Characterization, Concentrations and Emission Rates of Volatile Organic Compounds from Two Major Landfill Sites in Kuwait

Problem statement: The emission of pollutants from landfill sites in Kuwait is of major concern due to the associated adverse environmental a d health impacts. There are 18 landfill sites in Kuwait which are contributing to the emission of at mospheric pollutants including; methane, carbon dioxide and Volatile Organic Compounds (VOCs). Approach: Determine the concentration and composition of VOCs in LFG emissions from two major landfill sites in Kuwait and to investigate the influence of the " In-Situ Aerobic Stabilization" on the reduction of VOCs emission. VOCs samples were collected during an intensive, short-term fiel d sampling campaign conducted in 2010 where 50 individual volatile organic compounds were identifi ed and quantified in landfill gas samples collected from the two landfill sites and the Proje ct Area. Results: The concentration levels of VOCs were found to be significantly different withi n the same landfill site; however, the average total VOCs emissions were comparable between the tw o landfill sites. Concentration of total VOCs (i.e., sum of 50 compounds) in LFG emissions varied b tween 9.4-67.2 ppm in Jleeb Al-Shuyoukh landfill site and from 15.4-57.7 ppm in Al-Qurain l andfill site. Annual emissions of the well-known five VOCs (i.e., benzene, toluene, ethylbenzene, m, oand p-xylenes and styrene) were also computed for each vent pipe from Jleeb Al-Shuyoukh landfill using the measured average concentrations and LFG flow rates. The results, if calculated in terms of the average ΣBTEX+S quantity emitted per vent pipe per year, showed tha t t e magnitude of ΣBTEX+S emissions ranged between 0.108 -11.686 g y . Conclusion: The results of this pilot project demonstrated tha t e “insitu aerobic stabilization method” applied on old solid waste deposits in the projec t area of Jleeb AlShuyoukh landfill can significantly reduce the aver age VOCs concentration in LFG emissions from high-productivity wells in the project area down to (6.3±1.6 ppm), whereas VOCs concentration in LFG emissions from high-productivity wells in Jleeb Al-Shuyoukh landfill and Al-Qurain landfill sites remained relatively high, 57.1±6.95 and 49.8± 11.2 ppm, respectively.


INTRODUCTION
After placement of Municipal Solid Wastes (MSW) in landfills; many biological, chemical and physical processes start to take place which would gradually lead to the emission of Landfill Gas (LFG) to air and leachates through ground (Awomeso et al., 2010;Williams, 2005). A significant fraction of the biodegradable portion of MSW is ultimately converted to gaseous end-products during the anaerobic stabilization of solid waste organic fractions (Abushammala et al., 2009). Usually, gas production begins within a year of waste placement and may continue for as long as 50 years after landfill closure. Landfill Gas (LFG) consists usually of 50-60% CH 4 , 30-40 vol. %CO 2 and other trace gases (Wang-Yao et al., 2006). Non-Methane Organic Compounds (NMOCs) usually make up also less than 1% of landfill gas. Various trace gases such as hydrogen sulfide, water vapor, ammonia and a variety of volatile Organic Compounds (VOCs) are also present in LFG. European research has identified that landfill gas is composed of 140 trace components of which 90 were common to all studied landfill sites (Parker et al., 2002).
The emission of LFG is of major concern to local communities because of the bad smell and offensive odour as well as due to the various potential health hazards associated with toxic organic and inorganic compounds present in LFG. On the regional scale, LFG emissions are considered as a source of VOCs which contribute to the formation of photochemical oxidants including ground-level ozone (O 3 ). On the global scale, the emission of methane in LFG contributes to greenhouse effects. The waste sector is considered a significant contributor to Greenhouse Gas (GHG) emissions accountable for approximately 5% of the global greenhouse budget (IPCC, 2006). Atmospheric methane gas (CH 4 ) has more than doubled in concentration over the last 150 years (Stern et al., 2007).
Numerous investigations have been conducted with the objective of characterizing landfill gas emissions. More than fifty different VOCs have been identified in landfill gases (Kim et al., 2006). The list includes simple alkanes, olefins, aromatics and a wide array of chlorinated compounds. These VOCs include a number of known or suspected carcinogens (such as benzene, styrene and vinyl chloride). The concentrations of VOCs found in LFG typically range from a few parts per billion (ppb) to tens of thousands of ppb. Benzene, Toluene, Ethyl Benzene and Xylene (BTEX) compounds as well as methylated-and alkylated benzenes are frequently observed as trace contaminants in landfill gas.
The primary objective of the current study was to characterize VOCs emissions in LFG and to compare the composition and emission rates of VOCs between two major landfill sites in the State of Kuwait. The study also investigated the influence of in-situ aerobic stabilization of old solid waste deposits on the composition and concentration of VOCs in LFG emission.

MATERIALS AND METHODS
Landfill sites: The most common practised disposal method in the State of Kuwait for Municipal Solid Waste (MSW) is burial in landfills (UNDP, 2002;AlAhmad et al., 2003). Today, there are 18 landfills in Kuwait of which 14 sites are closed and 4 sites are still in operation (AlAhmad, 2009). Detailed information and data about these landfills, their waste input and composition or emissions measurements and characterization of VOCs in LFG do not exist. Due to the rapid development and the expansion in urban and residential areas in Kuwait, some of these landfills became on the boarders of residential and urban areas, as is the case of Jleeb Al-Shuyoukh and Al-Qurain landfill sites (Fig. 1).

Jleeb Al-Shuyoukh landfill:
The landfill of Jleeb Al-Shuyoukh is located in the south of Kuwait City close to the International Airport of Kuwait and adjacent to the south-eastern boarder of Abdullah Al-Mubarak residential area. This landfill site was licensed by Kuwait Municipality to receive MSW from 1970-1993. The site is considered to be the largest MSW landfill in Kuwait where it encompasses approximately 6 square kilometres and the waste vertical profile varies in depth from 4-23 m. Approximately, about 20 million cubic meters of municipal solid waste and 3 million cubic meters of demolition waste were dumped during the operation period of the landfill. After a major burning incident of the landfill in 2002, a surface capping system with 1m-soil layer was installed. In 2006, 50 boreholes (depth up to 29 m) were drilled for measurement of landfill gas emissions. Measurements of LFG emission was started in March 2008 by the Environment Public Authority of Kuwait (KEPA).
In November 2008, a small area of Jleeb Al-Shuyoukh (576 m 2 ) was used to conduct this research project in collaboration with the Department of Waste Management at Rostock University in Germany. Aerobic in-situ stabilization of old solid waste deposits (Heyer et al., 2003;2005;Cossu et al., 2006;Zanetti, 2008) was applied in the "Project Area" of Jleeb Al-Shuyoukh landfill to examine how this method would improve the emission behaviour and composition of landfill gas under the local conditions of Kuwait (AlAhamd, 2009). In-situ aerobic stabilization of MSW aims to achieve accelerated reduction of the emission and settlement potentials, reduction of the technical and financial expenditures during the aftercare phase and a reduction of the aftercare period. Extensive scientific research have shown that a sustained improvement of the emission and settlement behaviour of the landfill through aerobic in-situ stabilization measures can be achieved when the process technology is adapted to the local conditions of the landfill body and operated in a qualified manner (Spillmann et al., 2001;Heyer et al., 2003;2005).
Al-Qurain landfill site: As shown in Fig. 1 above, this site has become over the past years entirely surrounded by residential areas from all sides due to the expansion of nearby residential areas. The area of Al-Qurain landfill was originally used for dumping of municipal and construction waste from 1970-1985. The volume of the landfill is approximately 5 million m³ and the maximum depth of waste is 24 m. The surface is capped with a 1m soil layer. The landfill is equipped with an active LFG venting and collection system, a flare for burning-off LFG and a pre-treatment plant for leachate. The gas venting system has been in operation since 2005.
Sample collection: During the period May-August 2010, twenty eight samples were collected from selected monitoring wells (boreholes) in Jleeb landfill, the "Project Area" in Jleeb landfill and from Al-Qurain landfill site ( Fig. 2 and 3 for the locations of boreholes used for sampling of VOCs).  Table 1 gives short descriptions of the boreholes used for sampling. Boreholes 4 and 35 in Jleeb landfill were chosen to represent the native soils in the area with no waste buried underneath. Boreholes 21 and 46 in Jleeb Al-Shuyoukh landfill and borehole S17 in Al-Qurain landfill were chosen to represent wells of low methane productivity, whereas boreholes 16 and 49 in Jleeb landfill and borehole S12 in Al-Qurain landfill were chosen to represent wells of high methane productivity (i.e., reaching a mature methanization stage). Borehole No 18 in Jleeb landfill was chosen following the aeration experiment (i.e., insitu aerobic stabilization of buried wastes) applied in the in the "Project Area".
Prior to the sampling of VOCs, the borehole valve was opened and connected to a hand-held portable device (GA 2000 Plus infrared gas analyser, Geotechnical Instruments-UK) for the in-situ measurement of CH 4 , CO 2 , CO, O 2 and temperature in LFG. Sampling of VOCs was achieved using a clean Tedlar bag (1 L) and a small vacuum pump.
Sample analysis: Collected samples were brought to the analytical laboratory for the analysis of Volatile Organic Compounds (VOCs) in landfill gas. Fifty individual VOCs were identified and quantified in this study, ranging from simple aliphatic and aromatic hydrocarbons to di-and tri-methylated benzenes. The target volatile organic compounds identified and quantified in this study are listed in Table 2.
Analysis of VOCs in the collected gas samples was accomplished by following USEPA Method PAMS (Photochemical Assessment Monitoring Stations). The analytical system included a gas chromatography system (Perkin Elmer) equipped with flame ionization detector (GC/FID). The Gas Chromatography system (GC) was also equipped with a perkin elmer Automatic Thermal Desorber (ATD 400). The VOC samples contained in Tedlar bags were analyzed by introducing them into the GC/FID system with the aid of Peltier Cooling (PC) and the Thermal Desorption (TD) method (PC/TD system). Using this PC/TD system, the target VOC in LFG samples were then pre-concentrated in a liquid N 2 -free cold trap (packed with both Carbosil adsorbent) at-15°C. Trapped VOC were then released thermally by heating the cold trap for 2 min at 320°C.
A 30 m GC capillary column (BP1) was used for the chromatographic separation of the different VOCs. After elution from the capillary column, identification of individual VOCs compounds was achieved by the Flame Ionization Detector (GC/FID) connected at the end of the capillary column. Figure 4 and 5 show the GC/FID chromatograms recorded during the identification of light and heavy molecular weight VOCs in LFG samples, respectively. Appropriate calibration procedures were employed to ensure GC/FID reliability and accuracy. The GC/FID system was calibrated using a standard calibration cylinder (Spectra Gases, UK) containing all light and heavy molecular weight VOCs at a concentration of 100 ppb each. Detection limits for all VOCs was about 5 ppb. Low-productivity 1m-soil layer (LFG collection) BH S12 Waste buried CH4 = 50-60% 4 under 1m-High-productivity soil layer (LFG collection)

RESULTS AND DISCUSSION
Composition and concentrations of VOCs in LFG: Figure 6 and 7 compare the average concentrations of individual VOCs (50 compounds) measured in LFG samples collected from the different boreholes in the two landfill sites. It is evident from Fig. 7 and 8 that the composition of VOCs and the magnitude of measured concentrations are very much comparable between the high-productivity wells in the two landfill sites in Al-Jleeb and Al-Qurain where the correlation factor is relatively high (R 2 = 0.7966). The highest concentrations of VOCs in all sampling sites were observed for; styrene, m-methyltoluene and diethylatedbenzenes. Table 3 summarizes the results of total VOCs concentrations (sum of 50 compounds) measured in LFG emissions from the monitoring wells in Jleeb Al-Shuyoukh and Al-Qurain landfill sites. Concentrations of total VOCs ranged from as low as 1.3±0.5 ppm in wells located in native soil areas up to 57.1±6.9 ppm and 49.8±11.2 in wells of highproductivity areas in both of Jleeb Al-Shuyoukh and Al-Qurain landfill sites, respectively.
The result show that the total VOCs emission from the project area (i.e., borehole No 18) is about one-half of the emission from the low-productivity wells in Jleeb landfill and about one-tenth of total VOCs emission from high-productivity wells. This significant reduction in VOCs emissions from the project area can be attributed to the high and rapid biological aerobic reactivity taking place in the project area. If this significant difference is converted into percent reduction in total VOCs emission relative to the emission from the high-productivity wells, then the insitu aerobic stabilization can speed up the decomposition of the biodegradable organic wastes and significantly reduce VOCs emissions by about 89% in comparison with the slow anaerobic biological reactions which usually needs several tens of years to decompose the buried wastes. Table 4 represents a statistical summary of major aromatic VOCs concentrations measured in this study (i.e., benzene; toluene; ethylbenzene; m-, p-and o-xylenes and styrene). Benzene concentrations ranged from as low as 5 ppb in LFG emissions from lowproductivity wells and up to 252.1 ppb in LFG emissions from high-productivity wells.

The distribution of major aromatic VOCs in LFG emissions:
Xylene isomers (metha, para and ortho) and styrene were present in LFG emissions at much higher concentrations than benzene, toluene and ethylbenzene. The concentration of styrene reached as high as 4718.0 and 4057.8 ppb in high-productivity wells in Jleeb Al-Shuyoukh landfill and Al-Qurain landfill, respectively. Schrapp and Al-Mutairi (2010) reported the concentrations of 13 VOCs including BTEX and styrene in LFG emissions from Jleeb Al-Shuyoukh landfill. Table 4 compares the results of BTEX and styrene measurements obtained in this study with those reported in the literature (Schrapp and Al-Mutairi, 2010;Al-Mutairi, 2004;Kim et al., 2006).      (Kim et al., 2006)    As shown in Table 4 and Fig. 9 that the sum of BTEX and styrene emissions (ΣBTEX+S) was comparable between Jleeb Al-Shuyoukh high-productivity wells (7752.3 ppb) and Al-Qurain high-productivity wells (6229.4 ppb) and also with those reported for sites B and D in Korea, 5652.5 ppb and 6181 ppb, respectively. ΣBTEX+S emission from high-productivity wells in Jleeb Al-Shuyoukh are almost half of those calculated for BTEX and styrene measured in 2004 (Schrapp and Al-Mutairi, 2010). ΣBTEX+S emission from Jleeb Al-Shuyoukh low-productivity wells (1169.6 ppb) was also comparable with ΣBTEX+S emission from Al-Qurain low-productivity wells (1337.3 ppb). Interestingly, the average emission of ΣBTEX+S from monitoring wells in the project area was significantly reduced down to 326.5 ppb which is only 200 ppb higher than the measured ΣBTEX+S emissions from the native soil boreholes in the background of Jleeb Al-Shuyoukh landfill site.
As shown in Table 4, in the present study we observed low B/T ratios in the native soil wells and also in low-productivity wells in Jleeb Al-Shuyoukh landfill site of 0.6 and 0.8, respectively; whereas, higher B/T ratios of 6.1 and 5.6 were observed in the project area "In-situ aerobic stabilization" and in high-productivity wells in Jleeb Al-Shuyoukh and AlQurain landfill, respectively. These high B/T ratios in the project area and in the high-productivity wells can be attributed to the higher biological reactivity and reactions taking place in the vicinity of these. The temperature inside the waste layer is known to go up to 80°C occasionally. The exposure of the plastics in solid waste layer to such high temperature is probably one of the reasons for the release of VOCs from solid waste disposal sites. Figure 10 also shows that there was a good correlation (R 2 = 0.9242) between B/T ratios and ΣBTEX+S emissions for Jleeb Al-Shuyoukh and Al-Qurain high-productivity wells which further demonstrates the similarity in the chemical and biological processes, types and age of buried wastes as well as other local conditions between the two landfills leading to similar composition and concentrations of VOCs in LFG emissions. Estimation of VOCs annual emission rates: One of the objectives of the present study includes accurate identification and quantification of VOCs emissions from the two major landfill sites in Kuwait (i.e., Jleeb Al-Shuyoukh and Al-Qurain). The availability of this kind of information can help in evaluating the emission potential of a given landfill environment. For this purpose, the major five VOCs (i.e., benzene; toluene; ethylbenzene; m-, p-and o-xylenes and styrene) were computed for each sampled monitoring well in Jleeb Al-Shuyoukh landfill using their concentrations and the concurrently determined flow rates of LFG.
However, as our estimation is based on a relatively limited quantity of data sets such results may only be used at this stage as rough estimates for the extent of VOC emissions from landfill sites in Kuwait. Table 5 lists the results calculated in terms of the average ΣBTEX+S quantity emitted per vent pipe per year which showed that the magnitude of their annual emission rates can vary substantially, with the values ranging between 0.108-11.686 g y − 1 .

CONCLUSION
During this study it was possible for the first time in Kuwait to identify and quantify 50 Volatile Organic Compounds (VOCs) in LFG emissions from two old landfill sites in Kuwait. The compounds identified included the well-known four aromatic VOCs; Benzene, Toluene, Ethylbenzene and o-, m and p-Xylenes (BTEX). Styrene was also identified and its concentration level was the highest amongst aromatic VOCs. Concentrations of total VOCs (i.e., sum of 50 compounds) in LFG emissions varied between 9.4-67.2 ppm in Jleeb Al-Shuyoukh landfill site and from 15.4-57.7 ppm in Al-Qurain landfill site.
The results obtained in this study demonstrated that the concentration levels of VOCs were found to be significantly different within the same landfill site depending on the reactivity and productivity of the biological decomposition processes of buried wastes. In addition, the results also demonstrated that total VOCs emissions were comparable between the two landfill sites.
This study demonstrated that the "in-situ aerobic stabilization method" applied in the project area of Jleeb Al-Shuyoukh landfill for the treatment of old waste deposits in landfills can significantly reduce the emission of VOCs in LFG by as much as 89%.