Pilot Scale Testing of Adsorbent Amended Filters under High Hydraulic Loads for Highway Runoff ...

14 Pages·2017·1.06 MB·English

water
Article
Pilot Scale Testing of Adsorbent Amended Filters
under High Hydraulic Loads for Highway Runoff in
Cold Climates
CarlosMonrabal-Martinez*,AamirIlyasandToneM.Muthanna
DepartmentofCivilandEnvironmentalEngineering,NorwegianUniversityofScienceandTechnology,
7491Trondheim,Norway;[email protected](A.I.);[email protected](T.M.M.)
* Correspondence:[email protected];Tel.:[phone]
AcademicEditor:GlennBrown
Received:2January2017;Accepted:19March2017;Published:22March2017
Abstract: This paper presents an estimation of the service life of three filters composed of sand
andthreealternativeadsorbentsforstormwatertreatmentaccordingtoNorwegianwaterquality
standards for receiving surface waters. The study conducted pilot scale column tests on three
adsorbentamendedfiltersfortreatmentofhighwayrunoffincoldclimatesunderhighhydraulic
loads. The objectives were to evaluate the effect of high hydraulic loads and the application of
deicingsaltsontheperformanceofthesefilters. Fromprevioustheoreticalandlaboratoryanalysis
granulatedactivatedcharcoal,pinebark,andgranulatedolivinewerechosenasalternativeadsorbent
materialsforthepresenttest. Adsorptionperformanceofthefilterswasevaluatedvis-à-visfour
commonly found hazardous metals (Cu, Pb, Ni and Zn) in stormwater. The results showed that
thefilterswereabletopasswaterathighinflowrateswhileachievinghighremoval. Amongthe
filters,thefiltersamendedwitholivineorpinebarkprovidedthebestperformancebothinshortand
long-termtests. TheadditionofNaCl(1g/L)didnotshowanyadverseimpactonthedesorptionof
alreadyadsorbedmetals,exceptforNiremovalbythecharcoalamendedfilter,whichwasnegatively
impacted by the salt addition. The service life of the filters was found to be limited by zinc and
copper,duetohighconcentrationsobservedinlocalurbanrunoff,combinedwithmoderateaffinity
withtheadsorbents. Itwasconcludedthatboththeolivineandthepinebarkamendedfiltershould
betestedinfull-scaleconditions.
Keywords: stormwater runoff; alternative adsorbents; pilot scale; hydraulic loading; adsorption;
servicelife;toxicmetalremoval
1. Introduction
Infiltrationbasedsolutionshavebeenshowntobeanefficientmethodfortreatinghazardous
substances from stormwater in urban areas [1–4]. These solutions include different forms and
functions, depending on the area of application, such as rain gardens, bioretention swales, and
infiltrationtrenches,etc. Infiltrationbasedstormwateroptionsaimtorestore/mimicpre-development
conditions[5]byreducingrunoffvolumes,trappingsediments,andmitigatingpeakflowrates.Insome
cases, infiltrationbasedsystemsarealsodesignedtoremovedissolvedcontaminantsbyaddinga
specificadsorbentlayer[6],orrelyingoncombinedeffectsofplantsandsoils—bioretention[7]. Heavy
metalsarefoundinurbanrunofffrommultiplenonpointsourcessuchasvehiclecomponentswear,
exhaustemissions,lubricants,andgalvanizedelementsalongroads,amongothers[8]. Thepresenceof
thesemetalsvaryinbothspatialandtemporalresolution,aswellasphase(particulateanddissolved
forms). Itisthelatterformthatisthemostbioavailableandhazardousforbiota[1,9].
Water2017,9,230;doi:10.3390/w9030230 www.mdpi.com/journal/water
Water2017,9,230 2of14
Awiderangeofmaterialshavebeenidentifiedandtestedfortheirperformanceforremovalof
heavy metals [10], nutrients [11], and organic contaminants [12], among others. These adsorbents
materialsincludesecondarywastes,minerals,andbiologicalmaterials.Generally,adsorptionprocesses
aredependentonthespecificsurfaceareaofthematerial,whichincreaseswithdecreasingparticle
size. However, adecreaseintheparticlesizeleadstoalowerhydraulicconductivityofthefilters.
Instormwatersolutionsthataredesignedforacertainallowableponding,suchasbioretentionareas,
wetlands,anddetentionponds,alowerhydraulicconductivityandlargersurfaceareacanbeadequate
given the pooling capacity of such facilities. On the other hand, in areas close to road surfaces or
systemswithnopondingcapacity,therunoffmustbeinfiltratedasquickaspossibleforsafetyissues.
Therefore,highhydraulicconductivityisanimportantdesignfeaturetoallowforahighhydraulic
loading. Thisfavorsadsorbentswithalargerparticlesize.
Fortheenduser,theservicelifeoftheinfiltrationbasedfacilityisalsohighlyrelevant,because
it is an important factor in the selection decision. The service life of an adsorbent/filter is mainly
determinedbyacombinationofpollutantconcentrationintheeffluent,pollutantaccumulationin
thefilter,andlossofinfiltrationpotentialduetoclogging[13]. Severalstudieshavebeenundertaken
toquantifytheservicelifeofthefiltersfromthepollutionperspective[13–16]. Batchstudiesmight
beusedtopreselectpotentialadsorbentsbasedonadsorptioncriteria. Generally,isothermmodels
areadoptedtofitexperimentalbatchdata. However,thesemodelsaremeantforgasadsorptionon
solidsurfaces,whichdiffersfromsolution-solidconditionsoccurringininfiltrationbasedsystems.
Additionally,assumptionsmadebyisothermmodelswillintroduceuncertaintieswhendetermining
adsorption capacities of adsorbents. In contrast, column studies, which are also laboratory based
tests, can best reproduce field conditions of varying inflows, increasing liquid to solid ratios over
time,andinducingdynamicconditions. Breakthroughcurvesobtainedfromcolumnstudiescanhelp
determinethevolumeofwatertreatedbeforethefilternolongercanmeetacertainpollutantremoval
intheeffluent. Ontheotherhand,highintensityinflows,freezing-thawingcycles,andapplicationof
deicingsaltsaregenerallyignoredduringtheevaluationoftheperformanceofthesefilters,whichcan
affecttheadsorbentperformance. Consequently,thisposesanobstacleforanappropriatedesignof
infiltrationbasedfacilities.
Thisstudyevaluatedthreefilterscomposedofsandandthreealternativeadsorbents(pinebark,
olivine, and charcoal) in a pilot scale column study under high hydraulic loads. The adsorbents
wereidentifiedinapreviousstudy,whichusedmulticriteriaanalysisandbatchteststoevaluatethe
upscalingpotentialofeightadsorbentmaterials[17]. Inthefirstphaseofthestudy,theinfluenceof
highhydraulicloadsaswellasdeicingsaltsoverthepollutantretentionwasevaluated. Inthesecond
phase,thelong-termperformancewasstudiedinordertoobtaindataforestimatingtheservicelifeof
thematerials.
2. MaterialsandMethods
2.1. AdsorbentMaterials
Alltheadsorbentmaterialsandthesand(Table1)wereobtainedbycommercialsupplierslocally.
Thegranulatedactivatedcharcoal(extractedfromanthracitecoal)wasaSigmaAldrichASproduct
(Oslo,Norway),thesandwasmanufacturedbyRådasandAB(Lidköping,Sweden),thepinebark
PinusSylvestriswasprovidedbyNittedalTorvindrustrieAS(Bjørkåsen, Norway), andtheolivine
wassuppliedbySibelcoNordicAS(Rud,Norway)andbelongstotheBlueguard®series. Charcoal
andolivinewereusedwithoutanychemicalprocessingormodification. While,pinebarkwassieved
<4mmparticlesizepriortouseinordertofavorwaterretention. Theadsorbentswereplacedinpilot
scalecolumnswithcleanquartzsand,whichwasselectedforitsuniformparticlesizeandlittleorno
backgroundcontamination. Therefore,theinfluenceofthesandonthehydraulicconductivityand
removalperformancewasassumedhomogeneousthroughoutthestudy.
Water2017,9,230 3of14
Table 1. Material properties of the sand and adsorbents used in the study. UC stands for
uniformitycoefficient.
Parameter Sand Olivine Charcoal PineBark
ParticleDensityα(g/cm3) 2.66 3.12 1.91 -
MaxDryDensityβ(g/cm3) 1.77 - - -
Bulkdensity(g/cm3) 1.48 1.62 0.44 0.24
D γ(mm) 0.65 1.93 1.83 -
90
D γ(mm) 0.403 1.53 1.33 -
60
D γ(mm) 0.183 0.903 0.73 -
10
UC(D /D ) 2.22 1.66 1.85 -
60 10
BETSurfaceAreaδ(m2/g) 0.564 4.264 881.964 0.444
Notes:αDatafromthepresentstudyobtainedwithpycnometertest;βDatafromthepresentstudyobtainedwith
proctorcompactiontest;γDatafromthepresentstudyobtainedfromparticlesizedistributioncurves;δDatafrom
thepresentstudyobtainedwithBrunauer-Emmett-Teller(BET)test.
2.2. ColumnTests
Theadsorbentsweretestedforremovaloffourdissolvedmetals(Cu,Pb,Ni,andZn)commonly
foundinurbanandhighwayrunoffandofenvironmentalconcernforofficialauthoritiesduetotheir
toxicitytowardsthebiotainthereceivingwaterbodies. Forthecolumntests,syntheticstormwater
waspreparedinalargetank(1m3)bymixingtapwaterwithastocksolutioncontainingthemetals.
Metalchloridesaltswereusedforpreparingthestocksolution,andwerechosenfortheadditional
benefitofsimulatingsaltsinstormwater. Ontheotherhand,tapwatercontainsothermajorions(Na+,
Ca2+,etc.),whichmakesitarealisticsurrogateforactualstormwater(Table2). Thetargetmetalswere
addedinaquantitytoachieveintendedconcentrationof1mg/Lforeachmetalinthe1m3influent
tank. Thereasonbehindthishighconcentrationswastobeabletoobtaindetectableconcentrations
intheoutflowandearlybreakthroughsbecausehighadsorptionwasexpectedinthefilterbasedon
priorbatchtests[17]. ThepHofthesyntheticstormwaterwasapprox. 7.5,whichissimilartovalues
observedinlocalurbanrunoff.
Table2.Majorconstituentsinthetapwater.
Parameter Concentration(mg/L)
Calcium 21.7
Sodium 4.45
Magnesium 0.89
Potassium 0.45
Chloride 7.46
Sulphate 2.5
Plexiglascolumnswith45cmlengthand10cmdiameterwereconstructedandusedinthestudy.
The columns were filled with 35 cm sand overlying 5 cm of adsorbent (see Figure 1). Adsorbent
placementatthebottomwillprotectthematerialfromeventualfrostanderosion. Inaddition,bottom
placementforpinebarkmeanslessoxidationproblemsaslowerzoneswillremainwetterwithlower
O availability. Thelength(40cm)representsminimumrecommendeddepthforbioretentionfacilities
2
inNorwegianclimate[18],wherethesefiltersmightpotentiallybeused.
Three columns were set up for each filter media including a control column that was packed
onlywithsand. Allcolumnswereoperatedatroomtemperature(20±2◦C)andthetapwaterused
toproducethesyntheticstormwaterwasat8±2◦C.Multichannelperistalticpumpswithvariable
flowwereusedforpumpingthesyntheticstormwater. Theflowrateswerebasedonthesaturated
hydraulicconductivity(K )ofeachfilter,whichhasbeeninvestigatedseparately[19]. Therefore,full
sat
infiltrationatthelargestpossibleinflowratewasintendedwithnovisiblepondingwater.
Water2017,9,230 4of14
Water 2017, 9, 230 4 of 14

Figure 1. Schematic overview of the column setup with adsorbents placed at the bottom.
Figure1.Schematicoverviewofthecolumnsetupwithadsorbentsplacedatthebottom.
The study was divided in two phases. In the first phase flow rates, supplied by the peristaltic
Thestudywasdividedintwophases. Inthefirstphaseflowrates,suppliedbytheperistaltic
pumps, were controlled and set at the Ksat of each filter. The objective was to verify the adsorption
pumps,werecontrolledandsetattheK ofeachfilter. Theobjectivewastoverifytheadsorption
capacity of the filters under high hydrausaltic loads, specifically under the largest inflow rate that is
capacity of the filters under high hydraulic loads, specifically under the largest inflow rate that
expected to not generate water ponding. The experimental columns were continuously run for
is expected to not generate water ponding. The experimental columns were continuously run for
approx. 14 h, and each column received a water volume of approx. 50 L (liquid to solid ratio LS = 11).
approx. 14h,andeachcolumnreceivedawatervolumeofapprox. 50L(liquidtosolidratioLS=11).
After passing this volume of water, one of the two duplicate columns for each media was taken aside
Afterpassingthisvolumeofwater,oneofthetwoduplicatecolumnsforeachmediawastakenasideto
to study the effect of road salt on the desorption of already immobilized metals. For the salt
studytheeffectofroadsaltonthedesorptionofalreadyimmobilizedmetals. Forthesaltexperiment,
experiment, the columns were initially fed with approx. 50 L (LS = 11) of plain tap water, and then
thecolumnswereinitiallyfedwithapprox. 50L(LS=11)ofplaintapwater,andthenwiththesame
with the same amount of a solution composed of tap water with 1 g/L NaCl. The concentration of
amountofasolutioncomposedoftapwaterwith1g/LNaCl. TheconcentrationofNaClwasbased
NaCl was based on common concentrations found in highway stormwater in Norway, similar to the
oncommonconcentrationsfoundinhighwaystormwaterinNorway,similartothevalueadopted
value adopted by previous studies [20]. In the second phase, long-term operation was the objective,
bypreviousstudies[20]. Inthesecondphase,long-termoperationwastheobjective,andthestudy
and the study continued in each of the remaining columns for 2.5 months (Table 3). Samples were
continuedineachoftheremainingcolumnsfor2.5months(Table3). Sampleswerecollectedbiweekly
collected biweekly from the effluents of every column and analyzed for the target metals. After the
fromtheeffluentsofeverycolumnandanalyzedforthetargetmetals. Afterthecollection,pHand
collection, pH and electroconductivity of the samples were measured, then samples were filtered
electroconductivityofthesamplesweremeasured,thensampleswerefilteredthrough0.45µmpore
through 0.45 µm pore membrane filters for analyzing dissolved fraction of the studied target metals,
membranefiltersforanalyzingdissolvedfractionofthestudiedtargetmetals,andpreservedwith0.1M
HanNdO preasceidrv.eSda mwpitlhes 0w.1e Mre sHtoNreOd3 aatc4id◦.C Saumntpilleths ewaenrael ystsoisrewdi taht a4 h°iCg hurnetsilo ltuhtei oannianlydsuisc twiviethc oau philgedh
resolu3tion inductive coupled plasma HR-ICP-MS instrument from Thermo Fisher Scientific AS (Oslo,
plasmaHR-ICP-MSinstrumentfromThermoFisherScientificAS(Oslo,Norway). Eachindividual
Norway). Each individual sample was scanned three times and the results were corrected for blank
samplewasscannedthreetimesandtheresultswerecorrectedforblanksamples. Thequantification
samples. The quantification detection limits for Ni, Zn, Cu and Pb was 0.015, 0.025, 0.03, and 0.002 µg/L,
detectionlimitsforNi,Zn,CuandPbwas0.015,0.025,0.03,and0.002µg/L,respectively.
respectively.
Table3.Averagevolumepercolumn(AV)andhydraulicloadingrate(HLR)usedduringthetwophases
Table 3. Average volume per column (AV) and hydraulic loading rate (HLR) used during the two
ofthestudy.CRTstandsforcolumnrunningtime.
phases of the study. CRT stands for column running time.
IInnfflluueennttT Typyepe ExEpxepreimriemnetnPht aPshease AAVV(L ()L) HHLLRR ((ccmm//hh)) CCRRTT ((DDaayyss))
SSyynntthheettiiccs stotormrmwwataetrer 1 1 5050 4477 00..66
SSaallttw waatetrer 1 1 5050 4477 00..66
Syntheticstormwater 2 2500 18.8 73
Synthetic stormwater 2 2500 18.8 73
SSiimmiillaarr ccoolluummnn ssttuuddiieess ooff mmeettaall aaddssoorrppttiioonn aanndd nnuuttrriieenntt rreemmoovvaall aarree ffoouunndd iinn tthhee lliitteerraattuurree
((TTaabbllee 44)).. IInn tthhiiss ssttuuddyy,, lloonngg--tteerrmm ddaattaa wwaass nneeeeddeedd ttoo eexxpplloorree tthhee eexxhhaauussttiioonn ccaappaacciittyy ooff tthhee ssttuuddiieedd
fifilltteerrss bbeeccaauussee iinnppuutt ccoonncceennttrraattiioonnss wweerree llooww iinn ccoommppaarriissoonn ttoo tthhee ootthheerr ssttuuddiieess.. OOnn tthhee ootthheerr hhaanndd,,
hhiigghh hhyyddrraauulliiccr raatetessw wereereu suesdedto tsot ustduydtyh ethree mreomvaolvcaalp caacpitaycoitfyt hoef stehfiesltee rfsiltuenrds eurnidnteern isneteinnflseo winrfalotews
wraittehs ewxpitehc etexdpeloctweder locownetra cctotnimtacets twimitehs twheitfihl tthere. filter.
Water2017,9,230 5of14
Table 4. Experimental characteristics of similar column studies. AV stands for average volume
per column, HLR for hydraulic loading rate, CRT for column running time, IC stands for input
concentration,MDformediadepth,CDforcolumndiameter,andTPfortargetpollutants.
HLR CRT
AV(L) IC(mg/L) MD(cm) CD(cm) TP Reference
(cm/h) (Days)
120 70.8 27 5–16 23 1.8 MTBE,Naphthalene,Zn [15]
480 10 90 1 20 5.08 Cd,Cu,Pb,Zn [13]
300 - 70 0.004–0.28 800 37.7 Cd,Cu,Pb,Zn [21]
158 124 30 2.5–5 40 2 Cu,Ni,Zn [22]
300 4.1 183 0.048–0.6 31 31 Zn,Cu,Pb,Cd [23]
9 1.06 2 0.08–0.6 3.5 1.9 Zn,Pb,Zn [14]
2550 18.8 133 1 40 10 Zn,Pb,Ni,Cu Thisstudy
2.3. HydrologicalPerspective
Inordertorelatethesimulatedflowsbacktothedimensionofthestormevents,thefollowing
hydraulicapproachispresented. Thisapproachisconnectedtothefirstphaseoftheadsorptionstudy,
inwhichtheinfluentratewasadjustedtomatchtheK ofeachofthemedia.
sat
Inthelaboratorysetup(Figure1), thecolumnactsasaninfiltrationbasedsystem(P)andthe
pumped water from the tank represents the urban runoff from impervious surfaces (I). The ratio
betweenimpervioustoperviousarea(I/P)isoftenusedtosizesuchfilters[24,25]. Inareaswithahigh
percentageofimpervioussurfacessuchasroads,sidewalks,roofs,etc.,anempiricalrunoffcoefficient
(C)closeto1canbeassumed.
Equation(1),whichisbasedontherationalmethod,allowsforcalculatingtheidealstormintensity
(SI)in(mm/h)thatwillgeneratetheHLRin(mm/h)appliedonthecolumnsthroughtheperistaltic
pump. Foracertainhydraulicload,theintensityofthestormeventisindirectlylinkedtothesizeof
thefictitiouscatchmentfeedingthecolumns(I).
HLR
SI= (1)
C·I/P
2.4. ExpectedServiceLife
Theresultsfromthesecondphasewereusedtoestimatecumulativeadsorptioncapacitiesofthe
differentadsorbentamendedfiltersforthetargetmetalsunderthegivenconditions. Thecumulative
adsorptionforeachmetal,q(mg/kg),wasobtainedfromEquation(2).
(cid:82)Vd(Ci−Ce)·dV
q= 0 (2)
M
where Ci is the influent concentration (mg/L), Ce is the effluent concentration (mg/L), Vd is the
cumulative volume passed until a certain % removal (L), and M is the amount of material in the
filter(kg).
Expectedcumulativepollutantretention(mg)wasobtainedastheproductoftheareaofthefilter,
density,filterdepth,andqattherequiredremoval. Expectedpollutantinputload(mg/year)was
obtainedastheproductoftheaveragedissolvedpollutantconcentrationmeasuredatlocalstreets,
annualprecipitationdepth,areaofthetributarycatchment,andavolumecapturefactorof0.9,basedon
internationaldesignguidelines. Theexpectedservicelife(years)wasobtained,dividingtheexpected
cumulativepollutantretentionatarequiredremovalbythepollutantloadexpectedtobetreatedby
thefiltrationfacility.
Water2017,9,230 6of14
3. ResultsandDiscussion
Water 2017, 9, 230 6 of 14
3.1. ControlofFlowrate,FirstPhase
3. Results and Discussion
Inthisphase,flowratewascontrolledandfrequentsamplingperformedtocollectenoughdata
toeva3l.1u.a Cteontthroel pofe Frfloowrmrataen, Fceirsitn Pthhaeses horttermofthedifferentfiltersunderhighhydraulicloads.
In this phase, flow rate was controlled and frequent sampling performed to collect enough data
3.1.1. MetalRemovalbyAdsorbentAmendedFilters
to evaluate the performance in the short term of the different filters under high hydraulic loads.
Figure2presentsthepercentageremovalofthefourtargetmetals,bythreeadsorbentamended
3.1.1. Metal Removal by Adsorbent Amended Filters
filtersforstormwater,asafunctionofporevolumeofsyntheticstormwaterpassedthroughthefilter.
InthisstuFdiyg,uoren e2 pproerseenvtosl tuhme peeerqceunatlaegde troem16o0v0alc omf 3thaep fpouror xta.ragnedt mcoertarelss,p boyn tdhreede taodsthorebvenotl uammeenodcecdu pied
byvofiildtesrisn foar csteorrtmaiwnactoerl,u ams an f.uIntcvtiaorni eodf pfororem vocloulmume onf styoncthoelutimc sntobrmecwaautseer poafsdseidff ethreronutgmh athtee rfiialtlesr,. bulk
In this study, one pore volume equaled to 1600 cm3 approx. and corresponded to the volume occupied
densities and different porosities. From the curves in Figure 2, it is clear that all of the adsorbent
by voids in a certain column. It varied from column to column because of different materials, bulk
amendedfiltershadaveryhighremovalrates(>99%incaseofPb)evenunderconsiderablehigh
densities and different porosities. From the curves in Figure 2, it is clear that all of the adsorbent
hydraulicloads. TherearesomefluctuationsandvariationsintheadsorptionbehaviorofCuandZn
amended filters had a very high removal rates (>99% in case of Pb) even under considerable high
bothonthepinebarkandtheolivineamendedfilter,whichcouldbeduetovariableflowpatterns
hydraulic loads. There are some fluctuations and variations in the adsorption behavior of Cu and Zn
insideboththe ognr atvhiet ypibnaes beadrkfi latnerd. tThhee oglievnintlee aimncernedaesdin fgiltterre,n wdhfiocrh rceomulodv bael odfuteh teos evatwriaobmle efltoawls poanttpeirnnes bark
andoinlisvidinee thpeo ginratsvittoy tbiamseedd feilpteern. dTheen cgyenotflea idnscorerapstiinogn trreenadc tfioorn rse.mHoovwal eovf ethr,eisne ctwono tmraesttaltso oPnb p,iCneu and
Zn,thbearrke manodv oallivoifnNe piodiindtsn too ttifmolel odweptehnedesnamcye opf aadttseorrnptiinonth reeaccatisoenos.f Hthoewfielvteerr, ainm ceonndtreadst wtoi tPhb,c Chaur coal.
Thedaencdre Zanse, tohfeN reimreomvaolv oafl Nwii tdhidin ncoret afosilnlogww thaete srapmaes speadttienrnd iicna ttehse tchaaste Nofi thhaes failtreerl aatmiveenldyeldo wwiathffi nity
forthcehacrhcaoraclo. Tahl,ea dnedcrweaisteh oifn Ncrie raesminogvavl owluithm iencorfeapsainssge wdawtear tpearstshede cinodmicpateetsi ttihoant Nfoir htahse as rietelastimvealyy also
low affinity for the charcoal, and with increasing volume of passed water the competition for the sites
haveincreased. Nevertheless,withtheexceptionofcharcoalvis-à-visNi,thefluctuationsinremoval
may also have increased. Nevertheless, with the exception of charcoal vis-à-vis Ni, the fluctuations
ofmetals(±1%–2%)ontherestoftheadsorbentsweresmall,whichdemonstratesthatthepresented
in removal of metals (±1%–2%) on the rest of the adsorbents were small, which demonstrates that the
filterswouldperformrobustlyintheactualconditions.
presented filters would perform robustly in the actual conditions.
Pb Removal Zn Removal
100 100
al 98 al 95
v v
o 96 o
m Olivine AF m 90
e 94 e Olivine AF
R R
% 92 Pine Bark AF % 85 Pine Bark AF
Charcoal AF Charcoal AF
90 80
0 10 20 30 40 0 10 20 30 40
Pore Volume Pore Volume

Ni Removal Cu Removal
100
100
l al 95
a 80 v
v o
mo 60 Olivine AF em 90 Olivine AF
e R
% R 40 Pine Bark AF % 85 Pine Bark AF
Charcoal AF Charcoal AF
20 80
0 10 20 30 40 0 10 20 30 40
Pore Volume Pore Volume

Figure 2. Percentage removal of the four toxic metals as a function of pore volume. Note that the Y-
Figure2.Percentageremovalofthefourtoxicmetalsasafunctionofporevolume.NotethattheY-axis
axis is different in each case. AF stands for amended filter.
isdifferentineachcase.AFstandsforamendedfilter.
Water2017,9,230 7of14
3.1.2. DesorptionofMetalsDuetoSalts
Thecolumnswerefedwithsyntheticstormwatercontinuouslyforapprox. 14h(timetoreach
a liquid to solid ratio of 11), then one of the two replicate columns was taken apart to study the
influenceofsaltapplicationondesorptionofalreadyadsorbedmetals. Table5showstheresultsof
metalrelease(inpercentage)fromthecolumnsasafunctionofporevolume. Theresultsshowthat
thesalinesolutionhadvariableeffectsonthethreeadsorbentamendedfiltersandthefourmetals.
Asmallreleaseofmetals(<3%)wasobservedinmostofthefilters. Thisrelativelowreleaseindicates
thattheadsorptionwasstableandsaltswouldnothaveamajorinfluenceonthemetalreleaserates.
Thisfindingisinagreementwith[26], whichhaveshownthatNaClhasthelowestimpactonthe
desorptionofalreadymobilizedmetalscomparedwithotherstudieddeicers. Additionally,[20,27]
reportedthatmetalsadsorbedonsoilsdesignedforbioretentionwerescarcelyleachedduetoNaCl
applicationsand, therefore, retentionundercoldclimateconditionsislikelytobeeffectiveforthe
studied purpose. However, [28] detected a significant impact of salt addition on the removal of
dissolvedPbandCu,whichmightbeduetothefactthatthesaltfavorsdissolutionoforganicmatter
whichhasastrongaffinityofthesemetals. Inthepresentstudy,ahighreleaseofNi(9%–15%)fromthe
charcoalamendedfilterwasdetected. Thisbehaviormightbeduetothefactthatcharcoalhasbeen
foundtohavequitelowaffinityfortheNi,whichallowsNatoreplaceiteasilythroughionexchange.
Furthermore,bindingforcesofadsorbedcationsarealsodependentonhydratedradiusofthedivalent
ionsaswellasrelativeconcentrations,whichmeansthatsodium,duetosmallerhydratedradiusand
largerconcentrations,willfaceoptimalconditionsforreplacingadsorbedNi.
Thereleasebehaviorwithregardstothesamemetaldiffersfromadsorbenttoadsorbent. Asan
example,Ni,whichshowsanincreasingtrendbothinthecaseofthecharcoalandtheolivineamended
filter, is decreasing with increasing pore volume in the case of the filter amended with pine bark.
However,commonaspectsamongadsorbentsareobserved,forexample,extremelylowreleaseof
Pb. ThismightindicatethatPbisdifficulttoexchangebecauseofhavingsmallerhydratedradius
andhencebeingmorestronglyadsorbedtothesiteofthenegativecharge. Moreover,Pbmightform
innerspherecomplexeswiththechargesites, whichfurtherreducesthechancesofPbadsorption
reversingitself. Similarly,Ni,Zn,andCumobilizationfromtheolivineandthecharcoalamended
filterfollowagentleincreasingtrendwithporevolume. Thisshowsthattheirdesorptionisdependent
ontheexchangeprocesswithNa. Nonetheless,withtheexceptionofNi,thereleaseofmetalsfrom
all presented filters is below 3%, which is an encouraging aspect as this indicates that a minimal
environmentalimpactcanbeexpectedinfullscalesystems.
Table5. Percentagedesorptionoffourmetalsasafunctionofporevolumefromthreealternative
filters.Notethattheporevolumesaredifferentineachcase.NAstandsfornotavailableandAFfor
amendedfilter.
CharcoalAF OlivineAF PineBarkAF
Pore Pore Pore
Volume Pb Ni Cu Zn Volume Pb Ni Cu Zn Volume Pb Ni Cu Zn
(%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%)
2.8 <0.01 9.37 0.04 0.17 3.4 <0.01 0.06 0.41 0.20 2.7 0.02 2.15 0.23 2.78
8.6 <0.01 7.72 0.12 0.53 10.3 <0.01 0.07 0.27 0.21 8.2 0.03 2.62 0.35 2.72
14.3 0.01 5.57 0.09 0.32 17.3 0.01 0.23 0.49 1.89 13.7 0.04 1.73 0.34 1.39
20 0.01 15.26 0.11 0.49 24.2 0.02 0.26 1.13 2.02 19.2 0.02 1.19 0.24 1.43
25.8 0.03 9.65 0.11 0.36 31 0.01 0.34 1.06 2.09 24.6 0.04 2.06 0.31 1.65
31.5 0.01 11.64 0.14 0.41 38 NA NA NA NA 30.1 0.02 1.91 0.41 1.28
3.1.3. SimulatingStormEvents
Table6showsthat,inthecaseofthecharcoalamendedfilter,thehydraulicrateappliedtothe
columns corresponds with the runoff generated by a storm event with an intensity of 12 mm/h.
Thisstormintensityisslightlyhigherthanatwoyearreturnperiodandonehourdurationstormevent
inthecityofTrondheim(10.7mm/h). Inotherwords,ifthiseventfellinanimperviouscatchment
Water2017,9,230 8of14
50timesbiggerthanthefacility(I/P=50),itcouldbehandledbythisfilterwithoutponding. Onthe
otherhand,thefiltercomposedwithpinebarkandsandwouldonlybeabletomanagecompletelya
stormintensityof8.5mm/hforthesametributarycatchment. Thecloggingprocess,whichwillhave
anegativeimpactontheactualinfiltrationcapacityinafieldapplication,wasnotconsideredinthe
calculations. However,K values,whichwereusedtodimensionthesesystems,maycounterbalance
sat
thecloggingriskbecausethesevaluesrepresentaconservativeestimateofthepotentialinfiltration
rate[29].
Table6.Hydrologicalapproachusingformula1duringthefirstphaseoftheadsorptiontest.PSstands
forpumpspeed,HLRforhydraulicloadingrate,I/Pforimpervioustoperviousratio,SIforstorm
intensity,andAFforamendedfilter.Cistheempiricalrunoffcoefficient.
Filter PS(mL/min) HLR(cm/h) I/P SI(mm/h)ifC=0.9
CharcoalAF 72.2 55 50 12
OlivineAF 58.7 45 50 9.9
PinebarkAF 51.1 39 50 8.5
3.2. ControlofVolumes. SecondPhase
Inthisphase,highloadingwassimulatedbypassinglargevolumes(approx. 2500Lpercolumn)
tostudythelong-termperformanceoftheadsorbents.
MetalRemovalbyAdsorbentAmendedFilters
InFigures3–5,theresultsregardingremovalofthetargetmetalsoverincreasingporevolume
areshown. Lookingattheresults,completeexhaustionwasonlyobservedinthefilteramendedwith
charcoalforNi. Thefiltercomposedofcharcoalandsandshowedthelowestaffinityforthetarget
metals,whichisinagreementwithresultsfromasimilarstudy[26]. Incontrast,theolivineamended
filterwasstillachieving50%removalforallfourmetals.
Figure3showsthat,inthecaseofthefilteramendedwitholivine,theremovalcurvesofalltarget
metalsfollowanon-lineardecreasingtrend. TheremovalofPb,Ni,andZnshowsasharpdecrease
after1200porevolumes. Thismightindicatethatsphericalshapeallowstheinfluenttobypassthe
olivinesurfaces. Furthermore,sphericalshapeslimittheexposedsurface,whichasitbecomescovered
withmetalsstartstoreleasesomeintothesolution. Additionally,adsorptionanddesorptionmight
haveoperatedsimultaneouslyduetothelengthoftheexperimentaswellasfluctuationsintheflow
rate. Theuseofolivineasadsorbentfordissolvedmetalsisrelativelynew,andthenatureofitscharge
sites/surfacefunctionalgroups,andremovalmechanismsunderdifferentexperimentalconditions
havenotbeenfullyevaluatedyet. Therefore,toelucidatemainmetalremovalmechanismsofolivine
andtheirvariabilityinresponsetooperationalfactorswouldrequirefurtherdetailedinvestigation.
Inthecaseofpinebark(Figure4),theshapesofthecurvesforPb/CuandNi/Znaredifferent.
PbandCushowedahighremovalpercentage,83%and77%respectively,aftermorethan1500pore
volumes. However, Ni adsorption was close to exhaustion (Figure 4b), which would control the
operationallifeeventhoughitstillhasveryhighaffinityforuptakeofPbandCu. Asimilaradsorption
sequence for pine bark and the studied heavy metals have been previously reported in a batch
study[30].
Unliketheotheradsorbents,pinebarkhaslowersurfaceareabutachievedahighremovalof
metals. This can be attributed to different adsorption mechanism on pine bark, which has been
attributedtocompoundssuchaspectin,lignin,andtannin[31]thatprovidecarboxylic,phenolic,and
hydroxylgroupsfortheadsorptionofmetals. Ontheotherhand,pinebarkispronetoleachingof
some of these organic compounds and dissolved organic carbon (DOC), which can interfere with
theadsorptionprocessduetocomplexationofdissolvedmetalssuchasCuwithDOC[22]. Several
treatments have been reported in the literature to prevent the release of soluble organics, which
Water2017,9,230 9of14
can color and contaminate the effluent [32]. However, additional treatments can also reduce the
attractivenessofpinebarkamendedfiltersduetoincreasedcostsassociatedwithpre-treatmentand/or
post-treatmentdisposalofchemicals.
Forthecharcoalamendedfilter(Figure5),theremovalofmetals,withtheexceptionofCuand
Pb, decreased sharply within the first 200 pore volumes. For reduced adsorption of Zn and Ni as
comparedtotheothertwometals,variablebindingmechanisms,competitionfromothercationsand
Water 2017, 9, 230 9 of 14
Water 2017, 9, 230 9 of 14
dissolvedorganiccarbonintapwater,couldbetheprobablecause. Apreviousstudy[33]reportedthat
PbanddisCsoulvfeodr moregdancioc vcaarlebnont oinr statrpo wngatbero, ncdouslwd ibteh tbhieo psororbbaebnltes c.aHusoew. Aev perre,vNioiuasn sdtuZdny g[3e3n] erreaplolyrteadd sorb
dissolved organic carbon in tap water, could be the probable cause. A previous study [33] reported
that Pb and Cu formed covalent or strong bonds with biosorbents. However, Ni and Zn generally
onwethaakt ePlbe catnrods tCauti cfobrmineddin cgovsaitleens.t Tohr isstrkoinngd boofnbdisn wdiinthg bbieohsoarvbieonrtsc.a Hnorweseuvletri,n Nrie danudc eZdna gdesnoerrpaltliyo nfor
certaiaanddmssooerrbbta oolsnni fwwteheaaekkr eeeillseeccattrrcooosstmtaattpiicce tbbitiininoddniinnfggr o ssmiitteeoss..t hTTehhriissi okkniinsndd(i .ooeff., bbCiinnad2d+iinn).ggH bboeewhhaaevvviiooerrr , cctaahnne crreeossnuucllett niinntr arreetiddouuncceeoddf Ca2+
adsorption for certain metals if there is a competition from other ions (i.e., Ca2+). However, the
inouardssyonrpthtieotnic fsotro rcmertwaiant emrewtaalss sifu tbhsetraen itsia all ycolmowpettoitihona vferocmau ostehdera nioynss u(bi.es.t,a Cntai2a+)l. iHntoewrfeevreern, ctehein the
concentration of Ca2+ in our synthetic stormwater was substantially low to have caused any
adsorcpotnicoenntorfatmioent aolsf oCna2c+ hianr coouarl .synthetic stormwater was substantially low to have caused any
substantial interference in the adsorption of metals on charcoal.
substantial interference in the adsorption of metals on charcoal.
Olivine AF
Olivine AF
120
120
100
100
l 80
valova 80 Pb
om 60 Pb
% Rem% Re 464000 NNCuii
Cu
20 Zn
20 Zn
0
0
0 500 1000 1500 2000
0 500 1000 1500 2000
Pore Volume
Pore Volume

Figure 3. Percentage removal of the four metals by olivine amended filters as a function of pore
FigurFeig3u.rPee 3rc. ePnetracgenetraegme orevmaloovfatl hoef ftohuer fmouert amlsetbaylso bliyv ionleivainme eanmdeenddfiedlt efrilstearss aafsu an cfutinocntioofnp oofr epovroel ume.
volume. AF stands for amended filter.
AFstvaonldusmfeo. rAaFm steannddesd fofir latemr.ended filter.
Pine bark AF
Pine bark AF
120
120
100
100
valoval 8800 Pb
om 60 Pb
Rem% Re 6400 NNii
% 40 Cu
Cu
20 Zn
20 Zn
0
0
0 500 1000 1500 2000
0 500 1000 1500 2000
Pore Volume
Pore Volume

(a)
(a)
Figure4.Cont.
Water2017,9,230 10of14
Water 2017, 9, 230 10 of 14
Water 2017, 9, 230 10 of 14
1
0.19
00..98
00..87
Pb
00..76
C000..65 PNbi
C/0
C00..54 Ni
C/ Cu
00..43
Cu
00..32 Zn
00..21 Zn
0.10
0 0 500 1000 1500 2000
0 500 Pore1 V00o0lume 1500 2000
Pore Volume

(b)
(b)
Figure 4. Percentage removal (a) and breakthrough curve (b) of the four metals by pine bark amended
Figure4.Percentageremoval(a)andbreakthroughcurve(b)ofthefourmetalsbypinebarkamended
Ffiilgteurrse a4s. Pae frucenncttaiogne roefm poovrael v(ao)l uanmde .b rAeFak sttharnodusg hfo cru arvmee (nbd) eodf tfhilet efor.u Cr m aentda lsC b0 ya rpei nteh eb aerfkf laumenetn danedd
filtersasafunctionofporevolume.AFstandsforamendedfilter.CandC aretheeffluentandinfluent
finilftleures nats m ae tfauln ccotinocne notfr aptoiorne sv, roeluspmeec.t ivAeFl ys. tands for amended filter. C an0d C0 are the effluent and
metalconcentrations,respectively.
influent metal concentrations, respectively.
Charcoal AF
Charcoal AF
120
120
100
100
l 80
a
v
lo 80 Pb
vam 60
moRe 60 PNbi
Re% 40 NCui
% 40
Cu
20 Zn
20 Zn
0
0 0 500 1000 1500
0 500 Pore Volume 1000 1500
Pore Volume

Figure 5. Percentage removal of the four metals by charcoal amended filters as a function of pore
Fviogluumree 5. .A PFe srctaenndtasg feo rr eammoevnadle odf ftilhtee rf. our metals by charcoal amended filters as a function of pore
Figure5. Percentageremovalofthefourmetalsbycharcoalamendedfiltersasafunctionofpore
volume. AF stands for amended filter.
volume.AFstandsforamendedfilter.
The low removal of Ni by charcoal could also be due to the pH of the inflow solution, at 7.5,
whileT hope tliomwa lr Nemi aodvsaol ropft iNoni boyc ccuhrasr acto aplH c o6u [l3d4 ]a. lHsoo wbee vdeure, ctooa tlh bea pseHd oadf sthoreb iennftlo, aws isno ltuhtiiso cna, saet, 7h.a5s,
Twphohieinlleto oowpf trziememraolo cNvhaia larodgfeso Nartpi tbpioyHnc 7oh.ca2cr uc[3ros5a ]al, tc wpoHhuil cd6h [ a3ils4s ]oc. lHboesoewd tueove etthro,e c tophaHel p boaHfs etodhfe at hdinesfolirunbeflenontwt. , Tashso eilnrue ttfhiooirsne ,c, aatshtee7, .hp5aH,sw hile
optimpcaoolninNdti itoiaofd nzsse oarrorpe ctfihaoavnrogoreac bcalute r pfsoHar tc7pa.2tHi o[3n65ic[]3, m4w]e.htHaiclh oa wdisse ocvrleporst,ieoc noto.a Althbneao stpehHder aordef satoshorenb aeinbnfltle,u aeesxnpti.nl aTnthhaeitsrioecfnoa rsfoee,r, thlhoaews ppNHoii ntof
zeroccaohdnasodrrgitpeitoianotsn p acHroeu 7flad.2v ao[lr3sao5b ]bl,eew fdohuri ecc hatotii osthnceilc on msaeteuttraoel taohdfe sthopreHp atdioosfnot.r hbAeenniont,t flhweuhre irncehta. siTso nhdaeebrrilevef eoedrx epf,rloathnmae taipo mHn efctoaorm nloodrwipt ihNoinci sare
asodusorcrep—tioann tchorualcdit ea lcshoa brceo daul.e F toou trhieer ntraatunrsefo ormf t hine faradrseodr bsepnetc,t rwohscicohp yis (dFeTrIiRv)e dd aftrao mfro am m [3e6ta] mshoorpwheidc
favorableforcationicmetaladsorption. AnotherreasonableexplanationforlowNiadsorptioncould
sthoautr caen—tharnatchirtea cbitaes cehda rccaorablo. nFso ucroinert atirna nlsofwor mox iyngfreanr esdu srpfaeccet rofusncocptiyo n(FalT IgRr)o dupatsa, fwrohmic h[3 6c]a nsh oawffeecdt
alsobeduetothenatureoftheadsorbent,whichisderivedfromametamorphicsource—anthracite
tahdasto rapnttihorna ocift me ebtaaslse dsu cchar abso Nnsi . Acodndtaitiino nlaolwly , oaxdysgoerpnt isounr ofafc Ne i fhuansc btieoenna rle pgroorutepds t, ow bhe iscehv ecraanl oarfdfeercst
charcoal. Fouriertransforminfraredspectroscopy(FTIR)datafrom[36]showedthatanthracitebased
aodf smorapgtnioitnu dofe mloewtaelrs sthuachn aost hNeir. Amdedtailtsio snuaclhly ,a asd Csour patt iponH o <f N8 i[ 3h7a]s. bZene na nredp oPrbt esdh otow beed s einvietriaalll yo rhdiegrhs
carbonscontainlowoxygensurfacefunctionalgroups,whichcanaffectadsorptionofmetalssuchas
oafff imniatgyn bituutd iet dloewcleinr etdh aonv oerth teimr me, ewtahlsic shu icnhd aicsa Cteus asat tpuHra t<io 8n [o37f ]a. dZsno rapntdio nP bc asphaocwiteieds ionfi ttihalelsye htiwgho
Ni. Aadffdiniittiyo nbaultl yit, dadecsloinrepdt ioovnero ftiNmie,h washibchee inndriecpatoerst esadtutorabtieons eovf eardasloorprdtieorns coafpmaciatgiens iotuf dtheesloe wtweor than
othermetalssuchasCuatpH<8[37]. ZnandPbshowedinitiallyhighaffinitybutitdeclinedover
time,whichindicatessaturationofadsorptioncapacitiesofthesetwometalsorincreasedcompetition
forlimitedbindingsites. Thisemphasizesthemetamorphicnatureofcharcoalassuitableforremoval