Anaerobic digestion of biomass for methane production: A review

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<ul><li><p>Pergamon </p><p>Biomass and Biornergy Vol. 13, Nos. l/2, pp. 833114, 1997 mc 1997 Published by Elsevier Science Ltd. All rights reserved </p><p>Printed in Great Britain PII: SO961-9534(97)00020-2 0961-9534/97 $17.00 + 0.00 </p><p>ANAEROBIC DIGESTION OF BIOMASS FOR METHANE PRODUCTION: A REVIEW </p><p>V. NALLATHAMBI GUNASEELAN Department of Zoology, PSG College of Arts and Science, Coimbatore, 641 014, India </p><p>(Received 24 April 1996: revised 3 March 1997; awepred 31 Mnrch 1997) </p><p>Abstract-Biological conversion of biomass to methane has received increasing attention in recent years. Hand- and mechanically-sorted municipal solid waste and nearly 100 genera of fruit and vegetable solid wastes, leaves, grasses, woods, weeds, marine and freshwater biomass have been explored for their anaerobic digestion potential to methane. In this review, the extensive literature data have been tabulated and ranked under various categories and the influence of several parameters on the methane potential of the feedstocks are presented. Almost all the land- and water-based species examined to date either have good digestion characteristics or can be pre-treated to promote digestion. This review emphasizes the urgent need for evaluating the inumerable unexplored genera of plants as potential sources for methane production. c 1997 Published by Elsevier Science Ltd </p><p>Keywords-Biomass; methane yield; municipal solid waste; fruit and vegetable solid waste; grasses; woody biomass; weeds; aquatic biomass; anaerobic digestion; biochemical methane potential; renewable energy. anaerobic digesters </p><p>1. INTRODUCTION </p><p>Biomass has been defined as contemporary plant matter formed by photosynthetic capture of solar energy and stored as chemical energy. The recent oil crisis and the consequent price rises have spawned considerable interest in the exploration of renewable energy sources. Bioen- ergy will be the most significant renewable energy source in the next few decades until solar or wind power production offers an economi- cally attractive large-scale alternative. The energy that biomass contains can be reclaimed by various methods. The criteria for selection of the conversion process and the advantages of anaerobic digestion (AD) are outlined by Chynoweth et al. This paper surveys the primary biomass sources for methane (CH,) production reported in the literature. Animal manures, sewage sludges and effluents from biomass-based industries, which are secondarily derived from the vegetation are outside the scope of this review. Most of the data reported do not contain any statistical information on variability, only the mean values. A few of the data from the literature lack homogeneity in conditions of measurement, units, etc. and, in some cases, the data given by individual research groups are inadequate and are not included in this outline. </p><p>2. AD PROCESSES FOR BIOMASS </p><p>2.1. Conventional single stage digestion </p><p>2.1.1. Continuully fed digesters. In these digesters, the rate of feeding should be continuous for maximum efficiency, but for practical reasons the digesters are usually fed intermittently; the most common period being once a day. In climatically-heated continuous digesters, there are temperature fluctuations between day and night or between days, resulting in poor performance. In the continu- ously stirred tank reactor (CSTR), an influent substrate concentration of 3-8% total solids (TS) is added daily and an equal amount of effluent is withdrawn. The digester is maintained constantly at mesophilic or thermophilic tem- perature. The addition of large amounts of water requires large reactor volume and high post-treatment costs for the digester residue. In semi-dry digestion. substrate concentration in the range of 16-22% TS is used. </p><p>2.1.2. High solids anaerobic digestion. This process takes place at a TS concentration of more than 25% and is also called dry anaerobic fermentation. Most of the high solids AD studies have been confined to municipal solid waste (MSW). The Ref- COM, SOLCON, dry anaerobic cornposting (DRANCO), KWU-Fresenius, BIOCEL and </p><p>83 </p></li><li><p>84 V. NALLATHAMBIGUNASEELAN </p><p>sequenced batch anaerobic cornposting (SE- bacteria are attached to small glass spheres BAC) are the dry fermentation processes using which are freely suspended in the up-flowing MSW as the substrate, some of which were feed. discussed in a recent review.16 The SEBAC process have been developed at the University 2.2. Two-stage and two-phase digesters </p><p>of Florida for conversion of organic fraction of In a two-stage digester, the residual substrates MSW (OF-MSW) to CH, and compost. It from the first stage can be reduced at the employs three stages for enhanced conversion of second-stage digester, carrying out the same MSW to CH,. The SEBAC system, a promising reactions as the first stage but running at a concept for the AD of MSW, is described different retention time. For quickly fer- elsewhere.?, I3 mentable wastes, a two-stage reactor can have a </p><p>2.1.3. BIOGAS and BIOMETprocesses. The lower overall retention time than a single stage. BIOGAS process has been developed at the The second stage could be a stirred tank or a Institute of Gas Technology (IGT), U.S.A. This plug-flow digester or an anaerobic filter. concept combines the treatment of sewage A two-phase digester is a mechanically similar sludge (SEW) at 2-3% TS and solid wastes system of two stirred-tank digesters. In this (MSW at 55% TS) resulting in a substrate process, fermentation and methanogenesis are concentration of about 10% TS. A similar separated by using different retention times. co-digestion process called the BIOMET Liquefaction and acidification of the substrate is </p><p>has been studied at pilot scale in Sweden. accomplished in a first reactor, while only </p><p>2.1.4. BIOTIIERMGAS process. The BIO- methanogenesis takes place in the second </p><p>THERMGAS process carried out by the IGT, reactor. It was first promoted by Ghosh et al.* </p><p>U.S.A., combines biological and thermochemi- for the combined digestion of SEW and MSW. </p><p>cal unit operations into a scheme that can The total digestion time was considerably lower </p><p>convert the biomass efficiently (regardless of than the conventional single-stage digestion. </p><p>moisture and nutrient contents) to CH, with Some kinetic considerations argue in favour of </p><p>minimum process residues. Results of the the two-phase approach when optimal growth </p><p>preliminary systems analyses using Bermuda conditions for hydrolytic and methanogenic </p><p>grass and MSW as feedstocks indicate that this bacteria are considered.* Colleran et al.,** </p><p>process is technically superior to either biologi- Verrier et a1.,23 Mata-Alvarez24 and Viturtia et </p><p>cal or thermochemical processes and economi- a1.5 proposed this process for the digestion of </p><p>cally feasible. agricultural solid wastes. Two-phase AD of </p><p>2.1.5. Plug-Jlow digester. In tubular plug- OF-MSW was studied by Hofenk et a1.,26 who </p><p>flow digester, a volume of the medium with a concluded that there was no difference in the </p><p>suitable inoculum enters at one end of the tube biogas yields between single-stage and two- </p><p>and, if the rate of passage of the medium is phase systems. Unless the hydrogen produced in </p><p>correct, by the time the medium reaches the the fermentative phase can be collected and </p><p>other end the digestion is completed. For transferred to the methanogenic phase, a loss of </p><p>continuous operation, some of the digested potential CH, occurs. This process is techno- </p><p>effluent flowing from the end of the tube logically feasible, but an assessment of the </p><p>is separated and returned to the influent economic feasibility is more complex and has to </p><p>substrate. be reviewed for any given situation. </p><p>2.1.6. The anaerobic j3ter. This is primarily meant for digestion of easily fermentable 3. BIOCHEMICAL METHANE POTENTIAL (BMP) </p><p>factory waste waters produced in large quan- ASSAY </p><p>tities. Even a 6-day retention time would mean The BMP assay was developed to determine an impossibly large digester. Hence, in order to the ultimate CH, yield (B,) of organic substrates prevent washout, the bacteria are allowed to and for monitoring anaerobic toxicity.* B, of a attach to a solid support, such as stones packed variety of biomass were determined using a inside a tank and the waste water flows upward through the tank. This process requires a </p><p>modified method of Owen et a1.28m33 The BMP is a valuable, quick and inexpensive method for </p><p>retention time of only a few hours and the gas determination of the potential extent and rate of is collected from the top. In a fluidized-bed conversion of biomass and wastes to CH,. A digester, a modified form of anaerobic filter, the similar assay has otherwise been named as </p></li><li><p>Anaerobic digestion of biomass for methane production: a review 85 </p><p>anaerobic biogasification potential (ABP) as- say.34 </p><p>4. POTENTIAL SOURCES FOR METHANE </p><p>A wide range of biomass have been considered as potential sources for CH, production (Fig. 1). </p><p>4.1. Organic fraction of MSW </p><p>4.1.1. MSW composition. MSW has been identified as a heterogeneous material in which the composition varies widely. The composition of MSW is affected by various factors, including regional differences, climate, extent of recycling, collection frequency, season, cultural practices, as well as changes in technology.35 The qualities of the OF-MSW are influenced not only by the sorting system but also by various methods used for quantifying the OF-MSW. According to Mata-Alvarez et al. in mechanically-sorted MSW (MS-MSW), large amounts of suspended, non-biodegradable solids and unavoidable small pieces of plastic, wood, paper, etc. are present. The mechanically-sorted organic frac- tion of MSW (MS-OF MSW) used to feed the </p><p>I I </p><p>WOODS </p><p>GRASSES </p><p>1 ORGANIC I </p><p>digester in Treviso contained (on a TS basis) 50% putrescible fraction, 6% paper, 1% wood, 2% plastic and 36% inert fraction. The percentage of VS of the waste was 43%. These non-biodegradable solids are not present in the source-sorted organic fraction of MSW (SS-OF MSW) or hand-sorted organic fraction of MSW (HS-OF MSW) or in the organic fraction of MSW from a separated collection (SC-OF MSW). Consequently, the VS content of the waste was 88h.36 However, the MS-OF MSW from Sumter country contained (on a TS basis) 47% paper, 11% cardboard, 10% plastic, 6% yard waste and 23% miscellaneous and its VS content was 81h.2.3 The HS-OF MSW from Levy country contained (on a TS basis) 92% paper and the percentage of VS was 93%.,3 Rivard et a1.37 reported that most MSW processing technologies result in the separation and removal of the food and yard waste fraction to produce refuse-derived fuel (RDF). This results in the reduction of the nutrient value of the processed MSW as a feedstock for AD. Nevertheless, considering the percentages of VS of OF-MSW presented in Tables 1 and 2, two groups can be denoted. The first, with a VS </p><p>-I FRESHWATER BIOMASS I I I </p><p>MARINE BIOMASS </p><p>1 AQUATIC </p><p>Fig. 1. Selected types of methane yielding biomass </p></li><li><p>Feed</p><p>MS-</p><p>OF </p><p>MSW</p><p> C</p><p>ont. </p><p>= 30</p><p>&amp;35</p><p>% </p><p>TS </p><p>Tabl</p><p>e 1.</p><p> Dig</p><p>este</p><p>r pe</p><p>rform</p><p>ance</p><p> w</p><p>ith </p><p>mun</p><p>icip</p><p>al </p><p>solid</p><p> w</p><p>aste</p><p> fe</p><p>eds </p><p>at </p><p>mes</p><p>ophi</p><p>lic </p><p>tem</p><p>pera</p><p>ture</p><p>s </p><p>HR</p><p>T O</p><p>LR </p><p>CH</p><p>, yi</p><p>eld?</p><p> C</p><p>H, </p><p>PRP </p><p>VSr</p><p> Fe</p><p>rmen</p><p>ter </p><p>Tem</p><p>p. </p><p>(C)</p><p> (d</p><p>ays)</p><p> (k</p><p>g V</p><p>Sm- </p><p>d - </p><p>) (m</p><p> kg</p><p>- V</p><p>S,) </p><p>(m </p><p>rnm</p><p>J d-</p><p>) </p><p>(%) </p><p>Ref</p><p>eren</p><p>ce </p><p>g </p><p>3540</p><p> 16</p><p>-21 </p><p>NR</p><p> La</p><p>bora</p><p>tory</p><p> pl</p><p>ant </p><p>0.03</p><p>5 m</p><p> D</p><p>ranc</p><p>o pr</p><p>oces</p><p>s </p><p>[71 </p><p>MS-</p><p>OF </p><p>MSW</p><p> C</p><p>orm</p><p>. = </p><p>25-3</p><p>5% </p><p>TS </p><p>Pilo</p><p>t pl</p><p>ant </p><p>60 m</p><p>3 D</p><p>ranc</p><p>o pr</p><p>oces</p><p>s </p><p>3540</p><p> 14</p><p>-21 </p><p>10.0</p><p> 12</p><p>.1 </p><p>13.2</p><p>15 </p><p>0.26</p><p>0* </p><p>0.26</p><p>4* </p><p>0.23</p><p>5* </p><p>0.18</p><p>7* </p><p>2.6 </p><p>3.2 </p><p>3.1 </p><p>2.8 </p><p>NR</p><p> PI</p><p>MS-</p><p>OF </p><p>MSW</p><p> Pi</p><p>lot </p><p>plan</p><p>t C</p><p>ont. </p><p>= 35</p><p>% </p><p>TS, </p><p>500 </p><p>m </p><p>VS </p><p>= 58</p><p>.6%</p><p> TS</p><p> V</p><p>alor</p><p>ga </p><p>proc</p><p>ess </p><p>MS-</p><p>OF </p><p>MSW</p><p>: SE</p><p>W </p><p>85:lS</p><p> TS</p><p> ba</p><p>sis </p><p>Con</p><p>t. = </p><p>7710</p><p>% </p><p>TS </p><p>CST</p><p>R </p><p>20 </p><p>m </p><p>BIO</p><p>MET</p><p> pr</p><p>oces</p><p>s </p><p>HS-</p><p>OF </p><p>MSW</p><p> C</p><p>ont. </p><p>= 3-</p><p>5.6%</p><p> TS</p><p> V</p><p>S = </p><p>82-8</p><p>7% </p><p>TS </p><p>CST</p><p>R </p><p>Labo</p><p>rato</p><p>ry </p><p>plan</p><p>t </p><p>HS-</p><p>OF </p><p>MSW</p><p> C</p><p>ont. </p><p>= 6.</p><p>4% </p><p>TS, </p><p>VS </p><p>= 89</p><p>.9%</p><p> TS</p><p> C</p><p>STR</p><p> 3 </p><p>m </p><p>OF </p><p>MSW</p><p> (s</p><p>imul</p><p>ated</p><p>): SE</p><p>W </p><p>80:2</p><p>0 TS</p><p> ba</p><p>sis </p><p>Con</p><p>t. = </p><p>6.6%</p><p> TS</p><p> V</p><p>S=91</p><p>% </p><p>TS </p><p>CST</p><p>R </p><p>2.2 </p><p>m </p><p>Proc</p><p>esse</p><p>d M</p><p>SW </p><p>(TR</p><p>F): </p><p>Yea</p><p>st </p><p>extra</p><p>ct/m</p><p>iner</p><p>als. </p><p>5.78</p><p>: l(V</p><p>S ba</p><p>sis)</p><p>CST</p><p>R </p><p>Sem</p><p>i co</p><p>ntin</p><p>uous</p><p> 3.</p><p>5 I </p><p>TRF:</p><p> pr</p><p>edig</p><p>este</p><p>d SE</p><p>W </p><p>4.76</p><p>:1 </p><p>(VS </p><p>basi</p><p>s) </p><p>MS-</p><p>OF </p><p>MSW</p><p>, Su</p><p>mte</p><p>r co</p><p>untry</p><p> FL</p><p> Fr</p><p>esh,</p><p> V</p><p>S = </p><p>79.7</p><p>% </p><p>TS </p><p>Drie</p><p>d, </p><p>VS </p><p>= 84</p><p>.1%</p><p> TS</p><p>CST</p><p>R </p><p>Sem</p><p>i co</p><p>ntin</p><p>uous</p><p> 3.</p><p>5 1 </p><p>BM</p><p>P as</p><p>say </p><p>HS-</p><p>OF </p><p>MSW</p><p> Le</p><p>vy-l </p><p>coun</p><p>try </p><p>FL </p><p>VS </p><p>= 92</p><p>.5%</p><p> TS</p><p> Y</p><p>ard </p><p>was</p><p>te </p><p>sam</p><p>ples</p><p> G</p><p>rass</p><p>, V</p><p>S = </p><p>88.1</p><p>% </p><p>TS </p><p>Leav</p><p>es, </p><p>VS </p><p>= 95</p><p>% </p><p>TS </p><p>Bra</p><p>nche</p><p>s, V</p><p>S = </p><p>93.9</p><p>% </p><p>TS </p><p>Ble</p><p>nd, </p><p>VS </p><p>= 92</p><p>% </p><p>TS </p><p>BM</p><p>P as</p><p>say </p><p>BM</p><p>P as</p><p>say </p><p>37 </p><p>15 </p><p>13.7</p><p> 0.</p><p>230 </p><p>2.6*</p><p> 45</p><p> [9</p><p>1 </p><p>3742</p><p> 19</p><p> 2.</p><p>6 0.</p><p>230 </p><p>0.58</p><p> 41</p><p> 21</p><p> 1.</p><p>6 0.</p><p>290 </p><p>0.46</p><p> 48</p><p> I1</p><p>81 </p><p>35 </p><p>33-3</p><p>7 </p><p>33-3</p><p>7 </p><p>37 </p><p>37 </p><p>35 </p><p>35 </p><p>35 </p><p>1442</p><p>0 </p><p>9925</p><p>I 0.</p><p>390 </p><p>0.39</p><p> 1.</p><p>5 0.</p><p>360 </p><p>0.55</p><p> 2 </p><p>0.43</p><p>0 0.</p><p>87 </p><p>4 0.</p><p>430 </p><p>1.70</p><p>2.1-</p><p>6.9 </p><p>0.39</p><p>0 0X</p><p>2-2.</p><p>02* </p><p>NR</p><p>63-6</p><p>9 </p><p>14 </p><p>3.9 </p><p>0.29</p><p>0 1.</p><p>59* </p><p>70-7</p><p>5 </p><p>20 </p><p>14 </p><p>20 </p><p>14 </p><p>NA</p><p>NR</p><p> 0.</p><p>324(</p><p>0.04</p><p>3) </p><p>0.77</p><p>(0.1</p><p>8)* </p><p>1.14</p><p>(0.4</p><p>0)* </p><p>0.69</p><p>(0.1</p><p>7)* </p><p>1.04</p><p>(0.2</p><p>3)* </p><p>NA</p><p>NR</p><p>[381</p><p> 2 E 2;</p><p> F </p><p>[391</p><p> 8 6 2 </p><p>[401</p><p> g R</p><p>E </p><p>[371</p><p>0.33</p><p>6(0.</p><p>067)</p><p>NR</p><p> 0.</p><p>294(</p><p>0.03</p><p>8) </p><p>0.30</p><p>7(0.</p><p>037)</p><p> N</p><p>R </p><p>NA</p><p> 0.</p><p>222(</p><p>0.01</p><p>4): </p><p>0.21</p><p>5(0.</p><p>013)</p><p>$ N</p><p>R </p><p>NA</p><p> N</p><p>A </p><p>0.20</p><p>5(0.</p><p>01 </p><p>l)$ </p><p>NA</p><p> N</p><p>R </p><p>NA</p><p> N</p><p>A </p><p>0.20</p><p>9(0.</p><p>005)</p><p>$ 0.</p><p>123(</p><p>0.00</p><p>5)$ </p><p>0.13</p><p>4(0.</p><p>006)</p><p>$ 0.</p><p>143(</p><p>0.00</p><p>4)f </p><p>NA</p><p> N</p><p>R </p><p>[321</p><p>f321</p><p>[321</p></li><li><p>Anaerobic digestion of biomass for methane production: a review 87 </p><p>a </p></li><li><p>Tabl</p><p>e 2.</p><p> D</p><p>iges</p><p>ter </p><p>perfo</p><p>rman</p><p>ce </p><p>with</p><p> m</p><p>unic</p><p>ipal</p><p> so</p><p>lid </p><p>was</p><p>te </p><p>feed</p><p>s at</p><p> th</p><p>erm</p><p>ophi</p><p>lic </p><p>tem</p><p>pera</p><p>ture</p><p>s g </p><p>Feed</p><p> Fe</p><p>rmen</p><p>ter </p><p>Tem</p><p>p. </p><p>(C)</p><p> H</p><p>RT </p><p>OLR</p><p> C</p><p>H, </p><p>yiel</p><p>d? </p><p>CH</p><p>, PR</p><p>t V</p><p>Sr </p><p>(day</p><p>s) </p><p>(kg </p><p>VSm</p><p>-3d-</p><p>) </p><p>(m </p><p>kg- </p><p>VS,</p><p>) (m</p><p>l m</p><p>-l d-</p><p>) </p><p>(%) </p><p>Ref</p><p>eren</p><p>ce </p><p>MS-</p><p>OF </p><p>MSW</p><p> C</p><p>ont. </p><p>= 3&amp;</p><p>35%</p><p> TS</p><p> La</p><p>bora</p><p>tory</p><p> pl</p><p>ant </p><p>0.03</p><p>5 m</p><p> D</p><p>ranc</p><p>o pr</p><p>oces</p><p>s </p><p>Pilo</p><p>t pl</p><p>ant </p><p>0.06</p><p>0 m</p><p>SC</p><p>-55 </p><p>16-2</p><p>1 10</p><p>.0 </p><p>0.28</p><p>6* </p><p>2.86</p><p>* 12</p><p>.1 </p><p>0.28</p><p>2* </p><p>3.41</p><p>* 13</p><p>.2 </p><p>0.28</p><p>3* </p><p>3.74</p><p>* 14</p><p>.9 </p><p>0.31</p><p>0* </p><p>4.62</p><p>* 14</p><p>.7 </p><p>0.13</p><p>1* </p><p>1.92</p><p> 11</p><p>.8 </p><p>0.14</p><p>7* </p><p>1.74</p><p> 7.</p><p>8 0.</p><p>185*</p><p> 1.</p><p>44 </p><p>3.9 </p><p>0.24</p><p>6* </p><p>0.96</p><p> 17</p><p>.5 </p><p>0.13</p><p>3* </p><p>2.33</p><p> 14</p><p>.0 </p><p>0.18</p><p>0* </p><p>2.52</p><p> 9.</p><p>3 0.</p><p>236*</p><p> 2.</p><p>20 </p><p>4.7 </p><p>0.31</p><p>9* </p><p>1.50</p><p> 20</p><p>.6 </p><p>0.14</p><p>0* </p><p>2.88</p><p> 16</p><p>.5 </p><p>0.20</p><p>2* </p><p>3.34</p><p> 10</p><p>.9 </p><p>0.24</p><p>2* </p><p>2.64</p><p> 5.</p><p>4 0.</p><p>289*</p><p> 1.</p><p>56 </p><p>23.5</p><p> o.</p><p>ooo*</p><p> 0.</p><p>00 </p><p>18.8</p><p> 0.</p><p>128*</p><p> 2.</p><p>40 </p><p>12.4</p><p> 0.</p><p>160*</p><p> I .</p><p>98 </p><p>6.2 </p><p>0.27</p><p> I *</p><p> I .</p><p>68 </p><p>18-2</p><p>0 0.</p><p>220 </p><p>3.64</p><p>4.48</p><p>* 16</p><p>.5 </p><p>0.20</p><p>0 3.</p><p>3* </p><p>NR</p><p>MS-</p><p>OF </p><p>MSW</p><p> C</p><p>ont. </p><p>= 25</p><p>% </p><p>TS </p><p>VS </p><p>= 47</p><p>% </p><p>TS </p><p>55 </p><p>NR</p><p>MS-</p><p>OF </p><p>MSW</p><p> Pi</p><p>lot </p><p>plan</p><p>t C</p><p>ont. </p><p>= 30</p><p>% </p><p>TS </p><p>0.06</p><p>0 m</p><p>3 55</p><p> N</p><p>R </p><p>MS-</p><p>OF </p><p>MSW</p><p> Pi</p><p>lot </p><p>plan</p><p>t C</p><p>ont. </p><p>= 35</p><p>% </p><p>TS </p><p>0.06</p><p>0 m</p><p> 55</p><p>8 IO </p><p>15 </p><p>30 8 10 </p><p>I5 </p><p>30 8 IO </p><p>15 </p><p>30 8 IO </p><p>15 </p><p>30 9 12 </p><p>NR</p><p>MS-</p><p>OF </p><p>MSW</p><p> Pi</p><p>lot </p><p>plan</p><p>t C</p><p>ont. </p><p>= 40</p><p>% </p><p>TS </p><p>0.06</p><p>0 m</p><p> 55</p><p> N</p><p>R </p><p>MS-</p><p>OF </p><p>MSW</p><p> C</p><p>ont. </p><p>= 30</p><p>% </p><p>TS </p><p>Labo</p><p>rato</p><p>ry </p><p>plan</p><p>t 0.</p><p>015 </p><p>m1 </p><p>Val</p><p>orga</p><p> pr</p><p>oces</p><p>s </p><p>60 </p><p>50 </p><p>46 </p><p>MS-</p><p>OF </p><p>MSW</p><p> Su</p><p>mte</p><p>r co</p><p>untry</p><p>, V</p><p>S = </p><p>81%</p><p> TS</p><p>Pilo</p><p>t pl</p><p>ant </p><p>SEB</p><p>AC</p><p> pr</p><p>oces</p><p>s 55</p><p> 42</p><p> 3.</p><


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