Bioresource Technology 103 (2012) 16–20

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Bioresource Technology

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Removal and determination of trimethylsilanol from the landfill gas

Grzegorz Piechota a,⇑, Manfred Hagmann b, Roman Buczkowski a

a Nicolaus Copernicus University, Faculty of Chemistry, Department of Chemical Proecological Processes, Gagarina 7 Street, 87-100 Torun, Polandb SAS Hagmann GmbH, Weberstrasse 3, 72160 Horb am Neckar, Germany

a r t i c l e i n f o

Article history:Received 13 July 2011Received in revised form 30 August 2011Accepted 1 September 2011Available online 7 September 2011

Keywords:TrimethylsilanolVMSLandfillBiogasGC/MS

0960-8524/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.biortech.2011.09.002

⇑ Corresponding author. Tel.: +48 56 611 47 87; faxE-mail addresses: gpchem@doktorant.umk.pl (G. P

sas-hagmann.de (M. Hagmann), rbucz@chem.umk.pl

a b s t r a c t

The removal and determination of trimethylsilanol (TMSOH) in landfill gas has been studied before andafter the special E3000-ITC System. The system works according to principle of temperature swing. Theperformance of TMSOH and humidity removal was 20% and more than 90%, respectively. The six of activecarbons and impinger method were tested on the full-scale landfill in Poland for TMSOH and siloxanesdetermination. The extraction method and absorption in acetone were used. The concentration of TMSOHand siloxanes were found in range from 23.6 to 29.2 mg/m3 and from 18.0 to 38.9 mg/m3, respectively.The content of TMSOH in biogas originating from landfill was 41% out of all siloxanes. Moreover, the usedsystem is alternative to other existing technique of landfill gas purification.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction processes occurring inside the landfill. TMOH is the most volatile

In 2003, on the Polish territory were 1437 landfills. However,after the Polish accession to the European Union (2004), their num-ber began to steadily decline. In 2008, the number of landfills wasbelow 900, while in 2010 their number has fallen below 800. Largenumber of landfills in Poland creates a potential of landfill gas util-isation and it is an important contribution to development ofrenewable energy in Poland. Williams (2008) reported, the devel-opment of renewable energy has become particularly importantin the second half of the 20th century. The first projects relatedto landfill gas utilisation appeared in the late 1970s. According toUS Environmental Protection Agency (EPA, 2006) as of the middleof 2005, there were approximately 425 LFG recovery projects oper-ating in US. The output of biogas production was at least 2.1 billioncubic metre of biogas. The users generated approximately 10 bil-lion kilowatt hours of electricity every year. In addition, the EPAhas estimated the environmental benefits and energy savingsresulting from biogas utilisation. The estimated equivalent per an-num: planting 19 million acres of forest, supplementing the con-sumption of 150 million barrels of oil, eliminating the carbondioxide emissions from 14 million cars, or offsetting the use of325 thousand railcars full of cars.

The landfill biogas production, its utilisation and managementconstitute one of the greatest potential associated environmentaloperations of sanitary landfills. The silica-contaminants of biogasare often related to the natural polydimethylsilanol decomposition

ll rights reserved.

: +48 56 611 24 77.iechota), manfred.hagmann@(R. Buczkowski).

silica-component out of all siloxanes (VMS) presented in biogas.Furthermore, 90% of TMSOH in landfill gas is a final product ofdiethylsiloxane degradation, whereas volatile methylsiloxanesare created during decomposition of polydimethylsiloxane (PDMS)(Lehmann et al., 1995; Carpenter et al., 1995).

The siloxanes existing in landfill gas are linear and cycliccompounds, mainly: hexamethyldisiloxane (abbreviated as L2),hexamethylcyclotrisiloxane (abbreviated as D3), octamethylcyclo-tetrasioxane (abbreviated as D4), decamethylcyclopentasiloxane(abbreviated as D5) and dodecamethylcycloheksasiloxane (abbre-viated as D6). However, their concentration and compositiondepends on the age of landfill, waste profile and as Ohannessianet al. (2008) revealed a microbial decomposition of PDMS. Dewilet al. (2007) described the results of siloxanes analysis. The rangeof concentration from 4.8 to 36.3 mg/m3 were obtained in someof the landfills in Germany and Austria. Moreover, Häusler andSchreier (2005) found siloxanes in range 9–75 mg/m3 for thehundred of European landfills. The extend of the siloxanesproblem, become more visible as the biogas utilisation increasedin countries like Poland. This tendency will regularly develop andthe siloxanes removal system is necessary as more and more\biogas is recovered to produce electricity.

1.1. TMSOH and VMS removal

Nowadays, there are more than ten companies offering siloxanesremoval technologies. Non-regenerative adsorption on fixed form ofactive carbon or graphite is the most common concept. Alternatively,on the market are regenerative technologies based on the principleof the temperature swing. The systems working according to the

G. Piechota et al. / Bioresource Technology 103 (2012) 16–20 17

adsorption/desorption phenomena are consisted of two columns.The columns are packed by alumina or silica resin. Biogas is con-ducted through one adsorber column for purification. Simulta-neously, the contaminants are desorbed from exhausted media ofthe second adsorber by hot air (Ajhar et al., 2010a). The removal ofsiloxanes can also be achieved by modern practise. The destructionof VMS by peroxidaton, catalytic and biological process and refriger-ation were studied by Apples et al. (2008), Urban et al. (2009), Accett-ola et al. (2008), Hagmann et al. (1999), respectively. However, thebest efficiency of siloxanes removal (more than 90%) was obtainedfor adsorption on active carbon and in the deep chilling process. Itis claimed that, the siloxanes are almost completely destroyed bystrong bases and acids, respectively, high or low pH values (Hupp-mann et al., 1996; Schweigkofler and Niessner, 2001). On the otherhand, the potential application of these chemical agents is associatedwith safety, corrosion of absorbers and formation of carbonatestherefore likely induces higher costs (Schweigkofler and Niessner,2001; Urban et al., 2009).

1.2. TMSOH and VMS analysis

More relevant from an environmental perspective, an analyticalmethod to determine TMSOH in landfill biogas, sewage gas, wastewater samples, sewage sludge and leachate was developed by Grüm-ping et al. (1998). In described experiment, about 50 gas samples and60 water samples have been investigated. These authors reportedexclusively sampling procedure, sample preparation and analyseof environmental samples by using the LT-GC/ICP-OES technique.Using this technique, authors obtained results for TMSOH andVMS. The concentration of TMSOH in range from 0.3 to 17.5 mg/m3 and from 3.8 to 616 lg/L, for gas samples and water samples wereobtained, respectively. Moreover, for VMS concentration the rangefrom 0.1 to 66.1 g/m3 and from 0.1 to 1210 lg/L, respectively forgas samples and water samples results were found. It is worthemphasising that, there is no reference method for analysis ofTMSOH in the biogas matrix. It can be related to TMSOH chemicalinstability and its difficult availability on the chemical market(Grümping et al., 1998; Narros et al., 2009). Nevertheless, TMSOHin biogas originating from landfill were reported by Schweigkoflerand Niessner, 1999; Rasi et al., 2010. Alternatively, there are severalmethods for VMS determination. The methods of the sampling werebased on adsorption on active carbon, silica gel or absorption in li-quid organic solvents (e.g. n-hexane or methanol). Subsequent, sam-ples were analysed directly, by using gas chromatography technique(GC). Hagmann et al. (1999) reported, that the GC system with a massdetector coupled (GC–MS) has been the most appropriate and rec-ommended technique for organic-silicon compound determination.

In contrast to other papers about the siloxanes determination(Ajhar et al., 2010b; Dewil et al., 2007; Huppmann et al., 1996)and biogas purification (Boulinguiez and Le Cloirec, 2009) in gen-eral, our paper provides more practical way for the sampling tech-nique and TMSOH determination. The proposed system is a firststep in biogas purification technology. We successful used theE3000-ITC System of simultaneously drying biogas with partialTMSOH removal during the condensate forming. Moreover, duringabove process a part of VOCs and more than 95% of humidity is re-moved. From the economic point of view, the costs of using theE3000-ITC System are significantly lower than traditional methodsof siloxanes, VOCs and humidity removal which are based on activecarbon (it is not necessary to change the filter). In opposite to tra-ditional biogas purification systems, the described System canoperate in continuous made. Our study leads to better understand-ing of TMSOH importance in the environmental analysis. There-fore, the proposed method of TMSOH removal and determinationconstitutes a significant contribution to the research in biogaspurification technology.

2. Methods

2.1. Biogas source and location

The landfill (LF–Franki) is located in a central part of Poland, inFranki village. The LF–Franki has been operated since 2000 and95857 Mg of municipal waste is deposited on landfill area, annu-ally (Krajewska, 2005). As Drazkowski (2008) reported, the approx-imately 41% of refuse was organic fraction whereas glass, paper,plastic, metal and textile constituted approx. 59% of the total wastemass. Moreover, in the landfill there are not deposited fluids, haz-ardous, radioactive waste and toxic substances. LF–Franki is char-acterised by 51 biogas wells, which are deployed on the area of6.5 ha. The wells system for biogas utilisation has been operatedsince May 2007. The average biogas production was more than400 m3/h. All of the gas produced is used for energy production.The special gas drying System (E3000-ITC) was built in September2010. The raw biogas has been dried since October 2010. In theE3000-ITC System, the leachate is discharged daily and automati-cally, in amounts of 2.7–4.3 L/h. The obtained leachate has beenstored in a nearby well and returned back to the landfill, after-wards. The maximum output of the engine is 700 MW but usuallythe unit operates at 95–98% of its total capability.

2.2. Biogas sampling and samples preparation

The landfill gas samples used in the experiment were obtainedfrom the full-scale Franki landfill. The adsorption of TMSOH andsiloxanes was studied by using the real landfill gas. The five kindsof active carbons (AC-1–4 and 6) and one activated carbon (AC-5)were used. AC-5 was activated by thin layer of potassium iodideand potassium hydroxide mixture (5% of KI/KOH). All of the car-bons are available on the market and they are used for various pur-poses such as deodorisation (Matsui and Imamura, 2010) anddesulphurisation. In the experiment, the two separated places atoperating installation were selected for sampling. The first one,was installed before, and the second one after the E3000-ITCSystem.

In the experiment, six types of AC (1–6) and one solvent comingfrom impingers as the samples before and after E3000-ITC Systemwere used. The sampling procedure was repeated three times foreach sample. In the experiment 42 samples were taken.

The adsorption process was carried out in the tube with AC 1–6.The portion of AC in the tube was divided into two parts: sampleand control. The sample contained 1 ± 0.01 g of AC and the controlapproximately 0.25 g, respectively. The biogas flow rate was set to250 ml/min and approx. 20 litres of biogas went through the tube.The extraction procedure was applied to the each AC samples.Choosing the extraction solvent posed an importance aspect. Theextraction solvent should not be aggressive medium within GC–MS column and highly miscible in water. Therefore, the extractionprocedure was carried out in acetone for the sample and control,separately. The samples were introduced into a vial and filled upwith 4 ml of acetone, for each AC. The AC/acetone mixture was vor-tex-mixed at a mean speed for 120 min. Finally, the extracted solu-tion was filtered and injected into the GC–MS System. Moreover,the efficiency of TMSOH removal was compared with referencemethod which was the Oshita’s method (Oshita et al., 2007).

At the same time, the content of siloxanes was analysed in eachsample. The concentration of TMSOH and VMS in the landfill gaswas calculated from the weight of VMS in the solvent and the vol-ume of the total feed gas. Furthermore, the humidity and temper-ature of the biogas was analysed on spot, by using the TESTOSystem (TESTO AG, TestoSystem 635–2, Germany).

Raw landfillgas

Heating column

Chilling column /condensate forming

Rods

1 - 5 °C

25 - 35 °C

ENGINE

Condensate basin

waste heat

ice -coled water

Fig. 1. Scheme of E3000-ITC System.

MS Plot of TMSOH

75

76

m/zRel

ativ

e In

tens

ity

L2

D3 D4 TMSOH D5 D6

5 10 15 20 25 30minutes

Fig. 2. GC–MS chromatogram of raw landfill gas with the main ions of TMSOH mass spectrum.

18 G. Piechota et al. / Bioresource Technology 103 (2012) 16–20

2.3. Parameters of analysis and GC–MS system

VMS standards with purities 95–99% were obtained from Merck(Germany). The standards of siloxanes for GC–MS analysis wereperformed by dissolving a mixture of VMS (L2, D3, D4, D5, D6)and TMSOH in acetone. The standard of TMSOH was provided bySAS (SAS, Germany). The solvent for GC–MS analysis was acetoneSuprasolv 99%, (Merck, Germany).

The analysis of active carbon extracts (AC/acetone extract) andsolvents from the impingers were curried out using a Varian 3800gas chromatograph with a CTC autosampler. The auto-injectionvolume of sample was 2 lL. The separation was carried out onthe Carbowax capillary column (30 m � 0.32 mm, 0.25 film thick-ness). The GC–MS system was programmed as follows: 50 �C –5 min isothermal conditioning, internal oven temperature 55 �Cand the linear temperature threshold set 10 �C/min. The highest ob-tained temperature was 200 �C. Optional parameters of the system:Injector temperature, 250 �C, detector temperature, 300 �C. Carriergas: helium (linear velocity: 4 ml/min). The GC system was coupledwith a mass selective detector (Selective IT S2200). The mass selec-tive detector (MS) was characterised by the temperature of transferline 210 �C, type of activation and voltage EI max. 80 eV, mass win-dow from 15 to 400 m/z. The module of scanning was set as fullscale.

The TMSOH was analysed by means of the GC–MS technique.The integrated MS peak-signals of all standards were recognisedby using the MS NIST spectra library. The characteristic peak

(m/z = 75) and secondary fragment (m/z = 76) were observed onthe mass spectrum. The spectrum of the characterised peak was in-deed identified as TMSOH with a correlation of 99.2%. The peakwith a retention time at 11.69 min corresponds to TMSOH. Forthe quantitative analyse of TMSOH and VMS the calibration curveswith the range of linearity from 0.1 to 40 lg/g and correlation(R2 > 99.9%) were used. The calibration levels were chosen tomirror VMS and TMSOH concentration in the landfill gas. Thecalibration curves were used in range: L2 (from 0.1 to 10 lg/g),D3 (from 0.1 to 15 lg/g), D4 (from 0.1 to 40 lg/g), D5 (from 0.1to 27.5 lg/g), D6 (from 0.1 to 12.5 lg/g) and TMSOH (from 0.1 to30 lg/g). It was decided the calibration curves were a 7-pointcalibration lines. The GC–MS chromatogram of raw landfill gaswith characteristic peaks is shown in Fig. 2.

2.4. System for TMSOH removal

The Authors, jointly with Energia 3000 Sp. z o.o (Wolborz,Poland) and Institute of Heat Engineering – ITC (Lodz, Poland) havedesigned and built a special E3000-ITC drying System. The opera-tion of E3000-ITC System is based on two connected horizontalcolumns, which work according to principle of temperature swing.

The flowing biogas has come into direct contact between warmand cold surfaces within the columns. One column was warmed upto 25–35 �C by waste heat from working engine, the second one,was cooled to 3–5 �C by ice-cold water. The humidity from thebiogas (RH of 99%) was condensed during contact with the rod

Table 1TMSOH and VMS concentration in biogas.

AC number/extraction method 1 2 3 4 5 6 Reference method

Trimethylsilanol concentration (mg/m3)a

Raw gas 27.3 ± 0.1 27.7 ± 0.1 28.3 ± 0.1 28.1 ± 0.1 28.4 ± 0.2 29.1 ± 0.1 29.2 ± 0.1Gas after E3000-ITC System 24.1 ± 0.1 23.9 ± 0.1 26.3 ± 0.1 24.1 ± 0.1 24.2 ± 0.1 25.1 ± 0.1 23.6 ± 0.1

VMS concentration (mg/m3)a

Raw gas 28.3 ± 0.1 37.9 ± 0.1 31.1 ± 0.1 36.1 ± 0.1 19.3 ± 0.2 32.4 ± 0.1 38.9 ± 0.1Gas after E3000-ITC System 28.1 ± 0.1 37.4 ± 0.1 30.7 ± 0.1 35.1 ± 0.1 18.0 ± 0.2 31.1 ± 0.1 38.4 ± 0.1

a An average from three measurements ± SD.

G. Piechota et al. / Bioresource Technology 103 (2012) 16–20 19

surface placed inside. Finally, the condensate was formed. Thescheme of the E3000-ITC System is shown in Fig. 1.

3. Results and discussion

3.1. Removal and determination

The investigations on TMSOH and VMS determination were ini-tiated in November 2010. However, the breakthrough’s in ourexperiments was a fact, that high concentrations of TMSOH andsiloxanes were observed in the raw gas. Since January 2011, whenthe E3000-ITC System was operating proficiently, the analysis ofbiogas were curried out before and after the drying system.

The results of experiment are shown in Table 1. The concentrationof TMSOH in AC-extracted samples were in the range 27.3–29.1 mg/m3 and 23.6–26.3 mg/m3 before and after the E3000-ITC System,respectively. In the reference method, the values of TMSOH concen-tration were similar to results obtained by extraction (29.2 and23.6 mg/m3 for raw and dry gas, respectively). Moreover, the contentof TMSOH in raw landfill gas amounted 40% out of all silica-contam-inants. The concentration of TMSOH in the landfill gas was signifi-cantly higher in compare to gas samples analysed by Grümpinget al. (1998) in landfill gas and leachate as well as by Arnold and Kajol-inna (2010) in landfill gas samples from Finland and quoted: 3.4–17.5 mg/m3 (gas samples), 117–616 lg/L (liquid samples) and 0.01–2 mg/m3 (not directly, quantified as toluene equivalent), respectively.

The VMS were analysed in our experiment, simultaneously. Theresults in the range 19.3–38.9 mg/m3 and 18–38.4 mg/m3 were ob-tained for raw biogas and for biogas after E3000-ITC System,respectively. The VMS concentration was similar to average value(38 mg/m3) obtained from 50 landfills from US as reported byTower (2003).

In the experiment, the most important aspect was related to theactivated carbon number 5, which was additionally impregnated.In this case, the efficiency of VMS adsorption was significantly re-duced. Observed downturn was from 33.1 (an average) to 19.3 mg/m3 as well as from 32.5 (an average) to 18 mg/m3 before and afterthe E3000-ITC System, respectively. This reduction is probablycaused by the properties of AC-5. Active carbons with KI/KOHimpregnation layer usually are dedicated to removing hydrogensulphide. These results implied that the active carbons had betterinfluence on the adsorption of VMS. For performance of TMSOHadsorption, the downturn was not observed.

Matsui and Imamura (2010) as well as Schweigkofler and Niess-ner (2001) reported, the activated carbons showed the higheradsorption capacity than silica gel. However, in our practise, highersiloxanes removal efficiencies were obtained for AC withoutimpregnation layer. On the other hand, as Matsui and Imamura(2010) described, the performance of adsorption has been de-pended on activated carbon properties such as its surface area,pore volume and type of impregnation.

In our study, the landfill gas analysed by GC–MS contained var-ious volatile organic compounds (VOCs) such as pinene, camphene,

limonene, p-, o-, m- xylene, thiophene, tetrachloroethylene, andbenzene. Moreover, it was observed that, most of them were re-moved with condensate during process of biogas drying.

The E3000-ITC System has combined the removal of biogashumidity, partly the VOCs and TMSOH in one process of conden-sate forming. According to the results, the inlet concentration ofhumidity as well as the average values of TMSOH and VMS concen-tration were 98%, 28.3 mg/m3 and 32 g/m3, respectively. The effi-ciency of the drying process was over 90% whereas theperformance of TMSOH removal in the E3000-ITC System was20%. Therefore, the humidity, TMSOH ad VMS concentrations inthe outlet gas were 7%, 24.5 and 32.3 mg/m3, respectively. Thetemperature of biogas was decreased from 23 to 5 �C after drawingthrough the E3000-ITC System. In order to obtain the higher per-formance of humidity and TMSOH removal in short duration, it ispossible down the temperature to 1 �C. Due to the partial removalof TMSOH, humidity and VOCs from raw biogas the productivity ofengine can be increased considerably. Consequently, the downtime and costs of biogas utilisation can be significantly reduced.

4. Conclusion

The presented method and technique allows a rapid removeand determine of TMSOH from landfill gas based on the specialE3000-ITC System and analysis of AC-extracts by GC–MS. The mainadvantage of our determination method is the involving low vol-ume of extraction solvent. Moreover, the application of above sys-tem allowed to the removing 20% of TMSOH from raw landfill gas.Therefore, an additional biogas purification step can become a nec-essary to reduce the siloxanes concentration below the engine’smanufacturers limit. The E3000-ITC System based on our resultswill be running on the landfill and waste water treatment plantin Poland.

Acknowledgements

This study was supported by the Marshal Office of Kujawsko-Pomorskie Voivodship in Torun, Poland. (Project: ‘KROK W PRZYSZ-LOSC, UE Doctoral Scholarship Programme, Edition III, VoivodshipKujwsko-Pomorskie, 2010, Poland).

The Authors would like to thank Ms. E. Hesse, Ms. K. Graff andMr. T. Nab from SAS Hagmann laboratory (Horb am Neckar,Germany), Wojciech Kujawski D.Sc. and (Sz.P.D) MarzannaKurzawa Ph.D from Faculty of Chemistry of Nicolaus CopernicusUniversity (Torun, Poland) for Their help and discussion.

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