Performance of Four Full-Scale Artificially Aerated Horizontal Flow Constructed Wetlands for

15 Pages·2016·2.96 MB·English

water
Article
Performance of Four Full-Scale Artificially Aerated
Horizontal Flow Constructed Wetlands for Domestic
Wastewater Treatment
EleanorButterworth1,AndrewRichards2,MarkJones2,GabriellaMansi1,3,EzioRanieri3,
GabrielaDotro1,*andBruceJefferson1
1 CranfieldUniversity,CollegeRoad,Cranfield,BedfordshireMK430AL,UK;
[email protected](E.B.);b.jefferson@cranfield.ac.uk(B.J.)
2 SevernTrentWater,2StJohn’sStreet,CoventryCV12LZ,WestMidlands,UK;
[email protected](A.R.);[email protected](M.J.)
3 DICATECh,PolytechnicUniversityofBari,Bari70125,Italy;[email protected](G.M.);
[email protected](E.R.)
* Correspondence:g.c.dotro@cranfield.ac.uk;Tel.:[phone]
AcademicEditor:HansBrix
Received:2June2016;Accepted:15August2016;Published:24August2016
Abstract: Acomparisonoftheperformanceoffourfull-scaleaeratedhorizontalflowconstructed
wetlands was conducted to determine the efficacy of the technology on sites receiving high and
variable ammonia loading rates not yet reported in the literature. Performance was assessed in
termsofammoniaandsolidsremoval,hydraulicconductivityandmixingpatterns. Thecapabilityof
systemstoproduceammoniumeffluentconcentrations<3mgNH +-N/Lwasobservedacrossall
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sitesinsystemsreceivingvariableloadingsbetween0.1and13.0gNH +-N/m2/d.Potentialresilience
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issueswereobservedinrelationtoresponsetospikeloadingspositedtobeduetoaninsufficient
nitrifyingpopulationwithinthebeds. Hydraulicconductivityandflowmixingpatternsobserved
suggesteddeteriorationofthereactoreffectivevolumeovertime. Overall,thestudydemonstrates
theefficacyofthetechnologywhereammoniumremovalisrequiredonsmallsitesreceivinghigh
andvariableflowrates,withadequateremovaloforganicsandsolids,butnosignificantbenefitto
thelongtermhydraulicsofthesystem.
Keywords: aeration;clogging;dissolvedoxygen;nitrification;treatmentwetlands
1. Introduction
Horizontalsub-surfaceflowconstructedwetlands(HSSFCWs)arepassivewastewatertreatment
systemscommonlyusedfortheremovalofsuspendedsolids,organicmatter,andnitrate.Therelatively
largefootprintassociatedwiththetechnologyof5–10m2/personequivalent(p.e.) and0.7–1m2/p.e.
insecondaryandtertiarysewagetreatmentapplications,respectively,focusesapplicationstowards
rural small works (sub 2000 p.e.). In response to the challenges associated with achieving “good
ecologicalstatus”inEuropeanrivers,aspartoftheWaterFrameworkDirective,alargenumberof
theseruraldomesticwastewatertreatmentplantsarerequiringupgradinginordertodischargelower
levels of organic matter and ammonia into the receiving waters. To achieve this, the flowsheet is
typicallyupgradedbyreplacement/enhancementofthesecondarybiologicalprocessesorinclusionof
additionalaerobicbiologicalprocesses,suchassubmergedaeratedfilters[1].
Sub-surfaceflowwetlandscanalsobeconsideredtobeaformofbiofilm-basedbioreactorsand
hencefunctionallyhavethecapabilitytomeetthefutureneeds. However,traditionalHSSFbedsare
oftenhydraulicallyloadedatratesthatcauseanoxic/anaerobicconditionstopredominatewiththe
associatedsub-surfaceoxygenlimitation(sub0.5mg/L)restrictingobservednitrificationratesinfull
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scaletertiaryHSSFCWsto0.05–0.22gNH +-N/m2/d[2]. Thistypeofoperationandloadingratesare
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generallyinsufficienttomeetfuturedischargetargetswithintypicallylimitedavailablelandareas.
Acrossthefullspectrumofapplicationsforconstructedwetlandsanumberofinnovativeadaptations
havebeendevelopedtoovercometheoxygenlimitationincludingdecreasingthedepthofthebed[3];
recirculationofthetreatedeffluent[4];batchloadingincludingtraditionalverticalflowsystems[5]
andadaptiontohorizontalflowbeds,i.e.,tidalflow[6];andforced(artificial)aerationoftraditional
verticalflowsystems[7],floodedverticalflowsystems[8],orhorizontalflowbeds[2,9].
The general efficacy of the approach towards enhancing nitrification has been demonstrated
predominatelyatpilotscaleforarangeoffeedwatertypesincludingsyntheticwastewater[10,11],
heavilypollutedriverwater[12],andmunicipalsecondarysewage[8]. Illustrationsoftheefficacyof
thetechnologyhavealsobeenpresentedatfull-scaleintermsofthetreatmentoflandfillleachate[13],
industrialwastewater[14],andtertiarytreatmentofmunicipalsewage[2]. Inthelatter,hydraulic
loadingratesareconsiderablyhigherthanthoseutilisedelsewherewithtypicalratesof0.2–0.9m/d
reportedintheUK[15]comparedto0.001–0.049m/dforthesitestreatingindustrialwastewaters[14].
Ammonia concentrations feeding the tertiary beds can reach as high as 40 mgNH +-N/L on sites
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thatpreviouslyhadnorequirementtoremoveammoniaand,assuch,ammonia-loadingratescan
significantlyexceedthosepreviouslyconsidered.Toillustrate,non-tertiarycaseshavereportedloading
ratesintherange0.9gNH +-N/m2/dto6.9gNH +-N/m2/d[8,13],whichcomparestoamaximum
4 4
rate of 10.1 mgNH +-N/m2/d observed during an assessment of the initial stages of operation of
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afullscaletertiaryaeratedwetland[2]. Thesamestudydemonstratednearcompletenitrification(99%
removal)withoutnegativelyimpactingonsolidsandorganicmatterremovalefficiencies.Aerationalso
appearedtoincreasehydraulicconductivity,andimprovehydraulicefficiencyintheaeratedbedunder
sub-surfaceflow,resultinginamoreefficientreactor[2].
Apaucityofinformationremainsaroundfull-scaletertiarysystemstreatingvariableflowsand
loadsincludingstormflowsandtheinherentseasonalvariationsinwastewatercharacteristicsand
temperatures. Coupledtotheshortdurationofthemajorityofpreviousinvestigationatbothpilotand
fullscaletheappropriatenessofthetechnologyhasyettoprovensufficientlytoenhanceconfidence,
particularlyintermsoftheperformanceconsistencyacrossvariousapplicationsofthetechnology.
Thisstudyaimstorespondtothisknowledgegapthroughassessmentof four full-scalewetlands
retrofittedwithartificialaerationinsmalldomesticwastewatertreatmentworksintheUK.Thecurrent
studyextendsbeyondtheinitialstudycarriedoutonafullyaeratedtertiarysystemwithseparate
storm over-flow during its first year post commissioning [2], to assess suitability of the artificial
aerationacrossvarioussituationsincludingintermittentaeration,tertiarycombinedstormflowand
a secondary bed. Performance was assessed in terms of ammonia and solids removal, hydraulic
conductivityandmixingpatternsandintermsofprocessrobustnesstodeterminewhethertheuseof
aeratedHSSFCWsisviableasareliabletertiaryprocessforammoniumremovalonsmallsites.
2. MaterialsandMethods
2.1. SiteDetails
AerationsystemswereretrofittedintoexistingHSSFCWsduringrefurbishmentonthreeSevern
TrentWatersiteswithtighteningammoniumconsents(SitesA,B,andC)andonesecondarytreatment
systemwithadescriptiveconsentthatrequiredupgradingforimprovedresponsewithregardsto
odouremissionsonthesite(SiteD;Table1). Inallcases,theaerationsystemconsistsofa1.6kWair
blower,adistributionheaderandloopsofperforatedLDPE12mmpipingwith2mmholesdrilled
intoitat300mmintervalsplacedontopoftheimpermeablelinercoveringthesurfaceareaofthebed
floor. Theaerationgridwastestedbyfloodingthewetlandsandcheckingthebubblepatternonthe
floodedsurface,whichappearedhomogenous. Thebedscontained0.6mof6–12mmgravelmedia
givingameasuredporosityof0.4,andareplantedwithPhragmitesaustralisat4seedlings/m2withthe
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exceptionofSiteCwhichwasplantedwithTyphalatifolia. Thesiteshavebeenbuiltaccordingtothe
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standardUKcriteriaasdescribedinReference[15].
Table 1. Site details and current and future consents for aerated horizontal flow constructed wetlands. 
Table1.Sitedetailsandcurrentandfutureconsentsforaeratedhorizontalflowconstructedwetlands.
Hydraulic  Current Consent  Future Consent
Treatment  Process  Aeration  Average 
SSiittee  TSreStaatgtameg eent PEP E ArAeParr eomace2m ss2PowAPeeorr awWtieo/rmn3  RReetHtee(nyHndttRiirooaTnnu)  lTTdiici mmee  FAlovFwelor awmg3e/d  BCOuDrr entTCSoSn seNnHt4‐N  BOFDut ureTCSoSn seNntH4‐N 
A  Tertiary  393  200  2W6./7m 3 (HR0T.7) d m635/d  BO3D0  TS4S5  NHn4/-aN  BO2D1  TS4S5  NH44- N
BA  ComTebritniaerdy a  3963 93 3602 00 62.67. 7 01..72  6756  3025  4545  n/1a0  2114  4545  43 
CB  CCoommbbinineded a a 6003 96 6003 60 46.4.7  10..28  17860  2530  4550  1n0/a  1340  4550  312 
DC  SCeocomnbdianreyd a 586 00 2006 00 134..34  03..81  11860  30D  50D  n/Da  30D  50D  12D 
D Secondary 58 200 13.3 3.1 16 D D D D D D
Notes: a combined treatment refers to combined secondary treated water plus storm overflow. PE = 
Notes:acombinedtreatmentreferstocombinedsecondarytreatedwaterplusstormoverflow.PE=population
poepquuilvaatlieonnt; eBqOuDiv=a5le-Dnat;y BCOarDbo n=a 5ce‐DouasyB iCocahrebmonicaacleOoxuysg eBniDocehmeamndic(aml gOOx2y/Lg)e;nT SDSe=mToatnadlS (umspgeOnd2/eLd)S; oTliSdSs = 
To(mtagl TSSuSs/pLe);nNdeHd4 +S-Noli=dsa m(mmgoTniSuSm/Ln);i trNogHe4n+‐(Nm g=N aHm4m+-Non/iLu)m;D n=itdreosgcerinp t(imvegcNonHs4e+n‐Nt;P/Lo)w; eDr b=a sdeedscornipthtieve 
blowersizedusedperm3ofbed.
consent; Power based on the blower sized used per m3 of bed. 
TTrreeaattmmeenntt aatt SSiittee AA ccoonnssiissttss ooff aa pprriimmaarryy sseettttlliinngg ttaannkk ((PPSSTT)) ffoolllloowweedd bbyy aa ssuubbmmeerrggeedd aaeerraatteedd 
fifilltteerr ((SSAAFF;; FFiigguurree 11)).. TTeerrttiiaarryy ttrreeaattmmeenntt iiss vviiaa ttwwoo HHSSSSFF CCWWss wwiitthh aa sseeppaarraattee ccoommbbiinneedd sseewweerr 
oovveerrffllooww ((CCSSOO)) HHSSSSFF CCWW ththata rterceecievievse tshteh weawstaeswteawteart eerxceexecdeiendgi nsigx stiimx teism these dthrey dwreyatwheera tfhloewr.fl Soiwte. 
SAi tseeArvseesr avse sa acsoantcroonl tsriotle switeithw istihdes ibdye bsiydsei dweewtlaentldasn dosf eoqfueqalu sailzsei.z Ae.eAraetriaotnio onf othfeth teestte sbtebde dbebgeagna n3 
3MMaracrhc h2021011 1anadn dwwasa lselfet fdtodromrmanatn itni nthteh ecocnotnrotrlo blebde.d T.hTeh beebdesd asta tthtihs issitseit ewwereer edidscisocnonnencetecdte dfofro 5r 
5mmonotnhtsh (sD(Deceecmembebre r2021011–1A–Apprirli l22001122) )dduuee ttoo mmeecchhaanniiccaall mmaaiinntteennaannccee ooff tthhee sseeccoonnddaarryy ttrreeaattmmeenntt 
dduurriinngg wwhhiicchh ttiimmee tthhee flflooww wwaass rreemmoovveedd ffrroomm ssiittee.. TThhee mmeeaann flfloowwt tooe eaacchhb beeddi sis4 466m m33//dd,, rreessuullttiinngg 
iinn mmeeaann hhyyddrraauulliicc llooaaddiinnggss ooff 00.4.466m m33//mm22//dd. .AAvveeraraggee ininlelet tloloaaddininggss ttoo tthhee bbeedd dduurriinngg tthhee ttrriiaall wweerree 
1122 ggBBOODD//mm22/d/d, 2,52 5gTgTSSS/Sm/m2/d2,/ adn,da n9d.1 9g.1NgHN4+H‐N4+/m-N2//dm. 2/d.
10m 30m
Site B
Site A Tertiary 
HSSF CW 10m
SAF Combined storm water and 
Inlet of works Aerated Integral RBC tertiary HSSF CW
>6DWF HTSeSrFti aCrWy  Aerated 12m
CSO  Control
HSSF CW
>6DWF
Receiving water 
course
Receiving  Receiving 
water course water course
Site C Site D 25m
28m
Secondary 
RBCs Septic tank HSSF CW
Combined storm water and 
PST tertiary HSSF CW Aerated 8m
21.4m
Aerated
Receiving 
Receiving  water course
water course  
Figure 1. Site process flowsheets of aerated HSSF CW sites. 
Figure1.SiteprocessflowsheetsofaeratedHSSFCWsites.
Treatment at Site B is via an integral RBC followed by a combined wetland (Figure 1). The bed 
TreatmentatSiteBisviaanintegralRBCfollowedbyacombinedwetland(Figure1).Thebedwas
was retrofitted with aeration in October 2010 to provide a failsafe for occasional ammonia peaks 
retrofittedwithaerationinOctober2010toprovideafailsafeforoccasionalammoniapeaksobserved
observed  in  the  conventional  flow  sheet.  Since  its  retrofit,  the  bed  has  been  operating  with 
intheconventionalflowsheet. Sinceitsretrofit,thebedhasbeenoperatingwithintermittentaeration,
intermittent  aeration,  with  the  blowers  only  being  active  between  8:00  A.M.  and  8:00  P.M. 
withtheblowersonlybeingactivebetween8:00A.M.and8:00P.M.(continuously). Themeanflowto
(continuously). The mean flow to the bed is 45 m3/d, resulting in mean hydraulic loadings of 0.1 
m3/m2/d. Average loadings to the bed during the trial were 11 gBOD/m2/d, 1 gTSS/m2/d, and 1.6 
gNH4+‐N/m2/d. 
Site C consists of two integral RBCs and a combined tertiary reed bed (Figure 1). The aeration 
was activated on 26 January 2012. The driver for aeration at this site was the addition of an ammonia
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thebedis45m3/d,resultinginmeanhydraulicloadingsof0.1m3/m2/d. Averageloadingstothebed
duringthetrialwere11gBOD/m2/d,1gTSS/m2/d,and1.6gNH +-N/m2/d.
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SiteCconsistsoftwointegralRBCsandacombinedtertiaryreedbed(Figure1). Theaeration
wasactivatedon26January2012. Thedriverforaerationatthissitewastheadditionofanammonia
effluent consent at a site that was not originally designed to nitrify. The mean flow to the bed is
248m3/d,resultinginmeanhydraulicloadingsof0.4m3/m2/d. Averageloadingstothebedduring
thetrialwere8gBOD/m2/d,17gTSS/m2/d,and8.9gNH +-N/m2/d.
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SiteDistheonlysecondarybedinthetrial(Figure1). Treatmentconsistsofaseptictankfollowed
byacombinedreedbed. Consentsherearedescriptive,assetoutbytheEnvironmentAgency,andare
basedonvisualinspectionoftheeffluentintothewatercourse. ThebedwasrefurbishedinMarch2010
andfittedwithaerationon30March2011. Becausetheconsentedflowisbelow50m3/d,thissitehad
noflowmeasurementduringthetrial.
2.2. SamplingandAnalysis
Composite samples (every 15 min over 24 h) were collected fortnightly during the first year
andmonthlythereafterusingISCOauto-samplersattheinletandoutletsofthebeds. Sampleswere
collectedin1Lplasticsamplingbottlesandstoredinacoolboxwithiceblocksduringtransporttothe
laboratoryforsame-daytesting. Wheresame-daytestingwasnotfeasiblesampleswerestoredat4◦C
andallowedtoreachroomtemperaturepriortoanalysis. Samplingwasconductedfromtheonsetof
aerationatrespectivesitestoFebruary2013.
Hach-Lange test kits were employed for determining NH +-N according to Hach-Lange
4
procedures and read via a Hach-Lange DR2800 spectrophotometer. Portable meters were used to
determine dissolved oxygen and temperature (Hach-Lange HQ40D) in the top 5 cm of the water.
ProbeswerecheckedweeklywithhydrogensulphitesolutionandHachstandardswereusedperiodically
toensureaccuracyoftestkits. Totalsuspendedsolidswerequantifiedfollowingstandardprocedures
usingathreepiecefilterfunnelwitha70-mmfilterdiameterand1.2-µmporesize[16].
2.3. HydraulicCharacterisation
TracertestswerecarriedoutasinReference[2]andinvolvedtheadditionofa0.135gimpulse
of20%RhodamineWaterTracerLiquid(KeystoneEuropeLtd.,Huddersfield,UK)attheinletpoints
of both wetlands. Concentrations were monitored at the outlet over time using a fluorescence
spectrophotometer(YSI6seriessondefittedwithRhodaminesensor). Comparativetracerstudies
wereonlycarriedoutatSiteA.
In-situsaturatedhydraulicconductivitymeasurementsweretakenusingasteelpipeperforated
atthebaseandamodel3001Solinstlevelogger,followingthefallingheadmethodologyasdescribed
bytheauthorsof[17]. Measurementsweretakenintriplicatealongthreetransectpointsspanningthe
lengthofeachofthewetlands(minustheinletandoutletdistributionrocks). Thismeasurementgives
approximatesaturatedhydraulicconductivityvalues,asverticalconductivityismeasured,anddoes
nottakeintoaccountthehorizontalflow. Inaddition,acertaindegreeofcompactionoccurswhen
insertingthepipeintothebedpresentsasourceoferrorbuttheseerrorshavebeenevaluatedandare
consideredacceptable[18].
2.4. RobustnessandResilienceAnalysis
Robustness curves were generated by plotting the percentile distribution against the effluent
values. Inthiscontext,robustnessisdescribedastheabilityofatreatmentunittoproduceconsistent
effluent quality under varying influent characteristics and differentiates from resilience, which is
defined as the ability to return to normal after a dynamic event [19]. Resilience was assessed by
evaluating the response of Site B to an upstream process failure and time to restore nitrification
capacityinSiteAafteraperiodof5monthswherethebedsweretakenoffline.
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Arobustnessindex(RI)wascalculatedwithrespecttooverallammoniumremovalperformance
againstatreatmentgoal(T )andthepercentagetimespentunderthetreatmentgoal(Equation(1),[19]).
goal
Asthegoaltermheavilyinfluencestheoutcome,RIwascalculatedforarangeoftreatmentgoalsfrom
0.1to5mgNH +-N/L.Alowerrobustnessscoreindicatesamorerobustprocess.
4
(cid:20)(cid:18) (cid:19) (cid:21) (cid:34) (cid:35)
G% T T G%
RI = 1− × 90 + 50 × (1)
100 T T 100
50 goal
RI = Robustness index; G% = percentage time spent under T ; T = 90th percentile value
goal 90
(mgNH +-N/L);T =50thpercentilevalue(mgNH +-N/L);T =treatmentgoal(mgNH +-N/L).
4 50 4 goal 4
In accordance with Reference [19], the approach was used to assess overall robustness rather
thandirectlyassesstheabilityofthesitestomeetregulatorystandardsasRIismoreeffectivelyused
as an indicator of variation rather than directly about meeting a fixed goal. Accordingly the 90th
percentilewasusedtoavoidconfusionwithregulatorycomplianceatthe95thpercentile.
StatisticalanalyseswerecarriedoutusingGraphpadPrismv.5. Statisticalsignificancebetween
datasets was tested using the non-parametric Mann-Whitney unpaired, two-tailed test (p < 0.05).
WheremultiplecomparisonswererequiredtheKruskal-Wallistestwasused(p<0.05).
3. ResultsandDiscussion
3.1. AmmoniumRemoval
Lowammoniumeffluent(<3mgNH +-N/L)wasachievedinallaeratedsitesuptothemaximum
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measuredammonia-loadingrateof12.5mgNH +-N/m2/d(Figure2). Theefficacyofnitrification
4
wasconsistentacrossthefullrangeofvariableloadingratesobservedindicatingnodeteriorationin
effluentqualityathigherloadings. Consequently,associatednitrificationratesintheaeratedbeds
increasedlinearlywithincreasedloadingsfrom0.05to12.5mgNH +-N/m2/ddemonstratingastrong
4
causal relationship suggesting ammonia loadings were not a rate limiting factor. In comparison,
anon-linearrangeofnitrificationratesbetween0.04and7.0mgNH +-N/m2/dwasobservedinthe
4
non-aerated wetland at Site A (Figure S1, Supplementary Materials). The current findings extend
thereportedmaximumloadingratesforeffectivenitrificationinaeratedwetlands[8,10,11,13]even
extending above the 10.1 mgNH +-N/m2/d previously reported during the initial months of the
4
trial [2]. In comparison, the control bed (Site A) exceeded 3 mgNH +-N/L once the loading rate
4
roseabove1.9mgNH +-N/m2/d;consistentwithpreviousfindingsconcerningsub-surfaceoxygen
4
deficiencylimitingnitrification[2]. Themedianmassremovalwas23%inthecontrolbedacrossall
loadingratestestedbutincreasedto72%belowaloadingrateof1.9mgNH +-N/m2/dsuggesting
4
adequateremovalcanbeachievedintertiaryHSSFCWsatsufficientlylowloadingrates.
Comparisonofthedataacrossthedifferentsitesrevealedmedianeffluentammoniaconcentrations
(mgNH +-N/L ± standard deviation) of 0.1 ± 0.3 (Site A), 0.2 ± 3.0 (Site B), 0.2 ± 0.2 (Site B not
4
including upstream failure), 0.2 ± 1.2 (Site C) and 0.6 ± 0.8 (Site D) equating to median mass
removalratesof98.8%,93.9%,94.7%,94.7%forSitesA–C,respectively(Figure3). Overall,median
outletconcentrationsof0.1–0.2mgNH +-N/Lwererecordedforthetertiaryaeratedbedsfrominlet
4
concentrationsof1.6–9.1mgNH +-N/Landaneffluentof0.6mgNH +-N/Lforthesecondarybedfrom
4 4
aninletof29.6mgNH +-N/L.Thiscomparestoamedianeffluentconcentrationof6.7mgNH +-N/L
4 4
in the non-aerated control. For context, typical literature values report influent concentrations of
22–54mgNH +-N/LfortertiaryHSSFCWs,correspondingtoeffluentsof5–31mgNH +-N/L[20–23],
4 4
whereas reported secondary systems achieve concentrations of 3–61 mgNH +-N/L from inlets of
4
15–225mgNH +-N/L[21,24,25].
4
Water2016,8,365 6of15
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25
25 Site A (aerated)
Site A (aerated)
Site A (control)
Site A (control)
Site B
Site B
Site B (including failure)
20 SSiittee  BC (including failure)
20 Site C
Consent
L) Consent
L)N/
+N/‐
+H‐NH4415
Nmg 15
g
+N (m‐N (
+‐H4
HN410
nt Nuent  10
EfflueEffl
5
5
0
0 0 2 4 6 8 10 12 14 16
0 2 4 6 8 10 12 14 16
NH +‐N Loading (gNH +‐N/m2/d)
NH4+‐N Loading (gNH4+‐N/m2/d)  
4 4  
FigFuirgeu2re. A2.m Ammomnoiunimumlo laodaidnigngr aratetessa anndd ccoorrrreessppoonnddiinngg eefffflluueennt taammmmoonniuiumm cocnocnecnetnrattriaotnios nast aaltl aslitlessi.t es.
Figure 2. Ammonium loading rates and corresponding effluent ammonium concentrations at all sites. 

Figure 3. Box and whisker plot of NH4+‐N, concentrations at the inlet and the outlet of the control and 
FigFaueigrraeutr3eed. 3 B.b oBexodxsa .na n(dnd w =w hhSiisistkeke erBr  ppdllooattt aoo ffe NxNcHlHu4+d‐+Nin-N,g c ,otchnoecn enuctpernsatttrrieoaantmiso a npts trhaoetc etinshsle eftia nainlleudtr etah)n.e d Tohuthetle ebto oouxft  ltrehetep ocrfoesntehtnreotslc  oatnnhdter  ol
aerated beds. (n = Site B data exclud4ing the upstream process failure). The box represents the 
andintaeerrqautaerdtilbee rdasn.g(en; t=heS liitneeB inddaitcaateexs ctlhued mineganth aendu pthsetr weahmiskperros ctehses 2f5atihlu arned). 7T5thhe pbeorcxernetpileres.s entsthe
interquartile range; the line indicates the mean and the whiskers the 25th and 75th percentiles. 
interquartilerange;thelineindicatesthemeanandthewhiskersthe25thand75thpercentiles.
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MoredetailedprofilingatSiteArevealedNH +-Nconcentrationsof0.8,0.7and0.2mgNH +-N/L
4 4
withcoMrroersep doentadiilnedg pDrOofsilionfg2 a–t3 S,it3e– A4 arenvdea>l5edm NgHO42+‐/NL caotn0c.e7n,t1ra.2tioannsd o1f 00.m8, 0f.r7o amndt h0e.2 imnlgeNtoHf4+t‐hNe/Lb ed,
wiwthitthh ceofirrneasplovnadluinegc DorOres sopf o2n–3d,i 3n–g4 taontdh >e5fi mngaOle2/fLfl uate 0n.t7,f r1o.2m antdh e10b emd frcoomm pthaer eindletto oaf nthien bfleude, nwtitlehv el
oft9h.e1 f±ina7l .v6amlugeN coHrr4e+s-pNo/nLdi.nAg ctcoo trhdei nfignlayl, eoffnlulyenatn frionmiti tahlef rbaecdt icoonmopfatrheed btoe dana ipnpfleuaernetd letvoelb oef u9t.1il i±s ed
for7.n6i tmrifigNcaHti4o+‐nN,i/nLd. iAcactcionrgditnhgaltyt,h oenmlya jaonri tiynitthiael bferdacwtioans uonf ntehcee sbseadri lyapapeeraarteedd stuo pbpeo rutitnilgisepdr efvoiro us
labnoitrraiftiocraytioinnv, einstdigicaattiionngs tthhaat ttlhime imteadjoarietrya ttihoen btoedt hweafsr ounntnpeocretsisoanriolyf taheerabteedd tsoupaplloorwtinagr epdreuvcieodusD O
enlvaibroornamtoerny tincovnesdtuigcaitvioenosf tdheant iltirmifiitceadt iaoenratthioerne taof ttehre[ 9fr]o.nt portion of the bed to allow a reduced DO 
envGirroenamteernvt acroinadbuilcitivye ionf dtheenietrfiflfiucaetniotna tmhemreoanftiaer c[o9]n. centrations was observed in Sites C and D
comparGerdeatoteAr vaanrdiaBb.ilSitiyte iCn (ttheer tieafrflyuceonmt abminmedonstioa rmconflcoewnt,rcaotinotninsu wouass lyobaseerravteedd )isnh oSwiteesd Cth eangdre aDt est
vacroiamtipoanreind etfofl uAe nantdco Bn.c eSnitter aCti o(tnerwtiiatrhy ecfoflmuebninteadm smtoornmi ufmlowco, nccoenntitnruatoiuosnlsy oaveerrat1e.d0) mshgoNwHed+ -tNhe /L
4
greatest  variation  in  effluent  concentration  with  effluent  ammonium  concentrations  over  1.0 
recordedon11occasionsoutof43(25%). Thiscomparesto2%and0%fortheothertertiarySitesA
anmdgBN(Hex4+c‐lNu d/Lin rgecuoprsdterdea omn f1a1i loucrcea)s,isoungs goeustt ionf g43th (e25o%b)s.e Trvheisd cionmstpaabrielist ytow 2a%s annodt d0%ire fcotrl ythdeu oethtoert he
tertiary Sites A and B (excluding upstream failure), suggesting the observed instability was not 
inclusionofstormflows,increasedloadingratesorinadequatelevelofaeration. Diagnosticanalysis
directly due to the inclusion of storm flows, increased loading rates or inadequate level of aeration. 
ofthebedconfirmednolinktoaerationasDOprofilesrangedbetween3.3and9.5mgO /Lacross
2
Diagnostic analysis of the bed confirmed no link to aeration as DO profiles ranged between 3.3 and 
thelengthandbreadthofthebed. Furtherdiagnosticsconcerningalkalinityrevealednodefinitive
9.5 mgO2/L across the length and breadth of the bed. Further diagnostics concerning alkalinity 
explanation, and further investigation is required to establish a coherent diagnosis. However, the
revealed no definitive explanation, and further investigation is required to establish a coherent 
results show that process instability in aerated wetlands is possible, congruent with other tertiary
diagnosis. However, the results show that process instability in aerated wetlands is possible, 
nitrificationsystems[26].
congruent with other tertiary nitrification systems [26]. 
SiteB(tertiarycombinedstormflow,intermittentlyaerated)experiencedanoperationalissuewith
Site B (tertiary combined storm flow, intermittently aerated) experienced an operational issue 
thewuitphs ttrheea mupssetcroenamda rsyecboinodloagryic abliporloogciecsasl spurcohcethssa tsauscuh btshtaant taia lsiunbcsrteaansteiailn ianmcrmeaosne iainc oanmcemnotrnaiati on
wacsonloceandteradtioonn wtoast hloeadbeedd o(nF itgou trhee 4b)e.d D(Fuigriunrge 4t)h. eDruersionlgu tthioen reosofltuhteionu posf ttrheea mupsetvreeanmt, ethveenitn, flthuee nt
aminmflouneinutm amcomncoennituramti ocnontocetnhterawtieotlna ntod tihnec rweaesteladnfdro imnc1r.e2a±sed4 .0frmomgN 1H.2 4±+ -4N.0/ mLgtoN1H6.40+‐±N/8L.4 tom 1g6N.0H ±4 +8-.N4 /L
wimthgNaHp4e+‐aNk/Lc ownicthen at rpateiaokn coonfc3e3n.t2ramtiognN oHf 43+3-.N2 /mLgNdHur4+i‐nNg/Lt hdeurwinign ttehre pweirniotedr pwehrieond twhheene fflthuee nt
temeffpluereanttu treemrpaenrgaetudreb eratwngeeedn b5e.2twaenedn 95..32 a◦nCd. E9.f3fl °uCe.n Etfaflmuemnot namiampoenaikae pdeaatke1d5 amt g15N mHg4N+-HN4/+‐LN,/7L,d 7a ys
podsatyfasi lpuorset, afanidlubree,g aanndt obdegeacnre atos ed1e0crdeaayses a1f0t edratyhse aefvteern tthseta ertveedn.t Ustlatirmteadt.e lUy,lttihmeaeteffllyu, etnhter eeftfulurneendt to
berloetwur3nemdg tNo Hbe4l+o-wN /3L magftNerH340+‐Nda/Ly sa(fwtera t3e0r dteamysp e(wraattuerre t9em.5–p1e3ra◦tCur),e d9e.5s–p1it3e °cCo)n, sdisetsepnittely choingshisltoenadtliyn gs
cohmigpha rlaobaldeitnogtsh coosmerpeacreaibvleed tofr othmosteh eresceeciovnedda frryombe dth(eS isteecDon),daanrdy cboendfi (rSmiteed Dt)h, eaanbdi lictoynofifrmtheeda ethraet ed
syastbeimlityt ooft rtehaet aheirgahteadm symstoenmia toco tnrecaetn htrigahti oanmsmuonndiear csotnecaednytrsattaiotensc ounnddietrio sntesa.dy state conditions. 
35
Inlet
Period of resolution
Outlet
30
of upstream event
L)25
/
N
+‐
4
H20
N
g
m
N  (15
+‐
4
H
N10
5
0
0 100 200 300 400 500 600 700
Number of days

Figure4.InfluentandeffluentconcentrationsofammoniumatSiteCshowingtheperiodofincreased
Figure 4. Influent and effluent concentrations of ammonium at Site C showing the period of increased 
loalodaidnignsgasn adndti mtimeet otor eraeachchs steteaaddyys sttaattee ((3300 ddaayyss)).. 
FuFruthrtehrerc ocnonsisdideeraratitoionn ooff rreessppoonnssee ttiimmee ((rreessiilliieennccee) )wwasa spposossisbilbel aeta StitSei tAe A(te(stte satnadn cdonctornolt rsoitles, ite,
tertteiratriyarcyo cmobminbiendesdt ostromrmfl ofwlow)a)s atsh tehbee bdesdws ewreertea ktaekneonf flofinfleinfeo rfoar pae prieordioodf o5fm 5 omnothnsth,ds,u druinrginwg hwichhicthim  e
WWatearte2r0 21061,68,, 83,6 3565  8o8f o1f5 15 
time no flow was run through the beds. Upon re‐commencement of the flow to the wetlands, the 
noefflflouwenwt caosnrcuenntthrartoiuognh dtehcerebaesdesd. Utop boenlorwe- c1o mmmgNenHce4+m‐Ne/nLt oaffttehre sflevoewn tdoatyhse owfe otlpaenrdasti,otnh ewehffliluset nthte 
cocnocnetnrotrl abtieodn pdreocvriedaesde dontolyb meloinwim1aml rgeNmHov4+a-lN (F/iLguarfete 5r)s. eTvheen rdeasypsonosfeo opfe rtahtei osnyswtehmilss trtehlaetecos ntotr othle 
beadbupnrodvaindceed aonndl yamctiivniitmy aolfr ethmeo nviatlri(fFyiignugr epo5)p.uTlhateiorens. pOonncsee othfeth measyxismteumms rcealaptaebsleto rtahtee aobf uanmdmanocneia 
anodxidacattiivointy poerf cthelel nisi terxifcyeiendgedp,o tphuel asytisotnem. Os wnciell tshtaermt taox fiamilu umntcila spuafbfilceiernatte gorofwamthm oof nthiae opxoipdualtaiotinon 
peorcccuelrlsi stoe mxceeeetd tehde, dtheemsaynsdte [m27s]w. Nilol sdtairretctto qfuaialnutinfitcilastiuofnfi coife nthteg nroitwritfhiero fcothmempuopnuitlya twioans ococcnudruscttoed 
mdeuetritnhge tdheem caunrdre[n2t7 ]i.nvNeostidgiarteicotnq, ubauntt iifit ciast ipoonsoitfedth ethnaitt rtihfiee rcoconmsismteunntliyty lwowas acmonmdouncituemd dluoaridnigng 
theexcpuerrrieenncteindv persotihgiabtiitoend, besuttaibtliisshpmoseintet doft hlaatrgthe epcoopnusliastteionntlsy sluocwh atmhamt othnei usmysltoemad iwngase xinpcearpieanbcleed of 
prroehspibointeddinegs ttaob lcioshnmceenntrtaotfiolnar gspeipkoesp udluaeti oton sas ulacchk thofa tatbhuensdyasntecme owf aasctinivcea pnaitbrliefieorfsr easnpdo nhdenincge ttohe 
cosnycsetenmtra ltaiocknss ap idkeegsrdeue eotfo inahlaecreknotf raebsuilniednacnec. eTohfisa catgivreeensi wtriifithe rtshaen ldagh teinmcee tohbesesyrvsteedm inla Sciktse aCd (eFgigreuere 
of4i)n bheetrweenetnr etshieli etinmcee. frTohmis iangcrreeeassewdi tihnftlhueenlat gamtimmeonoibas leoravde danind SfuitlelyC n(iFtriigfiuerde e4f)flbueetnwt.e eTnhitsh heatsim aleso 
frboemeni nocbrseearsveedd iinnfl outehnetr atemrtmiaoryn inaitlroifaidcaatinodn fsuylsltyemnist,r iwfihederee faflnu iennctr.eTashei sinh eafsflaulesnot baemenmoobnsiae rhvaesd bienen 
otrheecrortedretdia rdyunriintrgifi tchaet ioauntsuymstne mwsh,ewnh tehree ainnleint carmeamseoinniuefmfl uiennctreaamsems ocnoinachuarrsebnete wnirtehc oar dteemdpdeurraintugre 
thdeearuivteudm dnewcrheeanset hine inniltertifaimcamtioonn iaucmtivinitcyr eians ethsec omncauinrr esnectownidtharay tepmropceersas tu[2r8e]d. eErfifvluedendt efcrroemas esuinch 
niptrrioficceastsioesn tahcetinv iitmypinrotvheesm aasi nthsee cnoitnrdifaicraytpiorno cpeossp[u2l8a]t.ioEnffl iunecnretafsroesm csoumchmpenroscuersastees wthiethn itmhep irnocvreesaasesd 
thaevnaiitlaribfilcea stuiobnstpraotpeu. lationincreasescommensuratewiththeincreasedavailablesubstrate.
35
Inlet
30 Outlet A
Outlet B
L)25
/
N
‐
+
4
H20
N
g
m
N (15
‐
+
4
H
N10
5
0
0 2 4 6 8 10 12
Number of days

Figure 5. Effluent ammonia concentrations from control and aerated CW in Site A on resuming 
Figure 5. Effluent ammonia concentrations from control and aerated CW in Site A on resuming
operation after 5 months of being offline. 
operationafter5monthsofbeingoffline.
In the case of the aerated wetlands, analysis of seasonal impacts revealed a slight increase in 
In the case of the aerated wetlands, analysis of seasonal impacts revealed a slight increase
effluent ammonium concurrent with increased hydraulic loading posited to be due to heavier rainfall 
in effluent ammonium concurrent with increased hydraulic loading posited to be due to heavier
and consequently less residence time in the bed (Table 2). Heavy rainfall could result in short 
rainfall and consequently less residence time in the bed (Table 2). Heavy rainfall could result
circuiting in the beds and therefore contribute to decreased performance. For instance, Sites C and D 
in short circuiting in the beds and therefore contribute to decreased performance. For instance,
recorded an increase in the median outlet concentrations in the aerated beds during winter of 0.9 and 
SitesCandDrecordedanincreaseinthemedianoutletconcentrationsintheaeratedbedsduring
1.6 mgNH4+‐N/L compared to 0.2 and 0.5 mg/L in the summer. In comparison, no difference was 
winterof0.9and1.6mgNH +-N/Lcomparedto0.2and0.5mg/Linthesummer. Incomparison,
observed at Site A with the a4erated bed where the mean effluent ammonium remained at 0.2 mgNH4+‐
no difference was observed at Site A with the aerated bed where the mean effluent ammonium
N/L during both summer and winter periods. In contrast, higher mean outlet concentrations of 8.4 
remainedat0.2mgNH +-N/Lduringbothsummerandwinterperiods. Incontrast, highermean
mgNH4+‐N/L were obs4erved in winter compared to 6.5 mgNH4+‐N/L when the temperature decreased 
outletconcentrationsof8.4mgNH +-N/Lwereobservedinwintercomparedto6.5mgNH +-N/L
to 4.1 °C.  4 4
whenthetemperaturedecreasedto4.1◦C.
In fact, no direct correlation was observed between effluent ammonia and temperature or 
Infact,nodirectcorrelationwasobservedbetweeneffluentammoniaandtemperatureorbetween
between increased ammonium in the inlet and the outlet during the reduction in activity of the 
increased ammonium in the inlet and the outlet during the reduction in activity of the upstream
upstream processes. Whilst this suggests that the combination of aeration and long residence time 
processes. Whilst this suggests that the combination of aeration and long residence time affords
affords a degree of robustness, the response to shock loads suggests that further enhancement of the 
adegreeofrobustness,theresponsetoshockloadssuggeststhatfurtherenhancementofthenitrifying
nitrifying population would be beneficial in terms of resilience. Given that it appears only a small 
populationwouldbebeneficialintermsofresilience. Giventhatitappearsonlyasmallproportionof
proportion of the bed is active, and only the aerated portions of the bed can sustain an active nitrifying 
population, it is posited that sequencing the portion of the bed that receives air in a pre defined cycle
Water2016,8,365 9of15
thebedisactive,andonlytheaeratedportionsofthebedcansustainanactivenitrifyingpopulation,it
ispositedthatsequencingtheportionofthebedthatreceivesairinapredefinedcyclewillenable
alargertotalcommunitytobemaintainedandwhenrequiredutilisedbyaeratingallsectionsofthe
bed. Previousworkontheintegratedfixedfilmactivatedsludgeprocess(IFAS)hasshownthatwhen
thenitrifyingmicrobialcommunityoccupynoncompetitiveniches(suchasthebiofilmcarriersinIFAS)
thenitrificationratecanbecontrolledbyaerationlevelsasitcorrelateswithDOupto5mg/L[29].
Combined,thesefeaturesofferthepotentialtoenhanceresilienceofthesystemandofferadegreeof
turnup/turndowncontrolwithregardstonitrificationthroughchangingaerationrates.
Table2.Summerandwinterammoniuminletloadingsandeffluentconcentrations.
Loading(gNH4+-N/m2/d) OutletConcentration(mgNH4+-N/L)
Season Site
Median Min Max Median Min Max n
SiteA(aerated) 2.0 0.3 11.5 0.1 0.02 1.4 19
SiteA(control) 2.0 0.3 11.5 6.5 0.03 20.6 19
Summer SiteB 0.08 0.02 1.9 0.1 0.01 1.5 20
SiteC 0.04 0.01 0.07 0.2 0.04 0.3 5
SiteD n/a n/a n/a 0.5 0.1 2.6 11
SiteA(aerated) 2.8 0.07 12.5 0.1 0.02 0.6 23
SiteA(control) 2.8 0.07 12.5 8.4 0.1 22.1 23
Winter SiteB 0.2 0.02 10.9 0.2 0.02 15.0 22
SiteC 4.3 0.4 11.9 0.9 0.2 5.3 29
SiteD n/a n/a n/a 1.2 0.1 13.3 20
3.2. ProcessRobustness
Excludingthevariationduetotheupstreamevents,statisticalanalysisrevealednosignificant
difference between the effluent concentrations between the tertiary beds A and B (Mann-Whitney
U=1434,p=0.7687).Whilststillachievingloweffluentconcentrations,theincreasedspreadinthedata
atSiteCcomparedtoconsistentlyextremelylowconcentrationsinSiteAandBmeanttheeffluentdata
couldnotbecategorizedasstatisticallythesame. However,effluentconcentrationswerestatistically
similar in Site C and the secondary bed D (Mann-Whitney U = 388, p = 0.7545). Accordingly, the
efficacyofartificialaerationappearsirrespectiveofconfigurationofthewetlandintermsofthetypeof
flowtreated(inclusionofstormflows,secondaryortertiary)acrosstherangeofconcentrationsand
loadingratesobservedinthecurrentstudy. Thisleadstothesuggestionthatnitrificationrateisnot
thecontrollingfactorinthedesignandoperationofsuchsystems.
TherobustnessprofileforthecontrolbedatSiteAexhibitedacurvedshapeacrossthemajority
of the data sets indicative of limited robustness (Figure 6). This is commensurate with the outlet
ammoniumconcentrationsthatwereabovethefutureconsentof4mgNH +-N/L63%ofthetime.
4
Incontrast,comparativedatafromtheaeratedbedsrevealedrelativelyrobustsystemswithregardsto
ammoniumremovalasillustratedbysteepnearverticallinesacrossthemajorityofthedata(Figure6)
andcommensuratewiththefactthattheoutletconcentrationswerebelowrespectivefutureconsents
100%ofthetime,withtheexceptionoftheupstreamprocessfailurerecordedatSiteB.
The use of RI enabled consideration of the impact of tightening consents through changing
the target goal level and hence an analysis of the link between tightening discharge consents and
robustness of the systems. A similar level of robustness was observed across all sites down to
atargeteffluentlevelof3mgNH +-N/LbelowwhichtheRIofthedifferentsitesdiverged(Figure7).
4
Thisextendeddowntoatargetconcentrationof2mgNH +-N/Lincludingthesecondarybed(SiteD)
4
whenSiteCwasexcluded,thesitethatwasidentifiedtohavesomegeneralnitrificationissues. SitesA
andBremainedrobustdowntotargetconcentrationsof0.5mgNH +-N/Lindicatingthatartificial
4
aeration can remain robust even when considered in relation to the most challenging consents of
0.5mgNH +-N/LdiscussedforsmallworksintheUKinthenearfuture[28].
4
Water 2016, 8, 365  10 of 15 
Water2016,8,365 10of15
Water 2016, 8, 365  10 of 15 
100%
100%
90%
90%
80%
80%
e 70%
ue 70%
ervalrvalu60%60%
de
nd
un50%
Percentile Percentile u3400%%345000%%% SSSSSSiiiiiitttttteeeeee      AABAAB    ((((cacaoeoenrnratattrtreoeodl)dl)))
20%20% SSiittee  BB  ((iinnccluluddiningg f afailiulurere))
SSiittee  CC
10%10%
SSiittee  DD
0%0%
0 01 12 23 34 45566778899110011111122113311441155116611771188119922002211222222332244
NNHH44++NN ( (mmgg//LL))   
Figure 6. Ammonium removal robustness curves for all sites. 
FFiigguurree 66.. AAmmmmoonniiuumm rreemmoovvaall rroobbuussttnneessss ccuurrvveess ffoorr aallll ssiitteess.. 
25
25 Site A (aerated)
Site A (aerated)
Site A (control)
Site A (control)
Site B (no failure)
20
Site B (no failure)
20 Site B (all)
Site B (all)
Site C
ex 15 SSititee D C
exnd15 Site D
nds i
ss ines 10
neust10
ustob
bR
o 5
R
5
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
0
0 0.5 1 1N.5H +‐N 2target 2e.5ffluent3 conce3n.t5ration4 (mg/L)4.5 5
4  
NH +‐N target effluent concentration (mg/L)
Figure 7. Robustness index (RI) of 4all sites against a range of target effluent concentration s. 
Figure 7. Robustness index (RI) of all sites against a range of target effluent concentrations. 
Figure7.Robustnessindex(RI)ofallsitesagainstarangeoftargeteffluentconcentrations.
3.3. Solids and Organics Removal 
3.3. SolidAs  asnigdn Oifricgaannti csre Rdeumctoivoanl  in effluent total suspended solids concentrations was observed in 
3.3. SolidsandOrganicsRemoval
comparison to inlet concentrations at sites B–D (Mann‐Whitney U = 172.5, 364, 45.5, p < 0.0001) 
A significant reduction in effluent total suspended solids concentrations was observed in 
reAcorsdiginngi fimceadnitanre edffulucteinotn coinnceenffltruaetinotnst obteallowsu 5s pmegn/dL efdor ssoitleisd sB acnodn cCe,n atnradt i2o0n msgwTaSsS/Lo bfoser rsviteed Di n
comparison to inlet concentrations at sites B–D (Mann‐Whitney U = 172.5, 364, 45.5, p < 0.0001) 
com(Fpiagruirseo n8; tToaibnlele St1c,o Snucpepnltermateionntasrya tMsaitteesriaBl–s)D. I(nM thaen nc-aWseh oift nSeiyte UA,= TS1S7 2c.o5n,c3e6n4t,ra4t5io.5n,s pw<er0e .0n0o0t 1)
recording median effluent concentrations below 5 mg/L for sites B and C, and 20 mgTSS/L for site D 
recosirgdniinfigcamnetldyi adnifefefrfleunet nbtectowneceenn ttrhaet ioinnlsetb ealnodw o5umtlegts/ Loff obrosthit etshBe aanerdatCe,da nandd2 0nomng‐aTeSrSat/eLd fboerdssit e
(Figure 8; Table S1, Supplementary Materials). In the case of Site A, TSS concentrations were not 
D ((FKigruusrkea8l‐;WTaalblilse sSt1at,isStuicp p2.l1e9m4,e npt a=r y0.3M33a8te).r iIanlsv)e.stIignatthioen ciansteo otfheS itceauAse, TrSevSecaolendc ean tsriateti osnpsecwifiecr e
significantly different between the inlet and outlets of both the aerated and non‐aerated beds 
notssaimgnpilifincga nistsluyed riefdfeurceinntg bceotnwfiedeenncteh eini nthleet saignndifoicuatnlceets oof fanbyo tfhintdhiengase rraeltaetdeda ntod tnheo ns-oaliedrsa tdeadtab aetd s
(Kruskal‐Wallis statistic 2.194, p = 0.3338). Investigation into the cause revealed a site specific 
(Kruthsakta sl-itWe.a Nllios rsetalatitsiotincs2h.i1p9 4w,aps= ap0.p3a3r3e8n)t. Ibnevtweseteigna TtiSoSn lionatdointhge rcaateu saenrde vefefaluleednta csoitnecesnptercaitfiiocns aamt apnliyn g
sisasmuinpedlriinevdgidu iucsasinlu gsei tcreeo odnrufi acdcienrongsc sce oailnnl fsitidhteeesn sccioeg mninbifi itncheaedn s cwiegintohiff tiahcnaeyn ecffiefln uodefin natn gTysS rSfei nrleadmtienadginstio nregthl abeteelsdoow ltio d4 s0th dmea gstTaoSlaiSdt/sLt h duaaptt atsoi ta et. 
thata  smitea.x Nimou rmel altoiaodnisnhgi pr awtea so af p2p5a rgeTnStS b/met2w/de ewni tThS Sth leo aedxcinegp trioante  oafn don eef flmueeanstu croenmceenntt r(aFtiigounr ea tS a2n, y 
NorelationshipwasapparentbetweenTSSloadingrateandeffluentconcentrationatanyindividual
indSivuipdpulaelm seitnet aorry a Mcraotsesr iaallls )s.i tes combined with the effluent TSS remaining below 40 mgTSS/L up to 
siteoracrossallsitescombinedwiththeeffluentTSSremainingbelow40mgTSS/Luptoamaximum
a maximum loading rate of 25 gTSS/m2/d with the exception of one measurement (Figure S2, 
load ingrateof25gTSS/m2/dwiththeexceptionofonemeasurement(FigureS2,SupplementaryMaterials).
Supplementary Materials).