ren

6N

Anaerobic bafed reactorAircraft de-icing uidEthylene glycol

lutebict dif(OLsoluoved

constant during the study. Biomass specic acetoclastic activity however, changed through the study;

eans on counl undeuse de

Canada, air transportation is responsible for the greatest volumeof release of EG-ADF into the environment. According to a surveycarried out under the authority of the Canadian EnvironmentalProtection Act (CEPA), an estimated 7700 tons of EG were used in1996 for aircraft de-icing/anti-icing operations (Environment Can-ada, 2000). Test results have indicated that 16% of the EG used todeice planes remains on the aircraft, 35% is blown behind the

runoff get usually mixed with the pavement de-icing used at thespecic airport (sodium acetate, urea, etc.) and other contami-nants such as grease, which at higher concentrations could inhi-bit the anaerobic digestion process. However, due to theequalization process during collection their inhibitory effect is re-duced (Marin and Kennedy, 2006). Strength of such wastewaterin airport collection systems is highly variable and depends inmany factors such as weather conditions, airport size, collectionsystem, etc. (Switzenbaum et al., 2001). Marin and Kennedy(2006), reported COD concentrations below 900 mg/l at a med-ium size airport.

* Corresponding author. Tel.: +1 613 562 5800x6070; fax: +1 613 562 5173.

Bioresource Technology xxx (2009) xxxxxx

Contents lists availab

T

els

ARTICLE IN PRESSE-mail address: jmari040@uottawa.ca (J. Marin).(ADF) to ensure that critical aircraft surfaces are free of ice, snowor frost formation. These elements can alter the shape of the wingsairfoil section and its surface ow characteristics, causing a loss oflift that might prevent the plane from taking off or cause it to crashif the ice develops in ight (Transport Canada, 1994). In NorthAmerica, the uids used to deice/anti-ice aircraft are usually com-posed of ethylene glycol (EG) or propylene glycol (PG) combinedwith water and other ingredients. The formulation is proprietaryand depends on the nal use of the product, but in general containswetting agents, corrosion inhibitors, colorants and thickeners. In

Narasiah, 1992); there is also evidence that the toxicity of ADFincreases due to the presence of additives in the formulation(e.g. triazoles, organic amine bases, etc.). It has been reportedthat ADF formulations were signicantly more toxic to the waterea Cercerodaphnia dubia, and the fat head minnow, Pimephalespromelas than pure EG and PG (Pilliard, 1995). Hence, in orderto protect the quality of the receiving waters the collection andtreatment of this type of wastewater is mandatory under federalauthority. ADF is applied at gate areas which have been speciallydesigned for the collection of such streams, during collection ADFGranular biomass

1. Introduction

In our global society, ying as a mcome a necessity. Every year northerchallenge of providing safe air travetions; to accomplish this, airports0960-8524/$ - see front matter 2009 Elsevier Ltd. Adoi:10.1016/j.biortech.2009.11.055

Please cite this article in press as: Marin, J., et al.of operation on granular biomass. Bioresour. Teincreasing two fold for the last three compartments and decreasing almost the same magnitude forthe rst compartment compared to inoculum, suggesting that a new distribution of microbial consortiawas established in each compartment of the reactor by the end of the study.

2009 Elsevier Ltd. All rights reserved.

f transportation has be-tries face the additionalr severe winter condi--icing/anti-icing uids

aircraft and about 50% falls to the ground in the vicinity of the air-craft following application (Simpson, 1997).

Runoff from aircraft de-icing activities results in the release oflarge quantities of dilute EG-ADF to the environment. While thehigh 5 d-biochemical oxygen demand (BOD5) of de-icing uids istheir main impact on the environment (Miller, 1979; Sabeh andKeywords:Acetoclastic activity

mental conditions tested and a four-month summer shut-down simulation had no signicant effect onreactor performance or on the settling characteristics of the granular biomass, which remained almostCharacterization of an anaerobic bafeduid and long term effects of operation o

Juan Marin *, Kevin J. Kennedy, Cigdem EskiciogluDept. of Civil Engineering, 161 Louis Pasteur, University of Ottawa, Ottawa, Canada K1N

a r t i c l e i n f o

Article history:Received 5 June 2008Received in revised form 3 December 2008Accepted 3 December 2008Available online xxxx

a b s t r a c t

Successful treatment of difour compartment, anaerov) were continuously fed aitant organic loading ratesABR achieved over 75%0.30 0.05 L CH4/g CODrem

Bioresource

journal homepage: www.ll rights reserved.

Characterization of an anaerobchnol. (2009), doi:10.1016/j.bioactor treating dilute aircraft de-icinggranular biomass

5

ethylene glycol based-aircraft de-icing uid (ADF) was achieved using abafed reactor (ABR). Three ADF concentrations (0.04, 0.07, and 0.13% v/ferent hydrological retention times (HRTs; 24, 12, 6 and 3 h) with concom-Rs) varying between 0.3 and 6 kg chemical oxygen demand (COD)/m3/d.ble COD removal and an average methane production potential ofat 33 C for the experimental conditions evaluated. The different experi-

le at ScienceDirect

echnology

evier .com/locate /bior techic bafed reactor treating dilute aircraft de-icing uid and long term effectsrtech.2009.11.055

(1999) reported the successful treatment of different types ofdilute wastewaters using ABR technology. However, no studies

2.2. Experimental design

To investigate the performance of ABR in terms of COD removala two-factor factorial design with one observation per cell was em-ployed. The two factors considered were HRT and inuent ADFconcentration (4 and 3 levels, respectively). Statistical AnalysisSystem (SAS, V.8) was used for data analysis.

echnology xxx (2009) xxxxxx

ARTICLE IN PRESShave evaluated the treatment of dilute ADF wastewater usingABR.

Seasonally generated wastewaters may have great variations instrength from the beginning to the end of the season. De-icing/anti-icing activities take place during the winter months and ex-tend depending on weather conditions. Therefore, it is importantto have a system robust enough to handle not only the variationsin OLR but also the ability to maintain a good performance aftera shut-down period. Anaerobic granular biomass can tolerate star-vation conditions with low detrimental effects on its activity (Mul-der et al., 2001) and its use has made the anaerobic treatment ofdiverse types of seasonally generated wastewaters possible. How-ever, in order to take the best advantage of such systems it isimportant to understand the long term effects that certain typesof wastewaters or operation conditions might create on granularbiomass.

The primary objective of this study was to evaluate the perfor-mance (in terms of soluble COD removal) of a mesophilic (33 C)ABR inoculated with granular biomass for the treatment of diluteEG-based ADF wastewater under different combinations of inuentADF concentration and HRT. In addition, the long term effects ofdifferent experimental conditions on the granular biomass werealso studied in terms of acetoclastic activity and settling character-istics. The recovery ability of the ABR granular biomass was reas-sessed after a four-month shut-down period.

2. Methods

2.1. Apparatus

Continuous-ow experiments were performed with two identi-cal Plexiglas ABRs (56 30.5 25.5 cm, LWH) as depicted else-where (Marin et al., 2007). Both reactors had four compartmentscomprised of a down-ow section which ended in a 45 angledportion and an up-ow section. Total reactor volume was 32 L(8 L for each compartment). Biogas sampling ports were connectedto a header by 380 PVC, Nalgene

tubing and directed to a wet-tip

gas meter for measurement. Dilute ADF wastewater owed fromthe top of the down-ow section of the rst compartment andthrough the portion of granular biomass retained in that sectionand then up through the bed section in the up-ow section. Theprocess was repeated for each compartment. Finally, the treatedefuent exited from the up-ow section of the fourth compart-To date, there are reports that show the efciency of anaerobictreatment for concentrated ADF (Darlington and Kennedy, 1999;Schoenberg et al., 2001; Pham, 2002; Zitomer and Tonuk, 2003);however, for dilute ADF wastewater the number of reports islimited.

The anaerobic bafed reactor (ABR) presents certain advanta-ges that make it suitable for the anaerobic treatment of diversetypes of wastewaters (Barber and Stuckey, 1999). The ABR iscompartmentalized horizontally, using a series of vertical bafes,which force the wastewater to ow over and under the bafesas it travels from the inlet to the outlet. ABR can achieve highvolumetric OLRs maintaining at the same time long SRT inde-pendent from the HRT. According to Weiland and Rozzi(1991), the most signicant advantage of the ABR is its abilityto separate acidogenesis and methanogenesis longitudinallydown the reactor, which allows it to behave as a two-phase sys-tem (Cohen et al., 1982; Baloch et al., 2007). Barber and Stuckey

2 J. Marin et al. / Bioresource Tment. No recycling was used during the regular operation (afteracclimation) and no direct control of biomass distribution in theABR compartments was used.

Please cite this article in press as: Marin, J., et al. Characterization of an anaerobof operation on granular biomass. Bioresour. Technol. (2009), doi:10.1016/j.bioTable 1Composition of synthetic ADF-based feed solution.

Component (g/L) 0.04% ADF (v/v) 0.07% ADF (v/v) 0.13% ADF (v/v)

COD 0.3 0.5 0.75NH4HCO3 0.06 0.1 0.15NaHCO3 2.1 2.4 2.4KHCO3 2.4 2.6 2.9KH2PO4 0.006 0.01 0.015K HPO 0.008 0.013 0.022.3. Experimental procedure

Both ABRs were placed in a temperature-controlled room(33 2 C) and inoculated with 10 L of anaerobic granular biomassequally distributed in the four compartments resulting in a totalreactor biomass concentration of 10.5 g VSS/L. Inoculum with spe-cic acetoclastic activity (SAA) of 0.20 g Ac/g VSS/d was obtainedfrom a full-scale anaerobic up ow sludge bed (AUSB) reactortreating chemical/thermal mechanical pulp efuent at Lake UtopiaPaper Ltd. (New Brunswick, Canada). The carbon source was a for-mulated ADF wastewater using EG based UCAR XL-54 de-icinguid from Union Carbide. Experiments were conducted at ADF con-centrations of 0.04, 0.07 and 0.13% (v/v), corresponding to solublediluted feed COD concentrations of 300, 500 and 750 mg/L, respec-tively. The feed solution also had other components to provide thegranular biomass with adequate sources of nitrogen, phosphorus,miscellaneous nutrients, and alkalinity was provided in excessfor pH control (Table 1). The average COD:N:P ratio of the feedsolution was 200:5:1. During acclimation, ADF wastewater wasprepared every other day with tap water and kept at 4 C. Forthe specic runs, feed was prepared as needed, based on HRTand because of the high ow rates it was pre-warmed in order tomaintain reactor mixed liquor at 33 C. After inoculation, acclima-tion was initiated by continuous feeding at a long HRT (80 h) withhigh strength ADF feed (4500 mg COD/L). Acclimation lasted twomonths, during which production of volatile fatty acids (VFAs) aswell as the pH was closely monitored. If the VFAs reached concen-trations higher than 500 mg acetate/L or the pH was lower than 7,the reactors were set in full recycling mode (64 L/d) until the nor-mal conditions of operation were restored (VFAs < 500 mg acetate/L and pH 7). After acclimation, the feed concentration was gradu-ally reduced and HRT gradually decreased until the base line con-ditions of 40 h-HRT and feed concentration of 750 mg COD/L wereachieved. From this base line, the feeding program of each run withdilute ADF was achieved by either increasing the ow rate 510%each day at constant ADF concentration, or the ADF concentrationwas increased or decreased by an increment of 0.01% ADF per dayat a constant HRT. During run-to-run transitions, the levels of VFAs,pH and efuent soluble COD were closely monitored. Total time forexperimentation was approximately 13 months (including thefour-month summer shut-down). Reactor performance was as-sessed according to data obtained during steady-state conditions.For the reactors to be considered at steady-state, the concentrationlevels of VFAs had to be constant (50 mg/L) as well as the COD re-moval efciency (10% uctuation) for a period of 5-HRTs. Once2 4

(NH4)2SO4 0.015 0.025 0.04Yeast extract 0.003 0.006 0.008

ic bafed reactor treating dilute aircraft de-icing uid and long term effectsrtech.2009.11.055

Tech

ARTICLE IN PRESSthis state was reached, reactors were kept at that condition forother 5-HRTs.

For every steady-state, triplicate measurements of VFAs, pH,efuent COD, compartment COD prole, efuent total suspendedsolids (TSS) and volatile suspended solids (VSS), were performed;biogas production and composition was measured once and bio-mass settling characteristics were measured by duplicate. SAAwas measured in duplicates only for the inoculums; for every com-partment of the ABR at the beginning of the summer shut-downand at the end of the summer shut-down.

2.4. Reactor restart up

After a four-month summer shut-down simulation, ABR contin-uous operation started with ADF inuent concentration of750 mg COD/L and 60 days HRT. Once base line conditions of750 mg COD/L and 40 h-HRT were reached four additional runswere performed at dilute ADF inuent concentrations of 750 and500 mg COD/L, and 24, 12 and 6 h-HRT. In this last part of the studyABR performance was assessed only in terms of COD removal.

2.5. Analytical methods

Methane content of biogas was determined with a HewlettPackard 5710a gas chromatograph (GC) (Agilent, Santa Clara, CA,USA); equipped with a thermal conductivity detector and a3380A model integrator using the method described by van Huyss-teen (1967). The GC column was a Porepak T(6.35 mm 304.3 cm) set at 70 C with a helium gas carrier owof 40 mL/min. Biogas samples were taken from a port at the topof the reactor, with an airtight syringe and 0.5 mL of biogas was in-jected into the GC for the determination. VFAs were determined bythe internal standard method described by Ackman (1972), using aHewlettPackard 5840A GC (Agilent, Santa Clara, CA, USA),equipped with a ame ionization detector, an auto sampler, a5840 model integrator and a Chromosorb 101 packed column(304.8 cm 2 mm ID, 80/100 mesh size). The oven temperaturewas 180 C, the injector temperature was 250 C and the detectortemperature was maintained at 350 C. The ow rate of the formicacid saturated helium carrier gas was 15 mL/min. Before injection(10 lL) to the GC, samples were centrifuged at 5000 rpm for 5 minin a micro centrifuge, and the supernatant was diluted with anequal volume of internal standard containing 1000 mg/L isobutyricacid. TSS and VSS determinations were based on procedures inStandard Methods (APHA, 1998). Well-mixed samples were l-tered through a pre-weighed GF/C berglass lter (VWR Interna-tional. Mississauga, ON, Canada) and dried to a constant weightin a 105 C oven. The dried lter was ignited at 550 C in a mufefurnace for 40 min for VSS determination. Soluble COD was deter-mined using colorimetric and titrimetric techniques based on pro-cedures in Standards Methods (APHA, 1998). Samples werecentrifuged for 15 min at 10,000 rpm and the supernatant wasused for COD determination. For the COD colorimetric technique,a PerkinElmer spectrophotometer (Waltham, MA, USA) was usedto measure the absorbance at 600 nm. For the titrimetric technique(COD < 400 mg COD/L), samples were titrated with 0.1 M ferrousammonium sulphate (FAS). Ferroin indicator solution was usedto indicate the end-point of the titration. Biomass acetoclasticactivity determination was based on Speece (1996); granular bio-mass (10 mL) from each compartment of the ABR were anaerobi-cally transferred to 130 mL glass serum bottles and diluted with30 mL of dened medium to give a biomass concentration ofapproximately 10 g VSS/L. To the sealed bottles 0.2 mL acetic acid

J. Marin et al. / Bioresourcestock solution (Pham, 2002) was injected to give an initial acetateconcentration in the range of 12001500 mg/L The acetate con-sumption rate was measured by monitoring the change in acetate

Please cite this article in press as: Marin, J., et al. Characterization of an anaerobof operation on granular biomass. Bioresour. Technol. (2009), doi:10.1016/j.bio3.2. Soluble COD and VFAs proles

Steady-state COD and VFAs proles were created in order to ob-serve the stabilization of inuent COD through each of the fourcompartments of ABR. A previous study using an ABR with theidentical number of compartments showed that the reactor be-haved as four continuous stirred tank reactors in series (CSTRs)(Barriault, 2003). Hence, the efuent from the rst compartmentwas considered the inuent for the second compartment and soon. Fig. 1 shows the typical COD consumption proles at variousHRTs for all ADF inuent concentrations tested. We can observefrom Fig. 1c that at lower ADF inuent concentrations, the CODconsumption from compartment-to-compartment was more irreg-ular in the rst two compartments compared to the COD consump-3. Results and discussion

3.1. ABR performance

Arithmetic means and standard deviations of six steady-statemeasurements from the 15 experimental conditions evaluatedduring this study are summarized in Table 2. From column 4 in Ta-ble 2, it can be observed that ABR COD removal efciency wasstrongly inuenced by HRT, reaching the highest COD removal(9296%) at 24 h-HRT for ADF inuent concentration of750 mg COD/L and 68% for the worst case scenario (3 h-HRT and750 mg COD/L inuent concentration). The same effect (higherCOD removals at low OLRs) was observed for all ADF inuent con-centrations tested (data not included). Since there was only oneobservation per cell in the experimental design, variables interac-tion can not be separated and the error variance can not be esti-mated, unless the interaction effect is zero. Using the testdeveloped by Tukey the presence of interaction can be detected(Montgomery, 2001). Tukeys test for interaction with 95% con-dence interval is F0.5,1,5 is 6.6, since Fo < F, it can be concluded thatthere is no evidence of interaction in the data and from the maineffects only HRT is signicant (Table 3).

It is also important to notice from Table 2 the low efuent VSS(9.5170.5 mg VSS/L); which were basically cell debris and somedisrupted granules. It was only at the lowest HRT (3 h) that a smallfraction of well dened granules (average diameter < 1 mm) wereobserved in the efuent; most likely, those small size granuleswere washed out of the reactors due to a combination of highow-rate and biogas production, nevertheless, ABR biomass inven-tory remained high through the study, indicating that over a widerange of operation conditions ABR can perform successfully, whichis desired during treatment of seasonally generated wastewaters.concentration over time at 35 C. Biomass settling determinationwas based on the procedure described by Andras et al. (1989). A10 mL granular biomass sample, taken from the lower samplingport of the up-ow section of each compartment, was placed in aglass up-ow velocity test tube (L = 20 cm, ID = 1.9 cm); tap waterat 35 C was pumped through the tube for 5 min at successivelyincreasing ow-rates. The fractions of biomass exiting from thetube were collected on pre-weighed Whatman

185 mm diameter

grade 1 lter paper (Fisher Scientic, Ottawa, ON, Canada) anddried overnight at 105 C. The difference in weight yielded theTSS fractions exited at each ow-rate. Settling curves were deter-mined by plotting the cumulative TSS exiting fractions versusup-ow velocity. The v50 was considered to be the up-ow velocityat which 50% of the granules were washed out.

nology xxx (2009) xxxxxx 3tion proles when treating higher ADF inuent concentrations(Fig. 1a and b). At low ADF inuent concentrations, the COD con-centration did not always decrease from one compartment to the

ic bafed reactor treating dilute aircraft de-icing uid and long term effectsrtech.2009.11.055

ech

ARTICLE IN PRESS4 J. Marin et al. / Bioresource Tnext as expected and as reported in other ABR studies (Barriault,2003; Baloch et al., 2007). Instead, for 300 mg COD/L ADF inuent

Table 2Typical steady-state data of overall ABR performance*.

Run HRT (h) OLR (kg COD/m3 d) COD removala (%) Total biog

BLb 40 0.3 96 1.2 2.4 0.3CRc 24 0.75 93 1.02 7 0.51 24 0.75 92 1.6 7.3 0.64 12 1.5 90.4 1.04 14.2 0.67 6 3 77 0.5 14 1.610 3 6 68 1.5 36 3.5

* Data shown correspond to the experimental runs with 750 mg/L ADF inuent concena Data indicates arithmetic mean standard deviations of triplicates (ve steady-stateb Data indicates arithmetic mean standard deviations of triplicate measurements foc Data indicates arithmetic mean standard deviation of triplicates for the 2 ABRs ru

Table 3ANOVA for no-interaction determination.

Source of variation Sum of squares Degrees of freedo

Concentration 33.35 3HRT 1362.05 2Non-additivity 0.5541 1Error 39.09 5Total 1413.77 11

750 mg COD/L

0

200

400

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Fig. 1. Steady-state COD consumption proles for ABR under different ADF inuentconcentrations of (a) 750 mg COD/L, (b) 500 mg COD/L, and (c) 300 mg COD/L at thedifferent HRTs. Figure shows the average values of three COD measurements perve steady-state conditions and error bars indicate the standard deviations.

Please cite this article in press as: Marin, J., et al. Characterization of an anaerobof operation on granular biomass. Bioresour. Technol. (2009), doi:10.1016/j.bioconcentration at 24 and 12 h-HRTs, the COD increased from com-partments 1 to 2. At higher ADF inuent concentrations (500 and750 mg COD/L), the COD concentration was high in each compart-ment and COD consumption occurred stepwise all through the fourcompartments (Fig. 1a and b). Compartment-to-compartment CODconsumption and VFAs production proles shown in Fig. 2 suggestthat at lower OLRs, only the biomass in the rst two compartmentswere being stressed (increased propionic acid concentration) whileat higher OLRs, the biomass in more compartments was beingstressed (Fig. 2c).

The production of soluble microbial products (SMP) can be an-other explanation for the observed compartment-to-compartmentCOD increase. SMP production associated with anaerobic digestion

as production (L/d) Biogas composition (%CH4) Efuent VSSa (mg/L)

64 9.5 1.668 12.8 3.163 13.7 1.369 51 10.469 64 5.654 170.5 14.1

trations at the different HRTs.s).r ABR run at base line conditions (BL).n at the same experimental conditions or control run (CR).

m Mean square Fo Pr > F

16.67 2.133 0.0448452.01 58.07

consumption of VFAs took place, it can also be stated that in thosecompartments, methanogenesis took place; its extent compart-ment-to-compartment was dependent on the experimental condi-tions. Hence, based on pH, COD and VFA compartment-to-compartment proles, it can be suggested that under high OLRs,the two rst compartments were used as acidogenic units whileat lower OLR only the rst compartment was used as the acido-genic unit.

3.3. Biomass settling characteristics

under determined reactor operation conditions, since this could

300 mgCOD/L and 24 h HRT

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100150200250300350

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n (m

g/L)

sCOD

Acetic acid

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J. Marin et al. / Bioresource Technology xxx (2009) xxxxxx 5

ARTICLE IN PRESSCompartment

300 mgCOD/L and 12 h HRT

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1 2 3 4reactor decreased, and the accumulation of VFAs started to in-crease gradually in each compartment. It is known that the ABRand its compartmentalization favor the separation of acidogenesisand methanogenesis, thus, the measurement of methane produc-tion from each compartment could have given more indicationsabout the extent of both processes; however, methane productionwas measured for the total system. Since in general the rst com-partment showed the highest COD and VFAs concentrations andlower pH values compared to the three remaining compartments,it can be assumed that this compartment was more acidogenic innature than the others. In the last three compartments, the

Compartment

750 mgCOD/L and 3 h HRT

0100200300400500600700800

1 2 3 4Compartment

Con

cent

ratio

n (m

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sCOD

Acetic acid

Propionic acid

Butyric acid

(c)

Fig. 2. Steady-state COD and VFAs production levels of an ABR with ADF inuentconcentrations of (a) 300 mg COD/L and 24 h-HRT (propionic and butyric acidswere undetected), (b) 300 mg COD/L, and 12 h-HRT and (c) 750 mg COD/L and 3 h-HRT. Figure shows the average values of three COD measurements and error barsindicate the standard deviations for ve steady-state conditions.

Table 4Typical settling velocity (v50) for granular biomass after steady-state conditions.

Seed granular biomass 27.6 0.28

Run CODinuent (mg/L) HRT (h) Compartment 1

v50 (m/h)1 750 24 26.65 500 12 269 300 6 2312 300 3 19.2

Average 24.5 2.8a

a Mean standard deviations of duplicate measurements for ve steady-state conditi

Please cite this article in press as: Marin, J., et al. Characterization of an anaerobof operation on granular biomass. Bioresour. Technol. (2009), doi:10.1016/j.bioCompartment 2 Compartment 3 Compartment 4

25.8 27.1 26.927.7 26.8 28.427.6 26.7 29.824.1 25.8 28.1eventually result in biomass washout and reactor failure. Table4 shows typical v50 values obtained for some of the experimentalconditions. From Table 4 it can be observed that no detrimentalchange occurred in the settling characteristics of the granularbiomass under the continuous operation of the ABR comparedto inoculum. An average v50 of 25.9 2.2 m/h suggested a stablegranular biomass under a wide range of operational conditions,the typical S shape of the curves for the determination of v50was also maintained during all the experimental conditionstested (Fig. 3a and b, for COD inuent concentration of 750 mg/L and HRTs of 24 and 3 h, respectively). These results are inagreement with other studies on settling characteristics of anaer-obic granular biomass treating ADF (Pham, 2002; Barriault,2003). Before summer shut-down, the v50 for the rst compart-ment of both ABRs was slightly lower (20.1 1.3 m/h) comparedto the remaining compartments and inoculum. Since the rstcompartments of both reactors were exposed to the highest OLRsand ADF inuent concentrations, the granular biomass startedlosing its original coloration and a crust-type formation aroundthe granules appeared. However, no granule disruption was ob-served. In other studies (Beloch et al., 2007) granule disruptionwas reported after exposure to a high OLR (13.4 kg COD/m3/d)for a brewery wastewater, which suggests that the type of waste-water and operation conditions have an impact on granular bio-mass stability hence, long term reactor performance. It isimportant to notice the high v50 values in the last two compart-ments (Table 4); if it is considered that methanogenic microor-ganisms are distributed more favorably in this portion of thereactor, biomass washout could have an adverse effect on totalABR performance.

3.4. Biomass specic acetoclastic activity

The specic acetoclastic activity (SAA) test results determinedfor the inoculum and granular biomasses contained in each com-partment at the end of the experimental runs and after summerThe success of high rate anaerobic reactors such as the ABR isrelated to its ability to maintain a high biomass inventory, whichallows for longer SRT independent of the HRT. It is important todetermine if the granular biomass can keep its ability to settle26.3 2.5a 26 1.2a 27.2 1.2a

ons evaluated.

ic bafed reactor treating dilute aircraft de-icing uid and long term effectsrtech.2009.11.055

cay during the shut-down period. Biomass settling characteris-tics decreased (Table 7 and Fig. 3c), and the effect was more

750 mg COD/L & 24 h HRT

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Fig. 3. Typical settling curve for granular biomass after steady-state run conditionsof (a) 750 mg COD/L and 24 h-HRT, (b) 750 mg COD/L and 3 h-HRT, and (c) aftersummer shut-down. C.1, C.2, C.3 and C.4 indicate compartment number 1 through4, respectively. Settling tests were performed in duplicates.

Table 5Specic acetoclastic activity (gAc/g VSS/d) for granular biomass.

At the end of steady-state conditions After summer shut-down

Inoculum 0.20 0.01Compartment 1 0.04 0.01 0.008 0.0098Compartment 2 0.33 0.02 0.305 0.021Compartment 3 0.36 0.04 0.290 0.028Compartment 4 0.30 0.01 0.341 0.056

Table 6Steady-state data of ABR performance after summer shut-down.

Run HRT (h) OLR (kg COD/m3 d)) CODin (mg/L) COD*

1 24 0.75 750 90.5 2 24 1 500 92.1 3 12 1.5 750 88 4 6 2 500 67.6

* Data indicate the mean standard deviations of triplicates (ve steady-state condition

Table 7Typical settling velocity (v50) for granular biomass after summer shut-downconditions*.

Compartment 1 Compartment 2 Compartment 3 Compartment 4

v50 (m/h)17.6 0.49 21.1 0.3 22.5 0.9 21.9 0.5

Average 20.7 2.2

6 J. Marin et al. / Bioresource Technology xxx (2009) xxxxxx

ARTICLE IN PRESS

Please cite this article in press as: Marin, J., et al. Characterization of an anaerobof operation on granular biomass. Bioresour. Technol. (2009), doi:10.1016/j.biopronounced in the rst compartment, for which v50 decreasedfrom an average 24.5 2.8 to 17.6 0.5 m/h. According toSchmidt and Ahring (1996), granular biomass can be dividedinto three fractions based on the settling velocities reported: apoor settling fraction (20 m/h), a satisfactory settling fraction(2050 m/h) and a good settling fraction (>50 m/h). Althoughthe granular biomass settling velocity of the rst compartmentfalls into poor settling category (Table 7), after the summershut-down, the average settling velocity for the whole reactorwas still acceptable (20.7 2.1 m/h). This also indicates thatnew granular biomass has to be eventually added to the reactorif its sole purpose is for ADF wastewater treatment. A decreasein the SAA was also observed after the summer shut-down,shut-down are presented in Table 5. From Table 5, it can be ob-served that SAA changed all through the compartments of ABR. Adecrease in SAA was observed for the rst compartment possiblydue to the acidogenic nature of this compartment. For the remain-ing compartments, the SAA increased, which indicates that differ-ent groups of bacteria were selectively developed in eachsubsequent compartment. The higher the SAA, the greater the pro-portion of acetoclastic methanogens compared to other microbesthat make up the consortia. Biomass contained in the last compart-ments had a high SAA (0.3 0.01 g Ac/g VSS/d), which reinforcesthe fact that ABR behaved as a two-phase system, where the meth-anogenic portion was localized most preferentially in that part ofthe reactor.

3.5. Reactor reassessment after summer shut-down

Results from the ABR reassessment runs are shown in Table6. Summer shut-down had no signicant effects on ABRs CODremoval efciency; which remained well over 67% for the high-est OLR (2 kg COD/m3 d) tested. However, granular biomasscharacteristics were affected: a slight increase in the efuentVSS was observed compared with the initial steady-state condi-tions and even though most of the granules washed out werediscolored and broken, some well dened granules were alsoobserved. This was most likely due to biomass endogenous de-

* Data indicate the mean and standard deviations of two measurements.especially for the rst and third compartments (Table 5). Itcan be speculated that the population of acidogenic bacteria inthe consortia increased in those compartments during the sum-mer shut-down.

Removal (%) Total biogas production* (L/d) Efuent VSS* (mg/L)

2.05 7.8 0.68 18.7 4.01.9 6.6 0.57 28.1 4.42.3 14.4 0.91 60.6 10.16.2 26.8 3.38 73.5 8

s).

ic bafed reactor treating dilute aircraft de-icing uid and long term effectsrtech.2009.11.055

4. Conclusions

The ABR proved to be effective for the treatment of diluteADF-based wastewater, reaching an average methane produc-tion of 0.30 0.05 L CH4/g COD removed at 35 C and solubleCOD removal efciencies over 75% for most of the experimentalconditions evaluated. Better COD removal efciencies wereachieved at high ADF concentrations and at HRTs longer than6 h.

The different experimental conditions evaluated did not havea signicant effect on the settling characteristic of the granularbiomass. The SAA of the granular biomass changed throughoutthe reactor, indicating that a different distribution of microor-ganisms occurred in each compartment by the end of this study.This nding supports the idea that the conguration of this reac-tor can effectively separate acidogenesis and methanogenesis ina single unit, which could have ramications in terms of specialtreatment applications such as sulfate reduction or maybe

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Characterization of an anaerobic baffled reactor treating dilute aircraft de-icing fluid and long term effects of operation on granular biomassIntroductionMethodsApparatusExperimental designExperimental procedureReactor restart upAnalytical methods

Results and discussionABR performanceSoluble COD and VFAs profilesBiomass settling characteristicsBiomass specific acetoclastic activityReactor reassessment after summer shut-down

ConclusionsReferences