effect of the initial total solids concentration and initial ph on the bio-hydrogen production from...

7/17/2019 Effect of the initial total solids concentration and initial pH on the bio-hydrogen production from cafeteria food wa…

http://slidepdf.com/reader/full/effect-of-the-initial-total-solids-concentration-and-initial-ph-on-the-bio-hydrogen 1/8

Effect of the initial total solids concentration and initial pH

on the bio-hydrogen production from cafeteria food waste

Carlos Ramos a,b, Germa n Buitro n a,*, Iva n Moreno-Andrade a, Rolando Chamy b

aLaboratory for Research on Advanced Processes for Water Treatment, Unidad Academica Juriquilla, Instituto de Ingenierıa,

Universidad Nacional Autonoma de Mexico, Blvd. Juriquilla 3001, 76230 Queretaro, Mexicob Biochemical Engineering School, Pontificia Universidad Cato lica de Valparaıso, General Cruz 34, Valparaıso, Chile

a r t i c l e i n f o

Article history:

Received 28 February 2012

Received in revised form

13 June 2012

Accepted 15 June 2012

Available online 15 July 2012

Keywords:

Biological hydrogen production

Initial pH

OFUSW

Total solids concentrationFood waste

a b s t r a c t

In this paper, the influence of the initial pH and the total solids (TS) concentration on

hydrogen production from the organic fraction of cafeteria food waste at mesophilic

conditions in batch reactors was determined. It was found that the yield and specific

hydrogen production rate were influenced by the initial pH and the initial total solids

concentration. The highest hydrogen production rate, 2.90 mmolH2 /d, was obtained at

90 gTS/L and a pH of 5.5. Under this condition, the TS and chemical oxygen demand (COD)

removal were the lowest (10% as TS and 14% as COD). However, considering the specific

values, the highest specific degradation rate (192.2 mLH2 /gVSremoved /d) was obtained with

the lowest TS concentration and an initial pH of 7.0. It was found that the influence of the

TS concentration on hydrogen production was more significant than that of the initial pH

for this type of residues.

Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rightsreserved.

1. Introduction

Currently, there is great interest in hydrogen (H2) production

as a clean fuel because, during its combustion, only water is

produced as a by-product and because hydrogen has a high

specific energy content (33.3e39.4 kWh/kg) compared with

those of other fuels [1]. Hydrogen is an alternative to

conventional fossil fuels, which can be produced by steam

reforming, electrolysis, gasification and biological processes.Because fossil fuel processing and water electrolysis are

expensive, the biological production of hydrogen is more cost

effective, particularly when organic wastes can be used [2].

The application of the hydrolytic-acidogenic stage of the

anaerobic digestion process is a viable alternative to produce

hydrogen and to obtain an effluent rich in dissolved organic

matter composed of volatile fatty acids (VFA), primarily acetic,

propionic and butyric acid, lactate and solvents (acetone and

ethanol). In this case, H2 production is an economically viable

process due to the possibility of using a wide variety of non-

expensive residues as the organic fraction of municipal

solids waste (OFUSW) [3e5].

The OFUSW include fruit- and vegetable-based market

waste, uneaten food and food preparation leftovers from

residences and restaurants and organic residues from indus-

trial food production. The OFUSW is a significant environ-

mental problem, particularly in large cities in developing countries, where the typical disposal method is using a sani-

tary landfill or open dumping, due primarily to their simplicity

and low cost [6]. For this reason, the use of this waste can

reduce the environmental problem with the valorization of

products as hydrogen.

The initial total solids (TS) concentration affects hydrogen

production in severalways [7]. A high initialTS content canlimit

the mass transfer between the substrate and microorganisms,

* Corresponding author. Tel.: þ52 442 1926165; fax: þ52 442 1926185.E-mail address: [email protected] (G. Buitron).

Available online at www.sciencedirect.com

j o u r n a l h o m e p a g e : w w w . e l s e v i er . c o m / l o c a t e / he

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 3 2 8 8 e1 3 2 9 5

0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.ijhydene.2012.06.051

mailto:[email protected]

http://www.sciencedirect.com/science/journal/03603199

http://www.elsevier.com/locate/he







http://www.elsevier.com/locate/he

http://www.sciencedirect.com/science/journal/03603199

mailto:[email protected]



which reduces the hydrogen production [8]. In addition, the

initial concentration of the substrate may result in inhibition of

H2-producing bacteria due to an increase in volatile fatty acids

production.It hasbeen observed thathydrogen productionfrom

OFUSW at mesophilic temperatures (34e37 C) is influenced by

the initial pH, initial total suspended solids and inoculum

characteristics [8e12].

The optimal initial TS concentration to obtain hydrogendepends on the composition of the residue, the type and

configuration of the reactors and the activity of the biomass.

Theinitial TS values used by several authors varied from 1.3 to

50 g/L [9e16]. It has been reported that as the initial TS

increased, the hydrogen production also increased until

a variable maximal concentration was reached, which

depended on the residues’ characteristics [12e18]. However, it

was observed that the yield of hydrogen production varied

when different initial TS were used [12e17]. Relatively low TS

concentration have been reported for residues from cafeteria

[19] or they are used mixed with night soil sludge and sewage

sludge from a wastewater treatment plants [16]. Because

diluting OFUSW demands fresh water, it is worthwhile toinvestigate the potential in using higher TS concentrations

than those that have already been studied and without the

addition of co-substrates.

Selecting a proper pH is also crucial to enhance hydrogen

production due to the effects of pH on the hydrogenase

activity or metabolic pathways. Fan et al. [20] and van Ginkel

et al. [21] have reported that the maximum hydrogen yield

occurred at a pH value of 5.5, whereas Lee et al. [22] reported

that the maximum hydrogen yield was achieved at an initial

pH of 9.0. Davila-Vazquez et al. [17] found that the maximum

hydrogen yield occurred with an initial pH of 7. These con-

flicting results seem to be due to a lack of buffering capacity

that would prevent the pH from decreasing. From a practicalpoint of view, it is important to investigate how the initial pH

influences the hydrogen production when no pH control is

used during fermentation.

In this study, the influence of the initial pH and high total

solids concentrationon hydrogen production from the organic

fraction of cafeteria food waste at mesophilic conditions in

batch reactors was determined.

2. Materials and methods

2.1. Inoculum

Anaerobic granular sludge obtained from an upflow anaerobic

sludge blanket reactor treating brewery wastewater was used

as the inoculum after thermal conditioning as described

by [23].

2.2. Waste characteristics

The OFUSW was obtained from the cafeteria at the Juriquilla-

UNAM campus. The waste was collected once a week and

refrigerated at 4 C for preservation. In each collection, bones

and inert material (paper and plastic) were discarded; only the

fermentable matter was preserved. After selecting the waste,

it was crushed and homogenized in a blender. Finally, the

waste was frozen until it was used. The characteristics of the

OFUSW used in this study are presented in Table 1.

2.3. Experimental procedure

A batch reactor with a useful volume of 150 mL was used in

this study (glass Schott bottles, 300 mL of total volume). To

help purge the biogas, the reactors were mixed using an

orbital mixer (150 rpm) at a constant temperature of 36 C

during a reaction time of 2.1 d. Different total solids concen-

trations were used: 1, 5, 10, 40 and 90 g/L. To evaluate the

influence of the initial pH, each batch bottle was adjusted

using 0.1 N HCl or 0.1 N NaOH until an initial pH of 5.5, 6.0 and

7.0 was obtained. The pH was fixed at the beginning of the test

and decreased as fermentation in the batch reactors occurred.

It has been reported that alkalinity affects the hydrogen

production [24]. Thus, a nutrient stock solution containing the

following components (per liter) was used to ensure a proper

level of alkalinity: 200 g of NH4HCO3, 100 g of KH2PO4, 10 g of

MgSO47H2O, 1.0 g of NaCl, 1.0 g of Na2MoO42H2O, 1.0 g of

CaCl22H2O, 1.5 g of MnSO47H2O, and 0.278 g of FeCl2. A

nutrient stock solution with a volume of 0.5 mL was added to

the batch bottles. Each reactor was inoculated with 4 g of pre-

treated anaerobic sludge as inoculum; therefore, the initial

inoculum concentration in the reactor was 26.7 g/L of TS. The

chemical oxygen demand (COD) was quantified at the begin-

ning of the test. During the experiments, the biogas produced

was measured at regular interval times. After the biogas

production ceased (2.1 d), the pH, biogas composition (H2, CH4

and CO2), total and dissolved COD, total solids, volatile solids,

sulfate, lactate and volatile fatty acid (acetic and propionic

acids) concentrations were quantified.

2.4. Kinetic analysis

To evaluate the cumulative hydrogen production in response

to the different conditions, a kinetic analysis was conducted

using the modified Gompertz Equation (1) as described by [23].

The experiments were conducted in triplicate.

HðtÞ ¼ Hmax exp

exp

2:71828 Rmaxðl tÞ

Hmaxþ 1

(1)

Here, H(t) (mL) represents the total amount of hydrogen

produced at time t (h); Hmax (ml) represents the maximal

amount of hydrogen produced; Rmax (mL/h) is the maximum

hydrogen production rate, and l

(h) represents the lag time.

Table 1 e Characterization of the OFUSW used in thisstudy.

Parameter Value

Moisture, % 79.12 0.19

TS Wet basis, %w/w 20.88 0.24

VS Wet basis, %w/w 19.48 0.22

Density, g/L 805.04 0.20

NH3eN, g/L 0.65 0.15

CODtotal, g/L 140.55 11.78

pH 4.6e5.0

Average of five tests standard deviation.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 3 2 8 8 e1 3 2 9 5 13289







2.5. Analytical methods

Quantification of the biogas produced was achieved through

the use of an automated system for biogas measurement and

monitoring [25]. The equipment is based on manometric

measurements of the biogas produced during the fermenta-

tion of the test substances in closed bioreactors. After each

measurement, the system is purged, compensating thereactor pressure to the atmospheric pressure. Hydrogen,

carbon dioxide and methane were analyzed with a gas chro-

matograph (Agilent 6890N) equipped with a thermal conduc-

tivity detector following the methodology reported in Ref. [23].

Lactate was determined by ion chromatography using a Dio-

nex ICS-1500 chromatograph that used an REIC IonPac AS23

250 4 mm column. The eluent consisted of a mixture of

0.8 mM NaHCO3 and 4.5 mM Na2CO3 using an isocratic flow at

1 mL/min and 30 C. An anion suppressor current of 25 mA

was used. Ammonia (NeNH3) and the COD were quantified

with a HACH kit. The TS and volatile solids (VS), as

well as alkalinity, were determined according to standard

methods [26].

3. Results and discussion

3.1. Hydrogen production

Fig. 1A shows the molar hydrogen production as a function of

the total solids concentration of the OFUSW and the initial pH.

A clear, direct relationship was observed; the hydrogen

production increased as the substrate concentration

increased. In general, the highest hydrogen production was at

a pH of 7.0, except with a concentration of 90 g/L, where1.21 mmol was produced.

The volumetric yields (Y H2 ) were evaluated considering the

total solids added and the fraction of the removed VS, as pre-

sented in Fig. 1B and C, respectively. An inverse relationship

was found between the hydrogen yield and total solids

concentration.Thehighestvalueswereobservedforthelowest

TS concentration. However, this analysis does not represent

the potentially available substrate due to hydrolysis. Hydro-

lysis is normally rate-limiting if the substrate is in a particulate

form, which is the case for the OFUSW [27]. Thus, the avail-

ability of fermentable substrate for hydrogen-producing

bacteria will depend on the hydrolysis rate. When the data

are analyzed by removing the VS (Fig. 1C), two sets of resultsdepending on the initial TS concentration were observed: first,

for 1 gTS/L and second, for higher initial TS concentrations. In

the case of 1 gTS/L, a maximal yield of 25.3 mLH2 /gVSremoved

wasfound. The increase in total solidsconcentration, from 1 to

5 g/L, produced a decrease in Y H2, which was similar for each

initial pH. However, the hydrogen production yield presented

a gradual increase as the TS concentration increased from 5 to

90 gTS/L; the trend was similar for the three pHs studied. The

highest hydrogen yield observed in the case of the lowest TS

concentrationcouldbebecausethereexistsagooddistribution

of the inoculum and the substrate, minimizing any local

shortages of nutrients and diluted potential toxins [28]. As the

concentration increased five-fold (5 gTS/L), the distribution of

the inoculum-substrate was not as goodas in themorediluted

TS concentration. However, as the TS concentration increased,

the availability of the substrate was higher, allowing the

reproduction of hydrolytic microorganisms and increasing the

bioavailability of the OFUSW for hydrogen-producing micro-

organisms. Thus, as the dissolved substrate increased, the

hydrogen yield increased [29].

Fig. 1 e Hydrogen production as a function of total solids

concentration of the OFUSW and pH. A) molar production,

B) volumetric yield considering the added TS and C)

volumetric yield considering the removed VS.








It has been reported that the yield obtained from several

agricultural wastes [30] showed large variations. For food

waste, Y H2 can vary from 3 to 196 mL/gVS and depends on the

temperature, composition of the substrate, inoculums and the

type of process used.

It was observed that the increase in Y H2 was not directly

relatedwith the increase in the initial solids concentration. An

increment of 18-fold in the concentration (from 5 to 90 g/L)only generated an increment of 7.6-fold in the Y H2 (at pH 6.0).

For all casesexcept when 90 gTS/L was used, a greateramount

of hydrogen was produced with a high initial pH of 7.0, fol-

lowed by 6.0 and 5.5. These results demonstrated that the Y H2

depends on the solids concentrations and pH. This behavior

can be attributed to the consumption of hydrogen by homo-

acetogenic bacteria [31].

3.2. Kinetics

To determine the hydrogen production rate, the kinetic coef-

ficients of the Gompertz model were evaluated. Fig. 2 showsan example of the fitted data obtained, and Table 2 summa-

rizes the obtained values. In general, the model was in good

agreement with the experimental data (the regression coeffi-

cients, r2, were greater than 0.9). The maximum hydrogen

production rate was 64.92 3.37 mLH2 /d (2.90 0.15 mmolH2 /

d) and was obtained at 90 gTS/L and a pH of 5.5. No lag periods

were observed for the conditions of 1 and 5 gTS/L concentra-

tions; however, a lag-time from 10 to 11.5 h was observed for

initial TS concentrations greater than 10 g/L (Table 2).

The specific hydrogen production rate (SHP) was evaluated

by dividing the Rmax by the total amount of removed VS or

COD for each test. Similar to the yield, the results can be

analyzed considering two sets of data. When the TS concen-tration was 1 g/L, the higher values for all the conditions

studied were obtained, irrespective of the pH value (Table 2). A

maximum value of 192.2 19.9 mLH2 /gVSremoved /d (and

135.3 12.3 mLH2 /gCODremoved /d) was obtained when the

initial pH was 7.0. From 5 to 90 gTS/L, the SHP varied from

8.7 1.0 to 66 3.8 mLH2 /gVSremoved /d, respectively. The

highest SHP observed in the case of the lowest TS concen-

tration could be because the good distribution of the inoculum

and the substrate. For all cases, the highest values for the SHP

were obtained when the initial pH was 7.0. No lag time was

obtained at low initial TS concentrations. Nevertheless, a lag

time of 10e11.5 h was observed when the initial TS concen-

tration was greater than 10 gTS/L. For all cases, the pH has no

influence on the lag phase.

Dong et al. [32] studied the hydrogen production from

seven varieties of individual components of OFUSW using

batch experiments at 37 C and observed that the SHP varied

from 49 to 112 mL H2 /gVS/d. The difference in the specificrates obtained in the present investigation and those obtained

by the other authors can be attributed to the complex nature

of the OFUSW and the inoculum used in each case.

3.3. COD yield

In Fig. 3 (A), the SHP based on the VS removal was plotted

versus the SHP based on the COD removal, and the linear

regression was adjusted. The slope of the curve representsthe

amount of COD removed per amount of VS removed. As dis-

cussed before, two clear sets of data were observed with an

excellent regression coefficient. The data obtained for 1 gTS/Lindicated that much more COD was removed per unit of VS

removed (0.142 gCOD/gVS) than for the other data

(0.041 gCOD/gVS) at the higher concentrations, which indi-

cates that for lower concentrations, more organic matter is

available per unit of total solids, implying that hydrolysis

occurs more rapidly than in the cases with high initial TS

concentrations. This result can explain the higher hydrogen

yield observed for the initial TS concentration of 1 g/L.

3.4. Hydrogen content

The hydrogen content of biogas at different TS concentrationsand initial pHs is shown in Fig. 3(B). For each total solids

concentration, the biogas was composed of only H2 and CO2,

with no methane detected for any case, indicating that the

pre-treatment was appropriate to avoid the growth of hydro-

genotrophic and acetoclastic methanogenic microorganisms.

The higher content (26.8%) was obtained for 1 gTS/L at an

initial pH of 7.0. For higher TS concentrations, the content

decreased, and at TS concentrations greater than 10 gTS/L, the

percentages stabilized at approximately 15%, with no signifi-

cant influence from the pH.

Fig. 2 e Kinetic data for selected values and the adjustment of the Gompertz model. A) Initial pH of 5.5 (1 and 5 gTS/L) and B)

Initial pH of 5.5 (40 gTS/L), 6.0 (90 gTS/l) and 7.0 (10 gTS/L).








3.5. Fermentation products

Acetic and lactic acids were monitored because it was found

that they were the principal fermentation products. Fig. 4(A)

shows the evolution of the acetic acid concentration as

a function of the total solids concentrations and initial pH. It

was observed that the increase in the initial TS concentration

produced an increase in the acetic acid concentration. A

considerable increase, greater than 1000 mg/L, was observed

when the initial TS concentration was greater than 10 g/L. The

highest value, 4016 98 mg/L, was obtained for 40 gTS/L at

a pH of 6. It is interesting to note that at 90 gTS/L and a pH of

7.0, the amount of acetic acid was greater than that when thepH was 6; however, the SHP did not increase. This behavior

indicates that the acetic acid fermentation is not the only

reaction present in this case; homoacetogenic reactions are

also occurring that consume the produced hydrogen. It has

been shown that homoacetogenic bacteria as Clostridium ace-

ticum can grow using H2 and CO2 to generate acetic acid and

water [33], where the optimum pH is 8.5. Thus, a pH of 7 could

create a more suitable environment for the reproduction of C.

aceticum. The aforementioned results indicate that hydrogen

production is associated with acetic acid production. The

lactate concentration increased proportionally to the total

solids concentration. The highest lactate value was observed

at 90 gTS/L and a pH of 7.0 (15.6 g lactate/L). It could be that the

hydrogen production was redirected to lactate, which could

possibly generate inhibition when its concentration becomes

greater than 3.4 g/L. This fact agrees with the increase of the

lag phases observed when the concentrations were greater

than 10 gTS/L. Other fermentation products were observed but

in lower concentrations, such as propionic (69e150 mg/L),

butyric (50e1000 mg/L), isobutyric (18e281 mg/L) and iso-

valeric (84e

419 mg/L) acids, acetone (116e

2419 mg/L) andethanol (26e487 mg/L). For these components, the higher

concentrations were observed at the higher TS concentration.

3.6. Alkalinity and pH variation

It has been observed that alkalinity influences the hydrogen

production [19,24,34]. The OFUSW used in this study as feed-

stock had a relatively low alkalinity (<100 mg CaCO3 /L).

Fig. 3 e (A) SHP based on VS removal as a function of SHP based on COD removal (all initial pH included) and (B) content of

hydrogen in biogas as a function of initial total solids concentration and pH.

Table 2 e Initial conditions and Gompertz model parameters for the OFUSW as a function of TS and initial pH. The volume values are at STP conditions.

Condition Hmax Rmax l SHP

TS, g/L Initial pH mL H2 mmolH2 /d mLH2 /d h mLH2 /gVSremoved /d mLH2 /gCODremoved /d

1.0 7.0 2.65 0.27 0.90 0.09 20.15 2.09 0.0 0.0 192.2 19.9 135.3 12.3

1.0 6.0 1.36 0.15 0.55 0.06 12.31 1.24 0.0 0.0 107.4 11.2 75.0 6.2

1.0 5.5 1.52 0.20 0.45 0.05 10.07 1.01 0.0 0.0 89.1 7.8 62.7 5.55.0 7.0 3.56 0.16 0.46 0.02 10.30 0.47 0.0 0.0 22.6 1.0 43.1 4.4

5.0 6.0 2.24 0.2 0.30 0.01 6.72 0.29 0.0 0.0 14.9 1.6 27.5 3.0

5.0 5.5 1.34 0.15 0.17 0.01 3.81 0.017 1.3 0.1 8.7 1.0 16.1 1.2

10.0 7.0 8.71 0.35 2.20 0.09 49.25 2.06 10.0 0.1 58.8 2.9 143.7 8.3

10.0 6.0 6.25 0.42 0.62 0.07 13.88 1.52 11.5 0.2 19.0 8.0 44.7 4.2

10.0 5.5 3.80 0.50 0.53 0.06 11.86 1.30 11.0 0.2 20.5 2.3 49.8 5.5

40.0 7.0 12.98 0.38 1.17 0.02 26.19 0.52 11.0 0.2 23.8 0.7 57.1 1.14

40.0 6.0 10.75 0.42 1.25 0.03 27.98 0.83 11.0 0.3 18.8 0.43 37.1 0.85

40.0 5.5 10.97 0.35 1.25 0.02 27.98 0.78 11.2 0.3 18.3 0.45 37.5 0.85

90.0 7.0 23.18 1.20 2.60 0.13 58.20 3.03 11.0 0.1 66.0 3.8 183.8 10.1

90.0 6.0 27.09 1.4 2.10 0.11 47.01 2.53 11.5 0.1 66.0 3.7 144.5 11.2

90.0 5.5 25.07 1.3 2.90 0.15 64.92 3.37 11.0 0.1 49.4 2.6 120.3 13.2

Average of three tests standard deviation.








However, the buffer capacity of the mixture, obtained after

the addition of the nutrients, increased the initial alkalinity to

1058 147 mg CaCO3 /L. The alkalinity/COD ratio was calcu-

lated considering the initial total COD of the mixture. The ratiovaried from 0.0146 0.002 to 0.808 0.138 gCaCO3 /gCOD, for

the initial TS concentrations from to 90 to 1 g/L, respectively.

This range is close to the value reported by Ref. [34] as the

optimum range (0.042e0.102 g CaCO3 /g COD) for the conver-

sion of sucrose into hydrogen in mesophilic conditions. Under

thermophilic conditions [24] a higher optimal alkalinity ratio

of 0.11 gCaCO3 /gCOD has been suggested as needed to maxi-

mize the hydrogen productivity of organic solid waste. In our

study an elevated hydrogen production and yield was

observed for the elevated TS concentration, indicating that

such amount of alkalinity was sufficient to sustain the

hydrogen production. Directly adding chemicals for buffering

will inevitably increase the cost of hydrogen production. Inpractice alternative cheap buffer sources could be considered

as municipal sewage sludge [19].

ThepH was fixed at the beginning ofthe test and decreased

asthefermentationinthebatchreactorsoccurred.ThefinalpH

was conditionedby the acids concentration in the reactor. The

higher final pH values were obtained with lower total solids

concentrations. The influence of the TS concentration on the

final pH was more significant than the initial pH on each TS

concentration. Fig. 5 shows the average final pH for the three

different initial pHs for each initial TS concentration tested.

The increase in the solids concentration decreased the pH to

nearly 4.0 when the TS concentration was 90 g/L. The buffer

capacity of the mineral media maintained the pH at approxi-mately 6.0 for the lower total solids concentrations (1e10 g/L);

however, the pH was less than 5.0 (nearlya pH of4.0) when the

solids content was greater than 40e90 g/L. A high organic acid

production was the cause of such variations. Additionally, in

Fig. 5, the average pH variation (D ¼ pHinitial e pHfinal) was

computed for each TS concentration. For the high TS concen-

trations (40 and 90 g/L), the delta values were 2.1 and 2.3 and

significant acidification was not observed.

3.7. TS and COD removal

The TS and total COD removal as a function of the initial TS

concentration of the OFUSW are presented in Fig. 6. It was

found that the total solids and COD removal decreased as the

initial total solids concentration increased, indicating that the

highest levels of substrate transformation occurred at 1 gTS/L

(80% as TS and 50% as COD). It has previously been observedthat the hydrolytic-acidogenic phase during solids waste

degradation can be the limiting step because waste is often

particulate material [35]. For this reason, an appropriate

solubilization and organic matter transformation process is

required, which is affected primarily by the substrate

concentration. A compromise between the hydrogen

production and TS degradation must be achieved. It was

observed that with low TS concentrations, a high SHP was

produced and high TS and COD removal were also observed.

However, to achieve such a low concentration, the OFUSW

must be diluted. On the contrary, when the TS concentration

increased, the hydrogen production and SHP increased;

however, the TS removal was poor, i.e., the maximal capa-bilities for hydrogen extraction are presented here. To finish

the stabilization of the TS and the removal of COD, the pre-

digested mixture can be treated in a methanogenic reactor

to produce methane in the biogas.

Fig. 4 e Effect of TS concentration and initial pH on acetic acid (A) and lactate (B) production.

Fig. 5 e Effect of the TS concentration on the final pH and

on the delta pH.








4. Conclusions

The influence of the initial pH and the initial total solidsconcentration on hydrogen production from the organic

fraction of urban solids waste was investigated. The highest

hydrogen production rate (2.90 mmolH2 /d) was obtained at

90 gTS/L with a pH of 5.5. Under this condition, the TS and

COD removal were the lowest (10% as TS and 14% as COD).

However, when the specific values were calculated consid-

ering the solids removal, a maximal specific degradation

rate of 192.2 mLH2 /gVSremoved /d was obtained at the lowest

TS concentration tested at an initial pH of 7.0. At this

condition, a higher hydrolysis efficiency of the TS was

observed (0.142 gCOD removed per g of VS removed),

producing a higher hydrogen content in the biogas (23%).

The Y H2 decreased as the solids concentration increased;however, for TS concentrations greater than 5 g/L, the SHP

increased as the initial TS concentration increased. No

significant differences were observed on the SHP at the same

initial TS concentration when the initial pH ranged from 5.5

to 7. It was observed that higher final pH values were

obtained with lower total solids concentrations. High SHPs

were produced at high TS concentrations but with low TS

and COD removal. To finish the stabilization of the OFUSW,

the pre-digested mixture can be treated in a methanogenic

reactor, concomitantly generating methane in the biogas.

Acknowledgments

This research was supported by CONACYT (Project 100298)

and DGAPA-UNAM (PAPIIT IB100612). The authors acknowl-

edge the technical help of Jaime Perez Trevilla.

r e f e r e n c e s

[1] Edwards PP, Kuznetsov VL, David WIF, Brandon NP.Hydrogen and fuel cells: towards a sustainable energy future.

Energy Policy 2008;36:4356e62.

[2] La Licata B, Sagnelli F, Boulanger A, Lanzini A, Leone P,Zitella P, et al. Bio-hydrogen production from organic wastesin a pilot plant reactor and its use in a SOFC. Int J Hydrogen

Energy 2011;36:7861e5.[3] Zhu H, Parker W, Conidi D, Basnar R, Seto P. Eliminating

methanogenic activity in hydrogen reactor to improve biogasproduction in a two-stage anaerobic digestion process co-digesting municipal food waste and sewage sludge. BioresTechnol 2011;102:7086e92.

[4] Mohan SV, Mohanakrishna G, Goud RK, Sarma PN.Acidogenic fermentation of vegetable based market waste toharness biohydrogen with simultaneous stabilization. BioresTechnol 2009;100:3061e8.

[5] Chu C-F, Li Y-Y, Xu K-Q, Ebie Y, Inamori Y, Kong H-N. A pH-and temperature-phased two-stage process for hydrogenand methane production from food waste. Int J HydrogenEnergy 2008;33:4739e46.

[6] Kanat G. Municipal solid-waste management in Istanbul.

Waste Manage 2010;30:1737e45.[7] Maintinguer SI, Fernandes BS, Duarte ICS, Saavedra NK,

Adorno MAT, Varesche MB. Fermentative hydrogenproduction by microbial consortium. Int J Hydrogen Energy2008;33:4309e17.

[8] Gomez X, Cuetos MJ, Prieto JI, Moran A. Bio-hydrogenproduction from waste fermentation: mixing and staticconditions. Renew Energ 2009;34:970e5.

[9] Fountoulakis MS, Manios T. Enhanced methane andhydrogen production from municipal solid waste and agro-industrial by-products con-digested with crude glycerol.Biores Technol 2009;100:3043e7.

[10] Shi Y, Zhao X-T, Cao P, Hu Y, Zhang L, Jia Y, et al. Hydrogenbio-production through anaerobic microorganismfermentation using kitchen wastes as substrate. Biotechnol

Lett 2009;31:1327e33.[11] Wang X,ZhaoY-C.A benchscalestudyof fermentativehydrogen

and methane production from food waste in integrated two-stage process. Int J Hydrogen Energy 2009;34:245e54.

[12] Liu D, Liu D, Zeng RJ, Angelidaki I. Hydrogen and methaneproduction from household solid waste in the two-stagefermentation process. Water Res 2006;40:2230e6.

[13] Ma J, Ke S, Chen Y. Mesophilic biohydrogen production fromfood waste. 2nd International Conference on Bioinformaticsand Biomedical Engineering 2008:2841e2844.

[14] Shin H-S, Youn J-H, Kim S-H. Hydrogen production from foodwaste in anaerobic mesophilic and thermophilicacidogenesis. Int J Hydrogen Energy 2004;29:1355e63.

[15] Kim S-H, Han S-K, Shin HS. Feasibility of hydrogenproduction by anaerobic co-digestion of food waste and

sewage sludge. Int J Hydrogen Energy 2004;29:1607e16.

Fig. 6 e Effect of the TS concentration and initial pH on TS and total COD removal.








[16] Lay JJ, Lee YJ, Noike T. Feasibility of biological hydrogenproduction from organic fraction of municipal solid waste.Water Res 1999;33:2579e86.

[17] Davila-Vazquez G, Alatriste-Mondragon F, de Leon-Rodrıguez A, Razo-Flores E. Fermentative hydrogenproduction in batch experiments using lactose, cheese wheyand glucose: influence on initial substrate concentration andpH. Int J Hydrogen Energy 2008;33:4989e97.

[18] Valdez-Vazquez I, Poggi-Varaldo HM. Hydrogen productionby fermentative consortia. Renew Sust Energ Rev 2009;13:1000e13.

[19] Zhua H, Parker W, Basnar R, Proracki A, Falletta P, Beland M,et al. Buffer requirements for enhanced hydrogen productionin acidogenic digestion of food wastes. Biores Technol 2009;100:5097e102.

[20] Fan Y, Li C, Lay J-J, Hou H, Zhang G. Optimization of initialsubstrate and pH levels for germination of sporing hydrogen-producing anaerobes in cow dung compost. Biores Technol2004;91:189e93.

[21] van Ginkel S, Sung S, Lay JJ. Biohydrogen production asa function of pH and substrate concentration. Environ SciTechnol 2001;35:4726e30.

[22] LeeYJ, MiyaharaT, NoikeT. Effectof pH onmicrobial hydrogen

fermentation. J Chem Technol Biotechnol 2002;77:694e8.[23] Buitron G, Carvajal C. Biohydrogen production from Tequila

vinasses in an anaerobic sequencing batch reactor: effect of initial substrate concentration, temperature and hydraulicretention time. Biores Technol 2010;23:9071e7.

[24] Valdez-Vazquez I, Poggi-Varaldo HM. Alkalinity and hightotal solids affecting H2 production from organic solid wasteby anaerobic consortia. Int J Hydrogen Energy 2009;34:3639e46.

[25] Moreno-Andrade I, Moreno G, Buitron G. Automated devisefor biogas production measurement during anaerobicwastewater degradation. Biomass and Waste to EnergySymposium. Venice 2006.

[26] American Public Health Association/American Water WorksAssociation/Water Environment Federation. Standardmethods for the examination of water and wastewater. 21thed. Baltimore: Port city press; 2005.

[27] Vavilin VA, Rytova SV, Lokshina LY. A description of hydrolysis kinetics in anaerobic degradation of particulateorganic matter. Biores Technol 1996;56:229e37.

[28] Zhang B, He P-J, Lu ¨ F, Shao L, Wang P. Extracellular enzyme

activities during regulated hydrolysis of high-solid organicwastes. Wat Res 2007;41:4468e78.

[29] Nopharatana A, Pullammanappallile PC, Clarke WP. Adynamic mathematical model for sequential leach bedanaerobic digestion of organic fraction of municipal solidwaste. Biochem Eng J 2003;13:21e33.

[30] Guo XM, Trably E, Latrille E, Carrere H, Steyer JP. Hydrogenproduction from agricultural waste by dark fermentation:a review. Int J Hydrogen Energy 2010;35:10660e73.

[31] Schiel-Bengelsdorf B, Du ¨ rre P. Pathway engineering andsynthetic biology using acetogens. FEBS Lett 2012;586:2191e8.

[32] Dong L, Zhenhong Y, Yongming S, Xiaoying K, Yu Z.Hydrogen production characteristics of the organic fractionof municipal solid wastes by anaerobic mixed culture

fermentation. Int J Hydrogen Energy 2009;34:812e20.[33] Sim JH, Kamaruddin AH, Long WS, Najafpour G.

Clostridiumaceticumda potential organism in catalyzing carbon monoxide to acetic acid: application of responsesurface methodology. Enzym Microb Tech 2007;40:1234e43.

[34] Lin CY, Lay CH. Effects of carbonate and phosphateconcentrations on hydrogen production using anaerobicsewage sludge microflora. Int J Hydrogen Energy 2004;29:275e81.

[35] Hussy I, Hawkes FR, Dinsdale R, Hawkes DL. Continuousfermentative hydrogen production from a wheat starch co-product by mixed microflora. Biotechnol Bioeng 2003;84:619e26.






effect of the initial total solids concentration and initial ph on the bio-hydrogen production from...

Documents