effect of alkaline pretreatment on anaerobic digestion of solid wastes

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Page 1: Effect of alkaline pretreatment on anaerobic digestion of solid wastes

Available online at www.sciencedirect.com

www.elsevier.com/locate/wasman

Waste Management 28 (2008) 2229–2234

Effect of alkaline pretreatment on anaerobic digestion of solid wastes

M. Lopez Torres *, Ma. del C. Espinosa Llorens

National Center for Scientific Researcher (CNIC), Environmental Pollution Department (DECA), Ave. 25 y 158, Cubanacan, Playa, Havana City, Cuba

Accepted 19 October 2007Available online 18 December 2007

Abstract

The introduction of the anaerobic digestion for the treatment of the organic fraction of municipal solid waste (OFMSW) is currentlyof special interest. The main difficulty in the treatment of this waste fraction is its biotransformation, due to the complexity of organicmaterial. Therefore, the first step must be its physical, chemical and biological pretreatment for breaking complex molecules into simplemonomers, to increase solubilization of organic material and improve the efficiency of the anaerobic treatment in the second step. Thispaper describes chemical pretreatment based on lime addition (Ca(OH)2), in order to enhance chemical oxygen demand (COD) solubi-lization, followed by anaerobic digestion of the OFMSW.

Laboratory-scale experiments were carried out in completely mixed reactors, 1 L capacity. Optimal conditions for COD solubilizationin the first step of pretreatment were 62.0 mEq Ca(OH)2/L for 6.0 h. Under these conditions, 11.5% of the COD was solubilized. Theanaerobic digestion efficiency of the OFMSW, with and without pretreatment, was evaluated. The highest methane yield under anaerobicdigestion of the pretreated waste was 0.15 m3 CH4/kg volatile solids (VS), 172.0% of the control. Under that condition the soluble CODand VS removal were 93.0% and 94.0%, respectively. The results have shown that chemical pretreatment with lime, followed by anaer-obic digestion, provides the best results for stabilizing the OFMSW.� 2007 Elsevier Ltd. All rights reserved.

1. Introduction

In Cuba, municipal solid waste management is currentlyfacing serious problems involving a lack of adequate trans-portation, environmental pollution as a result of the use ofhorse-driven cars, potential biohazards in landfill placesafter disposal without any treatment, and urbanization inexisting landfills.

In order to solve such problems, the Cuban governmenthas been working on a master plan for integrated manage-ment of municipal solid waste. Only a very short-term plan,basically an annual one, is currently available and the for-mulation of an integrated master plan having long-termperspectives is an urgent necessity. Since municipal solidwastes are rapidly increasing, thus provoking huge wastedisposal problems, the government is mainly concernedwith the incorporation of solutions for the treatment ofsuch complex wastes (JICA, 2004).

0956-053X/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.wasman.2007.10.006

* Corresponding author. Tel.: +53 7 271 8897; fax: +53 7 208 0497.E-mail address: [email protected] (M. Lopez Torres).

Anaerobic digestion can be an attractive option, both asa disposal route and as a source of alternative energy. Inthe last few years, much effort has been made at introduc-ing anaerobic digestion processes for treating the organicfraction of municipal solid waste (OFMSW) (Wu et al.,2006). However, the main obstacle in spreading this tech-nology is the lower biodegradation rate of solid wastes(due to the chemical composition and structure of lignocel-lulosic materials) in comparison to liquid ones. It is recog-nized that the rate-limiting step of anaerobic processes forwastes with a high solids content is the hydrolysis of thecomplex organic matter to soluble compounds (Pavlostas-this and Gosset, 1985; Delgenes et al., 1999; Chulhwanet al., 2005). Therefore, physical, chemical or biologicalpretreatment methods (or their combination) are required,in order to reduce the rate of such a limiting step.

Previous studies have pointed out that alkali pretreat-ment is the best known method for enhancing the biodeg-radation of complex materials, thus rendering the mostsignificant benefits (Hoon, 2004). In the last years, theuse of ozone in chemical pretreatment is gaining great

Page 2: Effect of alkaline pretreatment on anaerobic digestion of solid wastes

Table 1Characteristics of organic fraction of municipal solid waste used in theexperiments

Parameter Concentration (mg/L)a

Total COD 49,429Soluble COD 13,675Total solids 81,150Volatile solids 54,401Total dissolved solids 12,903Volatile dissolved solids 8154pH 7.5

a Except pH.

2230 M. Lopez Torres, Ma.d.C. Espinosa Llorens / Waste Management 28 (2008) 2229–2234

interest in the scientific community, not only by removingrecalcitrant and toxic compounds but also by increasingthe biodegradability of waste. However, this process is con-sidered to be very expensive if intended to eliminate all ofthe contaminants of the waste (Momenti and Cleto,2006). Special attention is afforded to the use of combinedpretreatment, including alkaline pretreatment for increas-ing the efficiency of anaerobic digestion of complex wastes(Bill et al., 1990; Rodrıguez-Vazquez et al., 1992; Delgeneset al., 1999; Chulhwan et al., 2005). The preferred chemical,in all cases, was sodium hydroxide (NaOH), which wasreported to yield greater solubilization efficiency than cal-cium hydroxide (Ca(OH)2). Although NaOH enhancesanaerobic digestion performance, the use of this reagentinvolves higher chemical costs and, therefore, a possibleincrease of pretreatment cost. Nevertheless, Ca(OH)2 is lessexpensive, US$0.07/kg (GECA, 2004), than many othermaterials and has been thoroughly applied in pretreatmentstudies from various biomass sources such as corn stover,wood, sugar-mill-mud waste (SMMW), municipal wasteand sludge (Bill et al., 1990; Espinosa et al., 1995; Hoon,2004; Lopez et al., 2005). Besides, the availability of limemust favor studying and expanding this alternative underCuban conditions.

The government has made a great effort to introduce theadequate management of solid wastes, with the assistanceof various developed countries. A study to prepare an inte-grated solid waste management plan was carried out, withthe capital (Havana) being the reference because it has thehighest population in Cuba. Currently, a study is beingconducted on the feasibility and selection of recommendedprojects, leading to the final formulation of appropriatepilot projects.

Thus, lime pretreatment might be an economical optionas a first step, in order to improve biodegradation of ligno-cellulosic materials. The objective of the present work is toevaluate the effect of alkaline pretreatment with lime inanaerobic digestion of solid wastes, especially on theorganic fraction of municipal solid waste.

2. Methods

2.1. Organic fraction of municipal solid waste (OFMSW)

For this study, samples from five municipalities ofHavana were collected and separated into fractions, thatis, plastics, glass, rubber, textiles, aluminum, general met-als, paper – cardboard, wood, yard waste, and kitchenwaste. A 10 kg sample of each organic fraction, mainlykitchen waste and other small organic materials, wereplaced in nylon bags and transported to the laboratory,where the OFMSW was mixed with water to obtain a con-centration of 8% total solids (TS).

The characteristics of OFMSW from all of the analysesare shown in Table 1. The data represent the average ofthree independent determinations from three independent

samples. Differences among the observed figures were lessthan 3% in all cases.

2.2. Alkaline pretreatment

Despite the chemical characteristics of lime, it wasemployed as a chemical agent for hydrolyzing in theOFMSW pretreatment. The higher lime availability andlow cost compared to any other chemical may allowscale-up of the process and further introduction of results.

The pretreatment was performed in batch, in a 1-L reac-tor, at room temperature under anoxic condition. Amechanical stirrer was used for continuous mixing of thecomponents. The experiments were conducted in triplicate.

The experimental work was designed to study the effectsof lime in OFMSW solubilization. Two independent vari-ables were considered: concentration of lime and time ofsolubilization. Furthermore, alkali concentration levels of40 and 100 mEq/L and solubilization times of 1 and 6 hwere considered in the statistical experimental design.The optimal parameters were obtained from a 32 factorialplan.The effectiveness of the pretreatment was evaluatedby the solubilization degree, based on the quantity of solu-ble organic matter and expressed as a function of chemicaloxygen demand (COD)

Sð%Þ ¼ SCODf � SCODi

TCOD� 100

where

S = Solubilization (%)SCOD = Soluble chemical oxygen demand (f – final andi – initial) (mg/L)TCOD = Total chemical oxygen demand (mg/L)

2.3. Anaerobic bioreactor

The effects of the OFMSW solubilization on the anaer-obic digestion process, with respect to a control digester(fed with no pretreated wastes), were evaluated in thissequence.

Both digesters consisted of 1 L stirred reactors, operatedon a batch basis, fed with loads of 40, 60, 80 and 100 mL.

Page 3: Effect of alkaline pretreatment on anaerobic digestion of solid wastes

Table 2Summary of the statistical analysis (ANOVA)

Source Sum ofsquares

Df Meansquare

F-Ratio p-Value

A: Concentration 20.944 1 20.944 11.59 0.0272a

B: Time 17.34 1 17.34 9.60 0.0363a

AA 46.4732 1 46.4732 25.73 0.0071a

AB 0.837225 1 0.837225 0.46 0.5334BB 6.13981 1 6.13981 3.40 0.1390Total error 7.22597 4 1.80649Total (correlation) 94.672 9

R-squared = 92.3674%.a Statistical signification at 95% confidence level.

Standardized effect0 1 2 3 4 5 6

AB

BB

B:Time

A:Concentration

AA

Fig. 1. Standardized Pareto chart for the effects on solubilization.

M. Lopez Torres, Ma.d.C. Espinosa Llorens / Waste Management 28 (2008) 2229–2234 2231

In all of the experiments, the digesters were run in a fill-and-drawn mode, with volumes of the settled supernatantremoved equal to volumes of feed added. The settlementperiod was 2 h, which was enough for separating andretaining biomass. Each experiment lasted the interval formaximum gas production, and COD removal in each loadand figures represent the mean of two runs.

The volume of methane was measured by using a 1-LBoyle–Mariotte reservoir, which was connected to thedigesters. To remove the CO2 produced, a tightly closedbubbler, holding a KOH solution (10%), was connectedbetween the two elements. The methane produced displacesa measurable volume of water from the reservoir, whichwas equivalent to the methane volume.

2.4. Analytical methods

All analyses were done by triplicate, following validatedsources such as the American Public Health Association(APHA, 1998) and involved chemical oxygen demand(COD), total solids (TS), volatile solids (VS), total dis-solved solids (TDS), volatile dissolved solids (VDS) andpH. Total and soluble COD were determined by the color-imetric method. The samples were centrifuged at10,000 rpm for 20 min.

2.5. Statistical processing

To study the effects of the different factors and to testthe statistical significance, the Analysis of Variance(ANOVA) and the t-Student were conducted, using thesoftware Statgraphic (Statgraphic, 2000).

3. Results and discussion

The most remarkable characteristic of this waste was thehigh content of organic matter, expressed as total CODand the fractions VS/TS and VDS/TDS (Table 1). The per-centages of VS in TS and VDS in TDS are 67.0% and63.0%, respectively. Anyway, the large amount of sus-pended solids (more than 80.0%) and the relatively lowcontent of dissolved matter make pretreatment necessary,in order to enhance the chemical oxygen demand (COD)solubilization. As a result, a higher efficiency of the anaer-obic digestion process must be achieved.

3.1. Pretreatment

The increase of the soluble chemical oxygen demand(SCOD) from 13,675 to 20,101 mg/L was noticed whenthe lime concentration was increased up to 70 mEqCa(OH)2/L. Under this condition, a solubilization of13.0% of was observed. On the other hand, the concentra-tion of volatile dissolved solids (VDS) was increasedslightly (5.8%) after the pretreatment, which may be dueto the progressive hydrolysis of the complex organic matterpresent in the feeding. Throughout the assays, the addition

of lime caused a sudden increase in pH followed by a grad-ual drop, which can be attributed to neutralization of theacidic products, previously formed. Such behavior was alsonoticed by other authors (Pavlostasthis and Gosset, 1985;Rajan et al., 1989; Espinosa et al., 1995).

The statistical results for the optimization of COD solu-bilization are summarized in Table 2. The analysis of var-iance (ANOVA, p < 0.05) involving three effects (alkaliconcentration, time and second-order interaction amongconcentration itself) indicates that they are statistically sig-nificant. Furthermore, the R-squared statistic indicates thatthe fitted model explains 92.4% of the variability insolubilization.

The analysis shown in the Pareto chart (Fig. 1) suggeststhat interaction among the alkali concentration itself, alkaliconcentration and time are the factors contributing signif-icantly to solubilization. All of them cross the vertical line,representing a significance of 95%.The equation of the fit-ted model, considering the values of the variables in theiroriginal units and only the significant coefficients, is

S ¼ �5:7351þ 0:6777 � C � 4:6436 � t � 0:0049 � C2

where

S = Solubilization (%)C = Alkali concentration (mEq Ca(OH)2/L)t = Solubilization time (h)

Page 4: Effect of alkaline pretreatment on anaerobic digestion of solid wastes

Table 3Characteristics of organic fraction of municipal solid waste afterpretreatment under optimal conditions

Parameter Concentration (mg/L)a

Total COD 47,445Soluble COD 19,359Total solids 80,035Volatile dissolved solids 12,861pH 8.5

a Except pH.

Table 4Comparison of the solubilization levels using lime pretreatment fordifferent solid wastes

Rajan et al.(1989)

Espinosaet al. (1995)

Lopezet al. (2005)

Thisstudy

Waste Waste activatedsludge

Sewagesludge

SMMW OFMSW

Concentration 40 60 86 62

2232 M. Lopez Torres, Ma.d.C. Espinosa Llorens / Waste Management 28 (2008) 2229–2234

A positive correlation (r = 0.961) was also demonstratedamong observed and fitted data (Fig. 2), which supportsthe model.

The optimal solubilization condition for OFMSW was62.0 mEq Ca(OH)2/L (equivalent to 2.3 g Ca(OH)2/L)and 6.0 h (Fig. 3). Under these conditions, solubilizationreached levels up to 11.5%. The characterization of the pre-treated OFMSW is shown in Table 3. Further addition ofCa(OH)2 has shown a decrease in solubilization, whichmay be associated with instability and formation of com-plex, non-soluble compounds. As a result, hydrolysis oforganic matter becomes unfeasible. Moreover, if alkaliconcentration was increased beyond the optimal concentra-tion (100 mEq Ca(OH)2/L), soluble COD decreased from19,359 to 14,664 mg/L, a finding that also supports theabove results.

Our results of alkaline pretreatment were compared tothose from other authors (Table 4). Rajan et al. (1989)

y = 0,9242x + 0,47R2= 0,9235

r = 0,961

00

2

2

4

4

6

6

8

8

10

10

12

12

14

14Observed value (%)

Fitte

d va

lue

(%)

Fig. 2. Relationship among observed and fitted (estimated applying themodel) values.

4

1.2152.43

3.6464.8616.076

7.2918.5069.721

10.93712.152above

Fig. 3. Surface plot. Chemical pretreatment of OFMSW (organic fractionof municipal solid waste).

(mEq/L)TS (%) 1 3 8 8Solubilization

(%)18 11.7 14.5 11.5

reported a solubilization of 14% (20 mEq/L of alkali) andonly 18% (40 mEq/L), for the same alkali (Ca(OH)2), 1%TS solids. However, it is important to clarify that thesedata represent the average values without any optimizationstudy. On the other hand, Espinosa et al. (1995) and Lopezet al. (2005) found similar results by treating sewage sludgefrom a wastewater treatment plant and sugar-mill-mudwaste (SMMW) from a sugar factory, respectively. In thepresent study, optimal levels of solubilization were alsosimilar to those results, irrespective of the type of waste.

All of the above results support the positive effect ofalkaline pretreatment with Ca(OH)2 on the organic frac-tion of municipal solid wastes. Not only was the level ofsoluble COD increased but also surface area of complexorganic matter, due to swelling. This fact makes thesewastes more susceptible to enzymatic attack by microor-ganisms, so that anaerobic digestion processes must be fur-ther enhanced.

3.2. Anaerobic digestion

Anaerobic digestion performance in both reactors isshown in Table 5. An initial OFMSW concentration of8% TS (adjusted prior to each feeding or pretreatment)was used. One of the reactors was loaded with the pre-treated waste with alkali at 62.0 mEq Ca(OH)2/L, equiva-lent to 2.8 g Ca(OH)2/100 g TS. The effect of pretreatmenton VS and SCOD removal was tested by applying t-Stu-dent, paired samples (two tails), p < 0.05. Differencesbetween digesters for VS (p = 0.000005) and SCOD(p = 0.00042) removals were statistically significant, so thatpretreatment must improve digestibility of complex wastes.The structural properties of the waste without pretreatment

Page 5: Effect of alkaline pretreatment on anaerobic digestion of solid wastes

Table 5Summary of digester performance

Load (mL/Lreactor)

Without pretreatment With pretreatment

40 60 80 100 40 60 80 100

VS removal (%) 78 76 76 75 95 95 94 94SCOD removal (%) 94 94 92 90 96 96 95 93(m3 CH4/kg VS) 0 0 0.053 0.055 0.041 0.053 0.101 0.150Maximum increase (%) 90.56 172.70pH 7.0 7.2 7.2 7.5 7.3 7.0 7.0 7.0

Table 6Comparison of the methane yield under different conditions

Del Borghi et al. (1999) Tiehm et al. (2001) Chulhwan et al. (2005) Chulhwan et al. (2005) This study

Waste OFMSW + SS WAS WAS WAS OFMSWPretreatment Chemical and bacteriala Ultrasonicb Biologicalc Thermochemicald Chemicale

CH4 yield (m3 CH4/kg VS) 0.39 0.3 0.29 0.52 0.15

a Organic fraction of municipal solid waste + sewage sludge (OFMSW + SS). Chemical hydrolysis with NaOH and selected hydrolytic bacteria.b Waste activated sludge (WAS). Ultrasonic disintegration.c Waste activated sludge (WAS). Aerobic bacteria and acidogenic process with selected bacteria.d Waste activated sludge (WAS). Thermal treatment with NaOH.e Organic fraction of municipal solid waste (OFMSW). Chemical hydrolysis with Ca(OH)2.

0

50

100

150

200

250

300

350

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19Time (day)

Cum

ulat

ive

Met

hane

Pro

duct

ion,

CH

4 (m

L)

WTW-40 WTW-60

WTW-80

WTW-100

Fig. 4. Behaviour of methane production from organic fraction ofmunicipal solid waste without pretreatment.

M. Lopez Torres, Ma.d.C. Espinosa Llorens / Waste Management 28 (2008) 2229–2234 2233

hamper anaerobic degradation, thus limiting surface areafor microbial attack and anaerobic decomposition.

Similar results were summarized for gas yield. The pre-treated digester yielded higher methane amounts than con-trol (significant differences, p = 0.0019), which suggeststhat pretreatment should improve anaerobic digestion,not only increasing organic solubilization but also surfacearea available for enzymatic action as a result of fiber swell-ing. The maximum increase in methane yield was 172.7%over the control for a feeding of 100 mL of pretreatedwaste. However, the methane yields were lower than thosefrom other authors (Table 6). As a whole, they have stud-ied various pretreatment combinations of different solidwastes, but very expensive ones (Del Borghi et al., 1999;Tiehm et al., 2001; Chulhwan et al., 2005). On the otherhand, the composition of the waste and the unavoidablesmall pieces of non-biodegradable materials present inthe waste (since it is not source-selected) contributed tothe results presented in this work. Mata-Alvarez et al.(1990) found similar results when compared source-selectedOFMSW and mechanically-selected OFMSW. Neverthe-less, when economic considerations are made, the pretreat-ment alternative studied in this work shows positive results,being affordable from the economic point of view, consid-ering the low cost (US$0.07/kg) of the Ca(OH)2, (GECA,2004).

Fig. 4. shows the variation of the cumulated methanevolumes as a function of time for different feed volumesin the control digester without pretreatment. The anaerobicdigestion of the OFMSW follows a step-wise reaction ordiauxic performance, as described by Aiba et al., 1970. Incontrast with that, Fig. 5. shows methane production in

the pretreated waste digester. It was observed, in all cases,a concomitant, gradual and continuous enhancement inmethane production with the increase of the volume ofwaste added. This result clearly demonstrates the advan-tage of this approach.

During the experiment, as consequence of the degrada-tion of low molecular weight compounds to final products(that might be acidic ones), it was necessary to continuouslyadd alkali in the control digester. In contrast, the digesterfed with pretreated waste maintained its alkalinity and neu-tral pH, thus helping the biotransformation process.

The above results suggest that under appropriatealkali treatment, complex organic matter becomes more

Page 6: Effect of alkaline pretreatment on anaerobic digestion of solid wastes

0

100

200

300

400

500

600

700

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Cum

ulat

ive

Met

hane

Pro

duct

ion,

CH

4 (m

L)

TW-40

TW-60

TW-80

TW-100

Time (day)

Fig. 5. Behaviour of methane production from organic fraction ofmunicipal solid waste pretreated.

2234 M. Lopez Torres, Ma.d.C. Espinosa Llorens / Waste Management 28 (2008) 2229–2234

biodegradable by roughly changing chemical structure. Thetreatment may also induce swelling, thus enhancing surfacearea available for further microbial enzymatic attack.

Thus, these results could be an alternative to includeinto the master plan for the integrated management ofmunicipal solid waste in Cuba.

4. Conclusions

The alkaline pretreatment renders a significant increasein the soluble COD, 11.5% of the total COD, thus improv-ing anaerobic digestion, measured by an increase of meth-ane yields up to 172% over the control withoutpretreatment.

From the above results, a procedure for the treatment ofthe organic fraction of the municipal solid waste can bedesigned. The two-stage design must involve lime alkalinepretreatment, followed by anaerobic digestion.

Acknowledgments

The authors wish to thanks Mrs. Janis Zral and Mr. CelsoPerez by their careful proofreading of and recommendationsto improve the manuscript. Also, the authors are grateful totheir colleagues Rigoberto Escobedo Acosta, Oneida CorreaSenciales, Xiomara Rodrıguez Petit, Yadiana Leon Hernan-dez, Yamile Alvarez Llaguno, Rosario Morejon Montano,Jacqueline Gutierrez Navarrete, and Antonio Ona, for con-ducting the analysis and collecting the samples.

References

Aiba, S., Humphrey A., Millis N., 1970. Biochemical Engineering.

Instituto del Libro. Ciencia y Tecnica (Book Institute. Science and

Technical). La Habana. Cuba.

APHA, AWWA, WPCF, 1998. Standard Methods for analysis of water

and wastewater. 20th ed. American Public Health Association,

Washington, DC, USA.

Bill, T., Jih-Gaw, L., Rajan, R.V., 1990. Low- level alkaline solubilization

for enhanced anaerobic digestion. Journal Water Pollution Control

Federation 62 (1), 81–87.

Chulhwan, P., Chunyeon, L., Sangyong, K., Yu, Ch., Howard, C.H.,

2005. Upgrading of anaerobic digestion by incorporating two different

hydrolysis processes. Journal of Bioscience and Bioengineering 100 (2),

164–167.

Del Borghi, A., Converti, A., Palazzi, E., Del Borghi, M., 1999.

Hydrolysis and thermophilic anaerobic digestion of sewage sludge.

Bioprocess Engineering 20, 553–566.

Delgenes, J.P., Penaud, V., Torrijos, M., Moletta, R., 1999. Thermo-

chemical pretreatment of an industrial microbial biomasa: Effect of

sodium hydroxide addition on COD solubilization, anaerobic biode-

gradability and generation of soluble inhibitory compounds. In:

Proceeding II International Symposium on anaerobic digestion of

solid waste. Barcelona, Espana. pp. 121–128.

Espinosa, M.C., Lopez, M., Montalvo, S., Escobedo, R., Ruız, M.,

Correa, O., 1995. Chemical solubilization and anaerobic treatment of

sewage sludge. In: Proceeding Earth Conference on Biomass for

energy, development and the environment. Havana, Cuba. p. 103.

GECA, 2004. Directorio de productores, industriales, agropecuarios y de

servicios de la Republica de Cuba. (Cuban producers, industrialists,

farming and services directory.) Third ed. <www.chasqui.cu>

(accessed 26.04.07).

Hoon, K.S., 2004. Lime pretreatment and enzymatic hydrolysis of corn

stover. Dissertation for the Degree of Doctor of Philosophy. Texas

A&M University.

JICA, 2004. Study on Integrated Management Plan of Municipal Solid

Waste in Havana City. Progress Report. Part 1. Cuba.

Lopez, M., Espinosa, M.C., Escobedo, R., 2005. Estudio comparativo del

pretratamiento quımico para mejorar la digestion anaerobia de

residuos solidos (Comparative study of chemical pretreatment to

improve the anaerobic digestion of solid wastes). Revista CNIC. vol.

36, Numero Especial. La Habana. Cuba.

Mata-Alvarez, J., Cecchi, F., Pavan, P., 1990. The Performance of

digesters treating the organic fraction of municipal solid wastes

differently sorted. Biological Wastes 33, 181–199.

Momenti, T.J., Cleto, E., 2006. Combination of an anaerobic process and

ozonation in the treatment of cellulosic pulp bleaching effluent. In:

Proceeding of the Second International Meeting on Environmental

Biotechnology and Engineering (2IMEBE). Edited by Hector Mario

Poggi-Varaldo, Elvira rıos-Leal, Jaime Garcıa-Mena, Fernando Espa-

rza-Garcıa, Ma Teresa Ponce-Noyola, Ireri Robles-Gonzalez, Isabel

Sastre-Conde, Herver Macarie, Jose Luis Sanz, Irene Watson-Craik,

Eugenio Foresti, Danny Reible and Claudio Garibay-Orijel. Mexico.

Pavlostasthis, S.G., Gosset, J.M., 1985. Modeling alkali consumption and

digestibility improvement from alkaline treatment of wheat straw.

Biotechnology and Bioengineering 27, 345–354.

Rajan, R.V., Lin, J.G., Ray, B.T., 1989. Low-level chemical pretreatment

for enhanced sludge solubilization. Journal Water Pollution Federa-

tion 64 (11/12), 1678–1683.

Rodrıguez-Vazquez, R., Villanueva-Ventura, G., Rios-Leal, E., 1992.

Sugarcane Bagasse pith dry pretreatment for single cell protein

production. Bioresource Technology 39, 17–22.

STATGRAPHIC plus 5, 2000. Statistical Graphics Corp., USA.

Tiehm, A., Nickel, K., Zellhorn, M., Neis, U., 2001. Ultrasonic waste

activated Sludge Disintegration for improving anaerobic stabilization.

Water Research 35, 2003–2009.

WU, M., Sun, K., Zhang, Y., 2006. Influence of temperature fluctuation

on thermophilic anaerobic digestion of municipal organic solid waste.

Journal of Zhejiang University SCIENCE B. ISSN 1673-1581 (Print);

ISSN 1862-1783 (Online).