Environ. Sci. Technol. 2006, 40, 6787-6791
Reduction of Nitrous Oxide Emission from Pig Manure Composting by Addition of Nitrite-Oxidizing Bacteria Y A S U Y U K I F U K U M O T O , * ,† KAZUYOSHI SUZUKI,† TAKASHI OSADA,‡ KAZUTAKA KURODA,† DAI HANAJIMA,† TOMOKO YASUDA,† AND KIYONORI HAGA† Pollution Control Research Team, National Institute of Livestock and Grassland Science, 2 Ikenodai, Tsukuba, Ibaraki 305-0901, Japan, and Hokkaido Research Subteam for Waste Recycling System, National Agricultural Research Center for Hokkaido Region, 1 Hitsujigaoka, Toyohira-ku, Sapporo, Hokkaido 062-8555, Japan
Nitrous oxide (N2O) is emitted from pig manure composting, and the emission correlates with nitrite (NO2-) accumulation in the composting material. In the present study, we added nitrite-oxidizing bacteria (NOB) to inhibit NO2- accumulation and evaluated its effect on N2O emission in a laboratoryscale composting experiment. Mature pig manure compost (MPMC) containing NOB at 106 MPN g-1 WM or cultured MPMC (cul-MPMC) NOB at 1011 MPN g-1 WM was added after the thermophilic phase of composting. The addition of these materials prevented NO2- accumulation, promoting oxidation to nitrate (NO3-), whereas the accumulation of NO2- occurred in the material to which NOB was not added as the result of the delayed growth of indigenous NOB compared with that of ammoniaoxidizing bacteria (AOB). The pattern of NO2- in the material agreed with that of N2O emission; therefore, N2O emission ceased rapidly when NOB was added. Emission rates of N2O were 88.5 (no addition), 17.5 (MPMC addition), and 20.2 (cul-MPMC addition) g N-N2O kg-1 TNinitial, respectively. Improving composition of nitrifying communities for complete nitrification promotion would be useful to establish a composting method with low N2O emission.
Introduction Recycling animal wastes is important for sustainable agricultural systems. Composting is a traditional treatment method changing odoriferous and unsanitary animal waste to odorless, sanitary, and marketable organic fertilizer (1, 2). However, the emission of harmful gases from composting of animal waste has been the cause of serious environmental problems such as complaints from residents around farms about odor and destruction of the natural ecosystem by greenhouse gases (GHGs) (3, 4). N2O is a GHG with important impacts on the environment. Its 100-year global warming potential is 296 times as strong as that of carbon dioxide, and its concentration continues to increase at a rate of 0.25% per year (5). In the stratosphere, * Corresponding author phone: +81-29-8388677; fax: +81-298388606; e-mail:
[email protected]. † National Institute of Livestock and Grassland Science (NILGS). ‡ National Agricultural Research Center for Hokkaido Region (NARCH). 10.1021/es0611801 CCC: $33.50 Published on Web 09/29/2006
2006 American Chemical Society
TABLE 1. Experimental Treatment in Composting Experiment classification
experimental treatment
no NOB addition NOB addition
control addition of mature pig manure compost (MPMC) addition of cultured MPMC (cul-MPMC)
N2O reacts with oxygen to form nitric oxide, which plays a role in destruction of the ozone layer (6). N2O can be produced from composting of animal waste. In a prior study, we showed that approximately 5% of TNinitial in the material could be emitted as N2O during pig manure composting (7). Zeman et al. (8) showed that N2O emission could be estimated ranging from 6% of total N depending on the composting management. Because the number of domestic animals worldwide has been increasing, the influences of N2O emission from livestock production systems on global warming will also increase (9). When obvious N2O emission was taking place, NO2- was accumulated in the material during pig manure composting (10). A good correlation between N2O and NO2- has also been found in food waste composting (11). The presence of NO2- seems to play an important role in N2O emission. Kester et al. (12) have showed that coculturing of AOB with NOB strongly reduced the level of N2O production in a continuous culture as an effect of the lowered NO2- concentration. Therefore, there is a possibility that N2O emission can be reduced by preventing NO2- accumulation in the material during the composting process. In the present study, we added NOB to prevent NO2accumulation by promoting oxidation of NO2- until NO3-, i.e., complete nitrification, and evaluated its effect on N2O emission during pig manure composting.
Experimental Section Composting Experiment. In the present study, we established the three experimental treatments shown in Table 1. For addition of NOB, two kinds of material, MPMC and cul-MPMC, were used in this study. The feature of cul-MPMC was that NOB has been included at high concentration, which made it possible to decrease the indispensable amount of mature compost addition for accomplishment of complete nitrification. This was to minimize the influence accompanying addition except for NOB. Pig manure compost aged over 1 year was used as MPMC. The cul-MPMC was made of MPMC according to the following procedure. MPMC (500 g WM) was incubated in 3 L of liquid medium according to Aleem and Alexander (13) containing 67 mM of NO2-. Incubation was conducted at 30 °C with continuous aeration (500 mL min-1) and agitation (250 rpm) using a fermentor (MBF-500M, Eyela Tokyo Rikakikai, Japan) and was continued for 7 weeks. A new sterile NaNO2 solution (final concentration of NO2- was approximately 67 mM) was added when NO2- was completely oxidized. After the incubation, the cultured-MPMC (culMPMC) was picked out from the fermentor and then washed with amounts of distilled water to remove NO3- in the material. After the washing, the cul-MPMC was dried at 20 °C overnight and then stored in a refrigerator at 4 °C until application. The characteristics of MPMC and cul-MPMC are shown in Table 2. Nitrifying microorganisms of these materials were counted 4 days before the bioaugmentation. MPMC and cul-MPMC were completely mixed with each composting material at an additional rate of 10 and 1% (w/w VOL. 40, NO. 21, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
6787
TABLE 2. MPN of Nitrifying Microorganisms and Inorganic Nitrogen Content in MPMC and cul-MPMC nitrifying microorganisms, MPN g-1 WM (95% confidence limit) AOB
NOB
NH4+
NO2-
NO3-
1.2 × (5.1 × 106-3.8×107) 1.7 × 105 (7.0 × 104-4.5 × 105)
1.7 × (7.5 × 105-5.2 × 106) 8.2 × 1011 (3.7 × 1011-3.0 × 1012)
0
0
0.65
0
0
0
107
MPMC
cul-MPMC
106
FIGURE 1. Schematic of composting apparatus.
TABLE 3. Characteristics of Mixture of Fresh Pig Manure and Sawdust nitrogen content, N% DM moisture content, % total NH4+ NO2- NO3- BOD, % DM 61.9
2.36
0.21
0
0.01
21.6
pH 7.5
based on WM), respectively. These additional rates were determined to achieve at least 105 MPN g-1 WM of NOB in whole material after the addition following Blouin et al. (14). The addition to MPMC and cul-MPMC was done just after the thermophilic phase of composting to avoid decreasing the number of NOB added at high temperature. The laboratory scale composting apparatus was a stainless steel, airtight box with two ports for inlet and outlet air. The top, bottom, and all of the walls were insulated by 25 mm of styrene foam to decrease heat loss (Figure 1). An airflow distributor, which distributed the inlet airflow in four directions, was set up inside the inlet port to disturb the headspace air. Continuous ventilation was conducted by an air pump (APN-110K, Iwaki Pumps, Japan) at a fixed rate of 10 L min-1 regulated by a flow-meter (RK-1600R, KOFLOC, Japan). Fresh pig manure was collected from the pigpen in our institute and mixed with sawdust (14.3% moisture; particle size,
