Evaluation of the Energy Capacity of the Controlled Landfill from Mohamedia Benslimane by Three Theoretical Methods – Land Gem, IPCC, and TNO

The objective of this study was to estimate the content of methane produced and generated by the anaerobic bio-degradation of the main organic fraction of municipal solid waste from the controlled landfill of Mohammedia-Benslimane (Morocco) by three theoretical models, based on the first order decay equation: LandGEM, IPCC and TNO. To carry out this study, the quantities of solid waste buried in this landfill since its inauguration in 2012 were used and the composition of the biogas in-situ in 2020 and 2021was determined. The quantities of waste that will be buried in this landfill from 2022 to 2032 were estimated by projection.The results of the analysis of the biogas generated in this controlled landfill in 2020–2021 indicate that it is composed of 59.59% CH 4 , 38.9% CO 2 , and 0.14% O 2 . This result indicates that the waste is in a stable methanogenesis phase. The results obtained by using the three methodologies show that the total volume of CH 4 generated during the period 2012–2021 was 32.59 Mm 3 according to the IPCC model, 20.95 Mm 3 according to the LandGEM model and 20.96 Mm 3 according to the TNO model. The total volume of CH 4 that will be produced during the period 2022–2032 has been projected to 107.48 Mm 3 by the IPCC model, to 76.84 Mm 3 by the LandGEM model, while the total volume of CH 4 projected under the TNO method will be 67.67 Mm 3 . The maximum methane production will reach a value of 12.07 Mm 3 , 9.46 Mm 3 and 7.82 Mm 3 for the IPCC, LandGEM and TNO models, respectively. In 2021, the volume of methane esti - mated by the three models is higher than that on-site measurement by a factor of 3.5(IPCC), 2.4 (LandGEM) and 2.3 (TNO). The results clearly indicate that the three models over predict methane generations when compared to the on-site generations. According to the LandGEM methodology, the electricity estimated will reach a maximum value of 33 GWh/year in 2032.The efficient use of methane generated by this controlled landfill as a source of electrical energy in the upcoming years can be an option for the sustainable management of waste.


INTRODUCTION
In the last decade, Morocco has a strong growth in the legal population which was estimated at 33,848,242 inhabitants following the statistical of the High Commission for Planning (RGPH) during 2014, and also the industrial expansion is increasing. Indeed, the improvement of lifestyles of Moroccan citizens and the proliferation of outlying neighborhoods around the largecities have led to an increase in the quantity of household and similar waste.
The management of municipal solid waste has become a major problem in modern society. Total national waste production is 6.98 million tons per year, including 5.5 million tons in urban areas, and can reach 9.3 million tons in 2030 [El-Ajraoui et al., 2019]. Good planning for the management of household solid waste (MSW) not only solves the problems of disposal of this waste, but also generates revenue for society. Management strategies depend primarily on the chemical composition of the waste and may include: recycling, composting, heat treatment, anaerobic Evaluation of the Energy Capacity of the Controlled Landfill from Mohamedia Benslimane by Three Theoretical Methods -Land Gem, IPCC, and TNO digestion and landfilling. It should be noted that landfill is considered to be the least expensive and most adopted way to treat waste (80% of the world practices) [Kumar and Sharma., 2014].
Uncontrolled landfills do not have landfill gas monitoring and recovery, leachate collection, base coating, compaction, and waste cover systems. By adopting the Sanitary Landfill concept, the problems of leachate contamination of groundwater increased greenhouse gas emissions, fire and hazard explosion, risks to human health, and sanitary problems can be avoided, while additional revenues can be generated from the production of landfill gas.
Since the Moroccan state ratified the Kyoto Protocolon 16 th February 2005, it has continued to improve environmental projects, including those of municipal solid waste management. These projects concern the construction of controlled landfills and their evolution into landfills and recovery centers, and the rehabilitation of old uncontrolled landfills, in order to fight against the potential risks of environmental degradation.
Cudjoe et al., conducted a study on a project in urban Africa, about the economic feasibility and environmental impact analysis of a landfill gas to energy conversion [Cudjoe and Han., 2021]. They showed on the one hand that a project to convert landfill gas into energy for Morocco has a positive net present value; on the other hand, they reported that on average a landfill gas to electricity conversion project could reduce the global warming potential with 72.2% but could lead to an 8.9% increase in acid gas emissions (SO 2 and HCl). It should be noted that methane has a warming potential 21 times that CO 2 [Noor et al., 2013].
For example, in the city of Fez (Morocco), the biogas produced by the anaerobic decomposition of solid waste buried in the controlled landfill is converted into electrical energy [Saghir et al., 2018]. To counter the nuisances induced by biogas and specifically methane, the Bikarane landfill in Greater Agadir (Morocco) was rehabilitated by installing an active degassing system. In this landfill, biogas is converted into thermal energy whose objective is to treat by forced evaporation leachates from the new controlled landfill of Agadir (Tamellast) [El-Ajraouiet al., 2019].
Mohammedia-Benslimane Intercommunal Controlled Landfill was selected as an appropriate case study, as it receives waste from nine municipalities (Waste Accepted Rate = 182 500 Mg/ year). It is worth noting that the biogas generated in this landfill is regularly monitored by analyzing its quality, and by measuring its composition and volume flow. This biogas is destroyed by flaring at a temperature above 900 °C to reduce its negative impact on the environment, but this type of management does not allow exploiting the potential of this biogas in the production of thermal energy or electrical energy.
In a previous study, the authors used the LandGEM model to estimate the methanogenic and energetic potentials as well as the evaluation of the carbon footprint of Mohammedia-Bensilmane controlled landfill [Oukili et al., 2022]. The purpose of this study is to estimate the biogas generated in this controlled landfill by three theoretical models (LandGEM, IPCC and TNO), widely described in the literature, and to predict its potential energy if a landfill biogas-to-electricity project is installed in the upcoming years.

Study area
The total surface of the controlled landfill of Mohammadia-Benslimane is 109 ha. The area reserved for burial is 47 ha. It has a capacity of 5 million cubic meters and was inaugurated on 27 th February 2012. The landfill is situated at 800 meters from Provincial Road RP 3313, 8 km southeast of the of Beni Yakhlef center, 24 km southwest of Benslimane and 17 km east of Mohammedia ( Fig. 1). During the year, in Beni Yakhlef, the average of precipitation and temperature is 461 mm and 18 °C, respectively.

Municipal solid waste characterization
The landfill receives a total of 500 tons/day of municipal solid waste (MSW). The landfill area is divided into five cells, used for MSW disposal, and it is expected to operate for 20 years (to 2032). The landfill was sequentially implemented cell by cell. Four cells were put into operation, totaling 13.33 hectares: Cell 1 (3.92 ha), Cell 2 (3.37 ha), and Cell 3 (2.38 ha) are closed. Cell 4 has an area of 3.68 hectares and is currently active, whereas the fifth cell with an area of 4.02 hectares is not yet operational. The total buried MSW was 2 million tons in 2021. The Annual MSW quantities are presented in Figure 2.
It can be seen that the largest fraction of household waste is found in waste buried in the Mohammedia-Benslimane landfill (79%). A study conducted at this landfill in 2016 (ECOMED), revealed that the organic fraction (composed mainly of food waste) is the largest in municipal solid waste leaking into this controlled landfill (60.81%), followed by plastics (13.09%), textiles and sanitary textiles (12.21%), paper and cardboard (8.08%), ceramic glassscrap (1.70%), others (1.58%), metals (1.36%) and wood (1.20%).   The amount of municipal solid waste (MSW) buried at this site from 2012 to 2021 was provided by the ECOMED group. That from 2022 to 2031 was extrapolated using the demographic data of these nine municipalities. The General Census of Population and Habitat (RGPH-2004(RGPH- -2014 mentioned that the population of the regions studied increased from 410, 832 inhabitants in 2004 to 518, 840 inhabitants in 2014 with an annual growth rate of 2.36%.
On the basis of the available data on the quantity of waste buried in this landfill and the population, during the three years 2019, 2020 and 2021, it was possible to estimate a weighted average value of the specific production of waste per day for this area (0.883 kg/inhabitant/day). It should be noted that this daily production represents only a fraction of the waste landfilled and not all the waste generated by the population in this area. On the basis of this value, it was possible to estimate the annual amount of waste that will be landfilled from 2022 to 2031, as well as the total amount of waste that will be in place at this landfill in 2032 (4.06 E+6 tons). A total waste quantity very close to that estimated by the specific daily production (0.883 kg/inhabitant/day) was obtained using the average annual growth rate of solid waste buried from 2012 to 2021 (2.96%). This average annual growth rate was calculated using the exponential model (Eq where: P n -MSW production in year n, 2012 (151,501 Mg/y); P o -MSW production in base year, 2021 (196,916 Mg/y); τ -annual rate of change (2.96%); n -number of years (n = 9).  The waste received in the landfill is regularly checked, weighed and the data are registered (average about 500 tons/day). This process has been ongoing since the opening of the landfill in 2012. In this study, the data available from 2012 to 2021 (ECOMED) was used and then projected to 2032, i.e. the year planned for the closure of the landfill. Table 2 shows the annual amount of waste landfilled in tons at the Mohammedia-Benslimane controlled landfill from 2012 to 2021.
On the basis of the amount of municipal solid waste landfilled for each month and in each municipality in this area from January 2019 to March 2022 (ECOMED), it has been remarked that the urban municipality of Mohammedia (Moh-C) is the main producer of household waste;it is larger compared with other municipalities (Fig. 3) since it has the highest population density. In addition, an increase in waste produced was observed during the summer period of each year (June, July, and August) in all the regions.

Estimation of methane generation using different methods (FOD)
To estimate the generation of biogas from the controlled landfill, the first-order models used were the Landfill Gas Emissions model LandGEM

Model of LandGEM
To estimate the amount of landfill gas generation using a first order equation (Eq. 2), the Land-GEM model is usually used.
The control technology center of the American Environmental Protection Agency (US.EPA) has developed this model for the prediction of gaseous pollutant generation by decomposition solid waste.
It considers (i) the characteristics and content of the buried waste during consecutive years, (ii) the characteristics of the biogas produced and (iii) particularly the meteorological conditions in the studied regions. It allows predicting of CH 4 and CO 2 quantities that will beproduced up to 140 years from the first-order decomposition equation [EPA USA 2008]. In order to increase the accuracy of the estimation process, the CH 4 generation equation (Eq. 2) considers increments of one tenth (1/10) of a year.
where: Q CH 4 -annual methane generation the calculated year (m 3 year -1 ); i -is the one year time increment; n -defines as (year of the calculation) -(initial year of waste acceptance); j -the 0.1 year time increment; L 0 -potential methane production capacity (m 3 /Mg); k -methane generation rate (year -1 ); M i -mass of waste accepted in the i th year (Mg); t i,j -age of the j th section of waste mass Mi accepted in the i th year ( decimal years, e.g., 3.2 years).
To conduct thestudy, the required inputs for estimating the amount of generated landfill gas are both the landfill opening and closure year, the annual waste acceptance rates from the opening to the closure year, the methane generation rate k (1/year), the potential generation of methane L 0 (m 3 CH 4 /ton-waste) and the methane proportion in the biogas and Nom Methane Organic Compound concentration (NMOC).
Methane generation potential (L 0 ) depends on the type and composition of waste buried in the landfill. Thewaste with higher cellulose content would have higher methane generation potential, while the waste having lignin content have lower L 0 value [Kumar and Sharma., 2014]. The methane generation rate k depends on four factors: moisture content, availability of the nutrients for bacteria, temperature and the pH of buried waste.
The model contains two sets of default parameters, Inventory defaults and CAA defaults (Table 3)   The degradable organic carbon (DOC) is simply calculated using equation 4 and the waste characterization data for this landfill (Table 4).
where: X -represents the average annual precipitation (in mm) of the area where the landfill is located.
IPCC first order decay method model is based on three main equations (Eq. 6, Eq. 7 and Eq. 8, with its parameters described in Table 5   Note: A -fraction of municipal solid waste (MSW) that is paper and textiles, B -fraction of MSW that is garden or park waste, C -fraction of MSW that is food waste, D -fraction of MSW that is wood or straw waste. Methane generation potential depends on the type and the composition of waste buried in the landfill. The waste composition in 2016 (ECOMED) was used in this study as the input for the IPCC method. The following default values of DOC fraction of degradable organic carbon (weight fraction, wet basis) were used in this study: DOC Foodwaste = 0.15, DOC Paper waste = 0.40, DOC Textiles waste = 0.24, DOC Hygiene nappieswaste = 0.24 and DOC Wood waste = 0.43.
Methane correction factor (MCF) and fraction of DOC dissimilated (DOC f ) were chosen at 1 and 0.50 respectively. Fraction of methane CH 4 (volume fraction) in biogas produced in this landfill was F = 0.60 (on-site measurement).

TNO model
Although the TNO model was developed for the waste characteristics of the Netherlands, it can be used for landfill gas estimation for other countries, as it has less relative mistake (22%) between the observed and calculated values. The TNO mod- where: α t -landfill gas production at a given time (m 3 /year); ϛ -dissimilation factor 0.58; 1.87 -conversion factor; A -amount of waste (in ton); C 0 -amount of organic carbon in waste (kg of C/ton of waste); k 1 -degradation rate constant (year -1 ); t -time elapsed since depositing (year).
To estimate the methane generated by the TNO model, the same parameters as the Land-GEM modelwere used.

Estimation of electrical energy
The electrical energy produced from methane generated in the landfill is a common application and its use is very beneficial. Electricity can be generated by burning in a generator or gas turbine the methane. The equation (Eq.10) [Saghir et al., 2018] was used to estimate the potential for electric power generation from landfill methane recovery. where: E elc -annual production of electricity in (kWh/year); LCV -lower calorific value of methane (9.94 kWh/m 3 ); Q CH 4 -annual methane generation in the year generated by anaerobic decomposition in Landfill in (m 3 /year); r elc -efficiency of the facility producing electricity from methane generated by anaerobic decomposition in Landfill (35%).

RESULTS AND DISCUSSION
The results of the conductedstudy are presented in three parts: • characterization of the produced biogas; • estimating the methane's amount produced using three models: LandGEM, IPCC, and TNO; • estimating the electrical energy potential of this controlled landfill.

Characterization of landfill biogas
The Mohammedia-Benslimane controlled landfill receives about 500 tons of waste per day, composed of biodegradable and nonbiodegradable fractions. The carbon dioxide CO 2 and methane CH 4 which are greenhouse gases, are the main products of biodegradable organic waste through anaerobic decomposition. At this site, the biogas analyses showed the average methane content of around 60% by volume. Table 6 gives the results of measures taken in 2020 and 2021. It is worth noting that the open fraction of the extraction of biogases valve is only 22.5%. The biogas is collected by a network of horizontal wells up to the flaring system to undergo the combustion reaction at a temperature above 900 °C. According to the results presented in Table  6, there is no significant variation in the composition of biogas overtime during the period 2020-2021, as the recorded values are very close. The value of the combustion temperature in the enclosed flare shows that the biogas is burned more efficiently to produce CO 2 , H 2 O and other pollutants in very small amounts. Since CH 4 methane has a global warming potential (GWP) of 21 more than CO 2 , captur- Either a reduction of 5511.5 kg eqCO 2 per hour or a reduction of 48.28 Gg eqCO 2 per year is achieved.
It can be concluded that the flaring system with active degassing, installed at this controlled landfill, will contribute to a reduction of emissions of 482.8 Gg eqCO 2 from 2022 to 2032. The percentages of CH 4 and CO 2 are in accordance to the values mentioned in literature during the methanogenesis phase anaerobic decomposition of the organic fraction of the waste: 60% CH 4 and 40% CO 2 (Williams., 2005). Similar results have been reported in the literature [Plocoste and Koaly, 2016]. The CH 4 /CO 2 ratio value of 1.53 and the very low amount of O 2 dioxygen (< 1% by volume) in biogas indicate that landfill waste is in an advanced and stable biodegradation state (maturation), and that the degassing system and waste cover layers are sealed. It can be concluded that this controlled landfill has a large capacity to produce methane, which could be upgraded for the production of electrical energy.
It The concentration measured of hydrogen sulfide H 2 S (1102 ppm in July 2021) at the landfill can be explained by the anaerobic decomposition of high levels of protein-rich food waste, especially amino acids (cysteine HS-CH 2 -CH(NH 2 )-COOH and methionine CH 3 -S-CH 2 -CH-CH(NH 2 )-COOH)), and reduction of sulfate ions by Bacteria (BSR) [Ko et al., 2015].
It should be noted that during the methanogenesis stage, more H 2 S is produced. Sulfur compounds are one of the dominant chemical groups in landfill gas and H 2 S hydrogen sulfide alone accounts for almost 90%, and its concentration in biogas from municipal solid waste landfills can be as high as 2340 ppm [Kim et al., 2005]. Low concentrations were measured in closed or old landfills, while the active landfills were respon-

Estimating the methanogenic potential of the controlled landfill
For the first year 2012, there was no biogas production. The models suppose that the anaerobic decomposition stage begins at least 6 months after the landfill of the waste. Several factors are responsible of the degradation of waste: climatic conditions, type of waste, moisture in the waste and the materials that cover the waste.
The quantities of CH 4 methane produced by the decomposition of the organic fraction of municipal solid waste buried in this controlled landfill over the period 2012-2032 (2032 is the year planned for closure of this site) are presented in It wasfound that the annual estimated amount of methane (m 3 CH 4 /year) by the three models increases with the years and reaches a maximum value in 2032 (Fig. 4), which is the year expected for the closure of the site. The maximum methane production will reach a value of 12.07 Mm 3 , 9.46 Mm 3 and 7.82 Mm 3 for the IPCC model, LandGEM model and TNO model, respectively. In 2021, the volume of methane estimated by the three models is higher than that on-site measurement by a factor of 3.5 (IPCC model), 2.4 (landGEM model) and 2.3 (TNO model). The results obtained with the models LandGEM and TNO were almost similar during the period 2012-2032.However, the IPCC model yields values differ markedly from those obtained by the LandGEM and TNO models. This difference can probably be explained by the fact that the k value used for the LandGEM and TNO models is low (0.024 year -1 ) compared to the k default values used for the IPCC model. This result clearly indicates that the three models over predict methane generations when compared to the onsite generations. After 2032, methane production decreases exponentially over time, as the site will  no longer be powered by waste sources of biodegradable organic matter. It should be noted that this result is in good agreement with the literal value [Kumar and Sharma, 2014].
The difference between the estimated amount of methane by the three theoretical models and that measured on the site can be explained by the fact that the opening of the valve of the biogas extractor (PID) is only 22.5%. It worth noting that theoretical models for estimating landfill gas may overestimate or underestimate the amount of biogas relative to that measured on the site.
A literature review of landfill biogas estimation models has shown that many researchers around the world have applied the LandGEM model. Indeed, this model gives current and future projections of the greenhouse gas (GHG) emission potential, in particular methane, and has the ability to estimate emissions of more than 46 gaseous pollutants such as organic and inorganic sulfur compounds, in particular H 2 S. If landfill-specific data are available, the resulting estimates will be more accurate. The LandGEM model is easily accessible and free of charge and was chosen to be applied to the estimation of the energy potential.

Energy potential estimation in this controlled landfill
The result of the annual estimation of the energy potential of this controlled landfill to produce electrical energy as a function of time is represented by Figure 5. It should be noted that the estimated values of methane by LandGEM model were used.
According to Figure 5, electrical energy differs in two different ways depending on the time: • When 2012 ≤ t ≤ 2032: the estimated electric energy increases linearly over the years to reach a maximum value of 33 GWh/year in 2032 (Eq. 13) (year planned for the closure of the landfill).
• When t ≥ 2032: the estimated electrical energy follows an exponential decrease as a function of time (Eq. 14). This growth is done with a slow rate.  (14) where: t -year.
These values show that the non-use of biogas produced in this landfill, as is the case in several Moroccan landfills, will lead to a great economic loss.

CONCLUSIONS
In this study, at the Mohammedia-Benslimane controlled landfill, LandGEM, IPCC and TNO models were used to estimate annual generation of methane. Its volumes estimated by Land-GEM and TNO are similar but larger than those measured on site. The IPCC model significantly overestimated methane generation. In general, when default parameters are used, the volumes of Figure 5. Annual estimated of electrical energy generation by methane produced at Landfill methane estimated by the theoretical models are larger than those measured on site.The composition of biogas, measured on-site, showed that the municipal solid waste buried in this landfill is in a stable methanogenic phase. It is clear from the results that the potential for methane generation is significant.
For the continuation of this research, a socio-economic study on the feasibility and the profitability of a future project of installation of a power plantwill be carried out. The objectives of this project are the valorization of the biogas produced in this controlled waste for the production of electric energy and the protection of the environment by reducing the greenhouse effect.