Investigation and Evaluation of Potential Options to Determine the Methane Gas

Izmir has been one of the cities in our country which firstly began to implement a regular solid waste disposal system with the operation of Harmandali Landfill Facility in 1992. An important part of municipal solid waste produced in contiguous area of Izmir during the period of 25 years was disposed in this facility in order to minimize any possible problems on health and environment caused from that solid waste. The most important factor for deciding on the energy potential of landfill is the amount of landfill methane gas in the landfill area. There are several approaches used to determine the amount of landfill gas. We used one method (When the facility conditions are taken into account (moisture, waste water, landfill leachate etc.) that it is the most appropriate method) and one Literature-Based Approximate Forecast to determine the amount of the landfill gas in Harmandali Landfill. This method is Multi-Phase method. The main objective of this study is to investigate the use of landfill gas as potential energy and electricity provided from municipal solid waste (domestic, industrial, medical waste and sewage sludge) stored regularly in Harmandali Solid Waste Landfill Area, within the boundaries of the contiguous area of Izmir.


Introduction
Energy recovery from waste represents an important way to reduce the amount of electric energy to be produced using fossil fuels, i.e. non-renewable sources of energy.Moreover, the energy recovery practice can present interesting economic revenues [1].Despite efforts to reduce generation and increase recycling of municipal solid waste (MSW), open dumps and sanitary landfills remain the most common solid waste management approach globally.For instance, in the US, 54% of the generated solid waste was landfilled in 2008 [2].According to the results of the Municipal Waste Statistics Survey of 2014 applied to municipalities in Turkey, it was determined that 1391 of the 1396 municipalities provide waste services.It was determined that 28 million tons of waste was collected from municipalities providing waste services.
Of the 28 million tones collected in the municipalities where waste collection and transportation services were provided, 63.5% were sent to the sanitary landfill facilities, 35.5% to the municipal rubbish tips, 0.5% to the composting plants and 0.5% have been disposed with different methods [3].This situation reveals the fact that sufficient infrastructure services are still not available for the disposal of solid wastes.In this context, especially under the name of examination of the disposal methods of solid waste of big cities, the example of İzmir has been the starting point.Within the scope of the study, the options for disposal and assessment of the emerging landfill gas and presentation of the existing conditions related to the formation of landfill gas and the gas collection system were investigated in Harmandalı Sanitary Landfill Area (HSLA) where urban solid wastes formed within İzmir contiguous area boundaries are stored regularly.

Municipal Solid Waste Amounts
The total amount of solid waste disposed between 1992 and 2010 in Harmandalı Sanitary Solid Waste Landfill Facility, which is the only sanitary solid waste landfill facility in İzmir, is shown in Table 1.When Table 1 examined, it is seen that the amounts of domestic solid waste increased regularly between 1992 and 1994, and showed a parabolic increase between 1994 and 1998.Between 1998 and 1999, the regular increase in the amount of waste continued, despite the slight declines between 1999 and 2007, again an increase is observed between 2007 and 2009.
A study has been conducted on a specific area to determine the potential for the formation of landfill gas in HSLA.This area is the currently operated region E, which will enable us to detect the gas composition and the flow rate in the area.This will be achieved on the basis of the existing gas collection system in the area and by making qualitative and quantitative gas measurements of the gas chimneys in this area.

Land Surface Studies
Harmandalı Sanitary Landfill Area is shaped according to the basin of the existing landfill area.The material is compacted on a daily basis with garbage compactors to keep it stable and not to slip, and it is covered with clay over it.In the area, 1/3 slope is given where the incline of slope of garbage is ideal for incline of slope of the garbage to remain stable [6].The storage of wastes in the landfill area continues in the basin, which can be seen in Figure 1, 2 and 3. Storage is performed from top to bottom.
At this stage of the work, the garbage volumes of the landfill area, the type of waste storage, the soil surface (filling, shavings, etc.) have been examined.In this context, orthophotographs of Harmandalı Sanitary Landfill Area for 1996 and 2010 have been examined (for 1992 and after, these two orthophotographs of the landfill area have been obtained).
In the light of this information, HSLA was differentiated into 14 separate sections by MapInfo program.We examined each section individually.The differences in garbage growth in the areas on the surface (North-South, West-East) and in the whole area are shown graphically.In graphical sections, the red lines show the year 2010 and demonstrate the height of the surface sections we have examined as of 2010.The green lines show the year 1996, which is the height of the surface sections of that year [6].As can be seen from the graphical section shapes, the red lines showing the cross-sectional values of 2010 in general are on a trend above the green lines showing the cross-sectional surface values of 1996.This shows that with the increase in the volume of garbage, the height has increased and continues to increase.However, the green lines at some points on the graph are above the red lines.This shows that the land is shaved in certain areas (the land is not a flat surface but it is mountainous.With opening new landfill lot areas and the improvements made in the land, land reclamation is performed with heavy equipment).At the same time, it can be understood that the land has slipped due to the slides in the area.As a matter of fact, the fact that some part of the old garbage leachate treatment plant is under the ground proves this situation.
Figure 4 and 5 detail the differentiation of the landfill area into sections and their heights.In the sections, the height is limited to a maximum of 300 meters.After this height, the settlements formed of hills occupy the land [6].The information about the sections can be seen in Figures 6-19.By means of the information of the obtained sections, 10.694.242,9cubic meters of garbage disposed in 666,282.8m² area that belongs to HSLA, between 1996 and 2010, and a large part of the area was shaved during these years.Within the garbage disposal volume, there are also soil volumes accumulated in the area due to fillings and slips.Within the determined cross-sections of the area, the average height is about 11.5 m [6].

Landfill Area Gas Measurement
Gas measurements were performed with GEOTECH GA 2000 Range Gas Analyzer (GA 2000) manufactured by Geotechnical Instruments Limited (UK), in 77 chimneys located in Harmandalı Sanitary Landfill Area (HSLA).The GA 2000 is a device designed to detect the rates of gases formed in storage areas [5].
The device has two separate measurement probes.One of them is used for the measurement of the orifice plate based flow rate and the other is used for the measurement of the gas components (CH4, CO2, O2, CO, H2S parameters).During the measurements it was necessary to isolate the chimney outlet from the atmosphere and direct all the gas to the measuring device.For this reason, a hat suitable for the top of the chimneys was produced in the site works (Figure 20) and sampling was made for the flow rate and gas components from the sampling outlet at the top of the hat [5].

Landfill Gas Measurement Results
The measurements performed in HSLA were carried out at a total of 77 places along with 73 gas chimneys (Z1-Z73) located in E region which is the current dumping area and 4 gas chimneys located in C region which is the old dumping area.The results of the measurements performed are given in Table 2.In the data provided in the table, the measured flow rate and gas component rates (%) in each gas chimney (or test well) are given.However, due to the very low gas velocity from some gas chimneys, the flow rate could not be measured and shown with "Undetectable" (UD) expression in the Table 2.When Table 2 is examined, we can see that the CH4 ratios are between 2.4 and 61.9%, and when the 77 chimneys we examined are considered, the CH4 average is 49.38%.In this context, we can take the methane average as 50% in the landfill gas modeling calculations to be made for the area.The CH4 average of 48 chimneys is 55.53%, if we exclude the chimneys where the gas flow rate cannot be detected.This value is a good CH4 ratio according to the literature based information.
Percentage of CO2 gas which is another important gas component in the landfill area was measured between 0.2 and 49.9 and the average of 77 chimney measurement results was 37.9%.The CO2 gas average of the 48 chimneys excluding the gas chimneys of which the gaseous flow rate cannot be determined is 42.8%.The ratio found in carbon dioxide gas as well as in methane gas is a good rate based on the literature and it is at an evaluable level.
It has been determined that the ratio of oxygen gas in the chimney in the region where the measurements have been performed is between 0.1-20.6%.It has been observed that methane gas ratios are low in the chimneys where the oxygen gas ratios are high.This is due to the fact that oxygen is inversely proportional to the bacterial growth in the landfill.Therefore, in places where the oxygen gas is high, there are few bacteria that will produce methane gas.On the other hand, the amount of oxygen shows how much the landfill area is connected to the atmosphere.
Regarding the other gases being measured; it has been found that the hydrogen sulphure gas changes between 0-546 ppm and the average value is calculated as 168 ppm.The carbon monoxide gas exchange interval is 0-530 ppm and the average value is 137 ppm.

Modeling Studies
The most important factor in determining the energy potential of sanitary solid waste storage areas is the amount of methane gas released from the landfill area.There are various approaches used to determine the amount of landfill gas.
In order to have information about the potential of gas in HSLA, theoretical estimation methods have been applied.All approaches other than the measurement-based approach are based on the current data about the site.This data shows the amount of garbage stored according to the years, the waste characteristic, the duration of operation of the site, and etc.

Literature Based Approximate Estimation
A range of 50-400 L / kg (m 3 / ton) has been given for the amount of theoretical landfill gas (LFG) that can emerge for full-scale solid waste landfill sites [7].The fact that the given range is such wide (there is a-8-fold difference between the minimum and maximum values) is an indicator that as mentioned above, the garbage characteristics, climate and landfill site-specific characteristics affect the amount of gas to be released.
When the figures given above are used specifically for HSLA, it can be said that the gas potential to be generated for approximately 4 million tons of garbage (2007-2010) stored in the existing domestic waste lot may vary between 200-1,600 million cubic meters.

Estimation with Multi-Phase Model
One of the models used for predicting the formation of landfill gas is the multi-phase model.In this model, the calculations are based on the proportion of biodegradable organic carbon in the waste and the amount of cumulative waste.The mathematical expression of the model is as expressed in Equation 1 [8]: (1) Explanation of the parameters in Equation 1: αt: The amount of landfill gas formation (Nm 3 / year) A: Amount of waste (ton) ϛ: Factor of production Co,i : The amount of organic carbon (kg C / ton waste) k1,i: Model variables (given separately for slow, medium and fast degradation) t: It is expressed with the time elapsed (by years) from the first year when the waste began to be stored Only fast, medium and slow degradable organic wastes are included in the model.In the model, the types of degradable wastes in the waste are treated in three groups according to their degradation rates.In the literature, it is expressed that for the fast degradable wastes kt, i can be taken as 0,076-0,694 year-1, for medium degradable wastes as 0,046-0,116 years-1, for slow degradable wastes as 0,013-0,076 years-1 [9,10].The amount of landfill gas to be formed in the multiphase model is obtained by the cumulative sum of waste quantities at different degradation rates.
In the scope of the study, considering the stated drawbacks related to the measurement and verification in the light of this information, using the parameters and variables of the multi-phase model, applied specifically in the HSLA.The factor of production (ς) for running the model is 0.58; the amount of organic carbon in the stored waste (Co) is 170 kg/ton waste; the landfill gas formation rate constant (kt, i) was accepted for fast, medium and slow degradable wastes as 0,185years-1, 0,100years -1, 0.030years-1, respectively.At the same time, the characteristics of organic wastes in domestic solid wastes have been included in the calculations and were summarized in Table 3. Fraction-1 in Table 3 demonstrates the proportion of kitchen wastes that is the fast-degradable organic waste in HSLA, Fraction-2 shows medium degradable park-garden wastes in HSLA and Fraction-3 presents the proportion of slow-degradable wastes of paper and derivatives in HSLA [6].Rate constant (k) 0,185 0,100 0,030

The Multi-Phase Model Estimation Results
In the model, the garbage dump times were taken for a total of four years that it is from of the 2007 year to 2010 year.We considered that storage will not be made after 2010 year.
It was obtained to be the order of about 290 million cubic meters, the amount of gas that may occur by the 2050 year, in the collection of the annual gas quantities.We predict landfill gas formation values that will be emerged until 2050 year.The maximum value of the gas is in 2011, the lowest gas value is in 2050 for this model according to Table 4 [6].

Hsla Landfill Gas Energy Evaluation
Controlling the landfill gas is essential due to the adverse environmental conditions it causes (global warming, bad smell, explosion risk, etc.) and is important because of the calorific value of the methane in the gas and as a result the possibility of it to produce energy.
Energy value of the study area; the amount of energy that can be obtained from the landfill gas can be calculated using the methane gas amount of the landfill and the calorific value of the methane.In the literature, the calorific value of 1 m 3 methane gas is given as 8500 kcal.Accordingly; the amount of energy can be calculated using the Equation 2 [11].
The issue to be considered when assessing the landfill gas is that a significant proportion of the total amount of gas has been released within a few years following the dumping of the waste.Therefore, in a covered area, a significant portion of the gas will be released in the first few years following closure, and lower gas exits will be achieved in subsequent years.In this case, the gas values of the yearly basis are as important as the total gas value in the feasibility of an investment to be made in order to obtain (electric) energy.
Within the scope of the HSLA Landfill Gas Measurement Studies, the methane gas ratio obtained in the measurements made in the land and as taken in the literature, the methane ratio of landfill gas was considered to be 50%.Anaerobic digestion (AD) is a biological process that can convert organic substrates to biogas in the absence of oxygen [12].The gas at the bottom of the reservoir is in contact with the oxygen because the gas does not exit at a higher level.
In the light of this information, the electric energy values to be obtained from the landfill gas are presented in Table 5 electric energy potential values have been calculated for Multi-Phase Model (model used to determine gas quantity) [6].

Results and Discussion
The application of renewable energy sources might modify not only the background system, but also further downstream aspects, such as consumer behavior.This effect is, however, strongly context and technology dependent [13].In this context, the data obtained in HSLA plant gas is important.
The results of approaches used to determine the potential of Harmandali Landfill Gas (literature based approximations, mathematical model) and electrical energy values obtained from these models are summarized in Table 6 following.
The results we have obtained from the mathematical estimation method we use to determine the potential of the area's depositional gas are highly optimistic.Electrical energy potential values of model (the model used to determine the amount of gas) are calculated separately.The approaches are used to determine the potential for landfill gas in the Harmandali landfill (approximately estimated based on the literature and mathematical model) and the results of electrical energy values obtained from these models as follows: Test chimneys: 10,000 Nm 3 , the multi-phase model: 291,897,215 Nm 3 .Based Literature-based approximate estimation; low speed: 200,000,000 Nm 3 , High speed: 1,600,000,000 Nm 3 .The results obtained from the landfill gas (as the potential gas used in the mathematical method) in the Harmandali Landfill are quite optimistic.
The amount of the landfill gas was calculated on the annual basis through mathematical method while it was achieved by summing the total amount of the gas.This enabled us to consider the advantages of the gas provided in terms of energy aspects.The amount of the methane gas was calculated on an annual basis, as shown in Figure 21 graphically.The maximum formation of the methane gas over a period from 2010 to 2013 was determined using the mathematical method.It has been determined that the amount of domestic solid waste that is examined in Harmandali Landfill and the mathematical modeling calculations considered has a high amount of depot gas potential.However, when considering an energy investment to be made in the field, the account must account for 60% of the gas potential of storage areas to be generated over the first 10 years [6].

Years
When we think about the field in which we are working, the multi-phase model will give better results in the investment study.Because the Multi-Phase model estimates the organic-based waste (high carbon content) in the waste in calculations.Therefore, the amounts of gas to be released from the field will be close to real values.In this context, the data for the energy plant to be constructed based on the depot gas to be produced by the Multi-Phase model are given in Table 5.
The data in Table 5 reflects only the process of establishing and operating the energy plant to be built in the area (does not include information on operating and operating conditions of the area).
According to the results obtained from the two different models used, the time period for which methane gas formation is highest is between 2010 and 2013.
In the following, the results obtained from the models used are discussed and compared with each other (literature based approximations, mathematical model).69% of the gas in the multi-phase model were emerged over the ten years in the Harmandali landfill.

Conclusions
Harmandali Landfill have high landfill gas potential obtained from municipal solid waste in area taken into account the measurement and mathematical modeling.Especially, due to the high energy values of solid waste materials, modeling calculations were high.
An important benefit of the leachate recycle is that the biochemical cycle required for the anaerobic digestion of the solid wastes in the repository becomes homogenous.Thus, the time required for stabilization of organic materials can be reduced 80-90%.In this system, the leaking water can be recycled by being sprayed on the waste site or given to injection wells.This will provide a significant benefit to the Harmandali landfill.
Landfill gas in the current circumstances in Harmandali Landfill is outside from area to the atmosphere.It is not desirable due to pose health and environmental impacts to giving freely into the atmosphere without being subjected to any processing.It can be reduced the impact of the environment and human health with landfill gas is collected and precautions to be taken to evaluate.Precautions to control landfill gas are summarized below;  The layer of the upper cover of landfill should be made impermeable; points of gas leakage caused by shifts in the structure should be closed with the impermeable area or the soil, the improvement of compacting.
 Landfill gas should be burned in the flare unit or the use of energy production to prevent giving atmosphere free.
 The gas collection system is required for the establishment of a landfill gas collection, so that steps have been taken for the establishment of electric generation facility. At the first stage, a 4.5 MW power plant to be established in the Harmandali Landfill will provide the following contributions;  8964 tons CH4/yr will be reduced with methane emitted directly from landfill  This value (8964 tons CH4/yr) is equivalent annual greenhouse gas emissions from 33486 passenger vehicles.Also, this value is equivalent carbon sequestered annually 36414 acres of pine or fir forests  It will be offset 21277 tons CO2/yr carbon dioxide from avoiding the use of fossil fuels  Power plant will be powered approximately 2657 homes based on project size entered.
According to Article 3 of the Kyoto Protocol of the United Nations Framework Convention on Climate Change, it is envisaged to reduce the atmospheric emissions of gases causing the greenhouse effect in 1990 for the period of 2008-2012 by 5%.
Given the law and the Kyoto Protocol, Turkey will need to reduce greenhouse gas emissions.Within this scope, reduction of greenhouse gas emissions to be achieved without working in Izmir will contribute to our country in a significant respect and contribution.