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Chemical Engineering Journal 171 (2011) 411– 417

Contents lists available at ScienceDirect

Chemical Engineering Journal

j ourna l ho mepage: www.elsev ier .com/ locate /ce j

he effect of different pretreatments on biomethanation kinetics of industrialrganic Fraction of Municipal Solid Wastes (OFMSW)

.A. Fdez.-Güelfoa,∗, C. Álvarez-Gallegoa, D. Sales Márquezb, L.I. Romero Garcíaa

Department of Chemical Engineering and Food Technology, Faculty of Science, University of Cadiz, 11510 Puerto Real, Cadiz, SpainDepartment of Environmental Technologies, Faculty of Marine and Environmental Sciences, University of Cadiz, 11510 Puerto Real, Cadiz, Spain

r t i c l e i n f o

rticle history:eceived 26 October 2010eceived in revised form 25 March 2011ccepted 28 March 2011

a b s t r a c t

This paper studies the effect of both thermochemical (under different pressures, temperatures and alka-line agent dosage) and biological (using mature compost, sludge and the fungus Aspergillus awamori)pretreatments on the kinetic of dry-thermophilic (20% Total Solids and 55 ◦C) anaerobic digestion ofindustrial organic fraction of the municipal solid wastes (OFMSW).Municipal solid waste, which was not

eywords:naerobic digestionFMSWretreatmentinetic

collected separately, from an industrial 30 mm-trommel placed in a Mechanical and Biological Treatment(MBT) plant was used in this study.The kinetic equations for substrate-utilization and product-generationfrom Romero’s model (1991) have been used to characterize process kinetics and determine the effect ofpretreatments on kinetic parameters. The results obtained in this study indicate than the best pretreat-ment is precomposting, since an increase of the microorganism’s maximum specific growth rate (�max)between 160 and 205%, with respect to non-pretreated OFMSW, can be achieved.

. Introduction

It is recognized that the methanogenic stage for soluble organicatter degradation is the rate-limiting step of anaerobic digestion.evertheless, studies developed with primary sludge and organicomplex substrate have concluded that the hydrolysis of organicarticles to soluble substrate is the rate-limiting step in solid wasteonversion during the digestion process [1]. Thus, for complexaste, the transport of easily assimilable hydrolyzed compounds

y microorganisms does not constitute the rate-limiting step ofhe process. In this respect, working with cellulose particles didot find a significant accumulation of hydrolyzed products in theeactor and concluded that the conversion of cellulose particles tooluble products was the rate-limiting step of the digestion process.

Lee and Donaldson [2] also observed a low concentration of sol-ble compounds in cellulose fermentation. The hydrolysis rate ofolymers as cellulose or fats, discussed by Soubes [3], turned out toe lower than the catabolic rate of the resultant products of hydrol-sis. Therefore, the hydrolytic stage is considered the rate-limitingtep in the digestion process. By applying activity tests to the solu-le and insoluble fraction of slaughterhouse wastewater, Galisteo

t al. [4] verified that the hydrolysis of complex organic materialas also the rate-limiting step in the degradation process.

∗ Corresponding author. Tel.: +34 956016379.E-mail address: alberto.fdezguelfo@uca.es (L.A. Fdez.-Güelfo).

385-8947/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.cej.2011.03.095

© 2011 Elsevier B.V. All rights reserved.

On the basis of conclusions extracted from previous studies,several methods – such as physical, chemical or biological pretreat-ments and combinations among them – have been developed toimprove the biodegradability of complex waste [5–8].

The main objectives of pretreatments for biomethanation pro-cesses are to modify the structure of complex material (generallylignin and cellulose fractions), decrease the degree of polymeriza-tion, weaken the lignin bonds with carbohydrates and increase thesurface area of waste particles.

All these results indicate the relevance of studying the pre-treatment of OFMSW in order to increase its degradation rate byenhancing the hydrolytic stage of complex wastes such as OFMSW.

1.1. Kinetic model description

Process modeling, based on kinetic models, allows the effect ofthe most important process variables on system performance to bepredicted. In this sense, the development of adequate models andtheir parameterization by model equations fitted to experimentalresults, obtained in specific assays, is a very important task.

In addition, industrial plants for the anaerobic treatment oforganic fraction of municipal solid waste are characterized by abroad variation in the waste composition fed to reactors and hence,process modeling acquires a special significance in determining the

optimum operating conditions.

In this study, the substrate consumption model proposed byRomero [9] was used. This model has been used successfully tofit the experimental results of the anaerobic digestion of different

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12 L.A. Fdez.-Güelfo et al. / Chemical E

rganic wastes: wine vinasses [9–11], sludge from WWTP [12] andFMSW [13].

The model assumes that the substrate consumption rate is giveny

rs = −dS

dt= �max

(h − S) · (S − SNB)h − SNB

(1)

here SNB represents the non-biodegradable substrate concentra-ion (ML−3). S represents the substrate concentration (ML−3); hs the maximum substrate concentration that can be invested inhe biomass formation (ML−3) and is equal to the initial viableoncentration of microorganism XV0/YX/S (expressed as substrateoncentration by means of the yield coefficient) added to the initialubstrate concentration S0

= XV0

YX/S+ S0

max represents the maximum specific growth rate of the microor-anisms (t−1); t is the operation time (t).

For batch processes, the expression relating substrate concen-ration to incubation time can be obtained by integrating Eq. (1):

= h(S0 − SNB) + Snb(h − S0)exp(�max t)(S0 − SNB) + (h − S0)exp(�max t)

(2)

simplified model equation is obtained when the initial con-entration of microorganisms is higher than the concentration oficroorganisms that can be generated during the fermentative

rocess. In this case, the active microorganism population is highnough to avoid the initial lag phase.

V0 � YXS(S0 − SNB) ⇒ h − S

h − SNB

∼= 1 (3)

rS = −dS

dt= �max(S − SNB) (4)

s in the previous case, the integration of the simplified modelEq. (4)) leads to the expression relating substrate concentrationo incubation time:

= (S0 − SNB) · exp(−�max t) + SNB (5)

n anaerobic processes, most authors assume that the formation ofhe main products of the process (volatile fatty acids and methane)esponds to a growth associate mechanism [14]; consequently, theifferent specific rates (microorganism growth, product generationnd substrate consumption) are directly proportional to each other.ence, assuming that a stoichiometric coefficient can be used to

elate the substrate consumption rate with the product generationate:

dP

dt= −˛

(dS

dt

)(6)

here “P” represents the product concentration (VFA, ammonium,iogas components or other product from the microbiologicalctivity) and “˛” is the stoichiometric yield coefficient from producto substrate.

On the basis of Eq. (6), the following expression can be obtainedor methane production:

(CH4) = P0(CH4) + ˛CH4 (S0 − S) (7)

ssuming that the initial methane P0(CH4) production is null, andeplacing the substrate concentration expression from Eq. (2) (gen-

ral model equation) in Eq. (7):

(CH4) = ˛CH4

[S0 − h(S0 − SNB) + SNB(h − S0)exp(�max t)

(S0 − SNB) + (h − S0)exp(�max t)

](8)

ering Journal 171 (2011) 411– 417

The term (h − S0) is equivalent to (XV0/YX/S); i.e., the quantity ofthe initial active biomass (expressed in terms of substrate con-centration) and (S0 − SNB) is equivalent to the initial biodegradablesubstrate (S0B). Thus, Eq. (8) can be written as:

P(CH4) = ˛CH4

[exp(�maxt) − 1

(1/(h − S0)) + (1/(S0 − SNB)exp(�maxt)

](9)

Reordering the terms:

P(CH4) = exp(�maxt) − 1(YXS/˛CH4 XV0) + (1/˛CH4 S0B)exp(�maxt)

(10)

The term (˛CH4 · S0B) represents the maximum attainable methaneproductivity (when all the initial biodegradable substrate were con-verted to methane) and is denoted as “�CH4 ”

P(CH4) = �CH4

1 − exp(−�maxt)(YXSS0B/XV0)exp(−�maxt) + 1

(11)

when the evolution of substrate concentration can be representedby the simplified model (no lag phase), a simplified model formethane production can also be proposed by replacing the expres-sion of substrate concentration given by Eq. (5) in Eq. (7):

P(CH4) = ˛CH4 (S0 − [(S0 − SNB) · exp(−�maxt) + SNB]) (12)

Reordering:

P(CH4) = ˛CH4 (S0 − SNB) [1 − exp(−�maxt)] (13)

Eq. (13) could be rewritten, since the term (S0 − SNB) is equivalent tothe initial biodegradable substrate (S0B). Furthermore, as in Eq. (11),the significance of the term (˛CH4 · S0B) is the maximum attainablemethane productivity “�CH4 ”. Hence:

P(CH4) = ˛CH4 S0B[1 − exp(−�maxt)] = �CH4 [1 − exp(−�maxt)]

(14)

1.2. Computer support

Linear and non-linear regressions were applied to fit the modelequations to the experimental data and determine the model’skinetic parameters by using a statistical program (Software Stat-graphics 5.0). The non-linear regression is based on Marquardt’sleast squares residual algorithm [15].

2. Materials and methods

2.1. Experimental design

A series of experiments were carried out to compare the effectof different pretreatments on the anaerobic degradation of OFMSWand determine their influence on biodegradation kinetics. A batteryof tests consisting of six batch 2-L stirred tank reactors with a tem-perature control device (Patent no. WO 2006/ 111598 A1 – WorldIntellectual Property Organization) was performed (Fig. 1).

One of the reactors was used as the control assay with non-pretreated OFMSW. Another three reactors were used to studythe effect of biological pretreatments on OFMSW when differentbiological agents were used: mature compost, sludge from wastew-ater treatment plants (WWTP) and the fungus Aspergillus awamori.Lastly, the remaining two reactors were used to study the effectof thermochemical pretreatments on OFMSW by modifying thetype of atmosphere (inert (N2) and oxidizing (synthetic air)) during

pretreatment.

The range of the operational conditions values for conductingthe thermochemical and biological pretreatments were establishedin accordance with the recommended values in the literature. In the

L.A. Fdez.-Güelfo et al. / Chemical Engineering Journal 171 (2011) 411– 417 413

6/111

criata

eoAob(aT

2

2

cOavTc

TC

The following analytical determinations were used to monitorand control the process: Total Solids (TS), Volatile Solids (VS), alka-

Fig. 1. Batch stirred tank reactor (Patent no. WO 200

ase of thermochemical pretreatments, the bibliography [16–20]ecommends NaOH as chemical agent with an applied dose rang-ng between 0.8 and 7 g/l. Generally, the procedure consists on theddition of NaOH over the waste with a contact time of 30 min atemperatures between 120 and 180 ◦C and pressures between 1nd 10 bars.

On the other hand, in the case of biological pretreatments, thenzymatic hydrolysis may be developed by different types of fungir combinations of them (Aspergillus niger, Aspergillus awamori,spergillus oryzae, Aspergillus terreus, etc.) depending of the typef waste [7,21,22]. The operation variables are usually the type ofiological agent, the inoculation percentage and the contact time6–72 h). In this work, the conditions to develop thermohemicalnd biological pretreatments were carried out according to [23].he proposed experimental design is detailed in Table 1.

.2. Methodology

.2.1. InoculumThe inoculum used in this study was effluent from a semi-

ontinuous stirred tank reactor fed with the same industrialFMSW employed in this work. The features of the inoculum

re detailed in Table 2. The semicontinuous digester was pre-iously used to determine the optimize the Solid Retentionime for thermophilic-dry anaerobic digestion of the OFMSWoming from an 880 t/d industrial municipal solid waste treat-

able 1onfiguration and operational conditions in batch pretreatment tests.

Reactor Pretreatment Conditions

1 Control –2 Biological – Mature compost 2.5% (v/v)3 Biological – Sludge (WWTP) 2.5% (v/v)4 Biological – Aspergillus awamori 2.5% (v/v)5 Thermochemical 180 ◦C – 5 bar – 3 g/L de NaOH (N2)6 Thermochemical 180 ◦C – 5 bar – 3 g/L de NaOH (O2)

598 A1 – World Intellectual Property Organization).

ment plant called “Las Calandrias” in Jerez de la Frontera (Cadiz,Spain).

2.2.2. Reactor features and experimental methodology2-L batch stirred tank reactors were used to carry out the

assays. All the reactors were filled with OFMSW with a contentof 0.71 g TS/g waste (Table 2), but reactors 2, 3 and 4, which wereused to study the effect of biological pretreatments on anaero-bic digestion, were inoculated with the corresponding biologicalagent (mature compost, sludge from WWTP and fungus Aspergillusawamori) in an inoculation percentage of 2.5% (v/v). The biologicalpretreatment was maintained for 24 h. Reactors 5 and 6 were usedto study the effect of thermochemical pretreatment on the anaer-obic biodegradability of OFMSW. These reactors were loaded withthermochemically pretreated waste. Then the TS concentration ofthe waste in all the reactors was adjusted to 20% by adding 215 mLof anaerobic inoculum (15% v/v), the pH was corrected to 8.5 with6 N NaOH and the temperature was adjusted to 55 ◦C.

2.3. Sampling and analytical methods

linity, pH, Dissolved Organic Carbon (DOC), ammonium, Volatile

Table 2Features of the industrial OFMSW and the inoculum.

Analytical parameter Industrial OFMSW Inoculum

pH 7.98 7.85Density (kg/m3) 650 1.11 × 103

Alkalinity (g CaCO3/L) 18.13 22.60Ammonia (g NH3-N/L) 0.79 0.59Total nitrogen (g/Kg) 29.0 16.6Total solids (g/g) 0.71 0.34Volatile solids (g/g) 0.16 0.08Dissolved organic carbon (mg/g) 11.90 3.64Total volatile fatty acids (mg AcH/L) 3.3 × 101 6.8 × 100

414 L.A. Fdez.-Güelfo et al. / Chemical Engineering Journal 171 (2011) 411– 417

Table 3Kinetic parameters obtained from substrate-consumption and product-generation fittings.

Reactors

Compost Aspergillus Sludge TC-O2 Control TC-N2

Substrate-consumption fitting r2 0.993 0.990 0.998 0.997 0.997 0.995S0 (mg/L) 1567 1575 1579 1603 1683 1758SNB (mg/L) 561 577 771 605 658 1.09 × 103

h (mg/L) 1574 1593 1607 1663 1856 1868(XV0/YX/S) = (h − S0) (mg/L)a 7.0 18 28 60 1.7 × 102 1.1 × 102

�max (day−1) 0.309 0.289 0.227 0.161 0.118 0.116

Product-generation fitting r2 0.995 0.992 0.993 0.988 0.983 0.990S0B (mg/L) 988.6 1152 1298 1639 1769 1233˛P/S (L CH4/mg COD) 0.040 0.019 0.023 0.019 0.023 0.041(XV0/YX/S) = (h − S0) (mg/L) 0.369 0.095 1.335 0.018 0.031 0.056�max (day−1) 0.540 0.413 0.401 0.201 0.178 0.117

��max (%) Between both regressions(substrate-consumption andproduct-formation models)

43 30 43 20 34 <1

With respect to Control reactoremploying substrate-consumptionmodel (A)

162 145 92 36 – −2

With respect to Control reactoremploying product-formation model(B)

203 132 125 13 – −34

Average between A and B 183 138 109 25 – −18

Fep

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ewNTaIr

3

m

elim

(motb

a It is not a parameter of the model. Its value has been calculated from h and S0.

atty Acids (VFA), biogas composition and volume. All the param-ters were analyzed once a day and the determinations wereerformed according to standard methods [24].

The biogas was stored in Tedlar gas bags and the biogas volumeas measured using a high precision flow gas meter (Wet drum

G01 by Ritter). Gas composition (hydrogen, methane and carbonioxide) was determined by gas chromatography (GC14B by Shi-adzu) with a stainless steel packed column (Carbosieve SII) and a

hermal conductivity detector (TCD). The injected sample volumeas 1 mL and the operational conditions were as follows: 7 min at

5 ◦C; ramped at 27 ◦C min−1 until 150 ◦C; detector temperature:55 ◦C; injector temperature: 100 ◦C. The carrier was helium andhe flow rate used was 30 ml min−1. A standard gas (by Carburos

etálicos, S.A; composition: 4.65% H2; 5.33% N2; 69.92% CH4 and0.10% CO2) was used for the system calibration.

Individual VFA (from C2 to C7, including iC4, iC5 and iC6) lev-ls were determined by gas chromatography (SHIMADZU GC-17 A)ith a flame ionization detector and a capillary column filled withukol (polyethylene glycol modified by nitro-terephthalic acid).he temperatures of the injection port and detector were 200 ◦Cnd 250 ◦C, respectively. Helium was the carrier gas at 50 ml min−1.n addition, nitrogen gas was used as make up at 30 ml min−1 flowate.

. Results and discussion

This section presents the results of the model fitting to experi-ental data of DOC removal and methane production.The evolution of the DOC was fitted by using the general model

quation for substrate-consumption (Eq. (2)). The results obtained,aid out in increasing order according to the microorganisms’ max-mum specific growth rate, are shown in Table 3, The results of the

odel fitting can be observed graphically in Fig. 2.The expression of the general equation for product-formation

Eq. (11)) was used for accumulated methane generation. The

odel assumes that the product (methane) is generated as a result

f substrate consumption (expressed as DOC, COD, VS, etc.) andhus, different values for the kinetic parameters ˛P/S and S0B cane obtained depending on the form in which the concentration

of substrate is considered. Therefore, S0B was not considered asan regression parameter and its value was fixed as S0B = S0 − SNB,using the S0 and SNB values previously obtained in the DOC fitting(Table 3); thus, the yield coefficient for product formation (˛P/S) isexpressed as the generated liters of methane per mg of consumedDOC.

The results obtained from applying the model to accumulatedmethane production are also presented in Table 3. They are laid outaccording to the microorganisms’ maximum specific growth rate.The results of the model fitting can be observed graphically in Fig. 3.

As can be seen in Table 3, the values of the maximum specificgrowth rate obtained indicate that biological pretreatments are ofgreat interest in enhancing the anaerobic degradation of OFMSW.With respect to the thermochemical pretreatments, the resultsobtained from the anaerobic biodegradability of pretreated wastesindicate that they are less effective than biological pretreatments.Furthermore, the use of an oxidizing atmosphere in thermochem-ical pretreatments is counterproductive and the results show adecrease in �max with respect to the control test.

Precomposting (pretreatment with mature compost) was thebest of all the pretreatments tested in this study. This pretreatmentachieved the highest increases in �max values for both DOC degra-dation kinetics and methane production kinetics. It is important topoint out that the increases in the process rate through precom-posting were in the 160–205% range with respect to the controlassay.

Thus, a classification of the pretreatments used, laid out onthe basis of the �max increases, are as follows: “Mature compost(precomposting)” > “fungus Aspergillus awamori” > “sludge fromWWTP” > “thermochemical (air)” > “thermochemical (N2)”

Moreover, Table 3 shows that the parameter “h” values arevery similar to the S0 values in all cases, which indicates thanthe active biomass concentration adapted to the waste was verylow at the beginning of the tests. This is very usual in theanaerobic digestion of municipal solid wastes and was reported

by Silvey et al. [25]. In the present study, considering that thereactors were inoculated with a specific microbiota from a semi-continuous stirred tank reactor treating OFMSW, a higher initialconcentration of viable microorganisms adapted to the process

L.A. Fdez.-Güelfo et al. / Chemical Engineering Journal 171 (2011) 411– 417 415

odel

moecsoF

ttmatgmiimoipma

Fig. 2. Experimental evolution (marks) and m

ight have been expected. However, one possible interpretationf the results obtained might be that pretreatments promote anxtensive organic matter solubilization (i.e., volatile fatty acids),ausing an initial inhibitory effect on the microorganisms respon-ible for the process. This effect may explain the initial lag phasef DOC degradation and methane production, which can be seen inigs. 2 and 3.

The values obtained for �max from the product generation equa-ion of the model are higher, in all cases, than those obtained fromhe substrate consumption model. One possible explanation for this

ay be that methane production takes place along two parallelnd independent routes: the acetoclastic route, in which acetate isransformed into methane, which consumes DOC, and the hydro-en utilizing route, in which H2 and CO2 are transformed intoethane, without DOC removal. Studies by several authors [26,27]

ndicated that approximately 27–28% of the methane generatedn anaerobic digestion comes from the activity of the H2-utilizing

ethanogenic Archaeas. As can be seen in Table 3, the resultsbtained in this study are in keeping with that hypothesis, since the

ncrements between the values of �max obtained from the methaneroduction model and those obtained from the DOC consumptionodel, are very similar to the prediction by the above mentioned

uthors.

fitting (line) for DOC effluent concentration.

A series of bibliographical values of �max for biomethanizationprocess is summarized in [28].

Kinetic modeling studies of the dry-thermophilic anaerobicdigestion of OFMSW [29] indicate that the maximum spe-cific growth rate of the populations involved in the hydrolyticand acidogenic stages ranged between 0.08 and 0.18 days−1;for the methanogenic acetoclastic Archaeas �max ranged0.23–0.28 days−1; whereas for the hydrogen utilizing Archaeas thevalues were 0.33–0.40 days−1.

Equally, these results can be compared with results obtained inthe research group. Thus, kinetic modeling studies of the anaerobicdigestion of wine vinasses in wet conditions indicate that the �max

of the Acetoclastic Archaeas was 0.3 days−1 in mesophilic range[30] and 0.6 days−1 in thermophilic range, both when using theChen and Hashimoto model [31–33] as when using the model ofRomero [9].

It is necessary to emphasize the results obtained by [13], sincetheir work was carried out with the same waste and in similarconditions to this study (batch mode and TS concentration). These

authors also applied Romero’s substrate-consumption model [9]for the biomethanization of OFMSW and obtained a value of �max

of 0.11 days−1, which is very similar to that obtained for the Controlreactor and the TC-N2 reactor in the present study.

416 L.A. Fdez.-Güelfo et al. / Chemical Engineering Journal 171 (2011) 411– 417

mod

4

gbsvtcTdwTd2

A

aoP(

Fig. 3. Experimental evolution (marks) and

. Conclusions

The use of Romero’s substrate-consumption and product-eneration models [9] to fit the experimental data allowed theiodegradation rate for the different pretreatments tested in thistudy to be compared on the basis of the kinetic parameteralues. On the basis of this comparison, it can be concludedhat biological pretreatments perform better than thermochemi-al pretreatments in enhancing the anaerobic biodegradation rate.he best pretreatment tested was precomposting. Organic matteregradation and methane production for precomposted OFMSWere faster than in the control reactor (with no pretreatment).

hus, the �max involved in both processes (organic matter degra-ation and methane production) increased between 160% and05%.

cknowledgements

This work was supported by the Spanish Ministry of Science

nd Innovation (Project CTM2007-62164/TECNO), the Ministryf Innovation, Science and Enterprise of Andalusia (Project07-TEP-02472) and the European Regional Development FundERDF).

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el fitting (line) for methane accumulation.

References

[1] S.G. Pavlostasthis, E. Giraldo-Gómez, Kinetic of anaerobic treatment, Water Sci.Technol. 24 (8) (1991) 35–59.

[2] D. Lee, T.L. Donaldson, Anaerobic digestion of cellulosic wastes, Biotechnol.Bioeng. Symp. 14 (1984) 503–505.

[3] M. Soubes, Microbiología de la digestión anaerobia. Memorias III Taller y Sem-inario Latinoamericano sobre Tratamiento Anaerobio de Aguas Residuales.Montevideo, Uruguay (1994).

[4] M. Galisteo, M. Mallo, J. Martínez, Degradabilidad anaerobia de efluentes com-plejos, in: Proceeding Fifth Latin-American Workshop-Seminar, WastewaterAnaerobic Treatment, Vinas del Mar, Chile, 1998.

[5] K. Hwang, E. Shin, H. Choi, A mechanical pretreatment of waste activated sludgefor improvement of anaerobic digestion system, Water Sci. Technol. 36 (12)(1997) 111–116.

[6] R. Rodríguez-Vázquez, G. Villanueva-Ventura, E. Rios-Leal, Sugarcane Bagassepith dry pretreatment for single cell protein production, Bioresour. Technol. 39(1992) 17–22.

[7] M. Ropars, R. Marchal, J. Pourquié, J.P. Vandecasteele, Large-Scale enzymatichydrolysis of agricultural lignocellulosic biomass. Part 1: Pretreatment proce-dures, Bioresour. Technol. 42 (1992) 197–204.

[8] Ch. Ying-Chih, Ch. Cheng-Nam, L. Jih-Gaw, H. Shwu-Jiuan, Alkaline and ultra-sonic pretreatment of sludge before anaerobic digestion, Water Sci. Technol.36 (11) (1997) 155–162.

[9] L.I. Romero García, Development of a general mathematical model for fermen-tation processes: kinetics of anaerobic digestion, Doctoral Thesis, University of

Cádiz, ISBN: 84-7786-109-9 (1991).

10] M. Pérez, L.I. Romero, D. Sales, Kinetics of thermophilic anaerobes in fixed-bedreactors, Chemosphere 44 (5) (2001) 1201–1211.

11] M. Pérez, L.I. Romero, D. Sales, Organic matter degradation kinetics in an anaer-obic thermophilic fluidised bed bioreactor, Anaerobe 07 (2001) 25–35.

ngine

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[cesses for purifying wine distillery wastewaters, Process Biochem. 25 (3) (1990)

L.A. Fdez.-Güelfo et al. / Chemical E

12] M.A. De la Rubia, M. Pérez, D. Sales, L.I. Romero, Municipal sludge degrada-tion kinetic in thermophilic CSTR pilot-scale reactors, AIChE J. 52 (12) (2006)4200–4206.

13] J. Fernández, M. Pérez, L.I. Romero, Kinetics of mesophilic anaerobic digestionof the organic fraction of municipal solid waste: influence of initial total solidconcentration, Bioresour. Technol. 101 (2010) 6322–6328.

14] J.E. Bailey, D.F. Ollis, Biochemical Engineering Fundamentals, 2nd ed., McGraw-Hill, New York, 1986.

15] D.W. Marquardt, An algorithm for least-squares estimation of non-linearparameters, J. Soc. Ind. Appl. Math. 11 (1963) 431–441.

16] T. Bill, L. Jih-Gaw, R.V. Rajan, Low-level alkaline solubilization for enhancedanaerobic digestion, J. Water Pollut. Control Fed. 62 (1) (1990) 81–87.

17] J. Lin, C. Chang, S. Chan, Enhancement of anaerobic digestion of waste activatedsludge by alkaline solubilization, Bioresour. Technol. 62 (1997) 85–90.

18] S. Sawayama, S. Inoue, K. Tsukahara, Y. Tatsuo, M. Tomoaki, O. Tomoko,Anaerobic treatment of liquidized organic waste, Renewable Energy 16 (1999)1094–1097.

19] K. Tsukahara, T. Yaguishita, T. Ogi, S. Sawayama, Treatment of liquid fractionseparated from liquidized food waste in an upflow anaerobic sludge blanketreactor, J. Biosci. Bioeng. 4 (1999) 554–556.

20] C. Lin, Y. Lee, Effect of thermal and chemical pretreatments on anaerobic ammo-nium removal in treating septage using the UASB system, Bioresour. Technol.83 (2001) 259–261.

21] L. Coulibaly, G. Gourene, N. Agathos, Utilization of fungi for biotreatment of rawwastewaters, Afr. J. Biotechnol. 2 (2003) 620–630.

22] J. Kim, C. Park, T. Kim, M. Lee, S. Kim, Kim, J. Lee, Effects of various pretreatmentsfor enhanced anaerobic digestion with waste activated sludge, J. Biosci. Bioeng.3 (2003) 271–275.

23] L.A. Fdez.-Güelfo, C. Álvarez-Gallego, D. Sales, L.I. Romero, The use of thermo-chemical and biological pretreatments to enhance organic matter hydrolysis

[

ering Journal 171 (2011) 411– 417 417

and solubilization from organic fraction of municipal solid waste (OFMSW),Chem. Eng. J. 168 (2011) 254–349.

24] APHA, AWWA, WEF, Standard Methods for the Examination of Water andWastewater, 19th ed., 1995, Washington, DC, New York, USA.

25] P. Silvey, P. Pullammanappallil, L. Blackall, P. Nichols, Microbial ecology of theleach bed anaerobic digestion of unsorted municipal solid waste, Water Sci.Technol. 41 (3) (2000) 9–16.

26] P.L. McCarty, et al., in: D.E. Hughes (Ed.), One Hundred Years of AnaerobicTreatment, Elsevier Biomedical Press, 1981, pp. 3–22.

27] P.H. Smith, R.A. Mah, Kinetics of acetate metabolism drug sludge digestion,Appl. Microbiol. 14 (1966) 368–371.

28] L.A. Fdez.-Güelfo, C. Álvarez-Gallego, D. Sales, L.I. Romero, Dry-thermophilicanaerobic digestion of simulated organic fraction of municipal solid waste:process modeling, Bioresour. Technol. 102 (2011) 606–611.

29] C.J. Álvarez Gallego, Testing different procedures for the start up of a dry anaer-obic co-digestion process of OFMSW and sewage sludge at thermophilic range,Doctoral thesis, University of Cádiz (2005).

30] D. Sales, M.J. Valcarcel, L.I. Romero, E. Martinez de la Ossa, Anaerobic diges-tion kinetics of wine-distilleries wastewaters, J. Chem. Technol. Biotechnol. 45(1989) 147–162.

31] L.I. Romero, D. Sales, D. Cantero, M.A. Galán, Thermophilic anaerobic diges-tion of winery waste (vinasses): kinetics and process optimization, ProcessBiochem. 23 (4) (1988) 119–125.

32] L.I. Romero, D. Sales, E. Martínez de la Ossa, Comparison of three practical pro-

93–96.33] L.I. Romero, E. Nebot, E. Martínez de la Ossa, D. Sales, Microbiological purifica-

tion kinetics of wine-distillery wastewaters, J. Chem. Technol. Biotechnol. 58(2) (1993) 141–149.