Geothermics 50 (2014) 3034

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Geothermics

journa l homepage: www.e lsev ier .com/ l

Adsorp rm

Halldor G jolfa Blue Lagoon Lb School of Scie

a r t i c l

Article history:Received 22 FeReceived in reAccepted 1 AuAvailable onlin

Keywords:Geothermal siChromatograpAdsorptionProtein separaPhycocyanin

uid dsed asen alghe sildsorpnt elu0nmuct o

1. Introdu

1.1. Geothermal silica

Geothermal resources are widespread throughout the worldalthough generally associated with areas of volcanic activity. TheHS-Energy geothermal powerplant is located in Svartsengi on theReykjanesows, theet al., 2010interlayersglacial perioclastite arepercolate dwith meteothrough theture (here rmeteoricwthe hot geo(Si) when ithe hot geoing, the siliof coagulategrow up toaggregated

CorresponE-mail add

c surtion

Steam from the ashed geothermal uid is used to produceelectricity (output power of 75MWe). The residual liquid is usedin a heat exchange process (output power of 150MWt) to heatup freshwater for district heating of local communities of roughly20,000 habitants. This heat exchange process limits the mini-

0375-6505/$ http://dx.doi.openinsula, southwest Iceland on a sequence of lavayoungest being roughly 800 years old (Saemundsson). The geological structure is further characterised byof scoria and hyaloclastite reecting interglacial andds. Since the lava ows, scoria and interlayers of hyalo-highly porous and permeable, they allow seawater toeep into their aquifers where it heats up and mixesric water (Arnorsson, 1995). Geothermal wells drilledlava ows to depths of up to 2000m discharge a mix-

eferred to as geothermal uid) of 2/3 seawater and 1/3aterwith a temperature of about 240 C. Due to leachingthermal uid contains a high concentration of silicont enters the wells. Originally, the silicon is present inthermal uid as silicic acid (SiOx(OH)42x)n. Upon cool-cic acid precipitates as a three-dimensional networkd primary silica (SiO2) particles. The primary particlessome nanometers in size before they coagulate to formclusters. Such a small particle size gives rise to high

ding author. Tel.: +354 5996200; fax: +354 5996201.ress: halldorsv@ru.is (H.G. Svavarsson).

mum temperature for heat extraction of the geothermal uid toabout 90 C. Most of the spent geothermal uid is reinjected intothe geothermal reservoir (6106 m3 annually) but some of it(1.2106 m3 annually) is discharged on the surface where itforms the Blue Lagoon (Grether-Beck et al., 2008; Petursdottir et al.,2009). A small fraction of the discharged uid is bypassed to sed-imentation tanks at the Blue Lagoon where it cools from 90 C toambient temperature. The cooling causes supersaturation of thesilicic acid which in turn precipitates as amorphous SiO2. The pHof the resulting supernatant is 7.70.2, sligthly higher than thepH of the Blue Lagoon which is 7.50.2. At 90 C, the geothermaluid contains about 600ppm SiO2 and thus the 7106 m3 of liq-uid being discharged and reinjected annually carries about 4000tonnes. At 1015 C, a realistic ambient temperature, the SiO2 con-centration has dropped by roughly an order of magnitude (FlemingandCrerar, 1982) and thus aprecipitationof over3000 tonnes couldpotentially be harnessed annually from uid discharged from theHS-Energy facility alone.

Few authors have reported on practical applications of modi-ed geothermal SiO2 and still fewer on applications of unmodiedSiO2. A possible use of geothermal SiO2 as a ller in paper (Johnstonet al., 2004) and as a precursor for silicates (Gallup et al., 2003) has

see front matter 2013 Elsevier Ltd. All rights reserved.rg/10.1016/j.geothermics.2013.08.001tion applications of unmodied geothe

. Svavarssona,b,, Sigurbjorn Einarssona, Asa Bryntd., Icelandnce and Engineering, Reykjavk University, Iceland

e i n f o

bruary 2013vised form 16 July 2013gust 2013e 6 September 2013

licahic

tion

a b s t r a c t

Silica, precipitated out of geothermal Reykjanes peninsula in Iceland, was uC-phycocyanin, from coccoid blue-greing the geothermal uid. Analysis of tand BrunauerEmmettTeller (BET) aphous. Upon adsorption and subsequeof the light absorbance of 620 and 28utilization of a mostly unused byprod

ction speciadsorpocate /geothermics

al silica

sdottir a

ischarged from a geothermal powerplant in Svartsengi on thea chromatographic adsorbent to extract blue colored protein,ae. The only supplement usedwas salt obtained by evaporat-ica, using scanning electron microscopy, X-ray diffractometrytion conrmed it has a high specic surface area and is amor-tion the purity of the extracted protein,measured as the ratio, increased from 0.5 to above 2.0. Our results could facilitatef geothermal powerplants as chromatographic material.

2013 Elsevier Ltd. All rights reserved.

face area, whichmakes the SiO2 a suitable candidate forand catalytic applications.

H.G. Svavarsson et al. / Geothermics 50 (2014) 3034 31

been described. In both cases the precipitation conditions had tobe controlled. The use of natural SiO2 modied with organosilicatematerials, as a chromatographic material has also been discussed(Tarasevich et al., 1990).

1.2. Chrom

Silica gematographifrom a mixsis of basicet al., 2001silica derivathetic chromreaction ste(Hoffmanncuss the chsilica. A com

1.3. Phycoc

The Blueits unique1997; Petugeothermalperature remCyanobactemicrobial etosyntheticprotein thasory pigmenin blue-grethe algaesteins haveaddition toing applicatand macromorant in fowhich are oto exhibit bchoice as anever, the usthe appropated as the280nm (A6C-PC and A0.7 is consi4.0 analyticpossible apthe high coused for puincludepreltration ch(Rito-Palommated at 5Thus, improsignicantheat and liatures abovconstraintsIn the experSiO2 precipan alternatifrom the coSiO2 powdethe C-PCwa

constituents (such as chlorophyll). The attached C-PC was releasedfrom the SiO2 adsorbent by washing with deionized water.

2. Experimental conditions

gae c

e-gremi-cC atnd.ol CewaspHringt% drmogHz (Soff.

min.) wa

rom

maed olt (rea anma

he seessud mawas

the BC fSEMnd B(MicThetion

otein

diffpplieus pr

Methsilicaackehe c2.1soluh thas eessung of

Methsilicae crcomd thctionn (apntrifatographic silica

l (SiO2xH2O) is widely used as an adsorbent in chro-c columns for isolation and purication of compoundsture. One of the most common methods for the analy-pharmaceuticals is liquid chromatography (McKeown), which conventionally relies on synthetic silica andtives as the stationary phase. The production of syn-atographic silica typically involves several chemical

ps followed by a series of after-treatment processeset al., 2006; Zhang et al., 2009). In this paper we dis-romatographic application of unmodied geothermalparison to sintered geothermal silica is also made.

yanin

Lagoon is a specic geothermal biotope known formicrobial ecosystem (Petursdottir and Kristjansson,rsdottir et al., 2009). It contains about 6000m3 ofuid that is replenished every 40h. The lagoons tem-ain constant at381 C. Thecoccoidblue-greenalgae,

rium aponinum, one of the dominating species in thecosystem, is used in this research. A water-soluble pho-pigment in blue-green algae, Phycocyanin (C-PC), is at belongs to a family of phycobiliproteins. It is an acces-t to the green-colored pigment chlorophyll, also found

en algae. Together they are an essential component oflight harvesting system (McCall, 1998). Phycobilipro-in common a similar three-dimensional structure intheir hydrophilic nature. Among the many interest-ions of C-PC is its use as a uorescent marker of cellsolecules (Ramos et al., 2010) and as a natural col-

od and cosmetic products, replacing synthetic dyes,ften unsafe or even toxic. C-PC has also been shownio-activity (Eriksen, 2008) which makes it an excellentadditive in food and pharmaceutical products. How-

e of C-PC in these products is dependent on obtainingriate grade of purity. The purity of C-PC can be evalu-ratio between the light absorbance at =620nm and20/A280), where A620nm is the maximum absorbance of280nm is the total absorbance of proteins. A purity ofdered food grade, 3.9 reactive grade and greater thanal grade (Rito-Palomares et al., 2001). Despite themanyplications of phycobiliproteins, their use is limited byst of extraction and purication. Most of the methodsrication of C-PC involve a sequence of operations thatcipitation, centrifugation, dialysis, ion-exchange andgelromatography and chromatography on hydroxyapatiteares et al., 2001). The purication cost has been esti-090% of the total production cost (Patil et al., 2006).vements in the purication procedure can lead to a

reduction in the production cost. C-PC is unstable toght in an aqueous solution and denatures at temper-e 45 C (Jespersen et al., 2005). This instability putson the possible processing methods that can be used.iments described in this paper, unmodied geothermalitated from Blue Lagoon geothermal uid was used asve to other chromatographic materials to extract C-PCccoid blue-green alga, cyanobacterium aponinum. Whenrwas soaked in a saline solution of a ruptured cellmass,s selectively adsorbed in contrast to other hydrophobic

2.1. Al

Bluin a seat 45

in Icelamass/vnationA xedrate du12.2wwas hoat 20kand 3 sfor 10extract

2.2. Ch

Rawconsistmal saBL-silicplasmafrom tat a prcrusheBL-salttics ofat 1000scope (area awidthlyzer).diffrac

2.3. Pr

Twowere awe foc

2.3.1.BL-

were p5 cm. TSectionBL-saltthrougC-PC wThe prpumpi

2.3.2.BL-

with thwas action an(see Sesolutiothen ceultivation

en algae, isolated from theBlue Lagoon,were cultivatedontinuous mode in a 1.2m3 tubular photobioreactorthe Blue Lagoon Research and Development CenterThe cultivation media was geothermal uid with 0.3%ll-hi WP nutrient from Varicon Aqua Solutions. Illumi-providedbyahighpressure sodium light (160E/m2/s).of 7.5 was maintained by regulating the CO2 gas feedgrowth. At harvesting, the algae suspension containedy weight of algae. A 360ml volume of the suspensionenized for 10min using a 900W ultrasonic cell crusherYJ900-D from Sharpertek) with a duty cycle of 2 s onSubsequently, the solution was centrifuged at 3200 gA 288ml volume of supernatant (referred to as crudes obtained and collected.

atographic silica

terials used for the chromatographic recovery of C-PCf geothermal SiO2 (referred to as BL-silica) and geother-ferred to as BL-salt). The chemical composition of thed the BL-salt was determined by inductively coupledss spectrometry (ICP-MS). The BL-silica was removeddimentation tank and pumped into a ltration pressre of 2bar. The resulting lter cake was dried at 60 C,nually and sieved. After removal of the BL-silica, theprepared by drying the supernatant. The characteris-L-silica (ground in a mortar), before and after sinteringor 2h,was determined using a scanning electronmicro-) andbymeasuring the specic surface area (BET), t-plotarrettJoynerHalenda (BJH) average adsorption poreromeritics TriStar 3000 surface area and porosity ana-mineralogy of the BL-silica was determined by X-rayanalysis (XRD: Bruker AXS).

extraction

erent approaches for adsorptionand subsequent elutiond; method 1 andmethod 2. In the following discussion,imarily on the latter procedure.

od 1agglomerates, ranging in size from 0.2 to 0.7mm,

d in a 30 cm tall plexiglas column with a diameter ofolumn was loaded with 190ml crude extract (seeabove) at a pressure of 0.4 bar. Afterwards, 2.2 l oftion (25wt% BL-salt in deionized water) was pumpede column to ush the chlorophyll. Subsequently theluted using a continuous ow of 2.0 l deionized water.re was gradually increased from 0.4 to 0.6 bar duringthe BL-salt solution and the eluent.

od 2that passed through a 125mmesh screen was mixedude extract and a BL-salt solution. The C-PC dischargeplished batchwise by alternating cycles of centrifuga-e addition of deionized water. A 100ml crude extract2.1 above) was mixed with 10ml of saturated BL-saltproximately 0.36g salt perml) and 20g of BL-silica anduged. The supernatant was discarded and the sediment

32 H.G. Svavarsson et al. / Geothermics 50 (2014) 3034

was slurrieand 10ml ostep of slurdeionizedwtainingelutextraction ation valuesthe crudeexspectrophothe A620nm/

Methodssilica, insteaof the silica

3. Results

3.1. Protein

The procin chronolophyll owsstationary Ba net 3-folddue to comeluent. Condecreased t

eparathe lol of bl deio

oncentration of C-PC (dashed line) and C-PC purity (solid line) as a function

Table 1Surface charac

BL-silica

UnsinteredSinteredFig. 1. A ow sheet of the C-PC extraction process.

d in 50ml of saline solution (40ml of deionized waterf saturated BL-salt solution) and centrifuged again. Thisrying the sediment and centrifuging was repeated withater indiscrete volumesof 10ml. The supernatant, con-edC-PC,wascollectedafter eachstep.Aowsheetof the

Fig. 2. Sstage ofwith 2.2with 2.0

Fig. 3. C

nd the purication process is shown in Fig. 1. Absorp-and absorbance spectra of the supernatant (eluent) andtractweremeasuredusingaUVvisibleCamspecM350tometer. The purity ratio (PR) of the C-PC was taken asA280nm ratio.1 and 2 were repeated with sintered (1000 C/2h) BL-d of unsintered silica, uponwhich the binding capacitywas completely lost.

and discussion

extraction method 1

eeding of the columns loading and elution is visualizedgical order in Fig. 2. As seen, the green colored chloro-through the column while the C-PC is retained at theL-silica. A good separation of C-PC was obtained, withincrement in the PR. The column, however, degradedpression of the agglomerates during pumping of thesequently the ow rate through the column graduallyo 4ml/min which is impractically low. The possibility

of eluent volu

of using thmatographstrengthenloss of perfface area frocome by emmatrix, but

3.2. Protein

The concet al., 2008and 652nm

CCPC = (A6A graph

is apparentand puritylinearlywit

teristics of the BL-silica.

BET spec. surf. area[m2/g]

Micropore surf.area t-Plot [m2/g]

50 61 0.3tion of C-PC at different stages in chronological order: (a) at earlyading, (b) after loading with 190ml crude extract, (c) after ushingrine solution (25% BL-salt in deionized water), and (d) after elutionnized water.me.

e geothermal SiO2 as a stationary phase in the chro-ic column requires further evaluation. An attempt tothe SiO2 agglomerates with sintering resulted in a totalormance accompanied by a decrease of its specic sur-m60 to 1m2 (see Table 1). This problemmight be over-bedding the unsintered SiO2 agglomerates in a rigidsuch speculations are beyond the scope of this paper.

extraction method 2

entration of C-PCwas determined using Eq. (1) (Mishra), where A620 and A652 are the absorption values at 620, respectively.

20 0.474A652)/(5.34)[mg/ml] (1)ical interpretation of the result is given in Fig. 3. Itfrom the gure that the shapes of the concentrationcurves resemble each other. Both lines rise roughlyh increasingeluentvolumeup to140ml.Athighervol-

Vol. of pores with diameter1.7300nm [cm3/g]

BJH adsorption av.pore width [nm]

0.24 230.001 N/A

H.G. Svavarsson et al. / Geothermics 50 (2014) 3034 33

Fig. 4. Absorption spectra for algae extracts of differentpurity: crudeextract (dottedline), collection #1 (dashed line), and collection #2 (solid line).

umes the concentrationdecreases throughout the elutionwhile thepurity line attens out rather abruptly at volumes above 200ml.The maxima of the PR, 2.0, and the CC-PC, 6.3mg/ml, appear atthe same eluent volume (140ml). As always, there is a trade-offbetween the purity of the protein and its recovery rate. Severaldifferent batches were collected. The 10ml volume with the high-est purity will be referred to as collection #1. The volume fractionswith PR1.0were later combined,making a total volume of 117ml(collection #2) with 4.9mg/ml C-PC and a PR of 1.3, which corre-sponds to31% recoveryof theC-PC. Combining thevolume fractionsbetween 40 and 250ml resulted in a PR of 1.0 and 50% recovery(collection #3). Absorption spectra, in the range of 250700nm, ofcollections #1 and #2, are shown in Fig. 4. A spectrum of the crudeextract is shown for comparison.

Fig. 5. X-ray diffraction pattern of BL-silica before (black solid line) and after sin-tering at 1000 C for 2h (red dotted line).

The PR and CC-PC values for the crude extract are between 0.46and 18.2mg/ml, respectively. It therefore contained 1.800mgC-PC (100ml18.2mg/ml) whereas the area under the mea-sured concentration curve (Fig. 3.) corresponds to 1100mg. Thisequals to a total recovery of 61% ((1.1/1.8)100%). A higher BL-silica/crude-extract ratio might increase the recovery rate of theC-PC but most likely at the expense of its purity.

3.3. Morphology analyses of the chromatographic silica

Values of the specic surface area, micropore surface area, porevolume and average adsorption pore width of the BL-silica, beforeand after sintering are given in Table 1. Table 2 shows the chemicalcomposition of the BL-silica and the BL-salt.

Fig. 6. SEM improcess.ages at two different magnications of the BL-silica: (a) before sintering; and (b) after sintering. The inset in (b) shows crystals formed during the sintering

34 H.G. Svavarsson et al. / Geothermics 50 (2014) 3034

Table 2Chemical composition of BL-silica and BL-salt (wt%).

Component SiO2 Cl Na Ca K Mg Total

BL-silica 92.9 3.9 2.2 0.49 0.39