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Low greenhouse gas emissions during composting of solid swine manure
Animal Feed Science and Technology 166–167 (2011) 550–556
Contents lists available at ScienceDirect
Animal Feed Science and Technology journal homepage: www.elsevier.com/locate/anifeedsci
Low greenhouse gas emissions during composting of solid swine manure K.-H. Park ∗ , J.H. Jeon, K.H. Jeon, J.H. Kwag, D.Y. Choi Animal Environment Division, National Institute of Animal Science, Suwon 441-706, Republic of Korea
a r t i c l e
Keywords: Climate change Chimney effect Natural composting Mega chamber
i n f o
a b s t r a c t Methane and N2 O fluxes during composting of solid swine manure were studied using three aeration systems being, forced aeration (FA), wire mesh (WM) and turnover (TO) and no aeration, for 85 d to suggest strategies of mitigating GHG emissions during composting. Manure was collected from a swine research barn by a scraper system and mixed with sawdust as a bulking agent. The manure sawdust mixture was placed in linear low density polyethylene containers for each composting method. A steady state chamber covering each container was used to measure CH4 and N2 O fluxes during composting in order to sample temporal and spatial heterogeneous fluxes. Air samples were continuously analyzed for CH4 and N2 O by a high frequency trace gas analyzer. Mean CH4 fluxes from FA, WM, TO, and no aeration were 5.2, 3.8, 7.5, and 34.6 g/m2 /s, respectively. Mean N2 O fluxes from FA, WM, TO, and no aeration were 1.6, 3.1, 7.9, and 11.4 g/m2 /s, respectively. Ratios of CO2 equiv. emitted from FA, WM, TO and no aeration were 0.14, 0.24, and 0.59, respectively. Nitrous oxide was the main contributor to CO2 -equiv. fluxes. The FA system had the lowest emissions, but WM had the advantage of not requiring electricity for aeration. This paper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors: K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Atmospheric concentrations of CO2 , CH4 and N2 O have increased over the last 200 yr. This increase has led to concerns related to enhancement of the greenhouse effect, and its implications for climate change (IPCC, 2001). The agricultural sector accounted for 2.5% of Korea’s total greenhouse gas (GHG) emissions in 2006 (Ministry of Knowledge Economy, 2009). Methane and N2 O are the main GHG emitted from livestock agriculture accounting for 20% and 13% of those gases emitted, respectively. Methane and N2 O emissions from enteric fermentation and manure treatment related to livestock accounted for ∼40% of the agricultural sector’s CO2 -equiv. emissions. The GHG emissions from the Korean livestock sector increased from 4.8 in 1990 to 6.1 Mt CO2 -equiv. in 2006 (Ministry of Knowledge Economy, 2009). Hence, mitigation of GHG from manure management could play a role in reduction of Korean GHG emissions. Anaerobically stored liquid manure is a source of CH4 , but not N2 O, while stored solid manure is a source of CH4 and N2 O (Thompson et al., 2004; Park et al., 2006). Composting has been proposed to mitigate GHG emissions when sufficient
Abbreviations: FA, forced aeration; GHG, greenhouse gas; LLDPE, linear low-density polyethylene; TO, turnover; WM, wire mesh. ∗ Corresponding author. Tel.: +82 31 290 1718; fax: +82 31 290 1731. E-mail address: [email protected] (K.-H. Park). 0377-8401/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.anifeedsci.2011.04.078
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aeration is used (Thompson et al., 2004; Pattey et al., 2005). Pattey et al. (2005) reported that GHG emissions from aerobic composting and a cattle manure stockpile on a CO2 -equiv. basis were 22–52% and 33–76% of emissions from slurry, respectively. Thompson et al. (2004) reported that CH4 and N2 O emissions during composting of liquid swine manure with straw were influenced by aeration. Total GHG emissions from forced aeration or mechanical turning after curing were 30–50% and 227–455%, respectively of emissions from stored liquid swine manure. Given the contrasting nature of optimal conditions for CH4 and N2 O production, and the contrasting global warming potential of these gases, comprehensive studies over the whole composting process are needed to define the extent to which these GHG are produced. Our objectives were to compare effects of aeration methods on CH4 and N2 O emissions and to suggest strategies of mitigating GHG emissions during composting. 2. Materials and methods 2.1. Composting operation The research took place at the National Institute of Animal Science (NIAS) in Suwon, Korea from June 15 to September 09 (2009). Solid swine manure was collected by scrapers and stored in a manure storage covered by a roof. Solid swine manure was mixed with sawdust as a bulking agent yielding a moisture content of 614 ± 5.8 g/kg (n = 4). To compare effects of aeration method on GHG emissions, composting used three methods being forced aeration (FA), wire mesh (WM), and turnover (TO), plus no aeration (Control). The manure sawdust mixture (Mixture; 400 kg) was placed in linear low-density polyethylene (LLDPE) containers (135 cm × 145 cm × 100 cm) for each composting aeration method. Two thermocouples were placed in the middle of each compost pile and temperature was recorded every minute using a datalogger (CR1000, Campbell Scientific Inc., Logan, UT, USA). The compost temperature was recorded from Day 3 at 19:00 h. An aeration fan was connected to the FA system through 100 mm diameter PVC pipes. Pipes within the container had a 1 cm diameter hole every 5 cm on the centerline of pipes and the mixture was placed over the PVC pipes. The aeration fan was controlled by the datalogger dependant on composting temperature. The WM system was designed to facilitate natural aeration through a ‘chimney effect’ early in composting. Wire mesh was tied on a 135 cm × 145 cm steel angle support and the 12 cm height support was placed in the composting container, which resulted in a 0.235 m3 space below the steel angle support. Hence, air was passively drawn through the bottom area of the mixture. The TO and Control systems were not continuously aerated but, for TO, compost was mixed by hand weekly. Air was continuously sampled, even during turnover. 2.2. Forced aeration Aeration for FA was started at 19:00 h on Day 3 for 15 min every 45 min. This aeration regime resulted in a sharp drop in temperature to 25 ◦ C. Aeration time was stopped at 11:15 h on Day 4 in order to allow the temperature to increase and to restart the regime of 15 min every h at 14:00 on Day 5. Aeration time was adjusted to 5 min every h at 14:00 h on Day 9 as compost temperature decreased below 50 ◦ C. Aeration was stopped at 11:00 h on Day 11 because compost temperature had declined below 50 ◦ C. Aeration was restarted at 11:30 h on Day 12 for 2 min every 30 min, then changed to 1 min/h at 11:30 on Day 13, and stopped at 15:30 h on Day 14 as compost temperature declined to 40 ◦ C. No aeration was supplied thereafter and compost temperature did not exceed 50 ◦ C. 2.3. CH4 and N2 O concentration measurement and compost composition analysis Each composting system was placed inside a 180 cm × 180 cm × 200 cm steady state chamber. Each chamber was connected by a flexible plastic tube with a 20 cm diameter to an air blower with a controller (Fig. 1). Air flow rate was controlled dependant on the extent of CH4 and N2 O emissions. Eight air intakes for background air samples were installed around the chambers and 2 air intakes for exhausted air samples were placed on the flexible tube of each chamber. Air samples collected from 16 air intakes were quasi-continuously analyzed by a trace gas analyzing system which consisted of one tunable diode laser trace gas analyzer (TGA100A, Campbell Scientific Inc., Logan, UT, USA), a 16 intake manifold unit, a dryer and a vacuum pump (RA0021, Busch, Virginia Beach, VA, USA). Air was sampled at 0.5 L/min through a Swagelok filter (Swagelok, Solon, OH, USA; F series, pore size 7 m) and directly sent to the 16 intake manifold unit through 6.4 mm OD, 3.2 mm ID polyethylene tubing. The manifold unit switched intake air sources every 15 s. At any time, air flow from one site was sent to the TGA100A and air samples from the other 15 intakes were discarded. Air samples were analyzed 10 times/s (10 Hz) with averages estimated during each measurement cycle every 4 min. Compost samples were collected at 3 depths from the surface (i.e., 5, 30, 50 cm) using the method of Carnes and Lossin (1970). Compost samples were sent to the laboratory of Animal Environment Division (Suwon, Korea) for analysis of DM, organic C, Kjeldahl N (TKN), NH4 + -N and NO3 − -N. Statistical difference of C/N ratio and moisture among the 4 systems during the experiment were calculated with linear mixed effects model in R (R Development Core Team, 2008). Sampling time was considered as a random effect, and aeration systems and the interaction of time by aeration systems were considered as fixed effects. Differences among means of treatments were tested using a t-test.
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Fig. 1. Schematics of a steady-state chamber, the placement of four chambers and a blower box, and the air flow in the chamber.
2.4. Calculation of CH4 and N2 O fluxes Methane and N2 O fluxes were calculated as: flux =
FR × c A
where FR is the air flow rate through the chamber (m3 /s), A is the surface area of emitting materials in the chamber (m2 ), and c (mg/m3 ) is the difference in gas densities in the air inlet and outlet of the chamber. The c was calculated as: c =
(cout − cin )TGA × P × M T ×R
where (cout − cin )TGA (ppm) is the concentration difference measured using the TGA100A, P is the atmospheric pressure (Pa), M is the molecular weight of CH4 or N2 O, T is the average temperature (K) of the analyzed air, and R is the universal gas constant (i.e., 8.314 × 103 Pa m3 /kmol/K). Air flow rate was measured vertically and horizontally at 9 positions by a hot wire anemometer (Model 8386A-M, TSI, St. Paul, MN, USA) at the center of the flexible plastic tube in each chamber, 5 and 8 cm from the center of the tube. Statistical difference among the 4 systems on every 4 min CH4 and N2 O fluxes were calculated with ANOVA by Matlab (2009) with function ‘anova1’. 3. Results and discussion 3.1. Temperature and C/N ratio changes Temporal trends of compost temperature every min are in Fig. 2. Compost temperature dropped with aeration and increased with no aeration, as reported by Thompson et al. (2004). Compost temperature of WM decreased slowly over time with the temperature reaching nearly 70 ◦ C. Given the high temperature in the center of the pile during active composting, convective air flow would have occurred (Sommer et al., 2004), and the wire mesh in the bottom of WM system facilitated this convection. Air flow rate measured at the air duct on the bottom of the container on Day 5 was 2.3 L/s. Hence active
K.-H. Park et al. / Animal Feed Science and Technology 166–167 (2011) 550–556
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Fig. 2. Temporal changes of compost temperature and CH4 () and N2 O () fluxes of forced aeration (A), wire mesh (B), turnover (C), and no aeration (D) system. Symbols indicate daily mean and vertical bar represents standard error of the mean.
microbial activity would be anticipated. Turning (TO) resulted in a steep drop in temperature, followed by a gradual increase confirming Thompson et al. (2004). Compost temperature of Control increased to 69 ◦ C on Day 7 and decreased gradually. The C/N ratio was calculated by the ratio of TOC concentration to (TKN + NO3 − -N) concentration (Table 1). In our study, the initial C/N ratio was ∼54 and final C/N ratios of the 4 systems were between 39 and 47. Low moisture content during composting and higher initial C/N ratio than optimal (i.e., 25–30; Smith and Collins, 2007) could slow decomposition of organic matter. Moisture content of compost in the 4 systems was between 500 and 600 g/kg at the beginning and decreased thereafter. Moisture content of FA compost was 300 g/kg after 9 d, whereas in the other 3 systems it was 500 g/kg after 15 d. The C/N ratios of 4 aeration systems were affected by day of composting (P<0.001). There was also an interaction of day of composting by aeration systems (P<0.05). However, there were no differences among aeration systems. The moisture content of the 4 aeration systems were affected by day of composting and aeration system (P<0.001). However, there was no interaction of day by aeration system (Table 1). Tiquia et al. (1996) reported that microbes in spent sawdust bedding
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Table 1 Moisture content and C/N ratio of compost samples from forced aeration (FA), wire mesh (WM), turnover (TO), and no aeration (Control) systems on various sampling dates during the study. The C/N ratio was calculated as the ratio of the concentration of TOC to concentration of (TKN + NO3 − -N). Day
C/N ratio a
FA Jun 15 Jun 24 Jun 29 Jul 13 Jul 20 Jul 27 Aug 03 Aug 10 Aug 17 Aug 24 Aug 31 Sep 07 SEM Day‡ Treatment‡ Day × treatment‡
1 10 15 29 36 43 50 57 64 71 78 85
Moisture content (g/kg) b
WM
ab
TO
ab
Control
†
54.27 59.5†† 63.5 52.6 69.8 64.6 61.5 58.2 63.6 48.6 42.4 47.5 1.70
FAa
WMab
TOb
Controlb
580.4†† 481.1 333.5 283.5 236.2 363.3 202.3 315.4 166.4 158.4 177.1 2.73
491.4 508.1 419.5 389.4 299.5 375.7 310.5 189.9 291.7 274.5 299.1 2.41
634.8†† 496.6 309.8 382.1 343.5 302.1 347.2 332.4 346.7 251.4 320.3 3.54
†
51.4†† 52.0 60.7 56.2 52.3 66.2 48.0 53.9 45.1 37.0 39.8 1.74
65.6 61.4 60.0 64.5 58.9 50.4 56.5 38.9 52.1 35.1 44.7 1.81
58.8†† 60.6 65.1 64.1 59.5 57.4 52.3 43.9 53.2 38.5 39.7 1.88
614.0 320.2†† 369.5 286.1 215.1 208.0 194.5 178.1 164.8 159.3 164.7 162.4 1.74
***
***
NS
***
*
NS
Means followed by different superscripts differ (P<0.05). Number of samples († : 4 samples; †† : 1 sample; no symbol: 3 samples). ‡ Main effects and their interactions on C/N ratio and moisture contents. NS: not significant. * P<0.05. *** P<0.001. a,b
Temperature (oC)
of pig pens remained active at moisture contents of 500–600 g/kg, suggesting that microbial activity in FA may have been compromised. Bernal et al. (2009) reported that the C/N ratio of most mature compost was <20, with ratios of <10 being preferable. Haga (1999) reviewed C/N ratios of composted livestock wastes and recommended a quality index of around 30. Wang and Schuchardt (2010) reported a wide range in C/N ratios of 23–50 for mature compost from vineyard pruning residues. Composts from our four composting systems were mature as they had <400 mg/kg NH4 + -N (data not shown), were dark brown in color and fell within USDA compositional guidelines (Cornell Waste Management Institute, 2004).
70 60 50 40 30 20
CH4 (μg/m2/s)
40 30 20 10 0
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40 30 20 10 0 26
27
28
29
30
Days of Composting Fig. 3. Temporal changes of compost temperature and CH4 fluxes before and after turning over the compost. Each dot of CH4 and N2 O fluxes was marked every 4 min. Arrow indicates the time of turnover.
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3.2. Methane and N2 O fluxes during composting with different aeration methods Methane and N2 O fluxes from the composting systems are in Fig. 2. Methane flux trends of all systems were similar except for scale. Methane fluxes in the FA system varied at the beginning of composting due to physical effects of forced aeration on gas transport. Sudden increases in CH4 fluxes occurred when aeration started and compost temperature decreased. Methane fluxes from the TO system increased during turnover and decreased thereafter. Methane fluxes before turning were higher (P=0.01) than those after turning (Fig. 3). Mean CH4 fluxes differed (P<0.05) among the systems. Nitrous oxide fluxes were low at the beginning of composting and gradually increased after peak compost temperature to be highest in Control followed by TO, WM and FA. Peaks of N2 O fluxes in FA, WM, and Control all occurred after 27 d of composting. Daily mean N2 O fluxes from the TO system peaked on Days 37 and 48. Mean N2 O fluxes differed (P<0.05) among systems. Nitrous oxide fluxes increased just after turning for ∼3 h and then decreased for ∼10 h forming a skewed flux pattern (Fig. 3). Methane and N2 O fluxes were negatively correlated. High CH4 and low N2 O fluxes were measured during periods of high compost temperature (Fig. 2). Thompson et al. (2004) and Sommer et al. (2004) also reported this pattern. The mixture pile had a cone shape so that the depth of the mixture on the side area was narrow. Hence it has been proposed that the lower temperatures on the side of the compost piles are a source of N2 O emissions (Sommer et al., 2004). Comparisons of GHG emissions on a CO2 -equiv. bases were estimated using a 100 yr global warming potential of 25 for CH4 and 298 for N2 O (IPCC, 2007). Methane and N2 O fluxes on a CO2 -equiv. basis differed (P<0.05) among systems and were 605, 1007, 2526, and 4265 g/m2 /s for FA, WM, TO and Control. The ratios of CO2 -equiv. of FA, WM and TO to Control were ∼0.14, 0.24 and 0.59. Ratios of CH4 fluxes of FA, WM, TO, and Control to the CO2 -equiv. were ∼0.22, 0.09, 0.07, and 0.20. Hence, N2 O was the main contributor to CO2 -equiv. That the WM system did not require electricity for aeration would lower CO2 -equiv. as fossil fuels were not required to generate power. 4. Conclusions Compost temperature increased at the beginning, peaked and then decreased in all composting systems. However, there were differences in temperature temporal trends among systems. In the FA system, compost temperature dropped with aeration and increased when aeration ceased. Compost temperature of WM decreased slowly over time. Temperature in the TO system sharply declined during turning and gradually increased thereafter. The Control system had the slowest decline in compost temperature. The C/N ratio decreased in all composting systems over time, but there was substantial variation among systems. Methane flux trends of all systems were similar, except the scale. Methane fluxes from the TO system had a sudden increase during turnover and then a decrease. Nitrous oxide fluxes were low at the beginning and gradually increased after peak compost temperature. Nitrous oxide fluxes were highest from the Control, followed by TO, WM and FA. Nitrous oxide fluxes increased immediately after turning and then decreased resulting in a skewed flux pattern. Expressed on CO2 -equiv., FA, WM, TO and Control systems emitted 605, 1007, 2526, and 4265 g/m2 /s. Nitrous oxide was the main contributor to CO2 -equiv., and the FA system had the lowest emissions, but the WM system has advantage because it did not use electricity for aeration. Conflict of interest statement None. Acknowledgements The authors thank Ms. M.S. Jeong and Ms. S.J. Lee for their help with laboratory work. References Bernal, M.P., Alburquerque, J.A., Moral, R., 2009. Composting of animal manures and chemical criteria for compost maturity assessment. A review. Bioresour. Technol. 100, 5444–5453. Carnes, R.A., Lossin, R.D., 1970. An investigation of the pH characteristics of compost. Compost. Sci. 11 (5), 18–21. Cornell Waste Management Institute, 2004. Compost Fact Sheet #2: Regulation and Certification of Composts., www.cwmi.css.cornell.edu/compostfs2.pdf. Haga, K., 1999. Development of composting technology in animal waste treatment – review. Asian-Aust. J. Anim. Sci. 12 (4), 604–606. IPCC, 2001. Climate Change 2001: The Scientific Basis. Cambridge University Press, Cambridge, UK. IPCC, 2007. IPCC fourth assessment report: climate change 2007 (AR4), Cambridge University Press, Cambridge, UK. Matlab, 2009. Matlab 7.8.0 (R2009a). The MathWorks Inc., Natick, MA, USA. Ministry of Knowledge Economy, 2009. 3rd national greenhouse gas inventory meeting, Ministry of Knowledge Economy, Gwacheon, Gyeonggi, Korea. Park, K.H., Thompson, A.G., Marinier, M., Clark, K., Wagner-Riddle, C., 2006. Greenhouse gas emissions from stored liquid swine manure in a cold climate. Atmos. Environ. 40, 618–627. R Development Core Team, 2008. R: a language and environment for statistical computing. In: R Foundation for Statistical Computing, Vienna, Austria. Pattey, E., Trzcinski, M.K., Desjardins, R.L., 2005. Quantifying the reduction of greenhouse gas emissions as a result of composting dairy and beef cattle manure. Nutr. Cycl. Agroecosyst. 72, 173–187. Smith, J.L., Collins, H.P., 2007. Management of organisms and their processes in soils. In: Paul, E.A. (Ed.), Soil Microbiology, Ecology, and Biochemistry. Academic Press, Burlington, MA, USA, pp. 471–502.
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Sommer, S.G., McGinn, S.M., Hao, X., Larney, F.J., 2004. Techniques for measuring gas emissions from a composting stockpile of cattle manure. Atmos. Environ. 38, 4643–4652. Thompson, A.G., Wagner-Riddle, C., Fleming, R., 2004. Emissions of N2 O and CH4 during the composting of liquid swine manure. Environ. Monit. Assess. 91, 87–104. Tiquia, S.M., Tam, N.F.Y., Hodgkiss, I.J., 1996. Microbial activities during composting of spent pig-manure sawdust litter at different moisture contents. Bioresour. Technol. 55, 201–206. Wang, Y.Q., Schuchardt, F., 2010. Effect of C/N ratio on the composting of vineyard pruning residues. Landbauforsch. Volkenrode. 60 (3), 131–138.
Contents lists available at ScienceDirect
Animal Feed Science and Technology journal homepage: www.elsevier.com/locate/anifeedsci
Low greenhouse gas emissions during composting of solid swine manure K.-H. Park ∗ , J.H. Jeon, K.H. Jeon, J.H. Kwag, D.Y. Choi Animal Environment Division, National Institute of Animal Science, Suwon 441-706, Republic of Korea
a r t i c l e
Keywords: Climate change Chimney effect Natural composting Mega chamber
i n f o
a b s t r a c t Methane and N2 O fluxes during composting of solid swine manure were studied using three aeration systems being, forced aeration (FA), wire mesh (WM) and turnover (TO) and no aeration, for 85 d to suggest strategies of mitigating GHG emissions during composting. Manure was collected from a swine research barn by a scraper system and mixed with sawdust as a bulking agent. The manure sawdust mixture was placed in linear low density polyethylene containers for each composting method. A steady state chamber covering each container was used to measure CH4 and N2 O fluxes during composting in order to sample temporal and spatial heterogeneous fluxes. Air samples were continuously analyzed for CH4 and N2 O by a high frequency trace gas analyzer. Mean CH4 fluxes from FA, WM, TO, and no aeration were 5.2, 3.8, 7.5, and 34.6 g/m2 /s, respectively. Mean N2 O fluxes from FA, WM, TO, and no aeration were 1.6, 3.1, 7.9, and 11.4 g/m2 /s, respectively. Ratios of CO2 equiv. emitted from FA, WM, TO and no aeration were 0.14, 0.24, and 0.59, respectively. Nitrous oxide was the main contributor to CO2 -equiv. fluxes. The FA system had the lowest emissions, but WM had the advantage of not requiring electricity for aeration. This paper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors: K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Atmospheric concentrations of CO2 , CH4 and N2 O have increased over the last 200 yr. This increase has led to concerns related to enhancement of the greenhouse effect, and its implications for climate change (IPCC, 2001). The agricultural sector accounted for 2.5% of Korea’s total greenhouse gas (GHG) emissions in 2006 (Ministry of Knowledge Economy, 2009). Methane and N2 O are the main GHG emitted from livestock agriculture accounting for 20% and 13% of those gases emitted, respectively. Methane and N2 O emissions from enteric fermentation and manure treatment related to livestock accounted for ∼40% of the agricultural sector’s CO2 -equiv. emissions. The GHG emissions from the Korean livestock sector increased from 4.8 in 1990 to 6.1 Mt CO2 -equiv. in 2006 (Ministry of Knowledge Economy, 2009). Hence, mitigation of GHG from manure management could play a role in reduction of Korean GHG emissions. Anaerobically stored liquid manure is a source of CH4 , but not N2 O, while stored solid manure is a source of CH4 and N2 O (Thompson et al., 2004; Park et al., 2006). Composting has been proposed to mitigate GHG emissions when sufficient
Abbreviations: FA, forced aeration; GHG, greenhouse gas; LLDPE, linear low-density polyethylene; TO, turnover; WM, wire mesh. ∗ Corresponding author. Tel.: +82 31 290 1718; fax: +82 31 290 1731. E-mail address: [email protected] (K.-H. Park). 0377-8401/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.anifeedsci.2011.04.078
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aeration is used (Thompson et al., 2004; Pattey et al., 2005). Pattey et al. (2005) reported that GHG emissions from aerobic composting and a cattle manure stockpile on a CO2 -equiv. basis were 22–52% and 33–76% of emissions from slurry, respectively. Thompson et al. (2004) reported that CH4 and N2 O emissions during composting of liquid swine manure with straw were influenced by aeration. Total GHG emissions from forced aeration or mechanical turning after curing were 30–50% and 227–455%, respectively of emissions from stored liquid swine manure. Given the contrasting nature of optimal conditions for CH4 and N2 O production, and the contrasting global warming potential of these gases, comprehensive studies over the whole composting process are needed to define the extent to which these GHG are produced. Our objectives were to compare effects of aeration methods on CH4 and N2 O emissions and to suggest strategies of mitigating GHG emissions during composting. 2. Materials and methods 2.1. Composting operation The research took place at the National Institute of Animal Science (NIAS) in Suwon, Korea from June 15 to September 09 (2009). Solid swine manure was collected by scrapers and stored in a manure storage covered by a roof. Solid swine manure was mixed with sawdust as a bulking agent yielding a moisture content of 614 ± 5.8 g/kg (n = 4). To compare effects of aeration method on GHG emissions, composting used three methods being forced aeration (FA), wire mesh (WM), and turnover (TO), plus no aeration (Control). The manure sawdust mixture (Mixture; 400 kg) was placed in linear low-density polyethylene (LLDPE) containers (135 cm × 145 cm × 100 cm) for each composting aeration method. Two thermocouples were placed in the middle of each compost pile and temperature was recorded every minute using a datalogger (CR1000, Campbell Scientific Inc., Logan, UT, USA). The compost temperature was recorded from Day 3 at 19:00 h. An aeration fan was connected to the FA system through 100 mm diameter PVC pipes. Pipes within the container had a 1 cm diameter hole every 5 cm on the centerline of pipes and the mixture was placed over the PVC pipes. The aeration fan was controlled by the datalogger dependant on composting temperature. The WM system was designed to facilitate natural aeration through a ‘chimney effect’ early in composting. Wire mesh was tied on a 135 cm × 145 cm steel angle support and the 12 cm height support was placed in the composting container, which resulted in a 0.235 m3 space below the steel angle support. Hence, air was passively drawn through the bottom area of the mixture. The TO and Control systems were not continuously aerated but, for TO, compost was mixed by hand weekly. Air was continuously sampled, even during turnover. 2.2. Forced aeration Aeration for FA was started at 19:00 h on Day 3 for 15 min every 45 min. This aeration regime resulted in a sharp drop in temperature to 25 ◦ C. Aeration time was stopped at 11:15 h on Day 4 in order to allow the temperature to increase and to restart the regime of 15 min every h at 14:00 on Day 5. Aeration time was adjusted to 5 min every h at 14:00 h on Day 9 as compost temperature decreased below 50 ◦ C. Aeration was stopped at 11:00 h on Day 11 because compost temperature had declined below 50 ◦ C. Aeration was restarted at 11:30 h on Day 12 for 2 min every 30 min, then changed to 1 min/h at 11:30 on Day 13, and stopped at 15:30 h on Day 14 as compost temperature declined to 40 ◦ C. No aeration was supplied thereafter and compost temperature did not exceed 50 ◦ C. 2.3. CH4 and N2 O concentration measurement and compost composition analysis Each composting system was placed inside a 180 cm × 180 cm × 200 cm steady state chamber. Each chamber was connected by a flexible plastic tube with a 20 cm diameter to an air blower with a controller (Fig. 1). Air flow rate was controlled dependant on the extent of CH4 and N2 O emissions. Eight air intakes for background air samples were installed around the chambers and 2 air intakes for exhausted air samples were placed on the flexible tube of each chamber. Air samples collected from 16 air intakes were quasi-continuously analyzed by a trace gas analyzing system which consisted of one tunable diode laser trace gas analyzer (TGA100A, Campbell Scientific Inc., Logan, UT, USA), a 16 intake manifold unit, a dryer and a vacuum pump (RA0021, Busch, Virginia Beach, VA, USA). Air was sampled at 0.5 L/min through a Swagelok filter (Swagelok, Solon, OH, USA; F series, pore size 7 m) and directly sent to the 16 intake manifold unit through 6.4 mm OD, 3.2 mm ID polyethylene tubing. The manifold unit switched intake air sources every 15 s. At any time, air flow from one site was sent to the TGA100A and air samples from the other 15 intakes were discarded. Air samples were analyzed 10 times/s (10 Hz) with averages estimated during each measurement cycle every 4 min. Compost samples were collected at 3 depths from the surface (i.e., 5, 30, 50 cm) using the method of Carnes and Lossin (1970). Compost samples were sent to the laboratory of Animal Environment Division (Suwon, Korea) for analysis of DM, organic C, Kjeldahl N (TKN), NH4 + -N and NO3 − -N. Statistical difference of C/N ratio and moisture among the 4 systems during the experiment were calculated with linear mixed effects model in R (R Development Core Team, 2008). Sampling time was considered as a random effect, and aeration systems and the interaction of time by aeration systems were considered as fixed effects. Differences among means of treatments were tested using a t-test.
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Fig. 1. Schematics of a steady-state chamber, the placement of four chambers and a blower box, and the air flow in the chamber.
2.4. Calculation of CH4 and N2 O fluxes Methane and N2 O fluxes were calculated as: flux =
FR × c A
where FR is the air flow rate through the chamber (m3 /s), A is the surface area of emitting materials in the chamber (m2 ), and c (mg/m3 ) is the difference in gas densities in the air inlet and outlet of the chamber. The c was calculated as: c =
(cout − cin )TGA × P × M T ×R
where (cout − cin )TGA (ppm) is the concentration difference measured using the TGA100A, P is the atmospheric pressure (Pa), M is the molecular weight of CH4 or N2 O, T is the average temperature (K) of the analyzed air, and R is the universal gas constant (i.e., 8.314 × 103 Pa m3 /kmol/K). Air flow rate was measured vertically and horizontally at 9 positions by a hot wire anemometer (Model 8386A-M, TSI, St. Paul, MN, USA) at the center of the flexible plastic tube in each chamber, 5 and 8 cm from the center of the tube. Statistical difference among the 4 systems on every 4 min CH4 and N2 O fluxes were calculated with ANOVA by Matlab (2009) with function ‘anova1’. 3. Results and discussion 3.1. Temperature and C/N ratio changes Temporal trends of compost temperature every min are in Fig. 2. Compost temperature dropped with aeration and increased with no aeration, as reported by Thompson et al. (2004). Compost temperature of WM decreased slowly over time with the temperature reaching nearly 70 ◦ C. Given the high temperature in the center of the pile during active composting, convective air flow would have occurred (Sommer et al., 2004), and the wire mesh in the bottom of WM system facilitated this convection. Air flow rate measured at the air duct on the bottom of the container on Day 5 was 2.3 L/s. Hence active
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Fig. 2. Temporal changes of compost temperature and CH4 () and N2 O () fluxes of forced aeration (A), wire mesh (B), turnover (C), and no aeration (D) system. Symbols indicate daily mean and vertical bar represents standard error of the mean.
microbial activity would be anticipated. Turning (TO) resulted in a steep drop in temperature, followed by a gradual increase confirming Thompson et al. (2004). Compost temperature of Control increased to 69 ◦ C on Day 7 and decreased gradually. The C/N ratio was calculated by the ratio of TOC concentration to (TKN + NO3 − -N) concentration (Table 1). In our study, the initial C/N ratio was ∼54 and final C/N ratios of the 4 systems were between 39 and 47. Low moisture content during composting and higher initial C/N ratio than optimal (i.e., 25–30; Smith and Collins, 2007) could slow decomposition of organic matter. Moisture content of compost in the 4 systems was between 500 and 600 g/kg at the beginning and decreased thereafter. Moisture content of FA compost was 300 g/kg after 9 d, whereas in the other 3 systems it was 500 g/kg after 15 d. The C/N ratios of 4 aeration systems were affected by day of composting (P<0.001). There was also an interaction of day of composting by aeration systems (P<0.05). However, there were no differences among aeration systems. The moisture content of the 4 aeration systems were affected by day of composting and aeration system (P<0.001). However, there was no interaction of day by aeration system (Table 1). Tiquia et al. (1996) reported that microbes in spent sawdust bedding
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Table 1 Moisture content and C/N ratio of compost samples from forced aeration (FA), wire mesh (WM), turnover (TO), and no aeration (Control) systems on various sampling dates during the study. The C/N ratio was calculated as the ratio of the concentration of TOC to concentration of (TKN + NO3 − -N). Day
C/N ratio a
FA Jun 15 Jun 24 Jun 29 Jul 13 Jul 20 Jul 27 Aug 03 Aug 10 Aug 17 Aug 24 Aug 31 Sep 07 SEM Day‡ Treatment‡ Day × treatment‡
1 10 15 29 36 43 50 57 64 71 78 85
Moisture content (g/kg) b
WM
ab
TO
ab
Control
†
54.27 59.5†† 63.5 52.6 69.8 64.6 61.5 58.2 63.6 48.6 42.4 47.5 1.70
FAa
WMab
TOb
Controlb
580.4†† 481.1 333.5 283.5 236.2 363.3 202.3 315.4 166.4 158.4 177.1 2.73
491.4 508.1 419.5 389.4 299.5 375.7 310.5 189.9 291.7 274.5 299.1 2.41
634.8†† 496.6 309.8 382.1 343.5 302.1 347.2 332.4 346.7 251.4 320.3 3.54
†
51.4†† 52.0 60.7 56.2 52.3 66.2 48.0 53.9 45.1 37.0 39.8 1.74
65.6 61.4 60.0 64.5 58.9 50.4 56.5 38.9 52.1 35.1 44.7 1.81
58.8†† 60.6 65.1 64.1 59.5 57.4 52.3 43.9 53.2 38.5 39.7 1.88
614.0 320.2†† 369.5 286.1 215.1 208.0 194.5 178.1 164.8 159.3 164.7 162.4 1.74
***
***
NS
***
*
NS
Means followed by different superscripts differ (P<0.05). Number of samples († : 4 samples; †† : 1 sample; no symbol: 3 samples). ‡ Main effects and their interactions on C/N ratio and moisture contents. NS: not significant. * P<0.05. *** P<0.001. a,b
Temperature (oC)
of pig pens remained active at moisture contents of 500–600 g/kg, suggesting that microbial activity in FA may have been compromised. Bernal et al. (2009) reported that the C/N ratio of most mature compost was <20, with ratios of <10 being preferable. Haga (1999) reviewed C/N ratios of composted livestock wastes and recommended a quality index of around 30. Wang and Schuchardt (2010) reported a wide range in C/N ratios of 23–50 for mature compost from vineyard pruning residues. Composts from our four composting systems were mature as they had <400 mg/kg NH4 + -N (data not shown), were dark brown in color and fell within USDA compositional guidelines (Cornell Waste Management Institute, 2004).
70 60 50 40 30 20
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40 30 20 10 0
N2O (μg/m2/s)
40 30 20 10 0 26
27
28
29
30
Days of Composting Fig. 3. Temporal changes of compost temperature and CH4 fluxes before and after turning over the compost. Each dot of CH4 and N2 O fluxes was marked every 4 min. Arrow indicates the time of turnover.
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3.2. Methane and N2 O fluxes during composting with different aeration methods Methane and N2 O fluxes from the composting systems are in Fig. 2. Methane flux trends of all systems were similar except for scale. Methane fluxes in the FA system varied at the beginning of composting due to physical effects of forced aeration on gas transport. Sudden increases in CH4 fluxes occurred when aeration started and compost temperature decreased. Methane fluxes from the TO system increased during turnover and decreased thereafter. Methane fluxes before turning were higher (P=0.01) than those after turning (Fig. 3). Mean CH4 fluxes differed (P<0.05) among the systems. Nitrous oxide fluxes were low at the beginning of composting and gradually increased after peak compost temperature to be highest in Control followed by TO, WM and FA. Peaks of N2 O fluxes in FA, WM, and Control all occurred after 27 d of composting. Daily mean N2 O fluxes from the TO system peaked on Days 37 and 48. Mean N2 O fluxes differed (P<0.05) among systems. Nitrous oxide fluxes increased just after turning for ∼3 h and then decreased for ∼10 h forming a skewed flux pattern (Fig. 3). Methane and N2 O fluxes were negatively correlated. High CH4 and low N2 O fluxes were measured during periods of high compost temperature (Fig. 2). Thompson et al. (2004) and Sommer et al. (2004) also reported this pattern. The mixture pile had a cone shape so that the depth of the mixture on the side area was narrow. Hence it has been proposed that the lower temperatures on the side of the compost piles are a source of N2 O emissions (Sommer et al., 2004). Comparisons of GHG emissions on a CO2 -equiv. bases were estimated using a 100 yr global warming potential of 25 for CH4 and 298 for N2 O (IPCC, 2007). Methane and N2 O fluxes on a CO2 -equiv. basis differed (P<0.05) among systems and were 605, 1007, 2526, and 4265 g/m2 /s for FA, WM, TO and Control. The ratios of CO2 -equiv. of FA, WM and TO to Control were ∼0.14, 0.24 and 0.59. Ratios of CH4 fluxes of FA, WM, TO, and Control to the CO2 -equiv. were ∼0.22, 0.09, 0.07, and 0.20. Hence, N2 O was the main contributor to CO2 -equiv. That the WM system did not require electricity for aeration would lower CO2 -equiv. as fossil fuels were not required to generate power. 4. Conclusions Compost temperature increased at the beginning, peaked and then decreased in all composting systems. However, there were differences in temperature temporal trends among systems. In the FA system, compost temperature dropped with aeration and increased when aeration ceased. Compost temperature of WM decreased slowly over time. Temperature in the TO system sharply declined during turning and gradually increased thereafter. The Control system had the slowest decline in compost temperature. The C/N ratio decreased in all composting systems over time, but there was substantial variation among systems. Methane flux trends of all systems were similar, except the scale. Methane fluxes from the TO system had a sudden increase during turnover and then a decrease. Nitrous oxide fluxes were low at the beginning and gradually increased after peak compost temperature. Nitrous oxide fluxes were highest from the Control, followed by TO, WM and FA. Nitrous oxide fluxes increased immediately after turning and then decreased resulting in a skewed flux pattern. Expressed on CO2 -equiv., FA, WM, TO and Control systems emitted 605, 1007, 2526, and 4265 g/m2 /s. Nitrous oxide was the main contributor to CO2 -equiv., and the FA system had the lowest emissions, but the WM system has advantage because it did not use electricity for aeration. Conflict of interest statement None. Acknowledgements The authors thank Ms. M.S. Jeong and Ms. S.J. Lee for their help with laboratory work. References Bernal, M.P., Alburquerque, J.A., Moral, R., 2009. Composting of animal manures and chemical criteria for compost maturity assessment. A review. Bioresour. Technol. 100, 5444–5453. Carnes, R.A., Lossin, R.D., 1970. An investigation of the pH characteristics of compost. Compost. Sci. 11 (5), 18–21. Cornell Waste Management Institute, 2004. Compost Fact Sheet #2: Regulation and Certification of Composts., www.cwmi.css.cornell.edu/compostfs2.pdf. Haga, K., 1999. Development of composting technology in animal waste treatment – review. Asian-Aust. J. Anim. Sci. 12 (4), 604–606. IPCC, 2001. Climate Change 2001: The Scientific Basis. Cambridge University Press, Cambridge, UK. IPCC, 2007. IPCC fourth assessment report: climate change 2007 (AR4), Cambridge University Press, Cambridge, UK. Matlab, 2009. Matlab 7.8.0 (R2009a). The MathWorks Inc., Natick, MA, USA. Ministry of Knowledge Economy, 2009. 3rd national greenhouse gas inventory meeting, Ministry of Knowledge Economy, Gwacheon, Gyeonggi, Korea. Park, K.H., Thompson, A.G., Marinier, M., Clark, K., Wagner-Riddle, C., 2006. Greenhouse gas emissions from stored liquid swine manure in a cold climate. Atmos. Environ. 40, 618–627. R Development Core Team, 2008. R: a language and environment for statistical computing. In: R Foundation for Statistical Computing, Vienna, Austria. Pattey, E., Trzcinski, M.K., Desjardins, R.L., 2005. Quantifying the reduction of greenhouse gas emissions as a result of composting dairy and beef cattle manure. Nutr. Cycl. Agroecosyst. 72, 173–187. Smith, J.L., Collins, H.P., 2007. Management of organisms and their processes in soils. In: Paul, E.A. (Ed.), Soil Microbiology, Ecology, and Biochemistry. Academic Press, Burlington, MA, USA, pp. 471–502.
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Sommer, S.G., McGinn, S.M., Hao, X., Larney, F.J., 2004. Techniques for measuring gas emissions from a composting stockpile of cattle manure. Atmos. Environ. 38, 4643–4652. Thompson, A.G., Wagner-Riddle, C., Fleming, R., 2004. Emissions of N2 O and CH4 during the composting of liquid swine manure. Environ. Monit. Assess. 91, 87–104. Tiquia, S.M., Tam, N.F.Y., Hodgkiss, I.J., 1996. Microbial activities during composting of spent pig-manure sawdust litter at different moisture contents. Bioresour. Technol. 55, 201–206. Wang, Y.Q., Schuchardt, F., 2010. Effect of C/N ratio on the composting of vineyard pruning residues. Landbauforsch. Volkenrode. 60 (3), 131–138.