Micro-positive pressure significantly decreases greenhouse gas emissions by regulating archaeal community during industrial-scale dairy manure composting

In this study, the effects of micro-positive pressure formed by covering with a semipermeable membrane in the heating phase of dairy manure composting on greenhouse gas emissions and the mechanism of reducing methane emissions by the archaeal community were investigated. A large-scale experiment was conducted with semipermeable membrane-covered composting (SMC), forced aeration composting (FAC), and traditional static composting (TSC) groups. The results showed that the oxygen concentration and methanogen abundance were key factors in regulating methane emissions. In the heating phase of SMC, the micro-positive pressure could enhance the O2 utilization rate and heating rate, resulting in Methanobrevibacter and Methanobacterium greatly decreasing, and the abundance of mcrA decreased by 90.03%, while that of pmoA did not increase. Compared with FAC and TSC, the cumulative methane emissions in SMC decreased by 51.75% and 96.04%, respectively. Therefore, the micro-positive pressure could effectively reduce greenhouse gas emissions by inhibiting the growth of methanogens.

Environmental and economic trade-offs of using composted or stockpiled manure as partial substitute for synthetic fertilizer

Manure generated from livestock production could represent an important source of plant nutrients in substitution of synthetic fertilizer. To evaluate the sustainability of partially substituting synthetic fertilizer with soil organic amendments (OAs) in horticulture, an economic and greenhouse gas (GHG) budget was developed. The boundary for analysis included manure processing (stockpiling vs. composting) and transport and spreading of manure and compost (feedlot and chicken) in intensively cultivated horticultural fields. The OA field application rates were calculated based on the nitrogen supplied by OAs. The GHG budget based on directly measured emissions indicates that the application of composted manure, in combination with reduced fertilizer rate, was always superior to stockpiled manures. Compost treatments showed from 9 to 90% less GHG emissions than stockpiled manure treatments. However, higher costs associated with the purchase and transport of composted manure (three times higher) generated a greater economic burden compared with stockpiled manure and synthetic fertilizer application. The plant nutrient replacement value of the OAs was considered only for the first year of application, and if long-term nutrient release from OAs is taken into account, additional savings are possible. Because the income from soil carbon sequestration initiatives in response to OA application is unlikely to bridge this financial gap, particularly in the short term, this study proposes that future policy should develop methodologies for avoided GHG emissions from OA application. The combined income from soil carbon sequestration and potentially avoided GHG initiatives could incentivize farmers to adopt OAs as a substitute for synthetic fertilizers, thereby promoting more sustainable farming practices.

Effect of micro-aerobic conditions based on semipermeable membrane-covered on greenhouse gas emissions and bacterial community during dairy manure storage at industrial scale

This study evaluated the greenhouse gas emissions of solid dairy manure storage with the micro-aerobic group (MA; oxygen concentration <5%) and control group (CK; oxygen concentration <1%), and explained the difference in greenhouse gas emissions by exploring bacterial community succession. The results showed that the MA remained the micro-aerobic conditions, which the maximum and average oxygen concentrations were 4.1% and 1.9%, respectively; while the average oxygen concentrations of the CK without intervention management was 0.5%. Compared with the CK, carbon dioxide and methane emissions in MA were reduced by 78.68% and 99.97%, respectively, and nitrous oxide emission was increased by almost three times with a small absolute loss, but total greenhouse gas emissions decreased by 91.23%. BugBase analysis showed that the relative abundance of aerobic bacteria in CK decreased to 0.73% on day 30, while that in MA increased to 6.56%. Genus MBA03 was significantly different between the two groups (p < 0.05) and was significantly positively correlated with carbon dioxide and methane emissions (p < 0.05). A structural equation model also revealed that the oxygen concentration and MBA03 of the MA had significant direct effects on methane emission rate (p < 0.001). The research results could provide theoretical basis and measures for directional regulation of greenhouse gas emission reduction during dairy manure storage.

Effects of semi-permeable membrane covering coupled with intermittent aeration on gas emissions during aerobic composting from the solid fraction of dairy manure at industrial scale

In this study, the effects of covering the compost pile with a semi-permeable membrane in combination with intermittent aeration on the gas emissions during aerobic composting from the solid fraction of dairy manure at industrial scale were investigated. A large-scale composting experiment was carried out to compare a membrane-covered (CT) group with a control (CK) group. The results indicated that the CT group could maintain a suitable aerobic and positive micro-pressure environment. The carbon dioxide, methane, nitrous oxide, and ammonia emissions outside the membrane during the aeration interval were reduced by 64.23%, 70.07%, 54.87%, and 11.32%, respectively, compared with that inside the membrane. It was also determined that the methane and nitrous oxide emissions from the CT group were reduced by 99.89% and 60.48% relative to the CK group, confirming that the combined process represented a novel strategy for reducing gas emissions during dairy manure composting.

Gas emissions during cattle manure composting and stockpiling

Manure composting is a common management practice for cattle feedlots, but gaseous emissions from composting are poorly understood. The objective of this study was to quantify ammonia (NH₃ ), nitrous oxide (N₂ O), carbon dioxide (CO₂ ), and methane (CH₄ ) emissions from windrow composting (turning) and static stockpiling (nonturning) of manure at a commercial feedlot in Australia. An inverse-dispersion technique using an open-path Fourier transform infrared (OP-FTIR) spectrometer gas sensor was deployed to measure emissions of NH₃ , N₂ O, CO₂ , and CH₄ over a 165-d study period, and 29 and 15% of the total data intervals were actually used to calculate the fluxes for the windrow and stockpile, respectively. The nitrogen (N) lost as NH₃ and N₂ O emissions represented 26.4 and 3.8% of the initial N in windrow, and 5.3 and 0.8% of that in the stockpile, respectively. The carbon (C) lost as CO₂ and CH₄ emissions represented 44 and 0.3% of the initial C in windrow, and 54.8 and 0.7% of that in the stockpile, respectively. Total greenhouse gas (GHG) emissions from the manure windrow were 2.7 times higher than those of the stockpiled manure. This work highlights the value that could be accrued if one could reduce emissions of NH₃ -N and N₂ O-N from composting, which would retain manure N content while reducing GHG emissions.

Energy from poultry waste: An Aspen Plus-based approach to the thermo-chemical processes

A particular approach to the task of energy conversion of a residual waste material was properly experienced during the implementation of the national funded Enerpoll project. This project is a case study developed in the estate of a poultry farm that is located in a rural area of central Italy (Umbria Region); such a farm was chosen for the research project since it is almost representative of many similar small-sized breeding realties of the Italian regional context. The purpose of the case study was the disposal of a waste material (i.e. poultry manure) and its energy recovery; this task is in agreement with the main objectives of the new Energy Union policy. Considering this background, an innovative gasification plant (300KW thermal power) was chosen and installed for the experimentation. The novelty of the investigated technology is the possibility to achieve the production of thermal energy burning just the produced syngas and not directly the solid residues. This aspect allows to reduce the quantity of nitrogen released in the atmosphere by the exhaust flue gases and conveying it into the solid residues (ashes). A critical aspect of the research program was the optimization of the pretreatment (reduction of the water content) and the dimensional homogenization of the poultry waste before its energy recovery. This physical pretreatment allowed the reduction of the complexity of the matrix to be energy enhanced. Further to the real scale plant monitoring, a complete Aspen Plus v.8.0 model was also elaborated for the prediction of the quality of the produced synthesis gas as a function of both the gasification temperature and the equivalence ratio (ER). The model is an ideal flowchart using as input material just the homogenized and dried material. On the basis of the real monitored thermal power (equal to about 200kW average value in an hour) the model was used for the estimation of the syngas energy content (i.e. LHV) that resulted in the range of 3-5MJ/m³ for an equivalence ratio (ER) equal to 0.2.