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International Journal of Hydrogen Energy 29 (2004) 33–39www.elsevier.com/locate/ijhydene

Biohydrogen production using an up-&ow anaerobic sludgeblanket reactor

Feng-Yung Chang, Chiu-Yue Lin∗

Department of Hydraulic Engineering, BioHydrogen Laboratory, Feng Chia University, P.O. Box 25-123, Taichung 40724, Taiwan

Accepted 24 March 2003

Abstract

Sewage sludge was acclimated to establish H2-producing enrichment cultures for converting sucrose (20 g COD=l) into H2

in an up-&ow anaerobic sludge blanket (UASB) reactor. The operating hydraulic retention times (HRTs) were 24–4 h. Theexperimental results indicated that this UASB system could be used for hydrogen production. The hydrogen productivity wasHRT dependent and nearly constant at the HRT of 8–20 h. However, it drastically decreased at an HRT of 4 or 24 h. Thehydrogen production rate (HPR) and speci9c HPR peaked at the HRT of 8 h and drastically decreased at all other HRTs. At anHRT of 8 h, the average granular diameter peaked at 0:43 mm and each gram of biomass produced 53:5 mmol H2=day with ahydrogen gas content of 42.4% (v/v). Butyrate and acetate were the main fermentation volatile fatty acids. The anaerobic granulesludge kinetic constants were endogenous decay coe<cient (Kd) 0:1 day−1 and yield coe<cient (Yg) 0:1 g VSS=g COD. Themean cell retention time was 22:2 h and the excess sludge discharge rate was 3:24 l=day.? 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Keywords: Hydrogen production; Sewage sludge; Biogranule; UASB

1. Introduction

Fossil fuels are the major global energy resource but theycause environmental problems during combustion. Hydro-gen is a promising energy alternative because it is clean, re-newable and has a high energy yield of 122 kJ=g. This yieldis 2.75-fold greater than that from hydrocarbon fuels. Thus,H2 is a promising clean energy source [1–3]. At present, hy-drogen is produced mainly from fossil fuels, biomass andwater using chemical or biological processes. Biological hy-drogen production processes have the advantages of beingless energy intensive. Fermentative biohydrogen productiongives high hydrogen production rates and is capable of con-verting organic wastes into more valuable energy resources[4].

An up-&ow anaerobic sludge blanket (UASB) processis an extensively applied anaerobic treatment system with

∗ Corresponding author. Fax: +886-4-24519746.E-mail address: cylin@fcu.edu.tw (C.-Y. Lin).

high treatment e<ciency and a short hydraulic retentiontime (HRT). Recently, UASB hydrogen production sys-tems have been used in granulation enhancement andgranule microstructure [5,6]. However, the performance ofhydrogen-producing UASB systems has not been discussedin detail. A systematic investigation of reactor characteris-tics, such as operation stability, HRT dependence, sludgegranulation and sludge discharge is still lacking. Sewagesludge contains a variety of micro&ora favoring biohydro-gen production in suspended growth systems [7–9] andmight be a good source for cultivating granular sludge forhydrogen production.

In light of the above developments, this work usedmesophilic sewage sludge as the seed sludge source forhydrogen production in a UASB system. Sucrose is readilyfound in a variety of industrial wastes and was thereforeused as the carboneous substrate for hydrogen fermentation.This work aimed to determine the hydrogen production ac-tivity of the granulated sewage sludge cultivated at variousHRTs. The results obtained from this study are expected to

0360-3199/03/$ 30.00 ? 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.doi:10.1016/S0360-3199(03)00082-X

34 F.-Y. Chang, C.-Y. Lin / International Journal of Hydrogen Energy 29 (2004) 33–39

Gasfliqure/solid separtor

Effhsent wastewater

Thermal insulating layer

Temp controller

H

P

Bed zone

Blanltet zone

saznping ports

Gas meter

P

Pump

Substrate tank

Fig. 1. Schematic description of the UASB reactor for continuous hydrogen production.

provide some valuable information toward the developmentof an eIective UASB system for converting carbohydratesubstrates into hydrogen.

2. Materials and methods

2.1. Seed sludge

The seed was obtained from the Li-Min MunicipalSewage Treatment Plant (Taichung, Taiwan). It was col-lected from a 9nal sedimentation tank and then screenedwith sieve No.8 (2:35 mm) to eliminate large particulatematerials. This seed sludge had the following characteris-tics. The pH, volatile suspended solids (VSS) to express thebiomass concentrations and total solids (TS) concentrationswere 7.4, 29 640 and 48 350 mg=l, respectively. Beforeseeded into the reactor, the seed sludge was heat treated at100◦C for 45 min to inhibit the methane-producing bacteriaactivity.

2.2. Substrate

The seed sludge was acclimated with sucrose(20 g COD=l). The substrate contained su<cient inor-ganics (mg=l): NH4HCO3 5240; K2HPO4 125; MgCl2 ·6H2O 15; FeSO4 · 7H2O 25; CuSO4 · 5H2O 5; CoCl2 ·5H2O 0:125; NaHCO3 6720 [10]. The substrate was fed ina continuous mode.

2.3. Reactor design and experimental procedure

Fig. 1 schematically describes the lab-scale UASB reac-tor (working volume 3 l, interior diameter 10 cm, height38 cm). The sampling ports were designed along 10 cmheight intervals from the bottom. The reactor was operated

at a temperature of 35±1◦C and a pH of 6:7±0:2 by adding1 N sodium hydroxide or 1 N hydrochloric acid. The re-actor was operated at the HRT of 24, 20, 16, 12, 10, 8, 6and 4 h starting from 24 h. The HRT reduction was con-ducted in a stepwise manner through 52, 23, 32, 28, 22, 26,23 and 18 days, respectively. At each HRT, the reactor wasoperated for 3 weeks to allow steady-state condition devel-opment. Steady-state conditions were established when thevariation in the product concentrations were constant (gasproduction rate, ±5%; eLuent COD concentration, ±10%)during 2 weeks of operation. After the parameter data wereobtained, the retention time was then shortened.

2.4. Monitoring

The reactor was monitored by examining the eLuentwastewater twice a week for COD, alkalinity, volatile fattyacid (VFA), TS and VSS concentrations. Gas productionwas measured using a gas meter; gas composition and vol-ume were monitored every day. Biomass was periodicallytaken from the sampling ports to determine the mixed liquorvolatile suspended solids (MLVSS) concentrations.

2.5. Analyses

The analytical procedures of Standard Methods [11] wereused to determine the above parameters of liquid content.VFA and gas composition were analyzed with a gas chro-matograph having a &ame ionization detector (glass column,145◦C; injection temperature, 175◦C; carrier gas, N2; pack-ing, FON 10%) and a thermal conductivity detector (col-umn, 55◦C; injection temperature, 90◦C; carrier gas, Ar;packing, Porapak Q, mesh 80

100 ), respectively. The gas vol-umes were corrected to a standard temperature (0◦C) andpressure (760 mm Hg) (STP). For estimating the size distri-bution, the sludge sample was taken from the port of 10 cm

F.-Y. Chang, C.-Y. Lin / International Journal of Hydrogen Energy 29 (2004) 33–39 35

0 40 80 120 160 200 240

Time (day)

0

2

4

6

8

10

H2

(L/L

-d)

0

20

40

60

H2

(%)

0

200

400

600

OR

P (

-mv)

4

6

8

10

pH

0

8

16

24

HR

T (

h)

Fig. 2. Daily variations in (a) HRT, (b) pH, (c) oxidation–reduction potential (ORP), (d) hydrogen content and (e) hydrogen volumetricproduction rate.

height. The granule sludge was separated into six fractionswith various openings (0.2, 0.6, 1.0, 2.0, 4:0 mm) and wasmeasured with an Image Analyzer System (Image-Pro Plus,Media cybernetics Co., USA).

3. Results and discussion

3.1. Reactor operation

It is time consuming to start-up a UASB system. At anHRT of 24 h, the reactor required 39 days to achieve con-stant digestion gas production, eLuent quality and biomassconcentrations. Stable conditions lasted for 13 days (day 39–day 52) and the HRT was then shortened to 20 h. A sim-ilar reactor operation was experienced for the other HRTs.Fig. 2 presents the daily variations in sucrose utilization,gas production and hydrogen content evolution in the pro-duced gas, ORP and pH. Before reaching stable reactorperformance, &uctuations were observed in pH, total gasproduction, hydrogen production and H2 content. These &uc-

tuations resulted from the increase in the organic loadingrate when the HRT was shortened. A similar experience wasreported for a methanogenic system [12]. An increase in theorganic loading rate forms a new environment to which themicroorganisms must adapt.

Table 1 summarizes the experimental data obtained understeady-state conditions at each HRT. Sucrose degradationincreased from 91.8% at HRT 4 h to 96.3% at HRT 24 h.Long HRT favored sucrose degradation but did not enhancehydrogen production (Fig. 3). The majority of the consumedsubstrate was converted into biomass. The biomass concen-trations were high at long HRTs (7220 mg=l at 24 h vs.3602 mg=l at 4 h). The alkalinity concentrations decreasedwith decreasing HRT. This related to a progressed acid fer-mentation at short HRT, which caused an accumulation inVFA concentrations and then a decrease in alkalinity [13].

3.2. Hydrogen production rate

Fig. 3 illustrates the relationships between the hy-drogen productivity (the ability to convert sucrose into

36 F.-Y. Chang, C.-Y. Lin / International Journal of Hydrogen Energy 29 (2004) 33–39

Table 1Data under steady-state conditions at each HRT

HRT (h) Organic loading rate Sucrose removal VSSa VSS/TSS Alkalinityb VFA(mmol sucrose/l day) (%) (mg/l) (mg/l as CaCO3) (mg COD/l)

24 58 96.3 7220 ± 832b 0.76 7043 ± 256 13697 ± 35720 70 95.5 7789 ± 761 0.82 6273 ± 324 12195 ± 22716 88 95.4 6291 ± 745 0.94 5624 ± 286 11404 ± 19412 117 94.6 5824 ± 602 0.98 4615 ± 337 10545 ± 32710 140 94.3 5674 ± 437 0.85 3168 ± 297 10058 ± 2078 175 93.7 5056 ± 512 0.84 3086 ± 318 9467 ± 1766 234 92.9 4735 ± 318 0.80 2764 ± 222 11691 ± 2184 351 91.8 3602 ± 322 0.77 2853 ± 217 11083 ± 236

aBed zone.bn = 3–6.

4 8 12 16 20 24

HRT (h)

0

1

2

HP

(mm

ol H

2/m

ol s

ucro

se)

0

20 0

40 0

HP

R(m

mol

H2/

L-da

y)

0

40

80

SH

PR

(mm

ole

H2/

g V

SS

-day

)

Fig. 3. Relationships between the speci9c hydrogen production rate(SHPR), hydrogen productivity (HP), hydrogen production rate(HPR) and hydraulic retention time (HRT).

hydrogen, mol H2=mol sucrose, HP), hydrogen produc-tion rate (the rate of hydrogen production from the fer-menter, mmol H2=l day, HPR), speci9c HPR (the hydro-gen production ability of the biomass in the bed zone,mmol H2=g VSS day, SHPR) and HRT. At an HRT of 8 hthe biogas production rate peaked with 47:2 l=day and thehydrogen content in the digestion gas was 42.4% (v/v).However, a constant HP value of 1:5 mmol H2=mol sucrosewas obtained at HRTs of 8–20 h. This HP value was higherthan values at 4–6 h (0.4–0:9 mmol H2=mol sucrose) and24 h (0:4 mmol H2 mol sucrose). HRT-dependent hydro-gen production characteristics were achieved with 8–20 h asthe optimal operating HRTs because of the high hydrogen

yield. At an HRT of 8 h, HPR and SHPR had peak valuesof 270:6 mmol H2=l day and 53:5 mmol H2=g VSS day,respectively. A decrease or an increase of 8–4 h in theHRT caused the HPR and SHPR values to decrease byabout 50% and 40%, respectively. Therefore, 8 h could beregarded as the optimal operating HRT based on the HPRand SHPR values. The marked decrease in HP, HPR andSHPR at short HRT resulted from hydrogen-producing mi-croorganism washout. The least biomass concentration wasexperienced at an HRT of 4 h (Table 1). Compared withother reactor systems, the SHPR value of the UASB systemwas low but the HP value was at the same level [6,14].Chang et al. [14] obtained e<cient hydrogen production(SHPR of 83:6 mmol H2=g VSS day at an HRT of 1 h)using a 9xed-bed reactor packed with activated carbon.

It is interesting to 9nd that the HRT-dependent character-istic of HP is diIerent from those of HPR and SHPR. HPmaintained nearly constant at the HRT ranges of 8–20 h.However, HPR and SHPR decreased with increasing HRT.HP denotes the hydrogen amount harvested from the con-sumed sucrose. A constant HP value implies that a similarincrement occurred between the produced hydrogen amountand degraded substrate sucrose. The hydrogen conversione<ciency was independent from HRT at 8–20 h HRT. HPRand SHPR denote the hydrogen production e<ciency of thereactor. The system’s hydrogen production e<ciency wasreadily aIected by HRT.

The hydrogen yield from sucrose is 6:0 mol H2=molsucrose [4]. Gibb’s free energy for hydrogen is56:7 kcal=mol. The lower hydrogen and sucrose heatingvalues were 58.3 and 1234 kcal=mol [4]. The followingenergy analysis was performed:

In theory, energy recovery from substrate = lower heat-ing value of hydrogen × H2 yield/lower heating value ofsucrose = 58:3 × 6:0=1234 = 28:34%. In this study, the en-ergy recovery from the substrate was 58:3×1:6=1234=7:6%.This is 26.7% of the theoretical value. This value is similarto a report of 28.34% [15].

F.-Y. Chang, C.-Y. Lin / International Journal of Hydrogen Energy 29 (2004) 33–39 37

HRT 12 h 10 h 8 h 6 h 4 h

120 160 200 240

Operation Time (d)

0.00

0.20

0.40

0.60

Gra

nule

Dia

met

er (

mm

)

Fig. 4. The change in mean granule diameter (bed zone).

3.3. Formation of hydrogen-producing granule

Granule formation is an indicator of successful USAB re-actor operation. The granule size distributions in the UASBreactor are illustrated in Fig. 4. An observation of the re-lationships between the granule diameter, HPR and SHPRdata indicates that these parameter values peaked at thesame HRT of 8 h (Figs. 3 and 4). This shows that thelarger the granules, the higher the hydrogen production abil-ity. However, the biomass (VSS) concentration was small(5056 mg=l) at this HRT. This suggests that at an HRTof 8 h, other dominant hydrogen-producing microorganismspecies were present. Another speculation is that at an HRTof 8 h, a shift in metabolic pathway to favor hydrogen pro-duction occurred. The sludge granulation was not obviousduring the start-up period but after 120 days of reactor oper-ation (an up-&ow velocity of 0:32 m=h). At this time, smallvisible 0.2–0:6 mm in diameter granules was observed inthe bed zone. At day 128, the average granule diameterwas 0:23 mm. As the reactor operation progressed, the aver-age granular diameter peaked (0:43 mm) at day 173 (HRT,8 h). This granular sludge diameter was smaller than that formethane-producing granular sludge (1.4–2:6 mm) [17,18].The up-&ow velocity of methane-producing granular sludgewas 0.19–0:26 m=h lower than hydrogen-producing granu-lar sludge (0:47 m=h) [16,17]. This resulted from vigorousreactor content mixing in the system. During hydrogen pro-duction the granulation arose from the joint action of pros-perous digestion gas release and rapid up-&ow velocity inthe reactor.

The biomass concentrations in the bed zone decreasedfrom 7220 mg VSS=l at an HRT of 24 h to 3600 mg VSS=lat an HRT of 4 h (Table 1). The biomass concentrations inthe bed zone were always 10% higher than that in the blan-ket zone (10 cm depth) throughout the experiment. How-ever, the biomass concentrations in the sedimentation zone(30 cm depth) were constant at 2500 mg VSS=l (Fig. 5).These biomass concentrations were higher than that for ananaerobic continuous-&ow stirred tank reactor feeding onsucrose (0.7–2:3 g VSS=l) [18]. This high level of biomass

4 8 12 16 20 24

HRT (h)

0

5000

10000

15000

20000

VS

S C

once

ntra

tion

(mg/

L)

Depth (cm)

10

20

30

Fig. 5. Biomass concentration pro9les as a function of reactor depth.

concentration is one of the expected characteristics of aUASB reactor.

The VSS to TSS concentration ratio (VSS/TSS ratio)in a biological reactor denotes the organic component inthe sludge. Because the in&uent was a synthetic wastewa-ter, no inorganic materials such as grit or clay contributedto decreasing the VSS/TSS value. Therefore, variationsin the VSS/TSS ratio indicate a change in the biomasscomponent. Table 1 shows that the VSS/TSS ratios variedwith HRT from 0.76 (HRTs 4 and 24 h) to 0.98 (HRT12 h). HRT-dependent changes in the biomass componentsoccurred during reactor operation. This phenomenon wasconsistent with the biomass concentration variation. Thedetails on the changes in the biomass component were notdetermined. A VSS/TSS ratio of 0.6–0.8 has been reportedin UASB reactors treating sewage [13]. In this study, thechange in the VSS/TSS ratios was not consistent with thehydrogen production.

Periodically discharging sludge is a viable means of deal-ing with sludge production from a biological system. Toevaluate the performance of a UASB reactor, it is importantto know whether the reactor is operated at its maximumsludge holdup. Alternatively, the reactor could be operatedunder conditions where the eLuent settleable solids con-centration is minimized by periodically discharging excesssludge before the maximum sludge holdup is attained [13].At an HRT of 8 h, based on the eLuent and sludge bed VSSconcentrations, the calculated mean cell retention time was22:2 h and the excess sludge discharge rate was 3:24 l=day.A high excess sludge discharge rate might enhance the domi-nant hydrogen-producing organisms by sorting other ineIec-tive hydrogen production micro&ora such as methanogens.There are few reports on excess sludge discharge [19].

3.4. Variation of VFA concentrations during hydrogenproduction

Anaerobic hydrogen production is always accompaniedwith VFA production. The VFA concentration distributionand their fractions have been successfully used as indicators

38 F.-Y. Chang, C.-Y. Lin / International Journal of Hydrogen Energy 29 (2004) 33–39

for monitoring hydrogen production [8]. The major liquidproducts were acetate, propionate, butyrate and ethanol withaverage concentrations of 2678–4665, 1240–2453, 3864–4650 and 864–2715 mg COD=l, respectively. At an HRT of8 h, the main eLuent VFA fractions were acetate 31.1% andbutyrate 54.1%. The high butyrate concentrations reveal thatthe reaction was butyrate fermentation. Clostridium speciesare, therefore, considered to be the dominant organisms inthe reactor because these organisms are responsible for bu-tyrate fermentation [20,21]. In our previous work C. pas-teurianum was also dominant in a CSTR fermenter seededwith sewage sludge for hydrogen production from sucrose[22].

3.5. Kinetic constants

Little information is available on the kinetics of biologicalhydrogen production processes. The following equation wasused for determining the Yg and Kd values [23]:

V =1YgD +

kdYg; (1)

V is speci9c substrate utilization rate, mg COD/mg day. Dis dilution rate (= HRT−1). Yg is yield coe<cient express-ing the cell mass produced per unit substrate. Kd is the en-dogenous decay coe<cient (day−1). The kinetic values forYg and Kd can be determined using the least-squares methodto plot V vs. D according to Eq. (1). The kinetic valueswere Kd 0:1 day−1 and Yg 0:1 g VSS=g COD. These dataprovide some useful information critical to designing an ef-fective UASB system for biohydrogen production. The Yg

value was at the same level as that in a hydrogen-producingUASB reactor fed on glucose (0.12–0:18 g VSS=g COD)[6]. Another Yg value for a mixed methanogenic granule cul-ture was 0:126 g VSS=g COD [24]. Comparing with otherreactor systems, the Kd of the UASB system was at the samelevel as for a methanogenic reactor fed on volatile fatty acid[25].

4. Conclusions

The system had a long period (8 months) of constanthydrogen production and substrate degradation e<cien-cies. These results demonstrate that stable and successfulhydrogen-producing UASB system performance can beobtained. Hydrogen production was HRT dependent withthe highest value occurring at an HRT of 8 h. The averagegranular diameter peaked at 0:43 mm and each gram of thesludge produced 53:5 mmol H2=day with a hydrogen gascontent of 42.4% (v/v) under optimal operation conditions.Butyrate and acetate were the main volatile fatty acids. Thekinetic values were Kd 0:1 day−1 and Yg 0:1 g VSS=g COD.A shorter HRT (¡ 8 h) might result in hydrogen-producingmicroorganism washout. Therefore, proper HRT control isnecessary to obtain e<cient hydrogen production.

Acknowledgements

The authors would like to thank the National ScienceCouncil of the Republic of China for 9nancially sup-porting this research under Contract No. NSC-89-2211-E035-035.

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