Preliminary qualitative and quantitative assessment of gases from biodigestion of solid wastes in the landfill of Londrina , Paraná State , Brazil

Trials conducted in controlled landfillsor dumps are still incipient in Brazil. This paper aimed to qualify and quantify the emission of biogas in the landfill of Londrina, Paraná State. Measurements were performed by three types of tests: static closed chamber for the characterization and quantification of gas leakage by the surface layer, inspection tubes for pressure quantification and qualification of the biogas produced below the surface layer and, finally, measurements in vertical drains to quantify and qualify the biogas. Results for the flow rates of methane gas in the vertical drains ranged from 0 to 190.2 N m 3 h, depending on the shape of the drain and to the age of solid waste deposition. The tests with static closed chamberhad results between 1.3 and 30.6 NL h m, influenced by changes in the age of solid waste deposition, different thicknesses of the surface layer, and excessive rainfall during the tests. With the data of methane gas flow obtained by thestatic closed chambertests and by the biogas drains, it was preliminary quantified the total emission of methane in the landfill of Londrina, Paraná State.


Introduction
Controlled landfills and dumps are the most used alternatives in Brazil for the final disposal of domestic solid wastes.These alternatives have a good cost-benefit relationship for the municipalities, but result in environmental setback with two potentially polluting components: leachate and biogas.
Each municipality has singular characteristics in the composition of its domestic solid wastes.Gravimetric tests can detect these particularities with variable percentage of organic matter, recyclable materials and inert waste (FRÉSCA et al., 2008).Diverse factors influence these parameters, including the social class of the populations, regional economy, public policy for collecting recyclable, landfill management, etc.The physical characterization of the solid wastes directly influences the quantification and qualification of the biogas produced in the controlled landfill or dump, making the studies peculiar to each region.
The production of biogas from domestic solid wastes comes from their biodigestion, mainly the anaerobic digestion.From the disposal of solid waste into controlled landfills or dumps, initially the aerobic digestion takes place by the direct contact of the waste with the atmosphere oxygen.The aerobic phase is prolonged until when these wastes are covered and the amount of dissolved oxygen is almost zero.Then the anaerobic phase begins and lasts for a few years (MACIEL;JUCA, 2000).
In Brazilian landfills, researches have presented results diverging from those obtained in Northern hemisphere countries.The factors that most influence the production of these gases in landfills are the composition of the waste, temperature, pH, internal and external humidity.In general, the literature brings humidity values around 50-60% for maximizing the anaerobic process; but high rates of waste decay with humidity ranging from 20 and 40% have already been registered in Brazil.Thus, the results of quantification and qualification of the biogas may change with the diversity of characteristics and climate in the regions of Brazil.
In general, on the upper layers of the garbage mass in the landfills, the waste decay occurs under alternate aerobic and anaerobic processes.This occurs mainly owing the infiltration of the rainfall that carries dissolved oxygen to the inner environment of the landfill and inhibits the anaerobic digestion.The anaerobic processes dominate at depths greater than 3 meters (MACIEL; JUCA, 2011).
The percolation of methane through the landfill surface is usually highly variable (BORJESSON et al., 1998;MARIANO;JUCA, 2010).In this study are presented results of an experiment of quantification and qualification of methane obtained inthe controlled landfill of Londrina, Paraná State, for three types of tests: static closed chamber, inspection tubes below the surface layer, and biogas measure in the vertical drains.
The US Environmental Protection Agency (USEPA, 1998) suggested a mathematical model to estimate the methane generation in landfills.This methodology is also adopted by other international organizations such as the World Bank.The model was applied to the landfill of Londrina, Paraná State, aiming to evaluate preliminarily the results gathered in the tests and those obtained by using the aforementioned methodology.

Controlled landfill of Londrina, Paraná State
The controlled landfill of Londrina is located at the Estrada do Limoeiro, km 3, Eastern area of the city.Its position conflicts with some environmental laws, including because it is located a few meters from the airport of Londrina.
The tests were performed on October 17th and 18th, 2009, by the Group of Solid Wastes of the Federal University of Pernambuco, with the aid of research engineers of the State University of Londrina.
With the results obtained in the tests, we developed a methodology to evaluate the emissions of gases in the landfill of Londrina, Paraná State, aiming to evaluate preliminarily the annual emissions of methane.The landfill was divided into three areas, considering the age of waste disposal in each area.The area 1 had the largest part filled by relatively recent waste with age equal to or lower than one year.The area 2 was operated before the area 1, with larger part of waste aged between 1 and 5 years.The area 3 was an ancient area of operation, with great part of disposed waste with age above 5 years.
On the occasion of the tests, the landfill was at the final stage of operation, with approximately 31 years.The sites selected for the tests aimed a general analysis of the emissions of gases in the landfill of Londrina, Paraná State.For this, it was chosen locations with different ages of disposed solid wastes, located at diverse levels.
Methods used to evaluate the emission of gas in the landfill of Londrina, Paraná State To characterize the gases emitted by the landfill of Londrina, Paraná State, three methods were used, described as follows: Monitoring of gases that escape through the surface layer It was chosen five sites for testing on the surface layer of the landfill.Three sites (EP-01, EP-02 and EP-05) were located in the area 1 of the landfill.
The other two sites (EP-03 and EP-04) were positioned in the area 2, where the age of the solid wastes did not exceed 5 years.On the area 3, with wastes with disposal age above 5 years, static chamber tests have not been performed.
There is a great diversity of static chamber employed under the most variable situations and places, and mentioned by the literature.In the tests on gases released by the landfill cover, it was used amodel called static chamber, illustrated in the Figure 1.During the fixing of the plate, the hoses remained open so that gases do not accumulate before starting the test.After fixing the plate on the soil, the devices were immediately coupled to measure the concentration of CH 4 , CO 2 , O 2 and H 2 S, and to read temperature and internal pressure in the static chamber.
The readings were made at time intervals ranging from 2 to 10 minutes (5 minutes, on average).The total time of the tests varied between 30 and 40 minutes.The lasting time of each test was necessary for the stabilization of the concentration readings, according to a typical procedure with chamber under static regime.

Monitoring of gases below the landfill cover
The tests with inspection tubes aimed to verify the characteristics of the gases below the cover layer.After each test with a static chamber plate, a 100 mm-hole was opened using an auger, at the exact place of the static chamber (tests T-01 to T-05).Then a 100-mm-diameter PVC pipe was inserted, with a closing cap adapted for coupling a plastic hose, where the gas meter was installed.The PVC pipe remained closed for about 1 hour to later characterize and quantify the biogas produced below the landfill cover and accumulated inside the pipe.
Another five particular tests with inspection tubes were conducted(T-06 to T-10), without performing tests with static chamber at these sites.

Monitoring of gases from the drains
The characterization of the biogas that escapes through the vertical drains was done by measurements at the upper end of the drains of gas in the landfill of Londrina, Paraná State (DV-01 to DV-12).These measures had the purpose to characterize quanti-and qualitatively the biogas percolated through the drains.
The biogas composition was determined with the device employed in theother tests, the portable detector Draeger X-am 7000, using a probe inserted from the end of the vertical drain to capture the biogas.
The flow of the biogas in the drains was checked by using a digital anemometer.The biogas speed was measured in three positions of the exhaust tube, commonly on the axis and at two peripheral points.From the partial measures, we determined the average speed and the biogas flow rate in the drain.

Results and discussion
The studies performed aimed to characterize qualiand quantitatively the emissions of biogas in the landfill of Londrina, Paraná State.For this, the tests were done on the landfill cover, below the landfill cover, and in the existing drains of gas.The Figure 2 shows the planialtimetric survey of the landfill of Londrina, separating the areas 1, 2 and 3 according to the age of the solid waste disposed, and with the location of the sites where the tests were conducted.

Emission of gases through the landfill cover
Five tests were conducted with static chambers to qualify and quantify the gas flow at those sites, called EP-01 to EP-05.The gas trapped inside the plate had a volume variation over time.The base time of test interruption was 30 minutes to minimize the effects of increase in pressure, concentration and temperature inside the compartment of the static chamber.The results in the Figure 3 show the curves obtained from data gathered in field with readings taken every 5 minutes.The unit of measure used to quantify the volume of gas in constructing the graph is Normal Liter (NL), resulting in a surface percolation in NL h -1 m 2 .The results presented values ranging from 1.3 to 30.6 NL h -1 m 2 , with a mean value of 13.9 NL h -1 m 2 (Table 1).This value is relatively higher than the mean observed in literature.
The cover layerof the landfill of Londrina, Paraná State was very humid, due to the heavy rainfall that have occurred in that period.For this reason, bubbles of gas were observed in several points, visually indicating the percolation of gases.The soil moisture determined in laboratory for the soil samples collected varied between 32.5 and 35.4%.

Concentration and pressure of gas under the landfill cover
In the tests with inspection tubes (T-01 to T-10), it was collected data of concentration of CH 4 , CO 2 and O 2 , and thickness of the cover layer at each test site (Table 2).The concentration of CH 4 varied between 2.1 and 42% (mean of 16.3%), of CO 2 , between0.8and 50% (mean of 17.1%), and of O 2 between 0.6 and 19.7% (mean of 12.9%).The most likely reason for the presence of O 2 at high amounts is the percolation of rainfall through the surface layer, carrying dissolved oxygen, and inhibiting thus the anaerobic decomposition in this region.
The average pressure of the biogas below the layer was 1,225 Pa.This value was probably associated with the great amount of liquid under the cover layer, observed in 70% of the holes performed in the tests.The presence of the liquids, mainly derived from infiltration of the rainfall, played a pressure on all the massive waste under the cover layer of the landfill.The thickness of the landfill cover varied between 0.35 and 1.00 m (mean of 0.48 m), an indicative of the need to correct the operational procedures to make this layer more homogeneous.

Emission of gases through the vertical drains
The drains monitored in the landfill (DV-01 to DV-12) were located in distinct regions, with diverse age of solid waste deposition (Table 3).The drain DV-01 was positioned near the entrance of the landfill by the Estrada do Limoeiro.The drains DV-02 to DV-05 were located next to the region of immediate disposal of solid wastes by the operator of the landfill.The drains DV-06 and DV-07 were situated at a lower level, at the back of the landfill, with waste aged more than 5 years.
The flow of CH 4 in these drains varied between 0 and 190.2 Nm 3 h -1 , evidencing the great emission of biogas by some drains, and possibly, the clogging of others.The maximum flow was observed at DV-07, in the lower part of the landfill, and built in concrete tube with 500 mm diameter.The drains externally made up by metal tubes with 73 to 80 mm have presented flows lower than the others, between 0 and 36.9Nm 3 h -1 .The possible cause for this is the bottleneck at the end of the drain for the installation of the gas burner.The bottleneck led to a great loss of load for the gas flow, allowing the leakage by other pathways, such as the own bottom edge of the drain.*concentration in ppm; **gas flow not detected with the equipment whose lower limit is 0.2 m s -1 ;***this measures was not considered because apparently the flow was in reverse, influenced by the wind.It was not possible to measure correctly because of the height of the drain (above 2.5 m).
In general, the CH4 concentration ranged from 0.7 to 54%.The drain DV-01 had a worthless reading by a possible clogging.The drain DV-03 could not be investigated since it remained burning throughout the period.The drains DV-02, DV-06 and DV-09 presented a reading incompatible to the age of the disposed wastes.The drain DV-02 was close to the solid wastes discharged by the trucks, which could justify the low performance.The drains DV-04, DV-05, DV-07, DV-08, DV-10, DV-11 and DV-12 presented biogas composition typical of the methanogenic phase of decomposition of urban solid wastes.

Quantification of the methane released in the landfill of Londrina, Paraná State
Despite the insufficient number of tests performed to draw a reliable assessment of the estimate of emission of gas in the landfill, it was carried out a preliminary evaluation of the emission of methane aiming to attain a preliminary parameter of analysis, by adopting some criteria: a) the landfill of Londrina was divided into areas 1, 2 and 3, according to the age of solid waste disposed (Figure 2).The information about the respective areas was provided by the landfill operator and by the Prefecture of Londrina.b) the results of the tests were considered within their respective area.In the case of the static chamber tests, it was considered the average of the tests performed in the respective catchment areato evaluate the emission of methane by the cover layer of the landfill.The tests EP-01, EP-02 and EP-05 were located in the area 1, the tests EP-03 and EP-04, in the area 2, and in the area 3, the surface emission of methane was not considered because it was not conducted tests of this nature in this area.c) the readings obtained for the methane flow in the vertical drains were added up in the context of the catchment areaconsidered.In the area 1, it was summed up the readings of the methane flow of the drains DV-01, DV-02, DV-04 and DV-05; in the area 2, it was added up the reading of the drains DV-06 and DV-07; and in the area 3, it was added up the readings of the flows of the drains DV-08 and DV-12.d) the total surface emission of methane in each area resulted from the multiplication of the average emission of methane in the area by the own area.From the basic parameters, the survey of the flows was carried out for each area considered in the landfill, so that it was achieved the total flow of methane.The total emission considered for the landfill was obtained by adding up the surface emissions of the cover layer and the methane emission from the vertical drains, totaling 16,840,830 Nm 3 year -1 , presented in the Table 4.
The upper part of the Table 4 lists the data relative to the surface emission of methane in the landfill.For the calculation of the mean values of the results of the static chamber tests, it was used an interpolation method called Inverse Square of Distance (ISD), considering the coordinates of the test sites.
The methane emission measured in the area 1 was 5,530,067 Nm 3 year -1 and in the area 2 was 8,748,463 Nm 3 year -1 .In the area 3, the area with older solid wastes, no plate flow tests were carried out.The total emission of methane by the surface layer was 14,278,530 Nm 3 year -1 .The vertical drains had heterogeneous flows, with great variations in the flow.The value calculated for the emission of methane in the area 1 was 241,776 Nm 3 year -1 , in the area 2 was 1,666,152 Nm 3 year -1 , and in the area 3 was 654,372 Nm 3 year -1 .The total emission recorded in the drains was 2,562,300 Nm 3 year -1 .
Quantification of the emissions of methane by the model USEPA for the controlled landfill of Londrina, Paraná State In order to estimate the emissions of methane it was used the model adopted by the United States Environmental Protection Agency, specific for municipal solid waste landfills (USEPA, 1998).The simplified model calculates the production of methane during the lifespan of the landfill, as well as the reduced production of methane from the closure of the landfill activities.
The mathematical equation adopted is presented below: where: Q CH4 = amount of methane generated in the year"t", (m³ CH 4 year -1 ); L 0 = potential of methane generation by ton of disposed waste (m³ CH 4 ton. - of waste); R = annual mean of input of waste in the landfill(ton waste year -1 ); k = production rate of methane (year -1 ); c = years from closure (c = 0 for active landfills); t = years from the start of the activity (years).The annual mean of waste input in the landfill was estimated using the information obtained with the Prefecture of Londrina (R = 127,750 ton.year -1 ).It was considered 31 years of contribution of solid waste in the landfill for the production of methane (start of activities in 1979).The values relative to the variables k and L 0 were standardized for all years of operation of the landfill of Londrina to the values suggested by USEPA (1998): L o = 170 m 3 CH 4 ton -1 waste, and k = 0.05 year -1 .
By applying the values, it was obtained the estimate of methane production of 17,332,601 m 3 CH 4 for the year 2010.
The graphic behavior of the mathematical model showed an increase in the production of methane over years, with the maximization of the production planned for the year of closure of the landfill activities (2010).From the closure, the model presented a downward estimate of methane production as presented in Figure 4.

Conclusion
The preliminary tests to characterize the biogas emitted through the cover layer of the landfill of Londrina were performed during two days.Regarding the methane, surface emissions between 1.3 and 30.6 NL h -1 m 2 were registered.With the obtained emissions, it was preliminarily calculated the value of 16,840,830 Nm 3 year -1 of methane.
The emission of methane observed through the cover layer of the landfill was higher than the flow by the vertical drains.The value preliminarily calculated was 14,278,530 Nm 3 year -1 , registering 84.8% of total methane emissions.
In the drains of biogas of the landfill we calculated the flow of 2,562,300 Nm 3 year -1 of methane, representing 15.2% of the total flow calculated to the gas.The amount of drains was not enough to collect the gases generated inside the solid wastes disposed.The internal drainage of methane inside the garbage mass was also ineffective.
The monitoring of gas emission through the surface layer has indicated high levels of methane.Most part of the waste, producer of biogas met the characteristics of the methanogenic phase, with ages ranging from 0 to 5 years.
The quantification of the methane attained with the preliminary tests presented values close to those estimated by the mathematical model suggested by USEPA (1998).Further studies performing tests might confirm or not our results.

Figure 2 .Figure 3 .
Figure 2. Plan of the landfill of Londrina, Paraná State, with the location of the sites of the tests and delimitation of the areas 1, 2 and 3.

Figure 4 .
Figure 4. Graphic behavior of the mathematical model (USEPA, 1998) applied to the landfill of Londrina, Paraná State.

Table 1 .
Results of the static chamber tests.

Table 2 .
Results of the tests with inspection tubes below the landfill cover.

Table 3 .
Summary of the results of the evaluation of the biogas in the vertical drains of the landfill of Londrina, Paraná State.

Table 4 .
Results of methane flow on the surface and in the vertical drains of the controlled landfill of Londrina, Paraná State.
*Readings not performed in the area; **ISD -Inverse Square of Distance (method of interpolation); ***on the area 2 the mean considered was the arithmetic given only two sampling data.