Effect of temperature and temperature fluctuation on thermophilic anaerobic digestion of cattle manure

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<ul><li><p>tedig</p><p>Zeb, G</p><p>f Agri</p><p>versity</p><p>16 J</p><p>line 8</p><p>Abstract</p><p>tainable development and problems due to the ozone</p><p>layer depletion have all contributed to the recognition ofthe value of anaerobic digestion as a technique to pro-</p><p>duce renewable energy (De Baere, 2000).</p><p>60 C rather than at 50 C are insignicant. An impor-tant advantage of the thermophilic process undoubtedlyis that it provides a high destruction of pathogens</p><p>and weed seeds. Larsen et al. (1994) concluded that</p><p>thermophilic as well as mesophilic digestion with</p><p>thermophilic pre-treatment will result in sucient</p><p>95 (*Corresponding author. Tel.: +20-50-2268606.The inuence of temperature, 50 and 60 C, at hydraulic retention times (HRTs) of 20 and 10 days, on the performance ofanaerobic digestion of cow manure has been investigated in completely stirred tank reactors (CSTRs). Furthermore, the eect of</p><p>both daily downward and daily upward temperature uctuations has been studied. In the daily downward temperature uctuation</p><p>regime the temperatures of each reactor was reduced by 10 C for 10 h while in the daily upward uctuation regime the temperatureof each reactor was increased 10 C for 5 h. The results show that the methane production rate at 60 C is lower than that at 50 C atall experimental conditions of imposed HRT except when downward temperature uctuations were applied at an HRT of 10 days. It</p><p>also was found that the free ammonia concentration not only aects the acetate-utilising bacteria but also the hydrolysis and</p><p>acidication process. The upward temperature uctuation aects the maximum specic methanogenesis activity more severely as</p><p>compared to imposed downward temperature uctuations. The results clearly reveal the possibility of using available solar energy at</p><p>daytime to heat up the reactor(s) without the need of heat storage during nights, especially at an operational temperature of 50 Cand at a 20 days HRT, and without the jeopardising of the overheating.</p><p> 2004 Elsevier Ltd. All rights reserved.</p><p>Keywords: Anaerobic digestion; Cattle manure; Eect of temperature; Renewable energy; Solar energy; Temperature uctuation; Thermophilic</p><p>1. Introduction</p><p>The depletion of non-renewable energy sources leads</p><p>to the need to search for otherrenewableresources</p><p>available at local conditions. There exist many renewable</p><p>sources, such as sunlight, wind and biomass, while</p><p>agricultural wastes represent an important source of bio-energy. The anaerobic digestion process is one of the</p><p>technologies used to produce energy as well as to reduce</p><p>the organic content of waste. Energy production remains</p><p>an important process, even at moderate energy prices in</p><p>non-oil-producing countries. The climate problems due</p><p>to the greenhouse eect, the recognised need for sus-</p><p>Among the many factors aecting the anaerobic</p><p>digestion process, temperature is an important one.</p><p>Anaerobic digestion can proceed under psychrophilic</p><p>(45 C) conditions. The digestion under thermo-philic conditions oers many advantages such as higher</p><p>metabolic rates, consequently higher specic growthrates but frequently also higher death rates as compared</p><p>to mesophilic bacteria (Van Lier, 1995; Duran and</p><p>Speece, 1997). Chen et al. (1980) revealed that there is a</p><p>kinetic advantage in fermentation of livestock manure at</p><p>thermophilic over mesophilic temperature. However, the</p><p>kinetic advantages in conducting the digestion process atEect of temperature andthermophilic anaerobic</p><p>Hamed M. El-Mashad a,*, GrietjeGerard P.A. Bot</p><p>a Department of Agricultural Engineering, Faculty ob Department of Agrotechnology and Food Sciences, Wageningen Uni</p><p>Accepted</p><p>Available on</p><p>Bioresource TechnologyE-mail address: hamedel_mashad@mans.edu.eg (H.M. El-Mashad).</p><p>0960-8524/$ - see front matter 2004 Elsevier Ltd. All rights reserved.doi:10.1016/j.biortech.2003.07.013mperature uctuation onestion of cattle manure</p><p>eman b, Wilko K.P. van Loon b,atze Lettinga b</p><p>culture, Mansoura University, E1-Mansoura, Egypt</p><p>Agrotechnion, Mansholtlaan 10, Wageningen 6708 PA, Netherlands</p><p>uly 2003</p><p>April 2004</p><p>2004) 191201reduction of vegetative pathogenic bacteria (both E. coli</p></li><li><p>bacterial composition of sludge. As already mentioned</p><p>by Van Lier et al. (1996) for large-scale thermophilic</p><p>192 H.M. El-Mashad et al. / Bioresource Technology 95 (2004) 191201and Enterococci) and intestinal parasites usually found</p><p>in animal wastes. This cannot be said for mesophilic</p><p>digestion when used alone. Salmonella and Mycobac-</p><p>terium paratuberculosis are inactivated within 24 h at</p><p>thermophilic conditions while it needs weeks or even</p><p>months at mesophilic temperatures (Sahlstrom, 2003).This in fact is an important criterion for the animal</p><p>waste treatment since the euent can be used as a soilconditioner. Some researchers, like Mackie and Bryant</p><p>(1995) mentioned that thermophilic (60 C) anaerobicdigestion of cattle waste is more stable than mesophilic</p><p>(40 C) at dierent HRTs (viz. 10, 15, and 20 days).On the other hand, thermophilic treatment suers</p><p>from some drawbacks such as lower stability compared</p><p>to mesophilic treatment (Buhr and Andrews, 1977; Wie-</p><p>gant, 1986; Van Lier, 1995). According to Duran andSpeece (1997), thermophilic systems produce somewhat</p><p>poorer euent quality. Moreover, the lower growth</p><p>yield combined with their high growth rates of ther-</p><p>mophilic organisms leads to longer start-up times, while</p><p>it also renders these processes more susceptible to tox-</p><p>icity and changes in operational and environmental</p><p>conditions. According to insights of Angelidaki and</p><p>Ahring (1994) the optimum temperature for digestion ofsubstrates with high ammonia loads diers from the</p><p>optimum temperature at low ammonia loads. Due to the</p><p>temperature/ammonia interactionship the eect of tem-</p><p>perature cannot be examined independently when the</p><p>ammonia concentration is in the inhibitory range.</p><p>According to results of Ahring et al. (2001), increasing</p><p>the operational temperature from 55 to 65 C resultsin an immediate unbalance between the fermenting,acids-producing micro-organisms and acids-consuming</p><p>micro-organisms. Another drawback of thermophilic</p><p>operation comprises its energy requirements and this</p><p>may reduce the net energy production from thermo-</p><p>philic compared to mesophilic digestion.</p><p>To maximise the net energy production from</p><p>anaerobic digestion we need to consider the steps in-</p><p>volved in the digestion process (e.g. the hydrolysis step)and the factors aecting these steps (e.g. temperature).</p><p>Particularly the complementary use of other available</p><p>renewable energy resources such as sunlight should be</p><p>considered. Utilisation of solar energy as a source for</p><p>reactor heating will save fossil fuel or biogas used for</p><p>heating and represents in this way a kind of solar en-</p><p>ergy storage in the form of biogas. However, the</p><p>incorporation of such a renewable energy source obvi-ously is accompanied with further investments. In order</p><p>to keep the (total) system as simple as possible, a sys-</p><p>tem design could be considered where the reactor is</p><p>heated up during period of sunshine without heat</p><p>storage to maintain the desired temperature during</p><p>night-time. Such a mode of operation might negatively</p><p>aect the process stability, as the reactor will be sub-jected to temperature uctuations between day andanaerobic installations, such as UASB reactors, it is of</p><p>utmost importance that the treatment system can tol-</p><p>erate moderate temperature uctuations. According to</p><p>Kroeker et al. (1979) temporary diurnal temperatureuctuations as high as 8 C in the anaerobic digestionof swine manure did not signicantly aect the process</p><p>stability at a process temperature of 35 C at retentiontimes of both 30 and 6 days. Evidently a serious lack of</p><p>information exists on the temperature uctuation eect</p><p>on the performance of thermophilic anaerobic digestion</p><p>of farm wastes (i.e. cow manure), and consequently,</p><p>this eect deserves to be investigated in more detail.</p><p>1.1. Objective</p><p>The objective of the present study is to investigate the</p><p>inuence of temperature and temperature uctuation onthermophilic anaerobic digestion of cow manure using a</p><p>CSTR system. Therefore the following eects were</p><p>investigated experimentally:</p><p>1. Assess the dierences of the digestion process of cow</p><p>manure using a CSTR system at two temperatures</p><p>(50 and 60 C) and at two dierent HRTs (20 and10 days).</p><p>2. Assess the eect of temperature uctuations on the</p><p>performance of the process:</p><p>(a) An imposed daily downward temperature uctua-</p><p>tion of 10 C for a period of 10 h.(b) An imposed daily upward temperature uctuation</p><p>of 10 C for a period of 5 h.</p><p>2. Methods</p><p>2.1. Experimental setup</p><p>Twelve experiments in six experimental runs have</p><p>been carried out. After steady state has established, at</p><p>least three sets of analysis were conducted, in duplicate,</p><p>and then the next run was started. Steady state wasdened as the situation where a stable methane pro-</p><p>duction coincides with stable euent volatile fatty acidsnight. This eect will be more pronounced for small</p><p>reactor volumes. Moreover, this mode of operation</p><p>might lead to overheating in case the control system is</p><p>not working properly or when there is an excess of</p><p>solar energy. Speece (1983) is one of the many</p><p>researchers postulating that anaerobic digestion is sen-</p><p>sitive to sudden change of environmental conditions.</p><p>According to Van Lier (1995) the eect of temperatureshocks depends strongly on the imposed temperature</p><p>change, the duration of the shock and also on theconcentrations. Table 1 presents the experimental setup.</p></li><li><p>2.2. Experimental reactors and inoculum</p><p>Two CSTR reactors with a working volume of 8 l</p><p>each were used in this study. The reactors were operated</p><p>in a daily draw-ll mode. The imposed operation tem-</p><p>peratures are shown in Table 1. The reactors were</p><p>heated using hot water recirculation through a water</p><p>jacket surrounding the reactors. In the rst run, thereactors were seeded with 8 l thermophilic sludge ob-</p><p>tained from a 2700 m3 reactor from VAGRON (Gron-</p><p>ingen, The Netherlands), a system treating municipal</p><p>the inoculum used in the fth run are shown in Table 2.</p><p>characteristics of the manure used are given in Table 3.</p><p>Table</p><p>1</p><p>Theexperimentalsetup</p><p>Firstrun</p><p>Secondrun</p><p>Thirdrun</p><p>Fourthrun</p><p>Fifth</p><p>run</p><p>Sixth</p><p>run</p><p>Theaim</p><p>isstudying</p><p>theeectof:</p><p>Constant</p><p>temperature</p><p>Downward</p><p>temperature</p><p>uctuations</p><p>Constanttemperature</p><p>Downward</p><p>temperature</p><p>uctuations</p><p>Upward</p><p>temperature</p><p>uctuations</p><p>Upward</p><p>temperature</p><p>uctuations</p><p>HRT(days)</p><p>20</p><p>20</p><p>10</p><p>10</p><p>10</p><p>20</p><p>Tem</p><p>perature</p><p>50C</p><p>(R2050)</p><p>50C</p><p>for14hand40C</p><p>for10h(R</p><p>2050d)</p><p>50C</p><p>(R1050)</p><p>50C</p><p>forl4hand40C</p><p>for10h(R</p><p>1050d)</p><p>50C</p><p>forl9hand60C</p><p>for5h(R</p><p>1050u)</p><p>50C</p><p>forl9hand60C</p><p>for5h(R</p><p>2050u)</p><p>60C</p><p>(R2060)</p><p>60C</p><p>for14hand50C</p><p>for10h(R</p><p>2060d)</p><p>60C</p><p>(R1060)</p><p>60C</p><p>for14hand50C</p><p>for10h(R</p><p>1060d)</p><p>60C</p><p>for19hand70C</p><p>for5h(R</p><p>1060u)</p><p>60C</p><p>for19hand70C</p><p>for5h(R</p><p>2060u)</p><p>Mixing</p><p>Continuouslyat6rpm</p><p>Continuouslyat6rpm</p><p>Interm</p><p>ittentat50rpm</p><p>for1min</p><p>every10min</p><p>Interm</p><p>ittentat50rpm</p><p>for1min</p><p>every10min</p><p>Interm</p><p>ittentat50rpm</p><p>for1min</p><p>every10min</p><p>Interm</p><p>ittentat50rpm</p><p>for1min</p><p>every10min</p><p>Organicloadingrate</p><p>(g[COD]/lday)</p><p>2.9</p><p>2.9</p><p>5.25</p><p>5.25</p><p>6.1</p><p>3.05</p><p>Elapsedtimebefore</p><p>steadystate(days)</p><p>49</p><p>49</p><p>35</p><p>42</p><p>31</p><p>62</p><p>H.M. El-Mashad et al. / Bioresource Technology 95 (2004) 191201 1932.4. Analysis</p><p>The total COD (CODt) was analysed as describedby Zeeman (1991). The dissolved COD (CODdis) and</p><p>the VFA concentrations were measured in a 20 times</p><p>diluted samples after they were centrifuged for 10 min at</p><p>3500 rpm followed by membrane ltration (0.45 lm,</p><p>Table 2</p><p>Characteristics of the inoculum used in the fth run with standard</p><p>deviations between brackets</p><p>Parameter Inoculum for R1050u Inoculum for R1060u</p><p>Total solids (g/l) 42.3 (0.4) 47.3 (0.2)</p><p>Volatile solids (g/l) 31.5 (0.4) 36.9 (0.2)</p><p>VFA (mg [COD]/l) 22.1 (2.8) 92.4 (1.3)</p><p>Ammonia (mg/l) 1215.8 (25.6) 1223.2 (8.7)</p><p>SMA (g [COD]/</p><p>g[VS] day)</p><p>0.1 (0.003) 0.12 (0.002)</p><p>*At 50 C.**2.3. Feedstock</p><p>The reactors were fed with diluted cow manure</p><p>originating from dairy cows weighing about 650 kg. Thediet of the cows was free of any antibiotic addition.</p><p>There were some variations in the manure composition</p><p>as it was not possible to obtain enough manure at one</p><p>time to carry out all the experiments. The manure was</p><p>stored in a refrigerator (4 C) until used. Before feeding,the manure was diluted with tap water to give a 5% TS</p><p>feedstock. The dilution used in these experiments was to</p><p>mitigate the high ammonia concentration eect. Inmany countries less protein rich feed is used, resulting in</p><p>a lower NH4 -N content of the manure. Importantwaste at a temperature of 5257 C at a retention time of18 days. One week after inoculation, feeding was star-</p><p>ted. For each of the next experimental runs the inocu-</p><p>lum was taken from the previous run except for the fth</p><p>run. After nishing the fourth run, the reactors wereoperated batchwise for about 2 months at constant</p><p>temperatures of 50 and 60 C. Some characteristics ofAt 60 C.</p></li><li><p>ets</p><p>secon</p><p>tal ru</p><p>Total COD g/l 57.9 (4.8)</p><p>Dissolved COD mg/l 9278.2 (662.7)</p><p>0.9)</p><p>.5)</p><p>)</p><p>)</p><p>)</p><p>)</p><p>32.4 (1) 43.7 (1.4)</p><p>.7) 1861.3 (62.5) 2116.6 (108.2)</p><p>2)</p><p>194 H.M. El-Mashad et al. / Bioresource Technology 95 (2004) 191201Schleicher and Schuell ME 25, Germany) and diluted</p><p>with formic acid. CODdis was measured using the</p><p>micromethod (Jirka and Carter, 1975). The VFAs were</p><p>determined by gas chromatography using a Hewlett</p><p>Packard 5890 equipped with a 2 m 4 mm glass column,packed with Supelcoport (100200 mesh) coated with</p><p>10% Fluorad FC 431. The temperatures of the column,</p><p>injection port and ame ionisation detector were 130,220, 240 C, respectively. The carrier gas was nitrogensaturated with formic acid (40 ml/min). TS, VS, Kjel-</p><p>dahl-nitrogen (Nkj) were analysed as described by</p><p>APHA (1992). The total ammonium concentration</p><p>(NH4 -N) was determined by steam distillation (APHA,1992). Methane produced was collected in gasbags after</p><p>the CO2 had been removed by passing the biogas</p><p>through a 36% NaOH solution. The daily methaneproduction was measured by using a wet gas meter. The</p><p>methane production was recalculated for standard</p><p>temperature and pressure (STP). The pH was measured</p><p>daily, whereas VFA was measured once weekly for 20</p><p>days HRT and twice a week for 10 days HRT till steady</p><p>state. Once steady state was reached, all euent anal-</p><p>yses were carried out immediately, thereby preventing</p><p>the need to store samples. The maximum specic meth-</p><p>Total VFAs mg [COD]/l 3299.3 (28</p><p>Acetate (C2) mg [COD]/l 2014.2 (31</p><p>Propionate (C3) mg [COD]/l 488.5 (8.6</p><p>Iso-butyrate (i-C4) mg [COD]/l 143.9 (6.7</p><p>Butyrate (n-C4) mg [COD]/l 128.1 (2.4</p><p>Iso-valerate (i-C5) mg [COD]/l 524.7 (330</p><p>Valerate (n-C5) mg [COD]/l 0.0 (0)</p><p>Nkj mg/l 1978.6 (26</p><p>NH4 -N mg/l 854.4 (15.Table 3</p><p>The composition of the inuent with standard deviation between brack</p><p>Parameter Unit First and</p><p>experimen</p><p>Total solids g/l 50 (1.3)</p><p>Volatile solids g/l 40.1 (0.5)anogenic activity test (SMA) has carried out in dupli-</p><p>cate, by VFA (acetate) depletion for two feeds as</p><p>described by Van Lier (1995). The initial sludge con-</p><p>centration was 3 g [VS]/l and acetate concentration in</p><p>both feeds was about 1.5 g [COD]/l. The results of the</p><p>second feed were used for the SMA calculations. The</p><p>average results of al...</p></li></ul>

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