Nitrogen (N) losses during composting reduce the value of the end product as a fertilizer. Nitrogen is lost during composting mainly by ammonia (NH3) volatilization in the thermophilic phase. We used three bench-scale aerobic bioreactors with a controlled temperature difference (CDT) system as an experimental approach to investigate the pattern of N losses during composting. N2O peak emission occurred much earlier (7h) than NH3 volatilization (48-60h) during the thermophilic phase (~55°C) of bench-scale composting. The NH3 volatilization peak rate occurred following the greater biological activity (O2 consumed/CO2 evolved) at 40°C which could coincide with greater ammonification, but immobilization of NH4+/NH3 also occurs at this point affecting NH3 volatilization. Differences in temperature curves and accumulated NH3-N were related to the biological activity in each vessel. Therefore, O2 consumed/CO2 evolved measurements must be part of the evaluation of composting in further studies for comparisons of techniques to reduce NH3 volatilizatio

ALVES, B. J. R.

CHALK, P. M.

INACIO, C. T.

URQUIAGA, S.

English

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 IV Symposium on Agricultural and Agroindustrial Waste Management  May 5-7, 2015 - Rio de Janeiro, Brazil   NITROGEN LOSS (NH3, N2O) PATTERNS IN BENCH-SCALE COMPOSTING  Inácio, C.T.*1,3; Urquiaga, S.2; Chalk, P.M.3; Alves, B.J.R.2  1CPGA-CS, Soil Science Department, UFRRJ, Seropédica-RJ-Brazil 2Embrapa Agrobiology, Seropédica-RJ-Brazil  3Embrapa Soils, Rio de Janeiro-RJ-Brazil *e-mail: caio.teves@embrapa.br  SUMMARY: Nitrogen (N) losses during composting reduce the value of the end product as a fertilizer. Nitrogen is lost during composting mainly by ammonia (NH3) volatilization in the thermophilic phase. We used three bench-scale aerobic bioreactors with a controlled temperature difference (CDT) system as an experimental approach to investigate the pattern of N losses during composting. N2O peak emission occurred much earlier (7h) than NH3 volatilization (48-60h) during the thermophilic phase (~55°C) of bench-scale composting. The NH3 volatilization peak rate occurred following the greater biological activity (O2 consumed/CO2 evolved) at 40°C which could coincide with greater ammonification, but immobilization of NH4+/NH3 also occurs at this point affecting NH3 volatilization. Differences in temperature curves and accumulated NH3-N were related to the biological activity in each vessel. Therefore, O2 consumed/CO2 evolved measurements must be part of the evaluation of composting in further studies for comparisons of techniques to reduce NH3 volatilization. Keywords: horse manure, bioreactors, respirometric method.  INTRODUCTION Composting of agricultural/agro-industrial wastes is a major process to produce organic and organo-mineral fertilizers, and compost is the major soil amendment for certified organic farming systems. However, the nitrogen (N) losses during composting reduce the value of the end product as a fertilizer. Nitrogen is lost during composting mainly by ammonia (NH3) volatilization in the thermophilic stage that can account for 60 to 99% of total N losses (Liang et al., 2006), while nitrous oxide (N2O) accounts for less than 5.0% to 22% of N losses (Fukumoto et al., 2011), depending on the composting conditions. A wide variation of total N losses might be expected in both laboratory- and full-scale composting. Many parameters affect NH3 volatilization such as substrate composition, pH, temperature, aeration, and moisture content. Various techniques have been proposed to reduce NH3 volatilization and enhance the value of compost as fertilizer e.g. struvite crystallization by addition of Mg and P salts (Jeong and Kim, 2001). However, little attention has been given to a comparative assessment of the efficacy of NH3 mitigation techniques. Diverse units used by different authors make direct comparisons difficult. Moreover, erroneous conclusions could be made when biological activity is not taken in account or comparisons are made between treatments having different biological activities or ammonification rates. An appropriate experimental approach seems to be crucial to assess the composting process. Bench-scale aerobic bioreactors have been used for many proposes in composting studies and it seems to be useful for N loss comparisons. In this abstract we report the results of NH3 volatilized and N2O emitted from a bench-scale composting system which will be used in further studies for comparisons of techniques to reduce NH3 volatilization during composting.   IV Symposium on Agricultural and Agroindustrial Waste Management  May 5-7, 2015 - Rio de Janeiro, Brazil MATERIAL AND METHODS Three bench-scale cylindrical bioreactors (3.0 L) of polypropylene equipped with insulation and electrical resistance tape were used to contain the composting process. Forced aeration was controlled by a rotometer coupled with a pressure regulator (ASA®) and monitored by a digital fluxometer (Omega®) at 150 and 50 ml min-1during the first 0-120h (0-5d) and 121-240h (6-10d), respectively. Temperature was controlled by a temperature differentials method (Magalhães et al., 1993) using Microsoll® II plus and Sitrad® software (FullGauge®) which also programmed the sampling of the exhaust air by a multi-sampler equipped with solenoid valves. Biological activity within each vessel was monitored by a respirometric method using an in-line O2-zirconia sensor and CO2 infra-red sensor (SST® Sensing). The air inlet was humidified prior to entry into the vessel and the air outlet was passed through an acid trap (0.5M H2SO4, 100ml, renewed each 6 hours) and a silica gel filter prior to gas sensing. Respirometry and flow meter data were stored in a datalogger (Campbell®). Aerobic-thermophilic composting was carried out for 10 days. Each vessel contained approximately 1000 g wet weight with 70% moisture of a 2:1 mixture (wet basis) of horse bedding manure and hydroponic lettuce (chopped leaves). The maximum temperature was set at 55°C. Volatilized NH3 was determined by a distillation/titration method. Gas samples were collected with syringes at 25, 30, 40, 50, 55°C for N2O analysis by gas chromatography. Solid samples were taken at 0, 1, 5 and 10 days for further chemical analysis.  RESULTS AND DISCUSSION The three simultaneous composting runs showed typical temperature curves, with an exponential increase of temperature reaching 56.0-57.1°C within 18 hours. Despite the similarity in temperature curves, bioreactor #1 had a faster temperature increase and a shorter thermophilic phase than the other two vessels (Fig.1A). After 10 days the organic material showed different visual and odor characteristics than the feedstock, and the lettuce leaves were totally decomposed. The loss of total dry mass was around 43.0 g (±0.7) or 14.3% (±0.3) of the initial dry mass and the greater proportion of dry mass was lost in the first 5 days. Biological activity was intense and similar among replicates, but with slight differences. O2 consumption reached its peak at 40°C (6h) within a range of 8 to 10% (Fig. 3). O2 consumption/CO2 evolved data showed that the smaller biological activity coincided with the shorter thermophilc phase of bioreactor #1 (Fig.1 and Fig.2). Nitrous oxide peak emission occurred much earlier (7h) than peak ammonia volatilization during composting (48-60h). Nitrous oxide (N2O) emission was inversely related to O2 consumption and initial temperature increase (20 to 40°C). The initial emission rate may be mainly related to the emission of N2O previously formed, emission being favored by forced aeration. A rapidly increasing N2O emission occurred at >40°C at the highest O2 consumption rate and the peak emission rate occurred just when the temperature reached 55°C (Fig.1B). Therefore, the peak N2O concentration was probably due to denitrification of nitrite/nitrate produced by the biodegradation of organic material and dead microbial biomass. Bioreactor #3 showed a different emission pattern (Fig.1B) for which there is presently no apparent explanation. Nitrite accumulation has been related to N2O emissions during the mesophilic (maturation) phase (Fukumoto et al., 2011). However, this pattern of emission was not observed in our bench-scale experiment, most likely due to the aerobic conditions (aeration) or the absence of nitrite accumulation. Ammonia volatilization curves were similar with rapidly increasing rates between 12 and 60h during the thermophilic stage (Fig.3A), except for bioreactor #1. However, the cumulative amount of NH3 trapped was different among replicates (Fig.3B). This  IV Symposium on Agricultural and Agroindustrial Waste Management  May 5-7, 2015 - Rio de Janeiro, Brazil difference might be attributed to the different temperature curves (shorter thermophilic phase) and biological activity (lower O2 consumption/CO2 evolved), which was pronounced for bioreactor #1. Nevertheless, 50 and 90% of the NH3 volatized was measured around 60 and 120h for all replicates (Fig. 3B). The pH rose from 7 to 8.3-8.4 which favors NH3 volatilization. The pH also varied consistently (7 to 7.2-7.3) during the initial thermophilic temperature increase (40-55°C).  The ammonia volatilization peak rate occurred following the greater biological activity i.e. the peak O2 consumed/CO2 evolved which could coincide with greater ammonification, but immobilization of NH4+/NH3 also occurs at this point affecting NH3 volatilization (Sasaki et al., 2005). Therefore, the peak volatilization rate was at 55°C (48-60h) when pH was higher but thermophilic biological activity was less intense than the mesophilic biological activity (<40°C). We hypothesize that most of the NH3 volatilized came from the dead microbial biomass during the mesophilic/thermophilic temperature transition. However, the effect of temperature (>50°C) on the diffusion coefficient of gases must be taken in account. The high pH drives the relatively high NH3 volatilization during the mesophilic (maturation) phase and the reduced air flow (low O2 demand) sharply reduced NH3 volatilization during this stage.  CONCLUSIONS NH3 volatilization and N2O emission occurred during the thermophilic phase of bench-scale composting as expected. However, an unexpectedly high variation of accumulated N losses was found among replicates. Differences in temperature curves and accumulated NH3-N were related to the biological activity in each vessel. Therefore, O2 consumed/CO2 evolved measurements were a useful parameter for evaluation of the composting process, which should be part of further studies for comparisons of techniques to reduce NH3 volatilization during composting. Furthermore, considering that NH3 volatilization is a major fractionation process of 15N, large variations of stable isotope signatures (15N) are expected to be found in evolved NH3 (Lee et al., 2011) of compost during the thermophilic phase, and 15N values of compost could be used to estimate N losses.  ACKNOWLEDGEMENT We thank Andrea Loviane Silva for gas chromatography analysis and FAPERJ for a visiting scientist fellowship for Dr. Phillip M. Chalk (No. 101.466/201) and fellowships (Scientist of the State of Rio de Janeiro) for Segundo Urquiaga and Bruno J. R. Alves.  REFERENCES Fukumoto, Y., Suzuki, K., Kuroda, K., Waki, M., and Yasuda, T. (2011) Effects of struvite formation and nitratation promotion on nitrogenous emissions such as NH3, N2O and NO during swine manure composting. Bioresource Technology, 102, 1468−1474. Jeong, Y-L., and Kim, J-S. (2001) A new method for conservation of nitrogen in aerobic composting processes. Bioresource Technology, 79, 129−133. Lee, C., Hristov, A. N., Cassidy, T., and Heyler, K. (2011) Nitrogen isotope fractionation and origin of ammonia nitrogen volatilized from cattle manure in simulated storage. Atmosphere, 2(4), 256−270. Liang, Y., Leonard, J. J., Feddes, J. J. R., and McGill, W. B. (2006) Influence of carbon and buffer amendment on ammonia volatilization in composting. Bioresource Technology, 97, 748−761. Magalhães, A. M. T., Shea, P. J., Jawson, M. D., Wicklund, E. A., and Nelson, D. W. (1993) Practical simulation of composting in the laboratory. Waste Management & Research, 11, 143−154.  IV Symposium on Agricultural and Agroindustrial Waste Management  May 5-7, 2015 - Rio de Janeiro, Brazil Sasaki, H. Yano, H., Sasaki, T., and Nakai, Y. (2005) A survey of ammonia-assimilating microorganisms in cattle manure composting. Journal of Applied Microbiology, 99(6), 1356−1363. 15202530354045505560 N2O SamplingA25°C30°C40°C50°C55°C55°C50°C40°C30°C25°C0 12096724824Temperature (°C)Time (h) Bio1 Bio2 Bio325°C 30°C 40°C 50°C 55°C 55°C 50°C 40°C 30°C 25°C050001000015000200002500030000 0h 120h19hBN2O (ppb)Samples Bio1 Bio2 Bio3 Figure 1. Temperature curves and sampling strategy of gas samples (A) and N2O emission results (B) of bench-scale composting of horse bedding manure and lettuce leaves. 0 12 24 36 48 60 72 84 96 108 120810121416182022AO2 % (v/v)Time (h) Bio1 Bio2 Bio30 12 24 36 48 60 72 84 96 108 1200246810BCO2 % (v/v)Time (h) Figure 2. Biological activity of bench-scale composting of horse bedding manure and lettuce leaves. Respirometry by in-line sensor of (A) O2consumed and (B) CO2 evolved. 0 24 48 72 96 120 144 168 192 216 2400510152025303540pHinitial = 7.0pH120h = 8.3-8.4Air Flow = 150 ml min-1Air Flow = 50 ml min-1ANH3-N (mg)Time (h) Bio1 Bio2 Bio30 24 48 72 96 120 144 168 192 216 240-50050100150200250300350400B95%93%91%48%55%52%NH3 -N(mg)Time (h) Figure 3. Ammonia volatilization in bench-scale composting of horse bedding manure and lettuce leaves. (A) NH3-N volatilization rate (6h intervals), (B) Cumulative NH3-N losses. 

Nitrogen loss (NH3, N2O) patterns in bench-scale composting.

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Nitrogen loss (NH3, N2O) patterns in bench-scale composting.

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