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

Temporal dynamics of fecal microbiota community succession in broiler chickens, calves, and piglets under aerobic exposure

Researchers have extensively studied the effect of oxygen on the growth and survival of bacteria. However, the impact of oxygen on bacterial community structure, particularly its ability to select for taxa within the context of a complex microbial community, is still unclear. In a 21-day microcosm experiment, we investigated the effect of aerobic exposure on the fecal community structure and succession pattern in broiler, calf, and piglet feces (n = 10 for each feces type). Bacterial diversity decreased and community structure changed rapidly in the broiler microbiome (P < 0.001), while the fecal community of calves and piglets, which have higher initial diversity, was stable after initial exposure but decreased in diversity after 3 days (P < 0.001). The response to aerobic exposure was host animal specific, but in all three animals, the change in community structure was driven by a decrease in anaerobic species, primarily belonging to Firmicutes and Bacteroidetes (except in broilers where Bacteroidetes increased), along with an increase in aerobic species belonging to Proteobacteria and Actinobacteria. Using random forest regression, we identified microbial features that predict aerobic exposure. In all three animals, host-beneficial Prevotella-related ASVs decreased after exposure, while ASVs belonging to Acinetobacter, Corynbacterium, and Tissierella were increased. The decrease of Prevotella was rapid in broilers but delayed in calves and piglets. Knowing when these pathobionts increase in abundance after aerobic exposure could inform farm sanitation practices and could be important in designing animal experiments that modulate the microbiome.IMPORTANCEThe fecal microbial community is contained within a dynamic ecosystem of interacting microbes that varies in biotic and abiotic components across different animal species. Although oxygen affects bacterial growth, its specific impact on the structure of complex communities, such as those found in feces, and how these effects vary between different animal species are poorly understood. In this study, we demonstrate that the effect of aerobic exposure on the fecal microbiota was host-animal-specific, primarily driven by a decrease in Firmicutes and Bacteroidetes, but accompanied by an increase in Actinobacteria, Proteobacteria, and other pathobionts. Interestingly, we observed that more complex communities from pig and cattle exhibited initial resilience, while a less diverse community from broilers displayed a rapid response to aerobic exposure. Our findings offer insights that can inform farm sanitation practices, as well as experimental design, sample collection, and processing protocols for microbiome studies across various animal species.

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.

Pilot-scale membrane-covered composting of food waste: Initial moisture, mature compost addition, aeration time and rate

The impact of different operational parameters on the composting efficiency and compost quality during pilot-scale membrane-covered composting (MCC) of food waste (FW) was evaluated. Four factors were assessed in an orthogonal experiment at three different levels: initial mixture moisture (IMM, 55 %, 60 %, and 65 %), aeration time (AT, 6, 9, and 12 h/d), aeration rate (AR, 0.2, 0.4, and 0.6 m3/h) and mature compost addition ratio (MC, 2 %, 4 %, and 6 %). Results indicated that 55 % IMM, 6 h/d AT, 0.4 m3/h AR, and 4 % MC addition ratio simultaneously provided the compost with the maximum cumulative temperature and the minimum moisture. It was shown that the IMM was the driving factor of this optimum composting process. On contrary, the optimal parameters for reducing carbon and nitrogen loss were 65 % IMM, 6 h/d AT, 0.4 m3/h AR, and 2 % MC addition ratio. The AR had the most influence on reducing carbon and nitrogen losses compared to all other factors. The optimal conditions for compost maturity were 55 % IMM, 9 h/d AT, 0.2 m3/h AR, and 6 % MC addition ratio. The primary element influencing the pH and electrical conductivity values was the AR, while the germination index was influenced by IMM. Protein was the main organic matter limiting the composting efficiency. The results of this study will provide guidance for the promotion and application of food waste MCC technology, and contribute to a better understanding of the mechanisms involved in MCC for organic solid waste treatment.

Semi-permeable membrane-covered high-temperature aerobic composting: A review

Semi-permeable membrane-covered high-temperature aerobic composting (SMHC) is a suitable technology for the safe treatment and disposal of organic solid waste as well as for improving the quality of the final compost. This paper presents a comprehensive summary of the impact of semi-permeable membranes centered on expanded polytetrafluoroethylene (e-PTFE) on compost physicochemical properties, carbon and nitrogen transformations, greenhouse gas emission reduction, microbial community succession, antibiotic removal, and antibiotic resistance genes migration. It is worth noting that the semi-permeable membrane can form a micro-positive pressure environment under the membrane, promote the uniform distribution of air in the heap, reduce the proportion of anaerobic area in the heap, improve the decomposition rate of organic matter, accelerate the decomposition of compost and improve the quality of compost. In addition, this paper presents several recommendations for future research areas in the SMHC. This investigation aims to guide for implementation of semi-permeable membranes in high-temperature aerobic fermentation processes by systematically compiling the latest research progress on SMHC.

Responses of greenhouse gas emissions to aeration coupled with functional membrane during industrial-scale composting of dairy manure: Insights into bacterial community composition and function

Greenhouse gas (GHG) emissions from manure management processes deserve more attention. Using three industrial-scale experiments, this study comprehensively evaluated the effects of different aeration coupled with semi-permeable membrane-covered strategies on the structure and function of bacterial communities and their impact on GHG emissions during dairy manure aerobic composting. The succession of the bacterial communities tended to be consistent for similar aeration strategies. Ruminiclostridium and norank_f__MBA03 were significantly positively correlated with the methane emission rate, and forced aeration coupled with semi-permeable membrane-covered decreased GHG emissions by inhibiting these taxa. Metabolism was the most active function of the bacterial communities, and its relative abundance accounted for 75.69%-80.23%. The combined process also enhanced carbohydrate metabolism and amino acid metabolism. Therefore, forced aeration coupled with semi-permeable membrane-covered represented a novel strategy for reducing global warming potential by regulating the structure and function of the bacterial communities during aerobic composting of dairy manure.

Nitrogen evolution during membrane-covered aerobic composting: Interconversion between nitrogen forms and migration pathways

Aerobic composting is a promising technology for converting manure into organic fertilizer with low capital investment and easy operation. However, the large nitrogen losses in conventional aerobic composting impede its development. Interconversion of nitrogen species was studied during membrane-covered aerobic composting (MCAC) and conventional aerobic composting, and solid-, liquid-, and gas-phase nitrogen migration pathways were identified by performing nitrogen balance measurements. During the thermophilic phase, nitrogenous organic matter degradation and therefore NH3 production were faster during MCAC than uncovered composting. However, the water films inside and outside the membrane decreased NH3 release by 13.92%-22.91%. The micro-positive pressure environment during MCAC decreased N2O production and emission by 20.35%-27.01%. Less leachate was produced and therefore less nitrogen and other pollutants were released during MCAC than uncovered composting. The nitrogen succession patterns during MCAC and uncovered composting were different and NH4+ storage in organic nitrogen fractions was better facilitated during MCAC than uncovered composting. Overall, MCAC decreased total nitrogen losses by 33.24%-50.07% and effectively decreased environmental pollution and increased the nitrogen content of the produced compost.

Effect of different multichannel ventilation methods on aerobic composting and vegetable waste gas emissions

Aerobic composting, especially semipermeable membrane-covered aerobic fermentation, is known to be an effective method for recycling and reducing vegetable waste. However, this approach has rarely been applied to the aerobic composting of vegetable waste; in addition, the product characteristics and GHG emissions of the composting process have not been studied in-depth. This study investigated the effect of using different structural ventilation systems on composting efficiency and greenhouse gas emissions in a semipermeable membrane-covered vegetable waste compost. The results for the groups (MV1, MV2, and MV3) with bottom ventilation plus multichannel ventilation and the group (BV) with single bottom ventilation were compared here. The MV2 group effectively increased the average temperature by 19.06% whilst also increasing the degradation rate of organic matter by 30.81%. Additionally, the germination index value reached more than 80%, 3 days in advance. Compared to those of the BV group, the CH4, N2O, and NH3 emissions of MV2 were reduced by 32.67%, 21.52%, and 22.57%, respectively, with the total greenhouse gas emissions decreasing by 24.17%. Overall, this study demonstrated a multichannel ventilation system as a new method for improving the composting efficiency of vegetable waste whilst reducing gas emissions.

Combined effects of amoxicillin and copper on nitrogen transformation and the microbial mechanisms during aerobic composting of cow manure

Pollutants in livestock manure have a compound effect during aerobic composting, but research to date has focused more on single factors. This study investigated the effects of adding amoxicillin (AMX), copper (Cu) and both (ACu) on nitrogen transformation and the microbial mechanisms in cow manure aerobic composting with wheat straw. In this study, compared with CK, AMX, Cu, and ACu increased NH₃ cumulative emissions by 32.32%, 41.78% and 8.32%, respectively, due to their inhibition of ammonia oxidation. Coexisting AMX and Cu decreased the absolute abundances of amoA/ nxrA genes and increased the absolute abundances of nirS /nosZ genes, but they had an antagonistic effect on the changes in functional gene abundances. Pseudomonas and Luteimonas were enriched during the thermophilic and cooling periods due to the addition of AMX and ACu, which enhanced denitrification in these two groups. Moreover, adding AMX and/or Cu led to more complex bacterial networks, but the effect of the two pollutants was lower than those of the individual pollutants. These findings provide theoretical and experimental support for controlling typical combined pollution with antibiotics and heavy metals in livestock manure.

Large Semi-Membrane Covered Composting System Improves the Spatial Homogeneity and Efficiency of Fermentation

Homogenous spatial distribution of fermentation characteristics, local anaerobic conditions, and large amounts of greenhouse gas (GHGs) emissions are common problems in large-scale aerobic composting systems. The aim of this study was to examine the effects of a semi-membrane covering on the spatial homogeneity and efficiency of fermentation in aerobic composting systems. In the covered group, the pile was covered with a semi-membrane, while in the non-covered group (control group), the pile was uncovered. The covered group entered the high-temperature period earlier and the spatial gradient difference in the group was smaller compared with the non-covered group. The moisture content loss ratio (5.91%) in the covered group was slower than that in the non-covered group (10.78%), and the covered group had a more homogeneous spatial distribution of water. The degradation rate of organic matter in the non-covered group (11.39%) was faster than that in the covered group (10.21%). The final germination index in the covered group (85.82%) was higher than that of the non-covered group (82.79%) and the spatial gradient difference in the covered group was smaller. Compared with the non-covered group, the oxygen consumption rate in the covered group was higher. The GHG emissions (by 30.36%) and power consumption in the covered group were reduced more significantly. The spatial microbial diversity of the non-covered group was greater compared with the covered group. This work shows that aerobic compost covered with a semi-membrane can improve the space homogeneity and efficiency of fermentation.

Effects of dicyandiamide, phosphogypsum and superphosphate on greenhouse gas emissions during pig manure composting

This study investigated the effects of dicyandiamide, phosphogypsum and superphosphate on greenhouse gas emissions and compost maturity during pig manure composting. The results indicated that the addition of dicyandiamide and phosphorus additives had no negative effect on organic matter degradation, and could improve the compost maturity. Adding dicyandiamide alone reduced the emissions of ammonia (NH₃), methane (CH₄) and nitrous oxide (N₂O) by 9.37 %, 9.60 % and 31.79 %, respectively, which was attributed that dicyandiamide effectively inhibited nitrification to reduce the formation of N₂O. Dicyandiamide combined with phosphogypsum or superphosphate could enhance mitigation of the total greenhouse gas (29.55 %-37.46 %) and NH₃ emission (18.28 %-21.48 %), which was mainly due to lower pH value and phosphoric acid composition. The combination of dicyandiamide and phosphogypsum exhibited the most pronounced emission reduction effect, simultaneously decreasing the NH₃, CH₄ and N₂O emissions by 18.28 %, 38.58 % and 36.14 %, respectively. The temperature and C/N content of the compost were significantly positively correlated with greenhouse gas emissions.

Membrane-covered composting significantly decreases methane emissions and microbial pathogens: Insight into the succession of bacterial and fungal communities

In this study, the effects of semipermeable membrane-covered on methane emissions and potential pathogens during industrial-scale composting of the solid fraction of dairy manure were investigated. The results showed that the oxygen concentration in the membrane-covered group (CT) was maintained above 10 %, and the cumulative methane emission in CT was >99 % lower than that in the control group (CK). Microbial analysis showed that the bacterial genus Thermus and the fungal genus Mycothermus were dominant in CT, and the richness and diversity of the bacterial community were greater than those of the fungal community. At the end of the composting, the relative abundance of potential bacterial pathogens in CT was 32.59 % lower than that in CK, and the relative abundance of potential fungal pathogens in each group was <2 %. Structural equation models revealed that oxygen concentration was a major factor influencing the bacterial diversity in CT, and the increase of oxygen concentration could limit methane emissions by inhibiting the growth of anaerobic bacteria. Therefore, membrane-covered composting could effectively improve compost safety and reduce methane emissions by regulating microbial community structure.

Micro-aerobic conditions based on membrane-covered improves the quality of compost products: Insights into fungal community evolution and dissolved organic matter characteristics

This study investigated the effects of micro-aerobic conditions on fungal community succession and dissolved organic matter transformation during dairy manure membrane-covered composting. The results showed that lignocellulose degradation in the micro-aerobic composting group (AC: oxygen concentration < 5 %) was slower than that in the static composting group (SC: oxygen concentration < 1 %), but the dissolved organic carbon in AC was greatly increased. The degree of aromatic polymerization was higher in AC than in SC. But the carboxyl carbon and alcohol/ether biodegradations were faster in SC than in AC, which promoted carbon dioxide and methane emissions, respectively. The relative abundances of pathogenic and dung saprotrophic fungi in AC were 44.6 % and 10.59 % lower than those in SC on day 30, respectively. Moreover, the relative abundance of soil saprotrophs increased by 5.18 % after micro-aerobic composting. Therefore, micro-aerobic conditions improved the quality of compost products by influencing fungal community evolution and dissolved organic matter transformation.

Oxygen dynamics, organic matter degradation and main gas emissions during pig manure composting: Effect of intermittent aeration

To investigate the effect of intermittent aeration on oxygen dynamics, organic matter degradation and main gas emissions, a lab-scale pig manure composting experiment was conducted with intermittent aeration (I_A, 30-min on and 30-min off) and continuous aeration (C_A). Although aeration volume and oxygen supply of I_A was only half of C_A, I_A could obviously enhance the oxygen utilization efficiency by 96.67 % and reduce energy dissipation for aeration by 50.87 %. Based on the comprehensive analysis of total organic matter, total carbon, total nitrogen, cellulose, hemicellulose and lignin contents, there was no significant difference in organic matter degradation between I_A and C_A (p > 0.05). Moreover, a reduction of 21.71 %, 38.93 %, 44.40 % and 62.19 % of CH₄, N₂O and the total GHG emission equivalent as well as NH₃ emissions was realized, respectively, in I_A compared with C_A. Therefore, adopting intermittent aeration was a useful strategy and choice for high-efficiency, high-quality and environment-friendly composting.

Exploring the microbial mechanism of reducing methanogenesis during dairy manure membrane-covered aerobic composting at industrial scale

In this study, the microbial mechanism of reducing methanogenesis during membrane-covered aerobic composting from solid dairy manure was investigated. An industrial-scale experiment was carried out to compare a static composting group (SC) and a forced aeration composting group (AC) with a semipermeable membrane-covered composting group (MC + AC). The results showed that the semipermeable membrane-covered could improve the oxygen utilization rate and inhibit the anaerobic bacterial genus Hydrogenispora and archaea order Methanobacteriales. During the membrane-covered period, the acetoclastic methanogenesis module in MC + AC, AC and SC decreased by 0.58%, 0.05% and 0.04%, respectively, and the cdhC gene in the acetoclastic pathway was found to be decreased by 65.51% only in MC + AC. Changes in methane metabolism pathways resulted in a 27.48% lower average methane concentration in MC + AC than in SC. Therefore, the semipermeable membrane-covered strategy can effectively reduce methane production during dairy manure aerobic composting by restricting the methanogenesis of the acetoclastic pathway.