ad morrocco

pr

us

kha

n th

nur

Morocco

are decomposed into simple, chemically stabilized com-

it d

re

mentative) bacteria along with ammonia (NH3), carbon

dioxide (CO2), hydrogen sulde (H2S) and other by-products

(Appels et al. ). The third step is acetogenesis. During this

phase, the main substrates of methanogenesis (acetic acid

2) are produced by fermentation

togenic bacteria. The fourth step is

biological production of methane

icroorganisms from methanogens

the presence of free or dissolved

ajor pathways for methane pro-

1):

1 IWA Publishing 2013 Journal of Water Reuse and Desalination | in press | 2013

Uncorrected Proofinsoluble organic material and high molecular weight com-

pounds, such as lipids, polysaccharides, proteins andpounds mainly formed of methane and carbon dioxide

(Naik et al. ).

Anaerobic digestion usually takes place in four stages.

The rst two stages are often grouped together as they are per-

formed by the same microorganism populations, according to

Couturier & Galtier (). The hydrolysis step degrades both

(CH3COOH), CO2 and H

through the action of ace

methanogenesis. It is the

mediated by anaerobic m

(organisms not requiring

oxygen). There are two m

duction (Hill ) (Figureable material, such as municipal wastewater, food waste,

fats, oils, grease and various other organic waste streams,

without using oxygen. Multi-molecular organic substancesELECTRE III method. The variables studied were the chemical oxygen demand reduction and biogas

volume measurements. The results show that the formula of Vedrenne (2007) is the most

appropriate equation to predict biogas production in Moroccan rural areas.

Key words | anaerobic digestion, biogas, ELECTRE III method, methanisation, Moroccan rural areas,

principal component analysis

INTRODUCTION

Anaerobic digestion is a series of biological processes in

which anaerobic microorganisms break down biodegrad-

hydrolysis are further spl

step. Volatile fatty acids anucleic acids, into soluble organic substances (e.g. amino

acids and fatty acids). The compounds formed during First, acetate methanogen

methane. This is respon

doi: 10.2166/wrd.2013.097E-mail: [email protected]

Mustapha MahiInstitut International de lEau et de

lAssainissement de lONEE,Rabat,Morocco

Christine WernerGIZ, Rabat,Morocco

Mohammed FekhaouiScientic Institute Mohammed V-Agdal University,Rabat,Morocco

uring acidogenesis, the second

produced by acidogenic (or fer-86 days in summer 2012 to measure gas production. The average gas production recorded was

about 1,870 l per day. This amount is sufcient for a farming family composed of 17 people. Our work

seeks to nd the most appropriate formula to predict biogas production under Moroccan conditions.

We compared and ranked different formulas by applying principal component analysis and theanaerobic conditions. It is used for heating and cooking. This biogas system could be an useful

sanitation technology due to its ability to treat wastewater. The biogas system was monitored over

Faculty of Science,Mohammed V-Agdal University,Rabat,Modelling of anaerobic digester biogas

study of a pilot project in Morocco

Youssef Abarghaz, Khiyati Mohammed El Ghali, M

Christine Werner, Najib Bendaou, Mohammed Fe

and Ben Houssa Abdelaziz

ABSTRACT

An anaerobic digestion pilot system was implemented in June 2010 i

Ifrah. The input material consists of toilet wastewater and cattle maoduction: case

tapha Mahi,

oui

e Moroccan village of Dayet

e. Biogas is produced under

Youssef Abarghaz (corresponding author)Khiyati Mohammed El GhaliNajib BendaouBen Houssa Abdelazizic bacteria convert acetate to

sible for 70% of the methane

2 Y. Abarghaz et al. | Anaerobic digester biogas plant Journal of Water Reuse and Desalination | in press | 2013

Uncorrected Proofproduction:

CH3COOH! CH4 CO2

Figure 1 | Flow chart of the Hill (1982) model. Second, CO2 and H2 are converted to methane:

2H2 CO2 ! CH4 O2

Other reactions arise from different compounds such as

methanol, formic acid and methyl or dimethyl compounds.

Sulfate-reducing bacteria are also present. They reduce sul-

fates and other sulfur compounds to hydrogen sulde

(H2S) and mercaptans, which give biogas its characteristic

odour.

In short, anaerobic digestion is the process of degra-

dation and stabilization of organic materials by the action

of anaerobic bacteria to produce biogas (biomethanation).

The main stages of anaerobic digestion are: hydrolysis, acid-

ogenesis, acetogenesis and methanogenesis.

Parameters affecting of biomethanisation

Within the anaerobic environment, various important par-

ameters, such as temperature, pH, alkalinity, retentiontime, carbon/nitrogen ratio and toxic elements, affect the

rates of the different stages of the biomethanisation process.

Temperature

Temperature has a signicant effect on the physicochemical

properties of the components found in the digestion sub-

strate. It also inuences the growth rate and metabolism of

microorganisms and hence the population dynamics in the

anaerobic reactor (Appels et al. ). In fact, anaerobic

digestion materials in a digester are optimal when the

methanogenic bacteria assimilate acids at the same speed

as they are produced. However, temperature variations in

the mixture can inhibit methanogens, disrupt the process

and thus cause failures in the chain of methane production

(Balsam ). Biogas sanitation is often applied in

countries where the ambient average temperature ranges

are above 15 WC. When the temperature is less than 8 WC,

digestion capability is much reduced. The process is also

sensitive to temperature variations of more than 3 WC; there-

fore, variations have to be kept within a limited range to

ensure steady biogas production. To cope with this con-

straint, the digester should be covered with a good thermal

insulation layer (mixture of soil and straw). Thus, the level

of gas production coming out the digester in Dayet Ifrah

could be maintained at a constant level even under negative

temperatures (winter).

pH

In order to form methane, the pH must be between 5.5 and

8.5, with an optimum around 78 (Al Saedi et al. ). The

system pH is controlled by CO2 concentration in the gas

phase and the HCO3 alkalinity of the liquid phase. If CO2

concentration in the gas phase remains constant, the poss-

ible addition of HCO3 alkalinity can increase the digester

pH (Turovskiy & Mathai ).

Alkalinity

Partial alkalinity, as a measure of bicarbonate concen-tration, and intermediate alkalinity, as a measure of the

concentration of volatile fatty acids (VFA) are useful par-

ameters for monitoring anaerobic digestion processes.

The biodigester implemented in Dayet Ifrah village oper-

ates normally and successfully without any problems, which

implies that biogas production is at its optimum.

The results of the Dayet Ifrah biogas system analysis car-

ried out from April 2011 to July 2011 are summarized as

follows:

As shown in the Table 1, the ratio of acidity on alkalinityis around 0.5, which shows that there is no accumulation

of VFAs (propenoic acid, acetic acid, butyric acid), which

would certainly disturb the anaerobic digestion process

and consequently the production of biogas.

As shown in Table 2, the pH in the biodigester entranceis lower than the pH in the outlet, which corresponds

Table 1 | Measurements of CaCO3 and fatty-acid concentrations

Alkalinity (g CaCO3) Acidity (g) Ratio acidity/alkalinity

13 June 2011 11 3 0.27

16 June 2011 14 6.75 0.48

23 June 2011 10.45 4.76 0.46

27 June 2011 12.23 5.66 0.46

Table 2 | pH measurements

pH pHinlet outlet


Uncorrected ProofA total alkalinity (partial alkalinity plus intermediate alka-

linity) of 1.5 g CaCO3/l is recommended for the adequate

performance of the anaerobic systems. However, the true

monitoring parameter used is the intermediate alkalinity to

total alkalinity ratio which must be maintained lower than

0.30.4 (Franco et al. ). A buffering capacity of 70 meq

CaCO3/l or a molar ratio of at least 1.4:1 of bicarbonate/

VFA should be maintained for a stable and well-buffered

digestion process, although it has been shown that the stab-

ility of the ratio is of great importance, and is not so reliant

on its level (Appels et al. ).

Solids and hydraulic retention time

The solids retention time (SRT) is the average time solids spend

in the digester, whereas the hydraulic retention time (HRT) is

the average time the liquid sludge is held in the digester. The

subsequent steps of the digestion process are directly related

to the SRT. A decrease in the SRT decreases the extent of the

reactions and vice versa. Each time sludge iswithdrawn, a frac-

tion of the bacterial population is removed thus cell growth

must at least compensate cell removal to ensure steady state

and avoid process failure (Appels et al. ).

Carbon/nitrogen (C/N) ratio

It is always important tomaintain byweight a carbon/nitrogen

(C/N) ratio between 15 and 30:1 to achieve an optimumdiges-

tion rate. The C/N ratio can be manipulated by combining

materials low in carbon with those that are high in nitrogen.

If the C/N ratio is very high, nitrogen limitation could cause

low gas production, since nutrients for the growth of anaerobic

bacteria are lacking. If the C/N ratio is very low, the pH value

may increase, with a toxic effect on bacteria, and also result in

lower biogas production (Van der Wal et al. ).

Toxic compounds

These may interfere with the process of digestion and alter

the quality of the digestate. Among these compounds,

there are usually interferents and pollutants. Interferentsinclude sand, glass, plastics, leather, pieces of metal, etc.,

while pollutants include disinfectants, heavy metals, anti-

biotics, etc. (Lesenfants ).01 April 2011 7.23 8.25

13 April 2011 7.75 8.13

14 April 2011 7.7 8.12

15 April 2011 7.6 8.2

04 May 2011 7.12 8.01

05 May 2011 7.5 8.5

06 May 2011 7.42 7.91

16 May 2011 7.08 7.91

17 May 2011 7.13 7.89

18 May 2011 7.18 8.21

01 June 2011 7.16 8.16

02 June 2011 7.35 8.2

03 June 2011 7.28 8.09

14 June 2011 7.18 7.9520 June 2011 7.32 7.92

23 June 2011 7.41 8.18

27 June 2011 7.60 8.30

to the results of research carried out by Kupper & Fuchs

().

According to the BOD5 analysis, the anaerobictreatment reaches a performance about 82% as shown

in Table 3.

According to the results shown in Tables 1, 2 and 3, the

Dayet Ifrah biogas system works normally and operates

properly. So, the low volume of biogas produced is only

due to the equation used to dimension the production of

biogas.

According to a study conducted in 2009 in order to

design the biodigester in Dayet Ifrah village, we predicted

that biogas production in summer can reach 35 l/kg of

fresh matter (Wauthelet et al. ). In winter, biogas pro-

duction could be reduced to 5 l/kg (Wauthelet et al. ).

The daily quantity of biogas produced by the slurry and

toilet wastewater is given in Table 4. When adding faeces,

improve the digestion performance and the biogas pro-

duction efciency, allowing the gas production to reach

3.34 m3/d.

Currently, the average biogas production recorded

during summer 2012 by the ow meter installed on site as

shown in Figure 2 is about 1.87 m3/d. So, the measurements

conrm that the quantity of biogas predicted in 2009 was

overestimated. It seems that the anaerobic digestion

system produces less biogas than expected. Thus, the follow-

ing question arises: which mathematical model could be

applied to predict biogas production in the case of this

biodigester?


Uncorrected Proofbiogas production is increased by only 190 l per day because

faeces have a relatively weak energy performance. Manure

was added to the anaerobic digestion process in order to

Table 3 | BOD5 analysis results

BOD5 inlet (mg/l) BOD5 outlet (mg/l)

18 May 2011 8,500 1,550

27 May 2011 9,200 1,200

13 June 2011 1,150

16 June 2011 9,550 1,400

23 June 2011 7,600 1,180

27 June 2011 8,500 1,100

Table 4 | Biogas production per day (slurries and wastewater)

Quantity of: Biogas production

Summer Winter

Slurry (kg/d) Wastewater (kg/d) (l/kg) (l/d) (l/kg) (l/d)90 35 3,150 5 450

42 190 190

132 3,340 640Our study aimed to nd the most appropriate math-

ematical model to predict biogas production and to

choose the one best adapted to Moroccan conditions. To

do this, we compared and ranked different formulas by

applying principal component analysis and the ELECTRE

III method. The variables studied were the chemical

oxygen demand (COD) removed and the biogas volume

measured.

Specications of biogas system in Dayet Ifrah

The domestic toilet linked biogas system implemented in

Dayet Ifrah village consists of a biodigester tank as shown

in Figures 3 and 4.

The biodigester of volume of 30 m3 is made of on-site

fabricated blocks tted in an excavated pit. The biodigesterFigure 2 | Gas ow meter installed on site for measuring the biogas production.


Uncorrected Proofis designed for 17 inhabitants. The calculated retention time

is approximately 150 days.

METHODS

Formulas used to calculate COD removed and biogas

production

We calculated the COD removed that corresponded to

each measured biogas volume by applying the different

The six formulas used are explained below:

Figure 4 | Schematic diagram of the Dayet Ifrah Biogas System.

Figure 3 | First biogas system of xed-dome during construction in June 2010.Model used in Dayet Ifrah according to Wauthelet et al.()

It has been estimated that biogas production can reach 35 l/formulas described below at 20 WC. We were limited to

this temperature as the biogas amount was measured

during summer.kg of fresh matter in summer and 5 kg in winter (Wauthelet

et al. ).

It was expected that the biogas production would be

about 3.34 m3/day.

The model used in Dayet Ifrah was:

Qbiogaz 0:3 COD reduced m3=d (1)

where: COD_reduced: chemical oxygen demand removed

per day (kg COD/d).

Formula according to Boursier ()

Vg Ps COD reduced (2)

where:Vg: the quantityof biogasproduced (m3); Ps: the specic

gas production (from 200 to 900 l gas) (Figure 5);

COD_reduced/d: chemical oxygen demand removed per day

(kg COD/d), is a measure of the oxygen required to oxidize

where K: inhibition constant depending on the value of Mo:

It depends on the nature of the substrate and its concen-

tration in organic matter. At low concentrations, the

kinetics of the gas production is faster (dilution of the


Uncorrected ProofChen ; Hashimoto )

Q m(m3=d) VVJ:V (4)Q Bo:Mo (3)

where: Q: amount of biogas produced (m3); Bo: the poten-

tial of biogas production, i.e. the total volume of biogas

produced per unit of treated organic matter; Mo: oxidisable

matter.

Model Hashimoto (Chen & Hashimoto ; Hashimoto &all decomposed compounds, both organic and inorganic, in

water.

Formula according to Bouille & Dubois ()

Figure 5 | Temperature effect on gas production (Nijaguna 2002).where VVJ: technological efciency (m3/m3.d). Daily

volume of biogas produced per unit volume of digester,

expressed in m3 of gas per m3 of digester per day; V: biodi-

gester volume (m3).

VVJ B: Mo=HRT

where B: biological efciency (m3 CH4/kg Mo). It denes

the progress of the anaerobic reaction, expressed in m3 of

gas produced per kg of feed material; Mo: oxidizable

matter; HRT: hydraulic retention time, i.e. the number

of days that organic matter or bacteria remain in the

digester.

B(m3CH4=kgMo) Bo:[(1K)=(Mm HRT K 1)]

ganic, in water; MCF: methane conversion factor; theproportion of the methane producing potential that is

achieved. The MCF can theoretically range from 0 to

100%; CODf: fraction of COD converted to biogas; F: frac-

tion of methane in gas (0.5, IPCC 2006); 16/12: fraction of

carbon converted to methane.

The daily COD removal depending on the biogas pro-

duction is shown in Figure 6.

Table 5 | Methane conversion factor (MCF) for storage of cattle slurry at different temp-eratures and durations

Temperature (WC) Retention time (Days) 10 15 20 30inhibitors). K 0.6 0.021 10(0.05Mo); Mm: kinetic coef-cient 0.013 T 0.129. It depends on the temperature Tand is positive only above 10 WC; Bo: potential production

of methane 0.35 m3/kg Mo potential production ofmethane per kg of oxidizable matter, i.e. the total volume

of biogas produced per unit of treated organic matter. It is

based on the biodegradability of the substrate.

Formula according to Vedrenne ()

Q Bo Mo MCF Sg (5)

where: Bo: potential production of methane per kg of oxidiz-

able matter, i.e. the total volume of biogas produced per unit

of treated organic matter. It is based on the biodegradability

of the substrate; Mo: oxidizable matter; Sg: part of cattle

excreta directed towards anaerobic system; MCF: methane

conversion factor (Table 5).

Formula according to Executive Board-CDM ()

Q Sy COD MCF CODf F 16=12 (6)

where: Sy: volume of wastes feeding the biodigester; COD:

chemical oxygen demand is a measure of the oxygen

required to oxidize all compounds, both organic and inor-30 0 0 0.02 0.34

100 0 0 0.31 0.63

180 0.15 0.27 0.41 0.77

decision aid, typically used in the eld of waste manage-

ment; its principle is to class different proposed actions

and select the most suitable one (Saaty ). We adopt

the ELECTRE III method in this work because it has been

executed with success during the last two decades on a

large range of real applications in ranking problematics.

RESULTS AND DISCUSSION


Uncorrected ProofMethods used to evaluate and compare formulas

A biogas ow meter was installed on site in 2012 and the

biogas production was measured. The measurements made

conrm that the quantity of biogas predicted in 2009 was

overestimated. It seems that the anaerobic digestion

system produces less biogas than expected especially

under high-temperature conditions (summer).

In this paper, in order to compare the equations described

above, we chose principal component analysis (PCA) (Le

Moal ). The results of the PCA were then compared and

ranked using the ELECTRE III multi-criteria method.

PCA is a well-known descriptive method that consists of

analysing data and representing through graphics the simi-

larities between individuals from all variables. PCA was

implemented according to the factor analysis procedure of

SPSS software (Statistical Package for the Social Sciences).

Figure 6 | Daily COD removal (kg/d) depending on the biogas production (m3/d).Factor analysis is based on the calculation of averages, var-

iances and correlation coefcients. It is a multivariate data

analysis technique whose main purpose is to reduce the

dimensions of the observations and thus simplify the analysis

and the interpretation of data, as well as facilitate the con-

struction of predictive models. PCA is a linear

dimensionality reduction technique that identies orthogonal

directions of maximum variance in original data, and projects

the data into a lower dimensionality space formed of a sub-set

of the highest variance components (Le Moal ).

ELECTRE (ELimination and Choice Expressing REa-

lity) is a family of multi-criteria analysis and decision-

making methods. ELECTRE III was developed by Roy

(, ) in response to the deciencies of existing

decision-making methods. It is a mathematical method ofFormulas evaluation calculating COD removed

By applying the methods previously mentioned, i.e. PCA

and ELECTRE III, it was found that the formula of Vedr-

enne is the most appropriate for estimating the production

of biogas in the context of our digester. Indeed, this formula

is ranked rst by applying the ELECTRE III method.

Results of the PCA

Figure 7 shows the position of each biogas production for-

mula compared to others.

To choose the appropriate formula, we applied the

ELECTRE III method.

Results of ELECTRE III method

All studied formulas were ranked by the ELECTRE III

method depending on the distance between the point of

each formula represented in the eigenvectors planeFigure 7 | Formulas estimating biogas production represented in the eigenvectors plane.

above and its projection in the line passing through the

barycentre point and the origin (0,0). Thus, the closest for-

mula to the line remains the most appropriate formula to

choose.

As shown in Table 6, the Vedrenne formula ranked rst

among all the formulas sorted by the ELECTRE III method.

It is then the most appropriate for calculating COD and

biogas amount.

In conclusion, the study carried out in 2009 predicted

that the biogas production will reach nearly 3.34 m3/d,

whereas, the biogas ow meter indicated lower production.

Evolution of biogas production volume versus time

We monitored the evolution of biogas production for 86

days. The results are shown in Figure 8.

We observe, in Figure 8, that the biogas production

varies around an average of 1.87 m3/d ranging between

0.25 and 3.79 m3/d. We also observe the alternation of

different values around the average of 1.87 m3/d of biogas

production. This alternation is explained by the succession

of biogas production and its consumption for cooking. The

gas is used immediately after its production. The value of

biogas volume increases and drops successively. Biogas is

produced after the addition of the continuous substrate of

manure and human excreta; which conrms that the pro-

cess of methanogenesis is operating normally and the

digester is fed with biodegradable organic substrates.

This also conrms that the continuous feeding of sub-

strate helps digestion and accelerates the development of

ometer was introduced to measure gas pressure Figure 10).

Table 6 | Ranking formulas using ELECTRE III method


Uncorrected ProofRanking formulas

Formula used in Dayet Ifrah 4

Formule according to Boursier 3

Formula according to Bouille and Dubois 2

Formula according to Hashimoto 6

Formula according to Vedrenne 1

Formula according to CDM-Executive Board 5Figure 8 | Daily biogas yield (in m3) versus time (86 days).Figure 11 shows the evolution of pressure in the gas-

ometer over a period of 41 days. It shows that biogas is

produced under an average pressure equal to 52.7 mbar in

the reactor. This pressure is sufcient in the case of directmethanogenic bacteria, hence triggering the methanogenic

stage (Djafri et al. ).

During this 86-day period, the digester produced

approximately 160 m3 of biogas as shown in Figure 9.

Evolution of the pressure of gas holder

Thebiogas is produced andaccumulates under the domewhen

the pressure is not zero. At themaximumpressure, the amount

of available biogas is limited by the level of the inlet nozzle. If

there is little gas in the gasholder, the gas pressure will be low

and the farmers needs cannot be satised.

In the biodigester built in Dayet Ifrah village, a man-


Uncorrected Proofuse of biogas (e.g. stoves), because it exceeds 50 mbar. This

is sufcient to provide a ow of gas for consumption

(Wauthelet et al. ).

According to Figure 11, the amount of biogas production

increased gradually along with increasing pressure and con-

sumption and vice versa. When gas is produced, the gas

Figure 10 | Manometer installed in Dayet Ifrah for measuring the pressure of the biogas.Photo: Abarghaz 2012.

Figure 9 | Cumulative biogas production during 86-day period.

Figure 11 | Pressure evolution in the gasometer during 41-day period.pressure pushes the inverted gasholder upwards and as the

gas is being used, the gasholder gradually lowers down. An

average amount of approximately 1.87 m3 was recorded for

cooking food with an average pressure value of about

52 mbar. According to plant owners, about 2 hours/day burn-

ing period of gas was noted during the measurements made.

The gas production was found to be approximately 1,870 l/

d. The gas ow meter works properly as indicated by the

measured high pressure.

Capital, operation and maintenance costsThe capital cost of the pilot biodigester constructed in Dayet

Ifrah in 2010 is about USD 84 per cubic meter of biodige-

ster. It was estimated that 3.34 m3/d of biogas would be

produced. In fact, the biogas production is only about

1.87 m3/d. So, this cost can be reduced by 56% using

Vedrennes formula. The produced biogas is sufcient for

cooking purposes throughout the whole year. The project

was assumed to be economically feasible because it shows

calculations.

October 2012).

Environmental Engineering 133 (2), 186.Hashimoto, A. G. & Chen, Y. R. Anaerobic fermentation of


Uncorrected ProofUnder local conditions, biogas systems with improved

efciency and decreased costs are economically feasible.

CONCLUSION

According to the PCA and ELECTRE III method, our

study nds that the amount of biogas production and

COD removed in the digester are governed by the Vedr-

enne formula. Therefore, we conclude that the Vedrenne

equation remains the most appropriate model for the Mor-

occan context in estimating biogas production and COD

removed.

The technology is new and needs to be shared and tested

in order to be better applied in other Moroccan rural areas.

The outcome of this study will help in the design of new

biogas systems planned in Morocco. The goal behind this

research is to optimize capital, operation and maintenance

costs. All in all, only a well-planned and carefully designed

biogas system will improve living conditions in rural areas.

These results will improve the design of future biodigesters

planned shortly in Dayet Ifrah by GIZ and in other locationsa payback period of 5 years as the farmer family needs USD

460 per year to buy wood, fertilizers and some bottles of

natural gas. In rural areas of Morocco, people usually use

rewood for cooking and heating.

The biodigester incurs very small operational and main-

tenance (O&M) costs. Annual O&M costs can be estimated

at 1% of capital costs. It was constructed in 2010 and is still

operating in good condition. Its lifetime ismore than 20 years.

Biogas generates economic benets. It is used in gas

stoves with high efciency and replaces energy from burning

wood. Switching from consuming wood to biogas would

have a positive effect on forest conservation. The potential

for biogas is even more relevant when considering that

wood is the main energy source in rural areas.

Using biogas will also generate social benets. People

will no more need to collect wood; indoor pollution will

be reduced. Monetisation of these benets is difcult and

has not been taken into the consideration in the economicin Morocco.

Other experiments using toilet wastewater in combi-

nation with cattle manure must be carried out tobeef cattle and crop residues, In: Proc. of III annual fuelsfrom biomass symposium, June 46, Golden, Co.

Hashimoto, A. G. Methane from swine manure. AgriculturalFranco, A., Roca, E. & Lema, J. M. Enhanced start-up ofupow anaerobic lters by pulsation. Journal ofdetermine whether satisfactory biogas production can be

achieved.

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First received 1 December 2012; accepted in revised form 21 February 2013. Available online 24 April 2013


Uncorrected Proof

Modelling of anaerobic digester biogas production: case study of a pilot project in MoroccoINTRODUCTIONParameters affecting of biomethanisationTemperaturepHAlkalinitySolids and hydraulic retention timeCarbon/nitrogen (C/N) ratioToxic compounds

Specifications of biogas system in Dayet Ifrah

METHODSFormulas used to calculate COD removed and biogas productionModel used in Dayet Ifrah according to Wauthelet et al. (1996)Formula according to Boursier (2003)Formula according to Bouille &'; Dubois (2004)Model Hashimoto (Chen &'; Hashimoto 1978; Hashimoto & Chen 1979; Hashimoto 1984)Formula according to Vedrenne (2007)Formula according to Executive Board-CDM (2008)

Methods used to evaluate and compare formulas

RESULTS AND DISCUSSIONFormulas evaluation calculating COD removedResults of the PCAResults of ELECTRE III method

Evolution of biogas production volume versus timeEvolution of the pressure of gas holderCapital, operation and maintenance costs

CONCLUSIONREFERENCES

ad morrocco

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