Estimating of gases emission from waste sites to generate electrical energy as a case study at Al-Hillah City in Iraq

Methane (CH4) is a greenhouse gas resulting from human activities, especially landfills, and it has many potential environmental issues, such as its major role in global warming. On the other hand, methane can be converted to liquid fuel or electricity using chemical conversion or gas turbine generators. Therefore, reusing such gases could be of great environmental and economic benefit. In this context, this study aims to estimate the emissions of methane gas from the landfills in Al-Hillah City, Iraq, from 2023 to 2070 and the producible electric energy from this amount. The estimating process was carried out using the Land GEM model and compared with traditional models. The obtained results demonstrated that the total estimated landfill methane emissions for 48 years are 875,217 tons, and the average annual methane emission is 18,234 tons based on a yearly waste accumulation rate of 1,046,413 tons and a total waste amount of 50,227,808 tons. The anticipated loads of methane gas can be utilized to generate about 287,442 MW/year of electricity from 2023 to 2070. In conclusion, the results obtained from this study could be evidence of the potential environmental and economic benefits of harvesting and reusing methane gas from landfills.

the solid waste generation rate in the capital of Iraq (Baghdad) rates increased from 0.63 kg/capita.day in 2006 to 0.74 kg/capita.day in 2010.Similarly, the solid waste generation in Mosul city, Iraq, in 2010 was 0.647 kg/capita.day, and it would increase within the next few years to reach 1.1 kg/capita.dayby 2028 21 .Unfortunately, solid waste management in Iraq is still unstable for many reasons, such as repeated wars and sanctions 22 .Additionally, population development has increased trash production, placing a significant burden on the facilities for handling and disposal 23,24 .Therefore, the expected emissions of GHGs from the landfills in Iraq are expected to be huge within the next few years, which in turn indicates the urgent need to explore efficient GHGs recycling methods.
A significant body of research, therefore, was carried out to minimize the effects of GHGs on the environment through several approaches 25,26 .For example, recycling of methane can be done by converting it into heat or electricity to control its emissions and support the responsible operation of landfills 27,28 .The selection of the best recycling approach depends on the generated amount of GHGs, which can be estimated using several methods.One of the most commonly used methods to estimate the emissions from landfills is the Land GEM developed by the United States Environmental Protection Agency (USEPA) [29][30][31] .
In this context, this research aims to estimate the total methane emissions from the local landfill in Al-Hillah City, Iraq, for the next 47 years (2023 to 2070) and the potential production of electrical power from the produced methane gas.The estimation process will be carried out using the Land GEM model.

The study area
Al-Hillah city is one of the major cities in Babylon Province (100 km south of the capital city of Iraq 32 ), and it is located between latitudes 32°36′1″ and 32°8′45″ North and longitudes 44°14′9″ and 44°33′39″ East (Fig. 2), with a total area of 860 km 212,23 .This city is the home of about 993,000 people, according to governmental reports in 2020 33 , with a population density of 1155 capita/km 2 , which is a relatively high density.Geographically, Al-Hillah city lies between the Tigris and Euphrates Rivers, making it rich in agricultural areas 34 .Typically, the average sunlight in the city is 12 h per day in summer and 6.8 h per day in winter.The city's climate is dry in summer and cloudy in winter, with average annual relative humidity and rainfall of 45.8% and 102 mm, respectively, and an average annual wind speed of 7.2 km/h.The weather temperatures extremely vary in this city depending on the season and daytime, where it could be less than zero °C in winter and more than 50°C in summer 12,35,36 .

Classification of solid waste in Al-Hillah City
The generated solid wastes in Al-Hillah City are divided into nine categories, namely organic, metals, plastics, wood, glass, paper, textile, aluminum, and others 37,38 .Organic solid wastes are the predominant type of solid waste in Al-Hilla City (55% of the total solid waste in the city), while aluminum represents the lowest percentage (2%).Figure 3 shows the percentages of these nine categories as a function of the total amount of solid waste produced in the city 12,23 .

Solid waste management in Al-Hillah City
Currently, solid wastes in Al-Hillah City are manually collected twice a day by the local authorities in the city.Then, the collected wastes are transported to the sorting stations by various waste-collecting vehicles, such as compactors, tractors, large dumpers, and mini-dumpers.The reusable wastes, such as aluminum, cans, and glass, are recovered in the sorting stations.Then, the remaining wastes, mainly organic solid wastes, are either burned or landfilled.Additionally, waste pickers often search wastes for valuable waste components, such as metals and cans, before the collection process to sell these components in the local markets 32,37,38 .
Generally, municipal waste management services at Al-Hillah City cannot manage the whole volume of solid waste; it has been reported that only 44% of the population is served by waste collection services due to the lack of collection sites (there are only four sites in the city) 23,38 .The first site is in the Al-Neel district (17 km to the North of Al-Hillah City), and it is used to collect trash from the Al-Neel and Abi-Ghraq districts.The second site is in the Al-Kifil district (35 km to the South of Al-Hillah City) and has not been effectively utilized.The third site is a transitory site used to gather waste from specific locations within the city before transporting it to the Al-Neel waste site.The fourth site is local and serves only the Al-Kifil district 23,38 . 12,18,19.

Materials and methods
Calculation method.Initially, the future population of Al-Hillah City in the year 2070 was estimated using Eq. ( 1), which is necessary to estimate the future solid waste generation in 2070 12,23 .P ex is the estimated population for the selected year.P c is the current population for the starting year.g is the rate of annual growth = 2.99%.y is the years number.
While the generation rate of solid waste (EGRSW) was calculated using Eq. ( 2) EGRSW is the calculated generation rate of solid waste for each year (kg/capita/day).GSW is the current generation rate of solid waste for the year 2023 (0.82 kg per capita per day).WGI is the annual increment rate of waste generation per year (1% according to the literature).
The main equation to calculate the quantity of solid waste (EQSW) generated for every year until the year 2070, based on Eqs. ( 1) and (2), is 12 : (1)    4), which yields the annual emission rate of the targeted gas after calculating two key parameters, namely k (decay rate) and L 0 (generation potential).The latter parameters can be calculated using either assumptions or actual data.These parameters were calculated in the current study using actual data gathered during a field survey.
The annual methane gas emissions were determined by the following land GEM model 39 : Q CH4 is the annually produced quantity of CH 4 gas (m 3 /year).n is the number of years used in the model for calculating.i is the period increment (1 year).j is the period increment (0.1-year).L o is the potential generation capacity of CH 4 gas (m 3 /Mg).k is the rate of methane (CH 4 ) production (1/year).W i is the accepted waste quantity for interval year (ith) (ton).t ij is the age of waste mass (W i ) for the part (jth) in the year (ith).
Governing equations.The capacity to generate methane at a rate of L 0 (m 3 /Mg) from the landfills in Al-Hillah City depends on the type and contents of solid waste 39 .
Land GEM is built on a first-order decomposition rate equation to estimate emissions from the degradation of landfilled MSW.The model offers a comparatively straightforward method for calculating landfill gas emissions.Methane yield is determined by the model using essential inputs, which are 39 : (i) The amount of waste dumped in landfills during the studied period.(ii) Degradable organic content (DOC).(iii) The form of organic waste.(iv) Decomposition rate.DOC represents decomposable organic carbon.A represents paper and cardboard trash in MSW.B represents textile waste in the MSW.C represents food waste in the MSW.D represents wood, bones, and straw waste in the MSW.E represents plastic and rubber waste in the MSW.S 1 , S 2 , S 3 , S 4 , S 5 represent organic carbon that is degraded for each fresh waste type (%).
The decay rate (k) is the half-life of biodegradation of organic waste in landfills, expressed in (1/year).The considerable degree of ambiguity and mistake related to k is acknowledged by the IPCC (2006) 40 .The decay rates in dumps located in arid, chilly areas can be from 1 to 50 years, and sometimes even longer.The following equation is used to estimate the decay rate: k represents a decay rate (year −1 ); x represents the yearly mean rainfall for the relevant time for the region where the location of the landfill is.
The value of L 0 increases with the cellulose waste content.Methane generation potential (L 0 ) has a value between 6.2 and 270 m 3 /Mg of waste.The EPA sets L 0 to a default value of 170 m 3 /Mg waste 39 .
L o represents the possible capacity of methane production (kg/ton); MCF represents a correction factor of methane, where its default value is equal to 1; DOC represents a degradable organic carbon (kg/ton); DOC f represents an assimilated fraction DOC, where (default of IPCC, 1996 = 0.77; default of IPCC, 2006 = 0.50; F represents the methane gas fraction in a landfill with a default value of 0.5 (Eq.7); (1.334) represents a conversion factor of methane (molecular weight ratio) to carbon 39 .
By applying the equation of the Land GEM model (Eq.4), the annual methane gas emissions can be determined for a specific period.

Results and discussion
The Land-GEM model stands as a critical tool for ensuring the proper management of landfills as it provides a realistic estimation of the generated amount of methane, which provides an accurate picture of the amount of methane and the necessary collection systems.Consequently, this model reduces the risk of explosions and leakage of landfills, and it provides an estimation of the generated heat and power from the harvesting of methane.
The waste generation rates and cumulative waste in place for the waste sites in Al-Hillah City in units of (tons/ year) for the period of (2023-2070) were estimated in the Land GEM model.Table 1 shows the estimated weight of solid wastes (tons) for 48 years based on the population in the study area during 2023-2070.Based on Eq. ( 3), the calculated quantity of EQSW generated for every year until 2070 was calculated using the present generation rate of GSW for 2023 (0.82 kg/capita.day), and WGI equals 1%.Additionally, the predicted population for every year from 2023 until 2070 (P ex ) with an annual growth rate of 2.99% using Eq. ( 1). ( 4) The methane estimation (ton/year) from landfills in Al-Hillah City for the selected periods (2023-2070) is shown in Table 2.In the Land GEM model, the annual generated rate of total methane was 1.32 × 10 -3 tons per 1 tan of solid waste from the landfills in Al-Hillah City.
According to Al-Rawi (2013) 41 , 6280 tons of methane gas can generate 11,304 kWh, which was used in the equation below to estimate the producible electricity power (GEP) (kW/year) from methane gas generation (MGG) in 2023: Table 3 shows the generated methane gas from the landfills in Al-Hillah City in the next 47 years and the producible electrical power in MW/year.The estimated amount of accumulated waste in the next 48 years is about 50,227,808 tons, which equals an average of 1,046,413 tons per year.This amount of waste produces 875,217 tons of methane gas, which equals an average of 18,234 tons of methane per year.Regarding energy production, about 13,797,190 MW/year of electricity could be produced from the methane gas.According to a statement from the Department of Electricity in Babylon, the current need for emergency electric power is projected to reach 100 MW in 2022, which means that recycling up to 65% of the emitted methane gas from landfills will supply 20% of the electric power used in the city.Thus, the idea of re-utilizing the methane emissions in Al-Hillah City is overwhelmingly beneficial in both environmental and economic aspects.Not only would this process be immensely economical, but it would also help the environment in numerous ways by reducing the amount of pollutants in the air.It is noteworthy to highlight that the obtained results about utilizing the GHGs from landfills to produce  energy are agreed with the final conclusions of a wide body of literature, such as the studies of Yi et al. 42 , Ghosh et al. 43 , Yaman 44 , Tan et al. 45 , Dace et al. 46 and Nabavi-Pelesaraei et al. 47 .
In conclusion, it could be said, according to the results of this study, this simple solution could pave the way for more efficient and sustainable energy production in the future.

Conclusions
Solid waste accumulation and the shortage of electrical power generation are two critical issues Iraq faces.In an effort to address them, this study was conducted to find a sustainable solution to these issues.The study has indicated the importance of properly managing MSW, which is essential for environmental protection, while the development of alternative energy sources can help fill the increasing gap between electricity production and consumption.
According to the obtained results from the Land GEM model, the amount of accumulated waste over 47 years is 50,227,808 tons, with an annual average of 1,046,413 tons.The generation of this amount of waste has also led to a massive amount of methane emission (about 875,217 tons in total and an annual average of 18,234 tons).The good news is this amount of gas can produce 13,797,190 MW/year of electricity.That's enough energy to power a large number of emergency services, hospitals, and businesses.In general speech, it can be said that harvesting 65% of the emitted methane gas from the landfills in Al-Hillah City can cover up to 20% of the electricity used for emergency power lines in the city.Not only would this drastically reduce energy expenses, but it could also help purify the air by reducing the amount of pollutants.
To further assess the impacts of the model's estimates on the environment, data regarding local policies and regulations should be incorporated.This additional information may support the implementation of strategies to successfully improve landfill management and reduce future emissions in Al-Hillah City.

Table 1 .
Waste generation and cumulative waste in the waste sites in Al-Hillah City (2023-2070).