Takashi Osada

Patterns and quantities of NH3, N2O and CH4 emissions during swine manure composting without forced aeration: effect of compost pile scale

To evaluate the NH(3), N(2)O, and CH(4) emissions from composting of livestock waste without forced aeration in turned piles, and to investigate the possible relationship between the scale of the compost pile and gas emission rates, we conducted swine manure composting experiments in parallel on small- and large-scale compost piles. Continuous measurements of gas emissions during composting were carried out using a chamber system, and detailed gas emission patterns were obtained. The total amount of each gas emission was computed from the amount of ventilation and gas concentration. NH(3) emission was observed in the early period of composting when the material was at a high temperature. Sharp peaks in CH(4) emission occurred immediately after swine manure was piled up, although a high emissions level continued after the first turning only in the large-scale pile. N(2)O emissions started around the middle stage of the composting period when NH(3) emissions and the temperature of the compost material began to decline. The emission rates of each gas in the small and large piles were 112.8 and 127.4 g NH(3)-N/kg T-N, 37.2 and 46.5 g N(2)O-N/kg T-N, and 1.0 and 1.9 g CH(4)/kg OM, respectively. It was found that changing the piling scale of the compost material was a major factor in gas emission rates.

Source of nitrous oxide emissions during the cow manure composting process as revealed by isotopomer analysis of and amoA abundance in betaproteobacterial ammonia-oxidizing bacteria.

ABSTRACT A molecular analysis of betaproteobacterial ammonia oxidizers and a N2O isotopomer analysis were conducted to study the sources of N2O emissions during the cow manure composting process. Much NO2−-N and NO3−-N and the Nitrosomonas europaea-like amoA gene were detected at the surface, especially at the top of the composting pile, suggesting that these ammonia-oxidizing bacteria (AOB) significantly contribute to the nitrification which occurs at the surface layer of compost piles. However, the 15N site preference within the asymmetric N2O molecule (SP = δ15Nα − δ15Nβ, where 15Nα and 15Nβ represent the 15N/14N ratios at the center and end sites of the nitrogen atoms, respectively) indicated that the source of N2O emissions just after the compost was turned originated mainly from the denitrification process. Based on these results, the reduction of accumulated NO2−-N or NO3−-N after turning was identified as the main source of N2O emissions. The site preference and bulk δ15N results also indicate that the rate of N2O reduction was relatively low, and an increased value for the site preference indicates that the nitrification which occurred mainly in the surface layer of the pile partially contributed to N2O emissions between the turnings.

Characterization and spatial distribution of bacterial communities within passively aerated cattle manure composting piles

The bacterial communities in the core, bottom, top, middle-surface, and lower-surface full-scale passively aerated cattle manure compost was investigated using DGGE of PCR-amplified 16S rRNA sequences. Some Bacillus species and strictly anaerobic thermophilic Clostridium species were dominant only in the core and bottom zones. In contrast, bands belonging to mesophilic bacteria such as Bacteroidetes, Clostoridia,alpha and gamma-proteobacteria were detected in surface zones, even in the initial thermophilic stage of the process. Our results clearly show the spatial distribution of the microbial community within full-scale composting piles, which indicates N or C conversion by zone-specific bacterial communities were occurring in each zone of the pile.

Microbiology of nitrogen cycle in animal manure compost.

Composting is the major technology in the treatment of animal manure and is a source of nitrous oxide, a greenhouse gas. Although the microbiological processes of both nitrification and denitrification are involved in composting, the key players in these pathways have not been well identified. Recent molecular microbiological methodologies have revealed the presence of dominant Bacillus species in the degradation of organic material or betaproteobacterial ammonia‐oxidizing bacteria on nitrification on the surface, and have also revealed the mechanism of nitrous oxide emission in this complicated process to some extent. Some bacteria, archaea or fungi still would be considered potential key players, and the contribution of some pathways, such as nitrifier denitrification or heterotrophic nitrification, might be involved in composting. This review article discusses these potential microbial players in nitrification–denitrification within the composting pile and highlights the relevant unknowns through recent activities that focus on the nitrogen cycle within the animal manure composting process.

The impact of using mature compost on nitrous oxide emission and the denitrifier community in the cattle manure composting process.

The diversity and dynamics of the denitrifying genes (nirS, nirK, and nosZ) encoding nitrite reductase and nitrous oxide (N2O) reductase in the dairy cattle manure composting process were investigated. A mixture of dried grass with a cattle manure compost pile and a mature compost-added pile were used, and denaturing gradient gel electrophoresis was used for denitrifier community analysis. The diversity of nirK and nosZ genes significantly changed in the initial stage of composting. These variations might have been induced by the high temperature. The diversity of nirK was constant after the initial variation. On the other hand, the diversity of nosZ changed in the latter half of the process, a change which might have been induced by the accumulation of nitrate and nitrite. The nirS gene fragments could not be detected. The use of mature compost that contains nitrate and nitrite promoted the N2O emission and significantly affected the variation of nosZ diversity in the initial stage of composting, but did not affect the variation of nirK diversity. Many Pseudomonas-like nirK and nosZ gene fragments were detected in the stage in which N2O was actively emitted.

Effect of covering composting piles with mature compost on ammonia emission and microbial community structure of composting process.

To control ammonia (NH(3)) volatilization from the dairy cattle (Bos taurus) manure composting process, a compost pile was covered with mature compost and the gas emissions evaluated using the dynamic chamber system. The peak of NH(3) volatilization observed immediately after piling up of the compost was reduced from 196 to 62 mg/m(3) by covering the compost pile with mature compost. The accumulation of NH(4)-N to the covered mature compost was also observed. Covering and mixing the compost with mature compost had no effect on the microbial community structure. However, over time the microbial community structure changed because of a decrease in easily degradable organic compounds in the compost piles. The availability of volatile fatty acids (VFA) was considered to be important for microbial community structure in the compost. After the VFA had disappeared, the NO(3)-N concentration increased and the cellulose degrading bacteria such as Cytophaga increased in number.

Mitigation of greenhouse gas emission from the cattle manure composting process by use of a bulking agent

The greenhouse gas (GHG) [methane (CH4) and nitrous oxide (N2O)] mitigation effects of mixing dried grass into passively-aerated manure during the composting process (which accounts for 68.7% of Japanese dairy manure management) were assessed. Gaseous emissions [CH4, N2O, carbon dioxide (CO2) and ammonia (NH3)] from about 4 t of fresh dairy manure with or without 400 kg of dried grass mixed in were measured by the dynamic chamber method. The addition of dried grass contributed to a decrease in GHG emissions from 20.8 ± 1.3 g kg−1 volatile solids (VS) to 5.4 ± 1.4 g kg−1 VS (74.3% mitigation) for CH4 and from 7.4 ± 2.6 g N2O-N kg−1 Ninitial to 2.7 ± 0.4 g N2O-N kg−1 Ninitial (62.8% mitigation) for N2O. By applying this strategy, the expected reduction of GHG emission would be 70,466 t CH4 yr−1 and 1379 t N2O-N yr−1 (1907 Gg CO2 eq. yr−1 in total) in the Japanese dairy sector. On the other hand, it was showed that CO2 and NH3 emissions increase [from 424.4 ± 214.9 g CO2 kg−1 VS to 603.8 ± 99.6 g CO2 kg−1 VS for CO2 and from 16.9 ± 7.1 g ammonium-nitrogen (NH3-N) kg−1 Ninitial to 38.3 ± 3.5 g NH3-N kg−1 Ninitial for NH3] by this method. Moreover, the mechanism of this significant N2O mitigation effect cannot be explained, and a better understanding of this effect could further improve the GHG mitigation strategy.

Swine wastewater treatment technology to reduce nitrous oxide emission by using an aerobic bioreactor packed with carbon fibres

From a global warming perspective it is important to control emissions of methane (CH4) and nitrous oxide (N2O) from excreta and manure management. To mitigate emissions of N2O during swine wastewater treatment, we examined aerobic treatment technologies that use carbon fibre carriers as an alternative to conventional activated sludge treatment. We used scaled-up experiment equipment (water volume, 700 L) to evaluate the treatment performance. The N2O emission factor was 0.008 g N2O-N/g total N load in an aerobic bioreactor packed with carbon fibres (CF reactor), compared with 0.021 gN2O-N/g total N load in an activated sludge reactor (AS reactor). The CF treatment reduced N2O emissions by more than 60% compared with the AS treatment. Combined CH4 and N2O emissions from the CF reactor were 504 g-CO2 eq/m3.day, whereas those from the AS reactor were 1333 g-CO2 eq/m3.day. Interestingly, N2O emissions from the CF reactor were reduced even when nitrate and nitrite accumulated.