contain-ure of F. solani were transferred to a poor nutrient agarCl and 5 g/L of bacteriological agar). After 1520 daysn at 25 C under UV-C radiation (Mercury lamp, 40W)were recovered by washing Petri dishes with sterileter yielding an average of 105 spores per mL. Sporeson was determined by direct counting with a Neubauer, Germany) using a phase contrast microscope (Nikon,

diluted in the tank of the CPC reactor until desired ini-ration, 103 colony forming units per mL (CFU/mL) for

acterization of SUWWE and UWWE.

SUWWE UWWE

35.80 1.10 193.9 4.4 2.70 1.00 38.6 19.4

3.40 0.60 27.1 2.0 17.20 0.30 32.5 2.9

21.63 2.30 66.1 2.2) 9.00 1.40 69.9 34.7

11.50 2.10 353.3 27.5) 130.40 7.60 15.1 13.4) 12.10 3.00 47.3 50.1

8.15 0.30 7.4 0.2 (S/cm) 362 12 1617.1 226.2TU) 1.50 0.10 15.1 0.1

2030 15290.54 5060

L) 1000 2501d organic carbon; DIC = dissolved inorganic carbon.

out the solwere platedof this expecounted aft

2.4. Genera

E. coli Kwas culturewith agitatafter 20 h, ysions were bacterial peand dilutedtion. The saa serial 10-ftriplicate oncounted aft[6,16,30]. Fwas evaluaon Chromo

2.5. Solar p

Titaniumas receivedwork [5]. Aat Plataformsolar exposector mirrors) with air injection points indicated (a), side view of CPC

ents. Plate counting technique with acidied malt agaralt extract, 20 g/L of bacteriological agar and 0.25 g/L ofas used to determine the spore concentration through-ar experiments. Samples volumes of 50250500 L by the spread plate method. The detection limit (DL)rimental method was 2 CFU/mL. Fungal colonies wereer 48 h of incubation at 28 C in dark.

tion and enumeration of E. coli

-12 (ATCC 23631) was spiked in SUWWE tests. E. colid in Luria broth (SigmaAldrich) and incubated at 37 Cion under aerobic conditions. Bacteria were collectedielding a concentration of 109 CFU/mL. E. coli suspen-harvested by centrifugation at 800 g for 10 min. Thellet was re-suspended in Phosphate Buffer Saline (PBS)

in the reactor to have a 106 CFU/mL initial concentra-mples were enumerated using plated counting throughold dilutions in PBS and volumes of 20 L were plated in

Luria agar Petri dishes (SigmaAldrich). Colonies wereer incubation of 24 h at 37 C, with a DL of 4 CFU/mLor UWWE experiments, the naturally occurring E. colited by spreading different sample volumes (25500 L)Cult Coliform Agar (Merck) plates (DL = 2 CFU/mL).

hotocatalytic experiments in the CPC reactor

dioxide (Aeroxide P-25, Evonik, Germany) was used at a concentration of 100 mg/L, according to previousll experiments were done under natural solar radiationa Solar de Almera (Southeast of Spain). Previously toure, in SUWWE assays, TiO2 powder and bacteria or

I. Garca-Fernndez et al. / Catalysis Today 240 (2015) 3038 33

fungal suspensions were added to the 60 L-CPC reactor in the darkand it was kept re-circulating for 15 min (adaptation and homoge-nization time). For UWWE assays, a similar procedure was followed,excluding the addition of E. coli suspensions as the naturally occur-ring E. coli wthe reactor under clearand evaluatmethods. Athe dark atat the end omerely outsviability. BaexperimenttemperaturNon-regrowwere done iirradiance. ducible. Thestandard deone-way ANLab Corp., Nthe averagesured with aall experim(kJ/L), the sphoto-react

2.6. Kinetic

Four difexperimentlog-linear adisinfectionganisms arapplicationchlorine, ozlog-linear kinactivation(3) A log-linrepresents experimentity and/or treatment [beginning (accumulatioa log-linear

Log(

N

N0

)=

Log

(N

N0

)=

dN

dt= k1

Log(

N

N0

)=

where N/N0is the disinfthe residua

All expeproposed eqcient werethese ttinparameters

all are obtained under same experimental (reactor, illumination,protocols, etc.) conditions.

3. Results

ntroctor

viousg-coo, andted O. Thlar r

are sactor

1.5 Cmentept f.

fect oation

trol o sol

temi spo0 mgU/mLnt at

less ed (df the.

Case 3a s

45

ationC. In

29.2ecre

of Qas obtivelyC, anof Dment

The and

solajected w

milarion w35 anwith

4a sraturd on

DL) tainO av

wereas evaluated instead. The rst sample was taken andwas uncovered and exposed to solar radiation for 5 h,

sunny days. Samples were taken at regular intervals,ed according to the previously described enumerationfter bacterial/fungi spiking, a water sample was kept in

room temperature and plated by that time and againf the experiment as a control, to check that any factoride of the solar process is affecting the microorganismcterial and spore re-growth counts were done for alls by leaving the last two experimental samples at roome for 24 h and 48 h overnight after the solar treatments.th was observed in any case (95%, Origin v7.03, Origin-orthampton, USA), reporting a 95% condence level for

colony concentration and error. UV radiation was mea- global UV-A pyranometer (CUV4, Kipp & Zonen) duringents. The inactivation curves are presented versus QUVolar UVA energy per unit of volume received in theor [17].

s evaluation

ferent kinetics models have been used to t theal data obtained during the photocatalytic tests: (1) according to the Chick law (Eq. (6)). This model reduces

to a bimolecular chemical reaction in which microor-e treated as molecular species. There is an extensive

of this equation using other disinfecting agents i.e.one, hydrogen peroxide and chloramines. (2) A doubleinetics (Eq. (7)), with a rst stage of very fast (k1 > k2)

and a second phase of attenuated inactivation (k2) [28].ear region followed by a tail (Eq. (8)). The tail shapethe bacterial population remaining at the end of the

due to a strong reduction on the photocatalytic activ-the presence of a population of cells resistant to the31,32]. (4) An initial delay or very smooth decay at theshoulder), attributed to lose of cells viability after then of oxidative damages during the process, followed by

decrease (Eq. (9)) [31,33].

k t (6)

k1 t; t = [0, t1]; Log(

N

N0

)= k2 t; t = [t1, t2] (7)

N N NresN0 Nres

= ek1t (8)

k1 t{

NN0; 0N < N0; ek1(NSL)

}(9)

is the bacteria or spores concentration reductions, kiection kinetic rate and t is the time of treatment, Nres isl population density, and SL = Shoulder length (min1).rimental data from disinfection tests were tted to theuations. Those results which led to a minimum R2 coef-

accepted as the best statistical tting. The results ofgs are shown in Table 2, including R2 values. Kinetic

obtained for the different equation are comparable, as

3.1. CoCPC rea

Preheatin25, 35conductime Dural soresultsCPC re45.0 experiair, exc(Fig. 2)

3.2. Efinactiv

Conously tof eachF. solanand 10106 CFconstawhereobserveffect ospores

3.2.1. Fig.

35 andinactivto 45

a QUV =5-log d40 kJ/Ltion wrespecat 35

ations experidition.5.5, 5.8

The45 C inenhancvery sireductof 25, of QUV

Fig.tempereduceing thewas obQUV. Dmentsl of water temperature and dissolved oxygen in the

to carry out the solar experiments, the capabilityling system to maintain the water temperature at 15,

45 C constant was evaluated. The experiments werewith and without air injection, measuring at the sameese tests were run in the CPC reactor for 5 h under nat-adiation in distilled water at 30 L/min of ow rate andhown in Fig. 2. The water temperatures measured in the

for each case were: 15.0 1.4, 25.0 1.9, 35.0 1.0 and. In all cases, the DO values measured were higher fors with air sparging than for those without injection ofor 15 C, where no signicant differences were observed

f temperature and dissolved oxygen on the of E. coli and F. solani spores

tests in the dark with air injection were done previ-ar experiments in SUWWE to determine the inuenceperature and air injection over the viability of E. coli andres in the 60 L-CPC reactor with a ow rate of 30 L/min/L of TiO2. The concentration of both pathogens, i.e.

for E. coli and 103 CFU/mL for F. solani spores, remained all temperatures evaluated for 5 h, except for 45 C,than 1-log reduction in the concentration of E. coli wasata not shown). Therefore, no signicant detrimental

operational conditions was observed over bacteria and

1: SUWWEhows the photocatalytic inactivation of E. coli at 15, 25,C without air injection. An enhancement of the E. coli

efciency was observed as temperature rises from 15the case of 15 C, a 4-log reduction was observed with

kJ/L, and the DO varied from 9.0 to 7.8 mg/L. At 25 C, aase was found, although the DL was not achieved withUV, and DO ranged from 6.0 to 5.0 mg/L. A 6-log reduc-served at 35 and 45 C with a QUV of 23.3 and 14 kJ/L,. In these experiments, DO varied from 6.3 to 5.1 mg/L

d from 5.1 to 3.7 mg/L at 45 C. Due to the slight uctu-O measurements from the beginning to the end of the, we report the average DO for each experimental con-DO values decreased as temperature increased, i.e. 8.1,

4.4 mg/L at 15, 25, 35 and 45 C, respectively.r photocatalytic inactivation of E. coli at 15, 25, 35 anding air is shown in Fig. 3b. Again, the inactivation kineticshen the temperature increased from 15 to 35 C, while

results at 45 and 35 C were observed. At 15 C, a 4.5-logas obtained (QUV = 37.6 kJ/L, DO = 8.9 mg/L). In the cased 45 C, DL was achieved with 25.9, 11.4 and 12.8 kJ/L

DO concentration of 6.8, 6.0 and 5.2 mg/L, respectively.hows the inactivation of F. solani spores at differentes without air injection. The concentration of fungi wasly 2-log at 15 and 25 C. At 35 C a 3-log decrease (reach-was observed with QUV = 44 kJ/L. Best inactivation resulted at 45 C, where the DL was reached with 18 kJ/L oferage values at 15, 25, 35 and 45 C in these experi-

7.1, 6.4, 5.2, and 5.5 mg/L, respectively. Fig. 4b shows F.

34 I. Garca-Fernndez et al. / Catalysis Today 240 (2015) 3038

Table 2E. coli and F. solani spores inactivation rates (k) during solar photocatalytic disinfection of SUWWE and UWWE.

T (C) k1 (min1) R21 k2 (min1) R22 SL (min) Log (Nres) Model #

E. coli, without air injection, SUWWE (Fig. 3a)15 25 35 0.97045 0.957

E. coli, with a15 25 0.69035 45 0.966

F. solani, wit15 25 35 0.86645

F. solani, wit15 25 35 45

E. coli, witho15 25 35 45

E. coli, with a15 25 35 45

F. solani, wit15 25 35 45

F. solani, wit15 25 35 45

k = inactivation3 = Log-lineal (

solani inactilar tendentemperaturmulated so35 and 45

tively. Best highest tem

3.2.2. Case Fig. 5a s

E. coli withremoval of cases excepQUV values 18.2 and 42at 35 C. DO9.2 mg/L at injected airfor 15 C, w23.8 kJ/L ofat 25 C. Beof 17.5 kJ/L,0.033 0.002 0.998 0.051 0.007 0.965 0.069 0.004 0.947 0.010 0.001 0.107 0.030 1.000 0.015 0.004

ir injection, SUWWE (Fig. 3b)0.026 0.004 0.974 0.053 0.011 0.920 0.006 0.0040.060 0.020 0.867 0.117 0.012 0.990 0.011 0.003

hout air injection, SUWWE (Fig. 4a)0.007 0.001 0.9679 0.009 0.001 0.9778 0.013 0.002 0.9830 0.003 0.002 0.020 0.005 0.9686

h air injection, SUWWE (Fig. 4b)0.013 0.001 0.995 0.023 0.001 0.998 0.041 0.001 0.999 0.059 0.001 0.999

ut air injection, UWWE (Fig. 5a)0.007 0.0005 0.9588 0.013 0.001 0.977 0.021 0.003 0.955 0.013 0.001 0.957 ir injection, UWWE (Fig. 5b)0.008 0.001 0.976 0.017 0.002 0.977 0.025 0.004 0.966 0.024 0.003 0.973

hout air injection, UWWE (Fig. 6a)0.001 0.001 0.966 0.005 0.001 0.997 0.005 0.001 0.953 0.022 0.003 0.980 0.0031 0.0003 0.967

h air injection, UWWE (Fig. 6b)0.001 0.001 0.817 0.004 0.001 0.955 0.005 0.001 0.967 0.024 0.002 0.983

rate (linear regression of Log (concentration) versus time); R2 = regression coefcient; k1) + tail (Log(Nres)); Model 4 = shoulder (SL) + log-lineal (k1).

ivation at same temperatures with air injection. Sim-cy as previously observed was obtained for differentes (1545 C). DL was reached for all cases, with an accu-lar UV-A energy of 19.4, 8.8, 5.2 and 3.0 kJ/L at 15, 25,C, with DO values of 7.8, 6.7, 5.7, and 5.1 mg/L, respec-spores inactivation efciency was observed again at theperature (45 C).

2: UWWEhows photocatalytic inactivation of natural occurringout air injection at different temperatures. CompleteE. coli, from 103104 CFU/mL to DL was achieved in allt for 15 C, where a 1.5-log reduction was observed. Therequired to reach the DL at 25, 35 and 45 C were 43.8,.5 kJ/L, respectively. Best inactivation results were found

concentration decreased as temperature increase, from15 C to 5.1 mg/L at 45 C. The same experiments with

are shown in Fig. 5b. DL was achieved in all cases excepthere a 2-log reduction of E. coli was observed with

QUV. 31.5 kJ/L was required for complete inactivationst inactivation results were found at 35 C with a QUV

while 31.1 kJ/L were necessary to reach DL at 45 C. DO

concentrati15 C to 6.4

Fig. 6a sin UWWE athe concentsimilar kinewere obserfaster inactonly at 45

Same experin Fig. 6b. T1-log reducobserved wobserved aiments hadE. coli.

Very simand withoualthough thhighlightindisinfectionthermal ina 1.83 3 0.30 3

2 2

1.20 3 2 1

2

160 4

2 1

1 1 1 1

90 4 1 1 1 1 1 1 1

130 4 1

8 2

1 1 1 1

Model 1 = Log-lineal (k1); Model 2 = double log-lineal (k1, k2); Model

on decrease as temperature increase from 9.4 mg/L at mg/L at 45 C.hows the photocatalytic inactivation of F. solani sporest different temperatures without air injection. At 15 C,ration of spores remained almost constant for 5 h. Verytics, which resulted in 1-log spore reduction after 5 h,ved at 25 and 35 C; although 35 C lead to a slightlyivation. Complete Fusarium inactivation was attainedC, a 3-log decrease until the DL, with 54.7 kJ/L of QUV.imental results in UWWE with air sparging are shownhe concentration of spores remained constant at 15 C.tion was observed at 25 C (47.1 kJ/L), a 2-log decay wasith 49.1 kJ/L at 35 C, while complete inactivation wast 45 C, with 19.7 kJ/L. The DO values of these exper-

similar tendency than in previous experiments with

ilar results in E. coli inactivation were observed witht air injection in both types of WW (Figs. 3 and 5),ere is an enhancement with air at 45 C (Table 2),

g the importance of temperature in the photocatalytic in spite that this temperature was not responsible forctivation (Section 3.2).

I. Garca-Fernndez et al. / Catalysis Today 240 (2015) 3038 35

Fig. 2. Registr ratur(- - -) represen each

For the cduced an eFigs. 4 and produce sigitively affecof DO in somand the air but to enhamicroorgan

4. Discussi

Our prewith CPC syertheless thcontrolled. to 40 C (duvary from 5inactivationdemonstratspores is en

It is wellthe temperionic produfrom 20 to tion of hydrholes in theform OH (Emakes the be more efacid to demmation and

incres thation of temperature in the CPC reactor in experiments conducted at water tempet DO concentration values measured in injected and no injected air experiments in

ase of F. solani, the air supply and thermal increase pro-nhancement in the photocatalytic efciency (Table 2,

in an explain6). Although the air sparging in the reactor does notnicant increases in the measured DO in water, it pos-ts the photocatalytic efciency due to local increasese parts of the reactor. The open design of this reactor

spargers did not permit increase the DO measurement,nce the photocatalysis efcacy observed only when theism is enough resistant.

on

vious studies on photocatalytic disinfection of waterstems did show very promising results [5,16,17], nev-e temperature in the whole reactor system was notThe ambient temperature at this place ranges from 15ring the experiments) and the water temperature can

to 55 C in the CPC reactor, depending of the season. The results at xed temperatures (15, 25, 35, and 45 C),ed that inactivation efciency of E. coli and F. solanihanced when the water temperature increased.

known that photo-excitation of TiO2 is not affected byature in the range of 2080 C [34]. Nevertheless, thects of water (OH, H3O+) increase with temperature60 C [35], which induces an increase in the concentra-oxyl anions. In aqueous solution, the photo-generated

TiO2 valence band are trapped by hydroxyl anions toq. (2)). Thus, the rise of OH as temperature increases

hole trapping and the hydroxyl radicals generation tocient. Actually, Janus et al. used 2-hydroxytepephthaliconstrate the correlation between hydroxyl radicals for-

temperature increase, from 20 to 60 C, which resulted

temperaturThermal

their inactivdark (Sectioviability los

E. coli gperature ofsignicant atures beloreduced anperature, thunpacked aoxidative stSOS responbeing consttemperaturefciency oincreased anicant diffthese tempria. Moreovbacteria de

Similar Spores are present in dture (rangeorganic andnation [39]process, whinux inside of 15 C (a), 25 C (b), 35 C (c), and 45 C (d). Solids lines (- - -) andtemperature.

ase on the photocatalytic activity of TiO2 [36]. Thise better photocatalytic inactivation efciency at higher

es that we observed in this work.

death of E. coli and F. solani is discarded as a reason foration during the solar experiments. Control tests in then 3.2) demonstrated there are no damages resulting ines for both pathogens during 5 h.rowths in the range of 1047 C, with optimum tem-

3744 C [18]. When temperature is far from optimal,changes in the metabolism of cells occur. At temper-w 10 C, the uidity of cell membrane is drasticallyd the metabolism slows down. At the optimum tem-e metabolic activity is maximal; the genetic material isnd completely active, and therefore more vulnerable toress due to increased surface of DNA [37]. The reducedse in E. coli when temperature increases from 10 to 20 C,ant until 40 C has been proven [38]. In our results, whenes raised from 15 to 35 C, we observed an increase inf the disinfection process, which can be explained by thectivity of the metabolism of bacteria cells; while no sig-erent results were observed between 35 and 45 C, as ateratures there are no metabolic differences in the bacte-er, at higher temperatures, the defence mechanisms ofcrease their capability.effect of temperature was observed for F. solani.biological structures of resistance against stress factorsifferent environments. Some parameters as tempera-

d from 25 to 30 C), acid pH, UV-light, water activity and inorganic chemical compounds, favor the spore germi-. Temperatures above 20 C promote the germinationich involves the modication of the cell wall for watere the spore core. During germination, the structure of

36 I. Garca-Fernndez et al. / Catalysis Today 240 (2015) 3038

0

-6

-5

-4

-3

-2

-1

0

E. c

oli

(Log

N/N

0)

D

0

-6

-5

-4

-3

-2

-1

0

E. c

oli (

Log

N/N

0)

D

a)

b)

Fig. 3. Photocat different te(a) and with (DL = 4 CFU/mL

the spore boxidative dacatalytic dis

In summobserved atacting simu(ii) and incrated to the temperatur

If we comresults, inclat same temtive than F. in other artThis differetion of Fusafungal sporars, proteinalso an outea high resismental studthat UV dosism dependclose to satuto 5 mg/L, with inject

0-3

-2

-1

0

D

-2

-1

0

0

a) 5 10 15 20 25 30 35 40

QUV (kJ /L)

L

F. s

olan

i (Lo

g N

/N0)

. sol

ani (

Log

N/N

)

b) 5 10 15 20 25 30 35 40QUV (kJ/L )

L

atalytic inactivation of E. coli under natural sunlight in SUWWEmperatures: 15 C ( ), 25 C ( ), 35 C ( ), and 45 C ( ) withoutb) air injection. Kinetic model ttings are also shown (solid line)..

ecomes vulnerable to environmental factors, includingmage of photocatalysis [29]. For this reason, the photo-infection of spores was faster at higher temperatures.ary, the enhanced inactivation photocatalytic efciency

higher temperatures can be explained by three reasonsltaneously: (i) an increase in generated OH by TiO2;eased activity of the chemical reaction kinetics associ-metabolic activity; and (iii) the non-lethal inuence ofe on E. coli and spores of F. solani metabolisms.pare E. coli (Figs. 3 and 5) and F. solani (Figs. 4 and 6)

uding the kinetic constants (Table 2) in same water typeperature, it is clear that E. coli is much more sensi-

solani spores to photocatalytic treatment, as publishedicles under different reactor and water conditions [6].nce is attributed to the resistant structure and composi-rium spores. Contrary to E. coli cells (vegetative forms),e walls are rigid structures composed of polymeric sug-s and glycoproteins. Additionally, spores wall containr xylan layer [6]. This multifunctional structure conferstance against different stress factors. Previous experi-ies on solar photocatalysis with TiO2 also demonstratede required for removal of different types of microorgan-s on cell structure [13,40]. The measured DO was veryration value at the given temperature, i.e. from 8 mg/L

for 15 to 45 C, respectively. The inactivation resultsed air showed an enhancement versus the absence of

0-3

F

Fig. 4. PhotocSUWWE at diwithout (a) anline). DL = 2 CF

injected airdifference iperatures. Tprocess is nthe photocfuses inside[41]. Air buby other aui.e. SODIS tof disinfectan increasepositive effE. faecalis. Tgenated) winjected inthat inactiv(0.0187 minvery fast (0the effect ofrom 0% tobility [44]. causing irreof DNA stabactivity [45 5 10 15 20 25 30 35 40 45

QUV (kJ/L)

L 5 10 15 20 25 30 35 40 45

QUV (kJ/L )

DL

atalytic inactivation of F. solani spores under natural sunlight infferent temperatures: 15 C ( ), 25 C ( ), 35 C ( ), and 45 C ( )d with (b) air injection. Kinetic model ttings are also shown (solidU/mL.

for both microorganisms (Table 2), although the onlyn DO measurements was 1 mg/L for all tested tem-he role of increased values of DO in the photocatalyticot only to avoid electron/hole pairs recombination in

atalyst but also to increase the levels oxygen that dif- cells increasing the ROS and internal oxidative stressbbling and mechanical agitation have been investigatedthors for solar water disinfection without photocatalyst,reatment. Kehoe et al. [23] attributed an enhancemention efcacy of E. coli after agitation of SODIS bottles to

of dissolved oxygen in water [42]. Reed [43] reportedects of DO concentration on inactivation of E. coli andhey compared SODIS results in air-equilibrated (oxy-ater with anaerobic (deoxygenated) water; helium was

SODIS bottles for these experiments. They reportedation process was blocked under anaerobic conditions1) while in air-equilibrated samples the reaction was

.071 min1) [43]. Other authors have demonstrated thatf increased concentrations of oxygen in a carrier gas

0.75% provoked an important reduction in MS2 via-High levels of ROS are known to be stressing for cellsversible damage to cellular components like reductionility and changes on proteins and lipids structure and].

I. Garca-Fernndez et al. / Catalysis Today 240 (2015) 3038 37

0

-3

-2

-1

0

E. c

oli

(Log

N/N

0)

D

0-4

-3

-2

-1

0

E. c

oli

(Log

N/N

0)

D

a)

b)

Fig. 5. Photocferent temperwith (b) air injsymbol. DL = 2

The prevoperationalworst resul41.5 kJ/L inthe presentachieved wat 15 C (thment time f

Inactivatfavorable co(0.059 0.0injection. Fnaturally o0.024 0.00Results in Tvation efcapplied. Alshigher thanwere loweratively highthe photocafates, nitratROS and posurface [5].

0-3

-2

-1

0

D

-1

0

0

a) 5 10 15 20 25 30 35 40 45 50

QUV (kJ/L)

L

F. s

olan

i (Lo

gN/N

0)la

ni (

LogN

/N)

b) 5 10 15 20 25 30 35 40 45 50

QUV (kJ/L)

L

atalytic inactivation of E. coli under natural sunlight in UWWE at dif-atures: 15 C ( ), 25 C ( ), 35 C ( ), and 45 C ( ) without (a) andection. Dark controls are represented with the corresponding empty

CFU/mL.

ious work [5] on F. solani inactivation under similar conditions without air neither thermal control showedts. A much higher QUV (29.9 kJ/L in distilled water and

well water) was required to achieve the DL, while in contribution with sparged air in SUWWE, the DL wasith 3 kJ/L at 45 C (the fastest result) and less than 20 kJ/Le worst case). This means a drastic reduction of treat-rom 4 h to 30 min for 60 L of polluted water.ion rate constants (Table 2) showed that the mostnditions for E. coli (0.117 0.012 min1) and F. solani01 min1) removal in SUWWE were 45 C with airor UWWE, the best inactivation rate constants forccurring E. coli was 0.025 0.004 min1 at 35 C, and2 min1 for F. solani spores at 45 C with air injection.able 2, show a well-dened trend to increase inacti-iency when temperature increases and air sparging iso, as explained before, inactivation rate for E. coli was

for F. solani in all cases evaluated. All inactivation rates in UWWE than in SUWWE. Real efuents content a rel-

amount of chemical compounds which may decreasetalytic activity due to the action ionic species like sul-es, chlorides and phosphates, which partially scavengeison the catalyst competing for the active sites of TiO2

Also a high content on inorganic carbon in the water

0-3

-2F. s

o

D

Fig. 6. PhotocUWWE at diffeout (a) and wiDL = 2 CFU/mL

samples uncarbonates OH scavensolved Orgdetrimentaradicals. Walytic procelight scatte15.2 0.1 N

As expeckinetics canresults (Tab(model 2, dcontinued wAs all thesemodied) tthe best disthe presencattacked byof reasons lcell, shadesthe cell wais more likeand 103 CFU 10 20 30 40 50

QUV (kJ /L)

L 10 20 30 40 50

QUV (kJ /L)

L

atalytic inactivation of F. solani spores under natural sunlight inrent temperatures: 15 C ( ), 25 C ( ), 35 C ( ), and 45 C ( ) with-th (b) air injection. Kinetic model ttings are also shown (solid line)..

der study decrease the efciency. Negative effect ofand bicarbonates on photocatalytic activity throughging and photo-absorption is well known [46]. Dis-anic Matter naturally present in UWWE may be alsol as it competes with microbial cells for generated OHater turbidity affects also negatively to the photocat-ss shading catalyst particles and microorganisms byring phenomena. The average UWWE turbidity wasTU, while in SUWWE was 1.5 0.1 NTU (Table 1).ted for photocatalytic disinfection with TiO2, rst-order

be considered the most common behavior for all thele 2). Only few cases are represented by biphasic modelouble log-linear) and less frequently by linear behaviorith a residual concentration (model 3, log-linear + tail).

equations are based on rst-order kinetics (simple orhe kinetic constants can be directly compared to assessinfection results. The tail shape can be explained fore of remaining population of bacteria which was not

the oxidative damage of the process due to a numberike: (i) the catalyst particle aggregates around bacteria

it and prevents the formation the hydroxyl radical inll surface; (ii) the oxidative attack of hydroxyl radicalsly to occur at high initial concentration of bacteria (106

/mL) than when viable bacteria population is very low

38 I. Garca-Fernndez et al. / Catalysis Today 240 (2015) 3038

(10010 CFU/mL); therefore, there is a clear deceleration of the pro-cess at the end of the reaction [31]. This tail is more evident whenthere is a strong competence between DOM and bacteria for thehydroxyl radicals, as suggested previously by other authors [29,31].Only very few experiments (Table 2) can be described with initialshoulder shtarget actioof oxidativecase: in terare very govery fast, thphase takesa more resisappears.

Our resudata reportpilot plant 0.0135 0.0reactor witGrieken et aslurry in WWand 16.6 5.7 104 ma lamp (365reactor withof 4.88 10days [48]. Rk1 = 0.483 mreactor of 4are few stuvious work(instead of in distilled calculate th0.792 0.07with injecteconsider th

5. Conclus

Solar phwater disinent contamof temperatfrom these rfrom 5 to this is attribin temperamight be coenergy costand provide

The air and spore pin F. solani photocatalyfor solar rea

Acknowled

The authCompetitiv(reference: contributiotal work. IGCIEMAT-PS

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e complexity of the WW.

ions

otocatalysis with TiO2 suspensions in a solar reactor forfection can be enhanced in real and simulated WW efu-inated with E. coli and F. solani spores by the increasingure. This has implications in the interpretation of resultseactors; when the low temperatures of the water range

15 C and the kinetics are very slow; but sometimesuted wrongly to other factors. Therefore, the changes

ture of photocatalytic reactors for water disinfectionnsidered to evaluate the efciency of the process. Thes of little increase of water temperature are very low

signicant treatment time reductions.sparging causes also an improvement in the bacterialhotocatalytic inactivation, which is specially marked

spores. This is in line with the important role of DO intic water disinfection, which should be also consideredctors design for water disinfection.

gments

ors wish to thank the Spanish Ministry of Economy andeness for nancial support under the AQUASUN projectCTM2011-29143-C03-03). We also acknowledge then of Elisa Ramos and Agustn Carrin in the experimen-F would like to thank the University of Almera and

A for her PhD research grant.

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Disinfection of urban effluents using solar TiO2 photocatalysis: A study of significance of dissolved oxygen, temperature,...1 Introduction2 Materials and methods2.1 Solar CPC pilot plant2.2 Water sources2.3 Generation and enumeration of F. solani spores2.4 Generation and enumeration of E. coli2.5 Solar photocatalytic experiments in the CPC reactor2.6 Kinetics evaluation

3 Results3.1 Control of water temperature and dissolved oxygen in the CPC reactor3.2 Effect of temperature and dissolved oxygen on the inactivation of E. coli and F. solani spores3.2.1 Case 1: SUWWE3.2.2 Case 2: UWWE

4 Discussion5 ConclusionsAcknowledgmentsReferences