- Email: [email protected]
Batch anaerobic co-digestion of Kimchi factory waste silage and swine manure under mesophilic conditions
Bioresource Technology 124 (2012) 489–494
Contents lists available at SciVerse ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Batch anaerobic co-digestion of Kimchi factory waste silage and swine manure under mesophilic conditions Gopi Krishna Kafle a,1, Sang Hun Kim a,⇑, Kyung Ill Sung b a b
Department of Biosystems Engineering, Kangwon National University, 192-1 Hyoja 2-dong, Chuncheon, Kangwon-do 200-701, Republic of Korea Department of Animal Life System, Kangwon National University, 192-1 Hyoja 2-dong, Chuncheon, Kangwon-do 200-701, Republic of Korea
h i g h l i g h t s " Kimchi factory waste silage (KFWS) was prepared by mixing Chinese cabbage (CC) and rice bran (RB). " The KFWS produced significantly higher (p < 0.01) biogas and methane than CC. " The biogas and methane yield was higher using a mixture of KFWS and swine manure (SM) than SM alone. " The volatile solids (VS) removal was higher using a mixture of KFWS and SM than SM alone. " Co-digestion of KFWS with SM could be promising to improve biogas production from SM digesters.
a r t i c l e
i n f o
Article history: Received 5 March 2012 Received in revised form 17 July 2012 Accepted 16 August 2012 Available online 26 August 2012 Keywords: Biogas Co-digestion Chinese cabbage Kimchi Rice bran
a b s t r a c t The objective of this study was to investigate the feasibility of anaerobic co-digestion of Kimchi factory waste silage (KFWS) with swine manure (SM). Chinese cabbage (CC) is the major waste generated by a Kimchi factory and KFWS was prepared by mixing CC and rice bran (RB) (70:30 on a dry matter basis). In Experiment I, the biogas potential of CC and RB were measured and, in Experiment II, the test was conducted with different ratios of KFWS and SM (KFWS: SM = 0:100; 33:67; 67:33; 100:0 by% volatile solids (VS) basis). KFWS produced a 27% higher biogas yield and a 59% higher methane yield compared to CC. The specific biogas yields increased by 19, 40 and 57% with KFWS-33%, KFWS-67% and KFWS-100%, respectively compared to SM-100% (394 mL/g VS). Similarly, VS removal increased by 37, 51 and 74% with KFWS-33%, KFWS-67% and KFWS-100%, respectively compared to SM-100%. These results suggested that Kimchi factory waste could be effectively treated by making silage, and the silage could be used as a potential co-substrate to enhance biogas production from SM digesters. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Kimchi is prepared by fermenting Chinese cabbage (CC). There are many Kimchi factories in Korea and a large quantity of waste is generated from each factory during the trimming processes. Choi and Park (2003) reported that the total annual production of CC is approximately three million tons in Korea and up to 30% of the total production is discarded as waste. Anaerobic digestion could be a good approach for CC waste utilization and energy generation; however, CC waste is seasonal and it may accumulate in quantities larger than needed for immediate use. The high moisture content (>95%) in CC causes fast spoilage, thus ensiling has been envisioned for storage before biogas production (Herrmann et al., 2011; Zubr, ⇑ Corresponding author. Tel.: +82 33 250 6492; fax: +82 33 255 6406. E-mail addresses: gopikafl[email protected] (G.K. Kafle), (S.H. Kim). 1 Tel.: +82 33 250 6490; fax: +82 33 255 6406.
[email protected]
0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.08.066
1986). Since CC has too high of a moisture content (>95%) for ensiling, its moisture content needs to be reduced by drying or maceration or mixing with the other feed materials with a low moisture content. Like CC, rice bran (RB) is an agricultural byproduct, which is produced in large quantities by rice processing industries. RB has a low moisture contents (10–15% w.b.), can be preserved for a long time, and could be mixed with CC in order to maintain a suitable range of moisture contents for silage preparation. Anaerobic digestion tends to fail without the addition of external nutrients and buffering agents (Demirel and Scherer, 2008); therefore, co-digestion with substrates having a high buffering capacity (alkalinity) such as manure can be a good alternative for effective treatment of highly biodegradable materials. Therefore, the objective of the present study was to determine the feasibility of anaerobic co-digestion of Kimchi factory waste silage (KFWS) with swine manure (SM). The biogas potential of CC, RB, and KFWS and of KFWS mixed at different ratios with SM was determined for mesophilic conditions.
490
G.K. Kafle et al. / Bioresource Technology 124 (2012) 489–494
2. Methods 2.1. Silage preparation KFWS was prepared by mixing CC and RB at a ratio of 70:30 (d.m. basis). The mixture was fermented in anaerobic plastic bags for 22 days at 30 °C. The characteristics of CC, RB, KFWS and inoculums are shown in Table 1. 2.2. Experimental design and biogas measurement The experimental design for each experiment is shown in Table 2. Experiments I and II were carried out in 1.2 L glass bottles (liquid volume of 0.8 L). The feed to inoculum (F/I) ratio was calculated based on the initial VS of substrate and inoculums. Each digester was mixed manually for 20–30 s once a day before gas volume measurements. The daily biogas production of each digester was determined by the volume of biogas produced, which was calculated from the volume and pressure in the headspace of the digester (EI-Mashad and Zhang, 2010; Liu et al., 2009). Biogas composition was analyzed using a gas analyzer (BioGas Check- Geotechnical Instruments (UK) Ltd.) (Kafle et al., 2012; Kafle and Kim, 2011). The measured wet biogas and methane volumes were adjusted to
the volumes at standard temperature (0 °C) and pressure (1 atm) (VDI 4630, 2006). The mass removal in the form of biogas at the end of the experiment was calculated using Eq. (1). The density of CH4 was taken as 0.000668 g/mL and density of CO2 as 0.00184 g/ mL.
BR ¼
V 0 qmix m
ð1Þ
Where,BR = mass of biogas removed per gram TS or VS added (g/g VSadded or g/g TSadded))V0 = volume of biogas produced (ml, at standard temperature and pressure (STP))qmix = mass concentration of CH4 + CO2 in the biogas (g/mL)m = TS or VS added (g) 2.3. Analytical methods Total solids (TS), volatile solids (VS), NH3–N, total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD) and pH were determined according to standard methods (APHA, 1998). Total Kjeldahl nitrogen (TKN) was analyzed using a Kjeldahl apparatus (Kjeltec 2100, Foss, Sweden) and ammonia (NH3–N) was determined using the Nessler method with measurements on a spectrophotometer (DR 2500, Hach, USA). TVFA (total volatile fatty acids), TA (total alkalinity) and TVFA/TA ratio were determined
Table 1 Characteristics of materials used. Feed
Units
TS VS VS/TS ratio TVFA TA TVFA/TA ratio pH TCOD SCOD TKN
% % mg/L mg/L
mg/L mg/L mg/L %, w.b. mg/L
NH3–N C/N ratio
Experiment I
Experiment II
CC
RBa
Inoculumb
KFWS
SM
Inoculumb
3.65 3.04 0.83 1147 591 1.941 6.5 34,800 17,560 1540 – 135 10.5
90.16 80.66 0.89 11,300 1940 5.82 5.50 – – – 2.052 2800 21.8
1.605 0.64 0.40 1164 12,778 0.091 8.25 8000 4907 2703 – 2930 1.3
33.47 30.2 0.90 9470 5690 1.664 5.10 406,200 61,600 – 0.987 1550 17.0
4.16 2.48 0.60 4200 15,053 0.279 8.05 53,000 12,100 6100 – 4420 2.3
1.15 0.469 0.41 536 10,650 0.050 8.20 7000 1560 2731 – 2280 1.0
–: Not determined. C/N ratio: Carbon to nitrogen ratio (TOC/ TKN). SM: Swine manure; CC: Chinese cabbage; RB: Rice bran; KFWS: Kimchi factory waste silage. a Fresh rice bran (without oil removal). b Digested slurry obtained from SM digester operating at mesophilic temperature.
Table 2 Experimental design. F/I ratio
Substrate loading (g VS/L)
Feed composition (% VS basis)
No. of replications
Purpose
Experiment I
0.5
2.5
3
To determine the biogas potential and biogas production rate of CC and RB.
Experiment II
0.5
2.5
CC: SM = 100:0 (CC100%) RB: SM = 100:0 (RB100%) KFWS: SM = 0:100 (SM-100%) KFWS: SM = 33:67 (CCRB-33%) KFWS: SM = 33:67 (CCRB-67%) KFWS: SM = 100:0 (CCRB-100%)
2
To determine the effect of different mixture ratios of KFWS and SM on biogas yield and digester performance.
F/I ratio: Feed to inoculum ratio (g VS substrate added/g VS inoculums added). g VS/L: Gram volatile solids per liter. SM: Swine manure; CC: Chinese cabbage; RB: Rice bran; KFWS: Kimchi factory waste silage.
G.K. Kafle et al. / Bioresource Technology 124 (2012) 489–494
491
Fig. 1. (a) Cumulative biogas yield; (b) methane contents for Chinese cabbage (CC-100%) and rice bran (RB-100%). The values are means ± standard deviations (vertical bars, n = 3rd deviations).
using the Nordmann-titration method (Kafle and Kim, 2011). The TOC (total organic carbon) was calculated using the formula, TOC = VS/1.8 (Haug, 1993). The TS and VS removal of feed during the batch test were calculated based on total mass removal from the testing reactors and the blank reactors (EI-Mashad and Zhang, 2010). 2.4. Statistical analysis The significance of differences in average biogas yields, methane yields, pH, and TS, VS removal were determined by single factor ANOVA (Analysis of Variance) using Excel software 2007. Least Significant Difference (LSD) was calculated to judge whether two or more averages were significantly different (EI-Mashad and Zhang, 2010). 3. Results and discussion 3.1. Biogas potential of CC and RB (Experiment I) The cumulative biogas yield (mL/g VS) and methane contents (%) during the digestion of CC (CC-100%) and RB (RB-100%) are
shown in Fig. 1. Biogas production started immediately on the first day. The specific biogas yield in CC-100% and RB-100% increased until day 40 and 43, respectively and gradually leveled off thereafter. Around 90% of biogas yield was obtained within 36 and 48 days of digestion for CC-100% and RB-100%, respectively. The biogas potential for CC-100% and RB-100% was 450 and 649 mL/g VS added, respectively on day 90. The LSD values for biogas yield were 58 and 82 mL/g VS added at significance levels of 5 and 1%, respectively. The biogas potential of RB was significantly higher (p < 0.01) than that of CC (Table 4). Thus the silage prepared from a mixture of CC and RB (used in Experiment II) was expected to increase the biogas yield compared to CC alone. The weight average methane contents from CC-100% and RB-100% were 57.7 and 60.4%, respectively (Table 4). Thus the methane potentials for CC-100% and RB-100% were 260 and 392 mL/g VS added. The LSD values for methane yield were 40 and 56 mL/g VS added at significance levels of 5 and 1%, respectively. The methane potential of RB was significantly higher (p < 0.01) than that of CC. Labatut et al. (2011) reported a similar methane potential of 256.6 mL/g VS added for cabbage. The H2S concentration in biogas from RB-100% was lower than that of CC-100% (data not shown). The initial and final characteristics of digester contents from the CC-100% and RB-100%
492
G.K. Kafle et al. / Bioresource Technology 124 (2012) 489–494
Table 3 Initial and final characteristics of the digester contents. Experiment
Experiment Ia
Feed
CC-100%
RB-100%
SM-100%
KFWS-33%
KFWS-67%
KFWS-100%
OLR (g VS/L) F/I ratio TVFA (mg/L)
2.5 0.5 856(26) 734(71) 9612(147) 10,417(61) 0.089(0.003) 0.070(0.007) 8.21(0.03) 7.84(0.02) 2160(60) 2360(310) 2773(20) 2822(10) – 6560(100) – 4480(324) 1.39(0.00) 0.87(0.07)
2.5 0.5 794(54) 621(80) 9887(206) 10,104(289) 0.080(0.004) 0.062(0.008) 8.14(0.01) 7.83(0.01) 2240(171) 2580(53) 2815(40) 2738(10) – 8320(427) – 2898(215) 1.46(0.05) 1.01(0.04)
2.5 0.5 813(31) 663(10) 9713(148) 10,295(8) 0.084(0.004) 0.064(0.001) 8.08(0.01) 8.03(0.04) 2080(0) 3260(28) – – 12,400(414) 10,240(0) 3960(170) 2053(0) – –
2.5 0.5 753(39) 718(56) 9077(151) 10,154(76) 0.095(0.020) 0.075(0.005) 8.08(0.01) 7.94(0.01) 1920(170) 2710(42) – – 11,547(37) 7520(830) 4094(207) 1920(0) – –
2.5 0.5 735(66) 680(54) 8605(137) 9414(108) 0.085(0.006) 0.072(0.007) 8.05(0.00) 7.86(0.01) 1820(28) 2390(14) – – 10,934(302) 6240(0) 5760(453) 1840(113) – –
2.5 0.5 554(35) 738(47) 8046(94) 9030(14) 0.069(0.004) 0.082(0.005) 8.05(0.01) 7.86(0.01) 1720(170) 2150(14) – – 10,960(490) 5814(377) 4613(113) 1520(0) – –
TA (mg/L) TVFA/TA ratio pH NH3–N (mg/L) TKN (mg/L) TCOD (mg/L) SCOD (mg/L) C/N ratio
Initial Final Initial Final Initial Final Initial Final Initial Final Initial Final Initial Final Initial Final Initial Final
Experiment IIb
OLR: Organic loading rate. F/I ratio: Feed to inoculum ratio. C/N ratio: Carbon to nitrogen ratio (TOC/TKN). SM: Swine manure; CC: Chinese cabbage; RB: Rice bran; KFWS: Kimchi factory waste silage. a Values are expressed as mean (standard deviation, n = 3). b Values are expressed as mean (standard deviation, n = 2).
digesters are shown in Table 3. There was no significant difference in final pH between CC-100% and RB-100%. The LSD values for TS removal were 14 and 20% and were 16 and 23% for VS removal; at significance levels of 5 and 1%, respectively. There was no significant difference in TS and VS removal between CC-100% and RB100%. 3.2. Effect of co-digestion of KFWS with SM (Experiment II) The cumulative biogas yield (mL/g VS) and methane contents (%) for different ratios of KFWS and SM are shown in Fig. 2. Biogas production started immediately. The specific biogas yield (mL/g VS) increased until days 23, 24, 29 and 32 in SM-100%, KFWS-33%, KFWS-67% and KFWS-100% digesters, respectively and then gradually leveled off. Around 90% of biogas yield was obtained within 25, 26, 28 and 31 days of digestion from SM100%, KFWS-33%, KFWS-67% and KFWS-100% digesters, respectively. The biogas potential was 394, 467, 552, and 620 mL/g VS added for SM-100%, KFWS-33%, KFWS-67% and KFWS-100%, respectively at 90 days. Thus, the specific biogas yield increased by around 19, 40 and 57% for KFWS-33%, KFWS-67% and KFWS100%, respectively compared to swine manure only (SM-100%). The weight average methane contents were 82.6, 75.7, 71.0 and 66.7% for SM-100%, KFWS-33%, KFWS-67% and KFWS-100%, respectively (Table 4). Thus the methane potential was 325, 353, 392, and 413 mL/ g VS for SM-100%, KFWS-33%, KFWS-67% and KFWS-100%, respectively (Table 4). There was no significant difference in methane yields between SM-100 and KFWS-33%; however, the methane yield significantly increased when the KFWS% increased to 67%. There was no significant difference in methane yield between KFWS-67% and KFWS-100%. The methane yield from SM-100% in the current study was higher than that reported by Zhang et al. (2011) (242 mL/g VS) but lower than that reported by Hashimoto (1983) (490–503 mL/g VS). The specific methane yields increased by 8.6, 20.6, and 27%, as compared to that obtained from SM-100% when 33, 67 and 100% of KFWS
were added. Li et al. (2011) reported an increase in methane yield from 162 to 220 mL/g VS when the addition of herbal extraction residue (HER) was increased from 10 to 50% during co-digestion with SM. In constrast, Gonzàlez-Fernàndez et al. (2011) reported a low methane yield with co-digestion of algal biomass with SM due to the lower methane potential of algal biomass. The H2S concentration in the biogas increased with an increase in KFWS% (data not shown). The TS and VS removal increased by 48 and 27%, respectively, when KFWS was increased from 33 to 100% (Table 4). 3.3. Relationship between TS, VS removal and mass of biogas removed The calculated mass of biogas removed (BR) and TS and VS removals at the end of the 90 days digestion period for Experiments I and II are shown in Table 4. The measured TS and VS removals showed good correlation (R2 > 0.90, data not shown) with BR. Theoretically, the calculated biogas mass removal should be higher than the measured VS destructions (Richards et al., 1991). In the present study, although there was good agreement between biogas mass removal and measured VS destructions, the calculated VS destruction was always higher than the calculated biogas mass removed (Table 4). The CC-100% showed a maximum difference of 29.3% compared to the calculated BR as shown in Table 4. Similar to these results, Liu et al. (2009) reported a maximum difference of 23% during anaerobic digestion of food and green waste. 4. Conclusions Kimchi factory waste silage (KFWS) produced significantly higher (p < 0.01) biogas and methane than Chinese cabbage (CC). The biogas yield and TS and VS removal were higher for the mixture of KFWS and swine manure (SM) than SM alone. The biogas yield was increased by around 19% to 57% and VS removal was increased by around 37% to 74% when KFWS content in the feed
493
G.K. Kafle et al. / Bioresource Technology 124 (2012) 489–494
Fig. 2. (a) Cumulative biogas yield; (b) methane contents for different feed mixture ratios of SM and KFWS. The values are means ± standard deviations (vertical bars, n = 2nd deviations).
Table 4 Calculated gas potential, TS and VS removal and BR values for different feed mixtures. Parameters
Units
Biogas potential Methane potential Methane content TS removal VS removal BR
mL/g VS mL/g VS % % % g/g VS added g/g TS added
Experiment Ia
Experiment IIb
CC-100%
RB-100%
SM-100%
KFWS-33%
KFWS-67%
KFWS-100%
450(27) 260(15) 57.7(0.4) 59.6(3.5) 88.9(4.0) 0.524(0.032) 0.435(0.027)
649(34) 392(21) 60.4(0.7) 69.0(5.1) 77.0(8.3) 0.734(0.039) 0.653(0.035)
394(44) 325(33) 82.6(0.4) 28.6(0.2) 43.4(1.9) 0.344(0.042) 0.206(0.025)
467(0) 353(1) 75.7(0.2) 46.3(3.6) 59.5(9.3) 0.445(0.001) 0.300(0.001)
552(4) 392(0) 71.0(0.6) 56.6(4.4) 65.5(4.5) 0.556(0.008) 0.430(0.006)
620(1) 413(2) 66.7(0.4) 68.5(11.9) 75.7(8.4) 0.656(0.004) 0.590(0.004)
BR: Mass of biogas removed. SM: Swine manure; CC: Chinese cabbage; RB: Rice bran; KFWS: Kimchi factory waste silage. a Values are expressed as mean (standard deviation, n = 3). b Values are expressed as mean (standard deviation, n = 2).
increased from 33% to 100%. Thus, the Kimchi factory waste can be treated in an environmentally friendly process by making silage which can be co-digested with SM to improve biogas production from anaerobic digesters operating with SM.
Acknowledgements This work was supported by a research grant from the Rural Development Administration (RDA), Republic of Korea.
494
G.K. Kafle et al. / Bioresource Technology 124 (2012) 489–494
References APHA, 1998. Standard Methods for the Examination of Water and Wastewater, 20th ed. American Public Health Association, Washington, DC. Choi, M.H., Park, Y.H., 2003. Production of Yeast biomass using waste Chinese cabbage. Biomass Bioenergy 25, 221–226. Demirel, B., Scherer, P., 2008. Production of methane from sugarbeet silage without manure addition by a single-stage anaerobic digestion process. Biomass Bioenergy 32, 203–209. EI-Mashad, H.M., Zhang, R., 2010. Biogas production from co-digestion of dairy manure and food waste. Bioresour. Technol. 101, 4021–4028. Gonzàlez-Fernàndez, C., Molinuevo-Salces, B., Garci9 a-Gonzàlez, M.C., 2011. Evaluation of anaerobic codigestion of microalgal biomass and swine manure via response surface methodology. Appl. Energy 88, 3448–3453. Hashimoto, A.G., 1983. Thermophilic and mesophilic anaerobic fermentation of swine manure. Agric. Wastes 6, 175–191. Haug, R.T., 1993. The Practical Handbook of Composting Engineering. Lewis publisher, Ann Arbor, MI. Herrmann, C., Heiermann, M., Idler, C., 2011. Effects of ensiling, silage additives and storage period on methane formation of biogas crops. Bioresour. Technol. 102, 5153–5161. Kafle, G.K., Kim, S.H., 2011. Sludge exchange process on two serial CSTRs anaerobic digestions: process failure and recovery. Bioresour. Technol. 102, 6815–6822.
Kafle, G.K., Kim, S.H., Shin, B.S., 2012. Anaerobic digestion treatment for the mixture of Chinese cabbage waste juice and swine manure. J. Biosyst. Eng. 37 (1), 58–64. Labatut, R.A., Angenent, L.T., Scott, N.R., 2011. Biochemical methane potential and biodegradability of complex organic substrates. Bioresour. Technol. 102, 2255– 2264. Li, Y., Yan, X.L., Fan, J.P., Zhu, J.H., 2011. Feasibility of biogas production from anaerobic co-digestion of herbal-extraction residues with swine manure. Bioresour. Technol. 102 (11), 6458–6463. Liu, G., Zhang, R., EI-Mashad, H.M., Dong, R., 2009. Effect of feed to inoculum ratios on biogas yields of food and green wastes. Bioresour. Technol. 100, 5103–5108. Richards, B.K., Uummings, R.J., White, T.E., Jewell, W., 1991. Methods for kinetic analysis of methane fermentation in high solids biomass digesters. Biomass Bioenergy 1 (2), 65–73. VDI 4630, 2006. Fermentation of organic materials, characterisation of substrate, sampling, collection of material data, fermentation tests, VDI gesellschaft energietechnik. Zhang, L., Lee, Y.W., Jahng, D., 2011. Anaerobic co-digestion of food waste and piggery wastewater: focusing on the role of trace elements. Bioresour. Technol. 102 (8), 5048–5059. Zubr, J., 1986. Methanogenic fermentation of fresh and ensiled plant materials. Biomass 11 (3), 159–171.
Contents lists available at SciVerse ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Batch anaerobic co-digestion of Kimchi factory waste silage and swine manure under mesophilic conditions Gopi Krishna Kafle a,1, Sang Hun Kim a,⇑, Kyung Ill Sung b a b
Department of Biosystems Engineering, Kangwon National University, 192-1 Hyoja 2-dong, Chuncheon, Kangwon-do 200-701, Republic of Korea Department of Animal Life System, Kangwon National University, 192-1 Hyoja 2-dong, Chuncheon, Kangwon-do 200-701, Republic of Korea
h i g h l i g h t s " Kimchi factory waste silage (KFWS) was prepared by mixing Chinese cabbage (CC) and rice bran (RB). " The KFWS produced significantly higher (p < 0.01) biogas and methane than CC. " The biogas and methane yield was higher using a mixture of KFWS and swine manure (SM) than SM alone. " The volatile solids (VS) removal was higher using a mixture of KFWS and SM than SM alone. " Co-digestion of KFWS with SM could be promising to improve biogas production from SM digesters.
a r t i c l e
i n f o
Article history: Received 5 March 2012 Received in revised form 17 July 2012 Accepted 16 August 2012 Available online 26 August 2012 Keywords: Biogas Co-digestion Chinese cabbage Kimchi Rice bran
a b s t r a c t The objective of this study was to investigate the feasibility of anaerobic co-digestion of Kimchi factory waste silage (KFWS) with swine manure (SM). Chinese cabbage (CC) is the major waste generated by a Kimchi factory and KFWS was prepared by mixing CC and rice bran (RB) (70:30 on a dry matter basis). In Experiment I, the biogas potential of CC and RB were measured and, in Experiment II, the test was conducted with different ratios of KFWS and SM (KFWS: SM = 0:100; 33:67; 67:33; 100:0 by% volatile solids (VS) basis). KFWS produced a 27% higher biogas yield and a 59% higher methane yield compared to CC. The specific biogas yields increased by 19, 40 and 57% with KFWS-33%, KFWS-67% and KFWS-100%, respectively compared to SM-100% (394 mL/g VS). Similarly, VS removal increased by 37, 51 and 74% with KFWS-33%, KFWS-67% and KFWS-100%, respectively compared to SM-100%. These results suggested that Kimchi factory waste could be effectively treated by making silage, and the silage could be used as a potential co-substrate to enhance biogas production from SM digesters. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Kimchi is prepared by fermenting Chinese cabbage (CC). There are many Kimchi factories in Korea and a large quantity of waste is generated from each factory during the trimming processes. Choi and Park (2003) reported that the total annual production of CC is approximately three million tons in Korea and up to 30% of the total production is discarded as waste. Anaerobic digestion could be a good approach for CC waste utilization and energy generation; however, CC waste is seasonal and it may accumulate in quantities larger than needed for immediate use. The high moisture content (>95%) in CC causes fast spoilage, thus ensiling has been envisioned for storage before biogas production (Herrmann et al., 2011; Zubr, ⇑ Corresponding author. Tel.: +82 33 250 6492; fax: +82 33 255 6406. E-mail addresses: gopikafl[email protected] (G.K. Kafle), (S.H. Kim). 1 Tel.: +82 33 250 6490; fax: +82 33 255 6406.
[email protected]
0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.08.066
1986). Since CC has too high of a moisture content (>95%) for ensiling, its moisture content needs to be reduced by drying or maceration or mixing with the other feed materials with a low moisture content. Like CC, rice bran (RB) is an agricultural byproduct, which is produced in large quantities by rice processing industries. RB has a low moisture contents (10–15% w.b.), can be preserved for a long time, and could be mixed with CC in order to maintain a suitable range of moisture contents for silage preparation. Anaerobic digestion tends to fail without the addition of external nutrients and buffering agents (Demirel and Scherer, 2008); therefore, co-digestion with substrates having a high buffering capacity (alkalinity) such as manure can be a good alternative for effective treatment of highly biodegradable materials. Therefore, the objective of the present study was to determine the feasibility of anaerobic co-digestion of Kimchi factory waste silage (KFWS) with swine manure (SM). The biogas potential of CC, RB, and KFWS and of KFWS mixed at different ratios with SM was determined for mesophilic conditions.
490
G.K. Kafle et al. / Bioresource Technology 124 (2012) 489–494
2. Methods 2.1. Silage preparation KFWS was prepared by mixing CC and RB at a ratio of 70:30 (d.m. basis). The mixture was fermented in anaerobic plastic bags for 22 days at 30 °C. The characteristics of CC, RB, KFWS and inoculums are shown in Table 1. 2.2. Experimental design and biogas measurement The experimental design for each experiment is shown in Table 2. Experiments I and II were carried out in 1.2 L glass bottles (liquid volume of 0.8 L). The feed to inoculum (F/I) ratio was calculated based on the initial VS of substrate and inoculums. Each digester was mixed manually for 20–30 s once a day before gas volume measurements. The daily biogas production of each digester was determined by the volume of biogas produced, which was calculated from the volume and pressure in the headspace of the digester (EI-Mashad and Zhang, 2010; Liu et al., 2009). Biogas composition was analyzed using a gas analyzer (BioGas Check- Geotechnical Instruments (UK) Ltd.) (Kafle et al., 2012; Kafle and Kim, 2011). The measured wet biogas and methane volumes were adjusted to
the volumes at standard temperature (0 °C) and pressure (1 atm) (VDI 4630, 2006). The mass removal in the form of biogas at the end of the experiment was calculated using Eq. (1). The density of CH4 was taken as 0.000668 g/mL and density of CO2 as 0.00184 g/ mL.
BR ¼
V 0 qmix m
ð1Þ
Where,BR = mass of biogas removed per gram TS or VS added (g/g VSadded or g/g TSadded))V0 = volume of biogas produced (ml, at standard temperature and pressure (STP))qmix = mass concentration of CH4 + CO2 in the biogas (g/mL)m = TS or VS added (g) 2.3. Analytical methods Total solids (TS), volatile solids (VS), NH3–N, total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD) and pH were determined according to standard methods (APHA, 1998). Total Kjeldahl nitrogen (TKN) was analyzed using a Kjeldahl apparatus (Kjeltec 2100, Foss, Sweden) and ammonia (NH3–N) was determined using the Nessler method with measurements on a spectrophotometer (DR 2500, Hach, USA). TVFA (total volatile fatty acids), TA (total alkalinity) and TVFA/TA ratio were determined
Table 1 Characteristics of materials used. Feed
Units
TS VS VS/TS ratio TVFA TA TVFA/TA ratio pH TCOD SCOD TKN
% % mg/L mg/L
mg/L mg/L mg/L %, w.b. mg/L
NH3–N C/N ratio
Experiment I
Experiment II
CC
RBa
Inoculumb
KFWS
SM
Inoculumb
3.65 3.04 0.83 1147 591 1.941 6.5 34,800 17,560 1540 – 135 10.5
90.16 80.66 0.89 11,300 1940 5.82 5.50 – – – 2.052 2800 21.8
1.605 0.64 0.40 1164 12,778 0.091 8.25 8000 4907 2703 – 2930 1.3
33.47 30.2 0.90 9470 5690 1.664 5.10 406,200 61,600 – 0.987 1550 17.0
4.16 2.48 0.60 4200 15,053 0.279 8.05 53,000 12,100 6100 – 4420 2.3
1.15 0.469 0.41 536 10,650 0.050 8.20 7000 1560 2731 – 2280 1.0
–: Not determined. C/N ratio: Carbon to nitrogen ratio (TOC/ TKN). SM: Swine manure; CC: Chinese cabbage; RB: Rice bran; KFWS: Kimchi factory waste silage. a Fresh rice bran (without oil removal). b Digested slurry obtained from SM digester operating at mesophilic temperature.
Table 2 Experimental design. F/I ratio
Substrate loading (g VS/L)
Feed composition (% VS basis)
No. of replications
Purpose
Experiment I
0.5
2.5
3
To determine the biogas potential and biogas production rate of CC and RB.
Experiment II
0.5
2.5
CC: SM = 100:0 (CC100%) RB: SM = 100:0 (RB100%) KFWS: SM = 0:100 (SM-100%) KFWS: SM = 33:67 (CCRB-33%) KFWS: SM = 33:67 (CCRB-67%) KFWS: SM = 100:0 (CCRB-100%)
2
To determine the effect of different mixture ratios of KFWS and SM on biogas yield and digester performance.
F/I ratio: Feed to inoculum ratio (g VS substrate added/g VS inoculums added). g VS/L: Gram volatile solids per liter. SM: Swine manure; CC: Chinese cabbage; RB: Rice bran; KFWS: Kimchi factory waste silage.
G.K. Kafle et al. / Bioresource Technology 124 (2012) 489–494
491
Fig. 1. (a) Cumulative biogas yield; (b) methane contents for Chinese cabbage (CC-100%) and rice bran (RB-100%). The values are means ± standard deviations (vertical bars, n = 3rd deviations).
using the Nordmann-titration method (Kafle and Kim, 2011). The TOC (total organic carbon) was calculated using the formula, TOC = VS/1.8 (Haug, 1993). The TS and VS removal of feed during the batch test were calculated based on total mass removal from the testing reactors and the blank reactors (EI-Mashad and Zhang, 2010). 2.4. Statistical analysis The significance of differences in average biogas yields, methane yields, pH, and TS, VS removal were determined by single factor ANOVA (Analysis of Variance) using Excel software 2007. Least Significant Difference (LSD) was calculated to judge whether two or more averages were significantly different (EI-Mashad and Zhang, 2010). 3. Results and discussion 3.1. Biogas potential of CC and RB (Experiment I) The cumulative biogas yield (mL/g VS) and methane contents (%) during the digestion of CC (CC-100%) and RB (RB-100%) are
shown in Fig. 1. Biogas production started immediately on the first day. The specific biogas yield in CC-100% and RB-100% increased until day 40 and 43, respectively and gradually leveled off thereafter. Around 90% of biogas yield was obtained within 36 and 48 days of digestion for CC-100% and RB-100%, respectively. The biogas potential for CC-100% and RB-100% was 450 and 649 mL/g VS added, respectively on day 90. The LSD values for biogas yield were 58 and 82 mL/g VS added at significance levels of 5 and 1%, respectively. The biogas potential of RB was significantly higher (p < 0.01) than that of CC (Table 4). Thus the silage prepared from a mixture of CC and RB (used in Experiment II) was expected to increase the biogas yield compared to CC alone. The weight average methane contents from CC-100% and RB-100% were 57.7 and 60.4%, respectively (Table 4). Thus the methane potentials for CC-100% and RB-100% were 260 and 392 mL/g VS added. The LSD values for methane yield were 40 and 56 mL/g VS added at significance levels of 5 and 1%, respectively. The methane potential of RB was significantly higher (p < 0.01) than that of CC. Labatut et al. (2011) reported a similar methane potential of 256.6 mL/g VS added for cabbage. The H2S concentration in biogas from RB-100% was lower than that of CC-100% (data not shown). The initial and final characteristics of digester contents from the CC-100% and RB-100%
492
G.K. Kafle et al. / Bioresource Technology 124 (2012) 489–494
Table 3 Initial and final characteristics of the digester contents. Experiment
Experiment Ia
Feed
CC-100%
RB-100%
SM-100%
KFWS-33%
KFWS-67%
KFWS-100%
OLR (g VS/L) F/I ratio TVFA (mg/L)
2.5 0.5 856(26) 734(71) 9612(147) 10,417(61) 0.089(0.003) 0.070(0.007) 8.21(0.03) 7.84(0.02) 2160(60) 2360(310) 2773(20) 2822(10) – 6560(100) – 4480(324) 1.39(0.00) 0.87(0.07)
2.5 0.5 794(54) 621(80) 9887(206) 10,104(289) 0.080(0.004) 0.062(0.008) 8.14(0.01) 7.83(0.01) 2240(171) 2580(53) 2815(40) 2738(10) – 8320(427) – 2898(215) 1.46(0.05) 1.01(0.04)
2.5 0.5 813(31) 663(10) 9713(148) 10,295(8) 0.084(0.004) 0.064(0.001) 8.08(0.01) 8.03(0.04) 2080(0) 3260(28) – – 12,400(414) 10,240(0) 3960(170) 2053(0) – –
2.5 0.5 753(39) 718(56) 9077(151) 10,154(76) 0.095(0.020) 0.075(0.005) 8.08(0.01) 7.94(0.01) 1920(170) 2710(42) – – 11,547(37) 7520(830) 4094(207) 1920(0) – –
2.5 0.5 735(66) 680(54) 8605(137) 9414(108) 0.085(0.006) 0.072(0.007) 8.05(0.00) 7.86(0.01) 1820(28) 2390(14) – – 10,934(302) 6240(0) 5760(453) 1840(113) – –
2.5 0.5 554(35) 738(47) 8046(94) 9030(14) 0.069(0.004) 0.082(0.005) 8.05(0.01) 7.86(0.01) 1720(170) 2150(14) – – 10,960(490) 5814(377) 4613(113) 1520(0) – –
TA (mg/L) TVFA/TA ratio pH NH3–N (mg/L) TKN (mg/L) TCOD (mg/L) SCOD (mg/L) C/N ratio
Initial Final Initial Final Initial Final Initial Final Initial Final Initial Final Initial Final Initial Final Initial Final
Experiment IIb
OLR: Organic loading rate. F/I ratio: Feed to inoculum ratio. C/N ratio: Carbon to nitrogen ratio (TOC/TKN). SM: Swine manure; CC: Chinese cabbage; RB: Rice bran; KFWS: Kimchi factory waste silage. a Values are expressed as mean (standard deviation, n = 3). b Values are expressed as mean (standard deviation, n = 2).
digesters are shown in Table 3. There was no significant difference in final pH between CC-100% and RB-100%. The LSD values for TS removal were 14 and 20% and were 16 and 23% for VS removal; at significance levels of 5 and 1%, respectively. There was no significant difference in TS and VS removal between CC-100% and RB100%. 3.2. Effect of co-digestion of KFWS with SM (Experiment II) The cumulative biogas yield (mL/g VS) and methane contents (%) for different ratios of KFWS and SM are shown in Fig. 2. Biogas production started immediately. The specific biogas yield (mL/g VS) increased until days 23, 24, 29 and 32 in SM-100%, KFWS-33%, KFWS-67% and KFWS-100% digesters, respectively and then gradually leveled off. Around 90% of biogas yield was obtained within 25, 26, 28 and 31 days of digestion from SM100%, KFWS-33%, KFWS-67% and KFWS-100% digesters, respectively. The biogas potential was 394, 467, 552, and 620 mL/g VS added for SM-100%, KFWS-33%, KFWS-67% and KFWS-100%, respectively at 90 days. Thus, the specific biogas yield increased by around 19, 40 and 57% for KFWS-33%, KFWS-67% and KFWS100%, respectively compared to swine manure only (SM-100%). The weight average methane contents were 82.6, 75.7, 71.0 and 66.7% for SM-100%, KFWS-33%, KFWS-67% and KFWS-100%, respectively (Table 4). Thus the methane potential was 325, 353, 392, and 413 mL/ g VS for SM-100%, KFWS-33%, KFWS-67% and KFWS-100%, respectively (Table 4). There was no significant difference in methane yields between SM-100 and KFWS-33%; however, the methane yield significantly increased when the KFWS% increased to 67%. There was no significant difference in methane yield between KFWS-67% and KFWS-100%. The methane yield from SM-100% in the current study was higher than that reported by Zhang et al. (2011) (242 mL/g VS) but lower than that reported by Hashimoto (1983) (490–503 mL/g VS). The specific methane yields increased by 8.6, 20.6, and 27%, as compared to that obtained from SM-100% when 33, 67 and 100% of KFWS
were added. Li et al. (2011) reported an increase in methane yield from 162 to 220 mL/g VS when the addition of herbal extraction residue (HER) was increased from 10 to 50% during co-digestion with SM. In constrast, Gonzàlez-Fernàndez et al. (2011) reported a low methane yield with co-digestion of algal biomass with SM due to the lower methane potential of algal biomass. The H2S concentration in the biogas increased with an increase in KFWS% (data not shown). The TS and VS removal increased by 48 and 27%, respectively, when KFWS was increased from 33 to 100% (Table 4). 3.3. Relationship between TS, VS removal and mass of biogas removed The calculated mass of biogas removed (BR) and TS and VS removals at the end of the 90 days digestion period for Experiments I and II are shown in Table 4. The measured TS and VS removals showed good correlation (R2 > 0.90, data not shown) with BR. Theoretically, the calculated biogas mass removal should be higher than the measured VS destructions (Richards et al., 1991). In the present study, although there was good agreement between biogas mass removal and measured VS destructions, the calculated VS destruction was always higher than the calculated biogas mass removed (Table 4). The CC-100% showed a maximum difference of 29.3% compared to the calculated BR as shown in Table 4. Similar to these results, Liu et al. (2009) reported a maximum difference of 23% during anaerobic digestion of food and green waste. 4. Conclusions Kimchi factory waste silage (KFWS) produced significantly higher (p < 0.01) biogas and methane than Chinese cabbage (CC). The biogas yield and TS and VS removal were higher for the mixture of KFWS and swine manure (SM) than SM alone. The biogas yield was increased by around 19% to 57% and VS removal was increased by around 37% to 74% when KFWS content in the feed
493
G.K. Kafle et al. / Bioresource Technology 124 (2012) 489–494
Fig. 2. (a) Cumulative biogas yield; (b) methane contents for different feed mixture ratios of SM and KFWS. The values are means ± standard deviations (vertical bars, n = 2nd deviations).
Table 4 Calculated gas potential, TS and VS removal and BR values for different feed mixtures. Parameters
Units
Biogas potential Methane potential Methane content TS removal VS removal BR
mL/g VS mL/g VS % % % g/g VS added g/g TS added
Experiment Ia
Experiment IIb
CC-100%
RB-100%
SM-100%
KFWS-33%
KFWS-67%
KFWS-100%
450(27) 260(15) 57.7(0.4) 59.6(3.5) 88.9(4.0) 0.524(0.032) 0.435(0.027)
649(34) 392(21) 60.4(0.7) 69.0(5.1) 77.0(8.3) 0.734(0.039) 0.653(0.035)
394(44) 325(33) 82.6(0.4) 28.6(0.2) 43.4(1.9) 0.344(0.042) 0.206(0.025)
467(0) 353(1) 75.7(0.2) 46.3(3.6) 59.5(9.3) 0.445(0.001) 0.300(0.001)
552(4) 392(0) 71.0(0.6) 56.6(4.4) 65.5(4.5) 0.556(0.008) 0.430(0.006)
620(1) 413(2) 66.7(0.4) 68.5(11.9) 75.7(8.4) 0.656(0.004) 0.590(0.004)
BR: Mass of biogas removed. SM: Swine manure; CC: Chinese cabbage; RB: Rice bran; KFWS: Kimchi factory waste silage. a Values are expressed as mean (standard deviation, n = 3). b Values are expressed as mean (standard deviation, n = 2).
increased from 33% to 100%. Thus, the Kimchi factory waste can be treated in an environmentally friendly process by making silage which can be co-digested with SM to improve biogas production from anaerobic digesters operating with SM.
Acknowledgements This work was supported by a research grant from the Rural Development Administration (RDA), Republic of Korea.
494
G.K. Kafle et al. / Bioresource Technology 124 (2012) 489–494
References APHA, 1998. Standard Methods for the Examination of Water and Wastewater, 20th ed. American Public Health Association, Washington, DC. Choi, M.H., Park, Y.H., 2003. Production of Yeast biomass using waste Chinese cabbage. Biomass Bioenergy 25, 221–226. Demirel, B., Scherer, P., 2008. Production of methane from sugarbeet silage without manure addition by a single-stage anaerobic digestion process. Biomass Bioenergy 32, 203–209. EI-Mashad, H.M., Zhang, R., 2010. Biogas production from co-digestion of dairy manure and food waste. Bioresour. Technol. 101, 4021–4028. Gonzàlez-Fernàndez, C., Molinuevo-Salces, B., Garci9 a-Gonzàlez, M.C., 2011. Evaluation of anaerobic codigestion of microalgal biomass and swine manure via response surface methodology. Appl. Energy 88, 3448–3453. Hashimoto, A.G., 1983. Thermophilic and mesophilic anaerobic fermentation of swine manure. Agric. Wastes 6, 175–191. Haug, R.T., 1993. The Practical Handbook of Composting Engineering. Lewis publisher, Ann Arbor, MI. Herrmann, C., Heiermann, M., Idler, C., 2011. Effects of ensiling, silage additives and storage period on methane formation of biogas crops. Bioresour. Technol. 102, 5153–5161. Kafle, G.K., Kim, S.H., 2011. Sludge exchange process on two serial CSTRs anaerobic digestions: process failure and recovery. Bioresour. Technol. 102, 6815–6822.
Kafle, G.K., Kim, S.H., Shin, B.S., 2012. Anaerobic digestion treatment for the mixture of Chinese cabbage waste juice and swine manure. J. Biosyst. Eng. 37 (1), 58–64. Labatut, R.A., Angenent, L.T., Scott, N.R., 2011. Biochemical methane potential and biodegradability of complex organic substrates. Bioresour. Technol. 102, 2255– 2264. Li, Y., Yan, X.L., Fan, J.P., Zhu, J.H., 2011. Feasibility of biogas production from anaerobic co-digestion of herbal-extraction residues with swine manure. Bioresour. Technol. 102 (11), 6458–6463. Liu, G., Zhang, R., EI-Mashad, H.M., Dong, R., 2009. Effect of feed to inoculum ratios on biogas yields of food and green wastes. Bioresour. Technol. 100, 5103–5108. Richards, B.K., Uummings, R.J., White, T.E., Jewell, W., 1991. Methods for kinetic analysis of methane fermentation in high solids biomass digesters. Biomass Bioenergy 1 (2), 65–73. VDI 4630, 2006. Fermentation of organic materials, characterisation of substrate, sampling, collection of material data, fermentation tests, VDI gesellschaft energietechnik. Zhang, L., Lee, Y.W., Jahng, D., 2011. Anaerobic co-digestion of food waste and piggery wastewater: focusing on the role of trace elements. Bioresour. Technol. 102 (8), 5048–5059. Zubr, J., 1986. Methanogenic fermentation of fresh and ensiled plant materials. Biomass 11 (3), 159–171.