Feasibility of anaerobic digestion from bioethanol fermentation residue

Download Feasibility of anaerobic digestion from bioethanol fermentation residue

Post on 25-Dec-2016

212 views

Category:

Documents

0 download

Embed Size (px)

TRANSCRIPT

<ul><li><p>Bioresource Technology 141 (2013) 177183</p><p>Contents lists available at SciVerse ScienceDirect</p><p>Bioresource Technology</p><p>journal homepage: www.elsevier .com/locate /bior tech</p><p>Feasibility of anaerobic digestion from bioethanol fermentation residue</p><p>0960-8524/$ - see front matter Crown Copyright 2013 Published by Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.biortech.2013.03.068</p><p> Corresponding author. Tel.: +82 41 589 8445; fax: +82 41 589 8580.E-mail address: jjyoon@kitech.re.kr (J.-J. Yoon).</p><p>Jeong-Hoon Park a,b, Sang-Hyoun Kim c, Hee-Deung Park b, Dong Jung Lim d, Jeong-Jun Yoon a,a Green Materials Technology Center, Korea Institute of Industrial Technology (KITECH), 35-3 Hongcheon-ri, Ipjang-myeon, Cheonan, Chungnam 330-825, Republic of Koreab Department of Civil, Environmental and Architectural Engineering, Korea University, Anam-dong, Seongbuk-gu, Seoul 136-714, Republic of Koreac Department of Environmental Engineering, Daegu University, Jillyang, Gyeongsan, Gyeongbuk 712-714, Republic of Koread Biolsystems Co. Ltd., Joong Pyung B/D 6F 64-1, Umyeon-dong, Seocho-gu, Seoul 137-900, Republic of Korea</p><p>h i g h l i g h t s</p><p>Maximum CH4 conversion rate of fermentation residue is 84.8% at 5 g COD/L of residue. Appropriate F/M ratio was significant on anaerobic digestion of fermentation residue. Inhibitory effects on anaerobic digestion can be overcome by increasing cell. Formic acid is strong inhibitor than levulinic acid on anaerobic digestion.</p><p>a r t i c l e i n f o</p><p>Article history:Available online 16 March 2013</p><p>Keywords:Red algaeAnaerobic digestionLevulinic acidFormic acidInhibition</p><p>a b s t r a c t</p><p>The focus of this study was the reuse of red algal ethanol fermentation residue as feedstock for anaerobicdigestion. Levulinic acid and formic acid, the dilute-acid hydrolysis byproducts, inhibited methanogene-sis at concentrations over 3.0 and 0.5 g/L, respectively. However, the inhibition was overcome by increas-ing inoculum concentration. A series of batch experiments with the fermentation residue showedincreased methane yield and productivity at higher inoculum concentration. The maximum methaneconversion rate of 84.8% was found at 5 g COD/L of fermentation residue at 0.25 g COD/g VSS of food-to-microorganism (F/M) ratio. The red algal ethanol fermentation residue can possibly be used as a feed-stock in anaerobic digestion at appropriate concentration and F/M ratio.</p><p>Crown Copyright 2013 Published by Elsevier Ltd. All rights reserved.</p><p>1. Introduction</p><p>Marine algal biomass has various advantages as a sustainablefeedstock for bioenergy production (Kim et al., 2010). Marine algaegrow faster and have greater carbon dioxide fixation ability thanland plants (Lning and Pang, 2003; Packer, 2009). Also, it can becultivated easily without extra addition of nutrient or fertilizersuch as nitrogen source (Buck and Buchholz, 2004). Furthermore,the lignin-free chemical structure would allow obtaining sugarswithout complex and expensive pretreatment such as lignin re-moval (Levin et al., 2004; Mosier et al., 2005).</p><p>More than 70% of red algal biomass, however, remains as fer-mentation residue in ethanol production (Park et al., 2012b). Ifthe residue can be converted to methane by anaerobic digestion,ethanol could be supplied at lower prices. Furthermore, the netenergy yield of ethanol fermentation would be enhanced. Already,numbers of research studies have investigated the feasibility ofenergy recovery from ethanol fermentation residue by anaerobicmicrobes. When used as feedstock for methane fermentation,</p><p>the fermentation residue had a chemical oxygen demand (COD)of around 50 g COD/L (Hunter, 1988). In 19831985, Stover inves-tigated the anaerobic digestion from 64 g COD/L of corn stillagewith suspended-growth and fixed-film digester (Stover et al.,1983, 1984, 1985). In 2008, Schaefer used 100 g COD/L and 60 gVS/L of ethanol waste under thermophilic condition (Schaeferand Sung, 2008); however, most of these studies did not investi-gate in detail the effect of inhibition on anaerobic digestion.Inhibitory effect should be investigated because potential to de-crease COD level can circumvent the expensive costs associatedwith directly processing water high in COD concentrations.Reducing COD levels will lower the cost of treatment; therefore,pretreatment via anaerobic digestion is a possible solution toachieve this reduction. Furthermore, this method will not only re-duce cost but it can recover energy as well further offsetting nettreatment expenses.</p><p>This study investigated the feasibility of the red algal ethanolfermentation residue as a feedstock for anaerobic digestion. The ef-fect of levulinic acid and formic acid as the potential inhibitors inthe residue was examined. In addition, the residue was used asthe feedstock for batch anaerobic digestion at various concentra-tions and food-to-microorganism (F/M) ratios.</p>http://crossmark.dyndns.org/dialog/?doi=10.1016/j.biortech.2013.03.068&amp;domain=pdfhttp://dx.doi.org/10.1016/j.biortech.2013.03.068mailto:jjyoon@kitech.re.krhttp://dx.doi.org/10.1016/j.biortech.2013.03.068http://www.sciencedirect.com/science/journal/09608524http://www.elsevier.com/locate/biortech</li><li><p>178 J.-H. Park et al. / Bioresource Technology 141 (2013) 177183</p><p>2. Methods</p><p>2.1. Inoculum sludge for anaerobic batch test</p><p>Granular sludge was taken from an anaerobic digester in a localbrewery wastewater treatment plant. The pH, total suspended sol-ids (TSS) and volatile suspended solids (VSS) concentration ofsludge were 7.1, 52.6 and 49.2 g/L, respectively. Solids were ana-lyzed by standard method from APHA (Eaton and Franson, 2005).</p><p>2.2. Red algal ethanol fermentation residue</p><p>Gelidium amansii obtained from a littoral area in Morocco wasused as the feedstock for ethanol production. The G. amansii com-position was as follows (%, dry base): cellulose (glucose) 14.9, gal-actose 23.1, 3,6 anhydrogalactose (3,6-AHG) 29.3, protein 15.6, ash5.7 and others 11.4 (Park et al., 2011). The red algal biomass waswashed using tap water to remove salt and milled to a size of</p></li><li><p>Fig. 1. Cumulative methane production profile at various levulinic acid concentrations (high F/M ratio): (a) acetic acid 3 g COD/L with inoculum volume 4.5 g VSS/L and (b)propionic acid 3 g COD/L with inoculum volume 4.5 g VSS/L.</p><p>Fig. 2. Cumulative methane production profile at various levulinic acid concentrations (low F/M ratio): (a) acetic acid 3 g COD/L with inoculum volume 20 g VSS/L and (b)propionic acid 3 g COD/L with inoculum volume 20 g VSS/L.</p><p>Fig. 3. Cumulative methane production profile at various formic acid concentrations (high F/M ratio): (a) acetic acid 3 g COD/L with inoculum volume 4.5 g VSS/L and (b)propionic acid 3 g COD/L with inoculum volume 4.5 g VSS/L.</p><p>J.-H. Park et al. / Bioresource Technology 141 (2013) 177183 179</p><p>values (Figs. 14) were very similar (error range </p></li><li><p>Fig. 4. Cumulative methane production profile at various formic acid concentrations (low F/M ratio): (a) acetic acid 3 g COD/L with inoculum volume 20 g VSS/L and (b)propionic acid 3 g COD/L with inoculum volume 20 g VSS/L.</p><p>Table 1The characteristics of methane production at various concentrations of levulinic acid with 4.5 g VSS/L of inoculum by the modified Gompertz equation.</p><p>Parameters Acetic acid (3 g COD/L) Propionic acid (3 g COD/L)</p><p>Levulinic acid (g/L)</p><p>Control 0.5 1.0 2.0 3.0 5.0 Control 0.5 1.0 2.0 3.0 5.0</p><p>Pa (mL) 354.4 418.4 528.9 619.5 697.7 875.8 350.54 443.2 545.1 611.2 734.5 635.5Rm</p><p>b (mL/day) 68.27 59.71 48.90 45.13 43.97 43.75 49.43 45.45 43.47 60.55 60.80 44.32kc (day) 1.74 1.69 1.85 1.93 2.60 5.05 2.16 2.54 3.45 4.63 5.34 10.1R2d 0.9937 0.9900 0.9973 0.9938 0.9960 0.9932 0.9960 0.9973 0.9932 0.9925 0.9840 0.9921</p><p>a P, ultimate methane production potential.b Rm, maximum methane production rate.c k, lag phase time.d R2, the coefficient of determination.</p><p>Table 2The characteristics of methane production at various concentrations of levulinic acid with 20.0 g VSS/L of inoculum by the modified Gompertz equation.</p><p>Parameters Acetic acid (3 g COD/L) Propionic acid (3 g COD/L)</p><p>Levulinic acid (g/L)</p><p>Control 0.5 1.0 2.0 3.0 5.0 Control 0.5 1.0 2.0 3.0 5.0</p><p>Pa (mL) 298.4 353.2 359.3 447.2 551.0 791.6 358.5 399.3 491.5 822.8 786.0 911.1Rm</p><p>b (mL/day) 114.4 108.5 111.2 90.54 56.89 51.36 119.3 97.93 90.59 69.37 60.65 49.37kc (day) N/De N/D N/D N/D N/D N/D 0.62 0.58 0.47 0.62 1.18 1.19R2d 0.9368 0.9049 0.9382 0.8870 0.9244 0.9440 0.9951 0.9951 0.9964 0.9936 0.9882 0.9853</p><p>a P, ultimate methane production potential.b Rm, maximum methane production rate.c k, lag phase time.d R2, the coefficient of determination.e N/D, not detected.</p><p>Table 3The characteristics of methane production at various concentration of formic acid with 4.5 g VSS/L of inoculum by the modified Gompertz equation.</p><p>Parameters Acetic acid (3 g COD/L) Propionic acid (3 g COD/L)</p><p>Formic acid (g/L)</p><p>Control 0.1 0.2 0.5 1.0 2.0 Control 0.1 0.2 0.5 1.0 2.0</p><p>Pa (mL) 343.2 349.8 354.1 358.7 393.2 388.1 319.2 319.0 334.8 343.3 477.0 416.3Rm</p><p>b (mL/day) 110.3 107.9 78.31 53.34 32.27 49.36 58.91 58.75 57.49 41.51 16.12 15.74kc (day) 0.36 0.21 0.36 1.16 1.34 9.77 1.61 1.38 1.34 1.49 6.81 14.82R2d 0.9837 0.9802 0.9914 0.9980 0.9968 0.9974 0.9963 0.9968 0.9964 0.9969 0.9851 0.9955</p><p>a P, ultimate methane production potential.b Rm, maximum methane production rate.c k, lag phase time.d R2, the coefficient of determination.</p><p>180 J.-H. Park et al. / Bioresource Technology 141 (2013) 177183</p><p>conditions, methane was instantly produced without an adaptionperiod. When the inoculum is sufficient, methane production is</p><p>not significantly inhibited by levulinic acid of concentrations rang-ing up to 5.0 g/L. In addition, methane production was higher than</p></li><li><p>Table 4The characteristics of methane production at various concentration of formic acid with 20.0 g VSS/L of inoculum by the modified Gompertz equation.</p><p>Parameters Acetic acid (3 g COD/L) Propionic acid (3 g COD/L)</p><p>Formic acid (g/L)</p><p>Control 0.1 0.2 0.5 1.0 2.0 Control 0.1 0.2 0.5 1.0 2.0</p><p>Pa (mL) 301.6 324.8 321.6 336.7 406.0 445.9 325.3 323.5 332.9 346.0 400.6 438.4Rm</p><p>b (mL/day) 220.0 241.1 217.0 187.3 142.5 65.76 126.5 122.8 125.6 126.0 117.5 85.82kc (day) 0.2803 0.0877 0.1248 N/Dd N/D N/D 0.3097 0.3079 0.2500 0.2307 0.0327 N/DR2e 0.9471 0.9273 0.9335 0.9349 0.9546 0.9811 0.9732 0.9740 0.9740 0.9804 0.0789 0.9848</p><p>a P, ultimate methane production potential.b Rm, maximum methane production rate.c k, lag phase time.d N/D, not detected.e R2, the coefficient of determination.</p><p>J.-H. Park et al. / Bioresource Technology 141 (2013) 177183 181</p><p>in the control of all levulinic acid containing experiments (Table 2).This implies that levulinic acid in concentrations up to 5 g/L couldbe used as an energy source for methane fermentation.</p><p>Formic acid has higher inhibition potential than 5-HMF and lev-ulinic acid. Although formic acid was produced in smaller propor-tion than other inhibitors, it was the strongest inhibitor of methanefermentation when dissolved at the same concentration as theother inhibitors. As shown in Fig. 3, only low concentration(0.5 g/L) of formic acid could retard methane production. The lagphase time sharply increased over 0.5 g/L of formic acid. The</p><p>Fig. 5. Statistical analysis of cumulative methane production by Gompertz equation: (methane production.</p><p>investigation of the effect of formic acid on methane fermentationhad almost the same trend as the previous levulinic experiments.Propionic acid resolution was more sensitive than acetic acid reso-lution to the inhibition of formic acid (Fig. 3). At 2.0 g/L of formicacid concentration, the lag phase time between acetic acid and pro-pionic acid were 9.77 days and 14.82 days, respectively (Table 3).With the increase of inoculum concentration from 4.5 to 20 gVSS/L, the lag phase time sharply decreased (Fig. 4). In addition,the maximum methane production rate increased 1.33-fold from49.36 mL/day at 4.5 g VSS/L of inoculum to 65.76 mL/day at</p><p>A) effect of levulinic acid on methane production and (B) effect of formic acid on</p></li><li><p>Fig. 6. Methane conversion rate from various concentration of fermentationresidue at 4.5 and 20 g VSS/L of inoculum concentration.</p><p>182 J.-H. Park et al. / Bioresource Technology 141 (2013) 177183</p><p>20.0 g VSS/L when acetic acid substrate was used with formic acidinhibitor (at concentration of 2.0 g/L). In the case of propionic acidsubstrate used in the same conditions, maximum methane produc-tion rate was 15.74 at 4.5 g VSS/L and 85.82 at 20 g VSS/L a 5.43-fold increase. In the presence of levulinic acid concentration lowerthan 5.0 g/L or formic acid at concentrations lower than 2.0 g/L, theincrease of inoculum did not affect methane production (Table 4).The cumulative methane production data was analyzed using theGompertz equation to quantify the methane yield, the methaneproductivity and the lag-phase time at each experimental condi-tion (Tables 14). Then, the effects of the inhibitors were assayedwith the value found at the modeling (Fig. 5). The cumulativemethane production had no specific correlation to F/M ratio, butthe case of maximum methane production rate and lag-phase timewas different results. At inhibitory levels, methane production ratesignificantly increased with decreasing F/M ratio for levulinic acidconcentrations up to 5.0 g/L and for formic acid concentrations upto 2.0 g/L. With the decrease of F/M ratio, the lag phase time alsosharply decreased. This result signifies that methane accumulatedrapidly even in the presence of inhibitor as F/M ratio decreased.</p><p>3.2. Methane production from fermentation residue of red algalbioethanol</p><p>In previous study, Parks research group strongly emphasizedthat anaerobic digestion of fermentation residue would have enor-mous energy potential. Energy production by anaerobic digestionis 2.24-fold higher than the energy produced by the main ethanolproduction process (Park et al., 2012b). Fig. 6 shows the relativepercentage of methane conversion, which is calculated based onthe theoretical maximum, according to fermentation residue con-centration. Methane production from various concentrations (530 g/L) of ethanol fermentation residue were investigated to studythe effect of inhibitor concentration on methane production at 4.5and 20 g VSS/L. First, 4.5 g VSS/L of inoculum was used as seed inthis experiment. Increasing fermentation residue concentrationgradually attenuated methane yield. Maximum methane conver-sion rate was observed as 84.8% at 5 g COD/L of fermentation res-idue. When fermentation residue concentration exceeded 5 g COD/L, methane yield gradually decreased. We investigated what ac-counted for this decrease in methane yield; our initial hypothesiswas excessive food to microorganism ratio or inhibitory substrate.However, levulinic acid and formic acid did not reach critical level(3.0 and 0.5 g/L) until 30 g/L of fermentation residue. At that resi-due concentration, levulinic acid and formic acid concentrationwere 1.2 and 0.4 g/L, respectively. The F/M ratio was a more signif-icant...</p></li></ul>