Sorption of Pure N2O to Biochars and Other Organic and Inorganic

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Sorption of Pure N2O to Biochars and Other Organic and Inorganic Materials under Anhydrous Conditions Gerard Cornelissen,‡,§,∥,* David W. Rutherford,†,* Hans Peter H. Arp,‡ Peter Dörsch,§ Charlene N. Kelly,† and Colleen E. Rostad† †

U.S. Geological Survey, Denver, Colorado 80225, United States Norwegian Geotechnical Institute (NGI), Department of Environmental Engineering, P.O. Box 3930, Ullevål Stadion, NO-0806 Oslo, Norway § Department of Plant and Environmental Sciences (IPM), Norwegian University of Life Sciences, P.O. Box 5003, NO-1432 Ås, Norway ∥ Department of Applied Environmental Sciences (ITM), Stockholm University, 10691 Sweden ‡

S Supporting Information *

ABSTRACT: Suppression of nitrous oxide (N2O) emissions from soil is commonly observed after amendment with biochar. The mechanisms accounting for this suppression are not yet understood. One possible contributing mechanism is N2O sorption to biochar. The sorption of N2O and carbon dioxide (CO2) to four biochars was measured in an anhydrous system with pure N2O. The biochar data were compared to those for two activated carbons and other components potentially present in soils uncharred pine wood and peatand five inorganic metal oxides with variable surface areas. Langmuir maximum sorption capacities (Qmax) for N2O on the pine wood biochars (generated between 250 and 500 °C) and activated carbons were 17−73 cm3 g−1 at 20 °C (median 51 cm3 g−1), with Langmuir affinities (b) of 2−5 atm−1 (median 3.4 atm−1). Both Qmax and b of the charred materials were substantially higher than those for peat, uncharred wood, and metal oxides [Qmax 1−34 cm3 g−1 (median 7 cm3 g−1); b 0.4−1.7 atm−1 (median 0.7 atm−1)]. This indicates that biochar can bind N2O more strongly than both mineral and organic soil materials. Qmax and b for CO2 were comparable to those for N2O. Modeled sorption coefficients obtained with an independent polyparameterlinear free-energy relationship matched measured data within a factor 2 for mineral surfaces but underestimated by a factor of 5−24 for biochar and carbonaceous surfaces. Isosteric enthalpies of sorption of N2O were mostly between −20 and −30 kJ mol−1, slightly more exothermic than enthalpies of condensation (−16.1 kJ mol−1). Qmax of N2O on biochar (50000−130000 μg g−1 biochar at 20 °C) exceeded the N2O emission suppressions observed in the literature (range 0.5−960 μg g−1 biochar; median 16 μg g−1) by several orders of magnitude. Thus, the hypothesis could not be falsified that sorption of N2O to biochar is a mechanism of N2O emission suppression.

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et al.7 deployed soil columns for two soils over 150 d, and 0.8 wt% biochar treatments decreased N2O emissions by 14−73%. Case et al.8 found in a soil core study that cumulative N2O production within 60 h of wetting was 19−98% lower in treatments with 1−10 wt-% biochar than in a biochar-free control. Van Zwieten et al.10 found in batch microcosms that amendment with 1 and 5 wt-% biochar reduced N2O emissions by 50% and 80%, respectively. In field studies across China, N2O emission reductions were 70%9 (40 t ha−1 biochar), 40%11 (20 t ha−1), and 60%11 (40 t ha−1). Kammann et al.2 found N2O emission reductions up to 60% in biochar−compost systems. In

INTRODUCTION Biochar is waste biomass charcoal that, due to its stability in soil, could provide a wedge in climate change mitigation, while simultaneously improving the fertility and quality of degraded or polluted soils.1 Apart from its carbon sequestration potential, biochar has also been observed to inhibit the formation or emission of the powerful greenhouse gas nitrous oxide (N2O).2−13 This gas is mostly formed as a nonstoichiometric byproduct during microbial ammonia oxidation to NO2− (“nitrification”), as an obligate intermediate during the respiratory reduction of NO3− to N2 (“denitrification”), and in the dissimilatory reduction of NO3− to NH4+ (“DNRA”).14,15 Yanai et al.5 found that 10 wt-% biochar in open laboratory incubations with soil reduced cumulative N2O emissions during a 168-h period by almost 90%. Spokas et al.,6 in 100 d-batch incubations, found N2O emission reductions of up to 75%. Singh © 2013 American Chemical Society

Received: Revised: Accepted: Published: 7704

February 12, 2013 May 24, 2013 June 13, 2013 June 13, 2013 dx.doi.org/10.1021/es400676q | Environ. Sci. Technol. 2013, 47, 7704−7712

Environmental Science & Technology

Article

Table 1. Approximate Literature Observations of N2O Emission Suppression by Biochar, Recalculated into Micrograms of N2O per Gram of Soil or Biochara N2O emissionsb

N2O emissionsb

no biochar

biochar

type of expt

biochar dosage (wt-%)

expt duration

cumulative emission (μg g−1 soil)

open Petri dishes lab; batch lab; batch lab; soil columns lab; soil core field; rice paddy field; sites in China lab; batch lab; batch field; Colombia field; bovine urine patches lab; two paddy soils

10% 1%; 5% 40% 0.8% 1; 2; 5; 10% ∼2% ∼1%; 2% ∼1% ∼2%e ∼1% ∼1.5% ∼2.5%

168 h 47 d 100 d 150 d 60 h 100 d variable 53 d 140 d 365 d 86 d 60 d

31.3 10 0.12 0.1 0.6 0.5 0.1−0.2 80 0.5 not rep.f 0.8 6.2; 28d

avg. prod. rate (ng N2O g−1 soil h−1) 186 9 0.05 0.03 10 0.2 63 0.15 0.4 4.3; 19.4

cumulative emission (μg g−1 soil)

suppression (μg N2O g−1 biochar)

3.3 5; 2 0.03 0.03−0.085 0.012−0.5 0.15 0.06−0.1; 0.05−0.1 130 0.25 not rep.f 0.4 2.4; 4.2 median IQRg

270 150−500 0.15 4−10 5−10 20 50−100 −50c 12 7.5 25 152; 960 16 7−124

ref Yanai et al.5 Van Zwieten et al.10 Spokas et al.6 Singh et al.7 Case et al.8 Zhang et al.9 Liu et al.11 Clough et al.16 Kammann et al.2 Rondon et al.13 Taghizadeh et al.3 Wang et al.12

a For comparison, in the present study the maximum sorption capacity, Qmax, of N2O on biochar was observed to be 50000−130000 μg g−1. In some cases values needed to be estimated from graphs, or recalculated assuming generic values for soil bulk density as well as fertilizer and biochar mixing depth. bEstimated values. cHigher N2O emission from biochar + urine − amended soil than from urine − amended soil. dFor two soils. eFor experiment I, where mean N2O emissions were reported. fNot reported. gIQR, interquartile range.

Table 2. Characteristics of the Sorbent Materialsa BET-SA 2

BC-1 BC-60 BC-176 BC-286 AC-569 AC-775 peat wood Fe2O3 Al2O3-9 Al2O3-175 SiO2-205 SiO2-598 a

wood Biochar; lab wood Biochar; lab wood Biochar; Biochar Engineer Corp. wood Biochar; lab Sargent Welch, SC-11368 Mallinckrodt, lot 4394 Internat. Humic Subs. Soc, Pahokee peat Colorado Ponderosa pine Fisher, FL-01-0987, lot 941503 Alcoa, A16-SG, lot 4R68182 Aldrich 26,774-0, lot 09806KY Sigma, S-5505, lot 96H1137 Scientific Adsorbent, Inc., lot 50419

−1

Cb

particle size (μm; %)

(m g )