Improvement of biochar and bacterial powder addition on gaseous emission and bacterial community in pig manure compost

Influence of bamboo biochar on mitigating greenhouse gas emissions and nitrogen loss during poultry manure composting

The effectiveness of specific concentrations of bamboo biochar (BB) on nutrient conservation based on gaseous emissions during poultry manure composting was investigated. The results indicate that the total carbon and nitrogen losses were significantly reduced with elevated of biochar from 542.8 to 148.9% and 53.5 to 12.6% (correspondingly with an additive of 0%, 2%, 4%, 6% and 8% to 10% BB dry weight based). The primary contributor was CO₂ and NH₃ losses (542.3-148.8% and 47.8-10.81%). The enzyme activities related to carbon and nitrogen metabolism indicated a positive and significantly enhanced with high concentration biochar amended composting. Simultaneously, the alteration of total organic carbon and total Kjeldahl nitrogen as well as maturity indexes during ultimate compost also confirmed a high quality product under higher content biochar amended composting. Carbon and nitrogen were best preserved with 10%BB and produced a superior final product. The analysis of a network and heat map illustrated the correlation of gaseous and physicochemical elements as well as enzyme activities, with an intersection of 68.81%.

Effect of aeration rates on enzymatic activity and bacterial community succession during cattle manure composting

In order to explore changes in microbial enzyme activity and bacterial community, a 60-day composting experiment was conducted using cattle manure and straw under aeration rates of 0.45, 0.68, and 0.90 L min^-1 kg^-1 fresh weight. High aeration rate increased the cellulase, urease, alkaline and acid phosphatase activities, but decreased that of invertase and catalase. Cellulase, alkaline phosphatase and catalase were the main enzymes that affected the composting process. Microbial analysis showed that high aeration rate increased the uniformity of bacterial community in thermophilic phase, but decreased that in mature phase. Different aeration rate affected the bacterial community structure and further influenced the relationship between enzyme and functional bacteria. Regulating the temperature, moisture content and EC in specific phases to affect bacterial community succession could provide guidance for improving maturity of composting.

Improved nitrogen conservation capacity during composting of dairy manure amended with oil shale semi-coke as the porous bulking agent

Oil shale semi-coke is the solid waste produced from the retorting process of oil shale, which may cause pollution to the environment without reasonable disposing. In this study, semi-coke was used as the bulking agent during composting to accelerate biodegradation of the organics as well as decrease the nitrogen loss. Results showed that the addition of semi-coke could accelerate biodegradation of the organics, with a raise in the organic matter loss from 44.99 % to 47.05 % compared with the control. Furthermore, the nitrogen loss significantly decreased from 40.00%-14.70 % in the treatment added with semi-coke due to less emission of NH₃ and much more transformation of NH₄⁺-N to NO₃^--N by nitrification, which could be explained by the increasing abundance of ammonia-oxidizing bacteria and archaea at the late composting stage and drastic shift of the microbial community like Chloroflexi, Firmicutes and Actinobacteria. After the composting cycle, the maturity of the produced compost was elevated greatly in the treatments amended with semi-coke. The result of PAHs detection suggested that there were low PAHs content in the raw oil shale semi-coke and they could be removed effectively to within the range for land application by composting especially when the surfactant was added.

Responses of enzymatic activity and microbial communities to biochar/compost amendment in sulfamethoxazole polluted wetland soil

Biochar and compost, two common amendments, were rarely conducted to investigate their combined influence on enzymatic activities and microbial communities in organic-polluted wetlands. This article described the effects of biochar/compost on degradation efficiency of sulfamethoxazole (SMX) and ecosystem responses in polluted wetland soil during the whole remediation process. 1% biochar (SB1) increased degradation efficiency of SMX by 0.067% ascribed to the increase of dehydrogenase and urease. 5% biochar (SB5) decreased degradation efficiency by 0.206% due to the decrease of enzymes especially for dehydrogenase. 2% compost (SC2), 1% biochar & 2% compost (SBC3), both 10% compost (SC10) and 5% biochar & 10% compost (SBC15) enhanced degradation efficiency by 0.033%, 0.015% and 0.222%, respectively, due to the increase of enzymes and biomass. The degradation efficiency was positively related to biomass and enzymatic activities. High-throughput sequencing demonstrated that HCGs (SB5, SC10, SBC15) improved the bacterial diversities but reduced richness through introducing more exogenous predominance strains and annihilated several inferior strains, while LCGs (SB1, SC2, SBC3) exhibited lower diversities but higher richness through enhanced the RAs of autochthonal preponderant species and maintained some inferior species. Additionally, HCGs raised the RAs of amino and lipid metabolism gene but lowered those of carbohydrate compared with LCGs.

RETRACTED: Increased abundance of nitrogen fixing bacteria by higher C/N ratio reduces the total losses of N and C in cattle manure and corn stover mix composting

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. The article duplicates significant parts of a paper that had already appeared in Bioresource Technology, Volume 297, February 2020, 122410, https://doi.org/10.1016/j.biortech.2019.122410. One of the conditions of submission of a paper for publication is that authors declare explicitly that the paper has not been previously published and is not under consideration for publication elsewhere. Re-use of any data should be appropriately cited. As such this article represents a misuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

Increased abundance of nitrogen transforming bacteria by higher C/N ratio reduces the total losses of N and C in chicken manure and corn stover mix composting

The aim of this work was to investigate how the initial C/N ratio during composting of chicken manure/corn stover mix affected the succession of dominant bacteria in the mix which led to the reduction of the total losses of N and C in the composting process. 16S rDNA sequencing indicated that the succession of predominant bacteria was significantly affected by the temperature and the initial C/N ratio during composting. Redundancy analysis showed that higher C/N appeared to promote the relative abundance of nitrogen fixing bacteria Thermoactinomyces, Planifilum, Flavobacterium, Bacillaceae, Pseudomonas,Sphingobacterium, Paenibacillus, Bacillus and Thermobifida, while compressing the denitrifying bacteria Pusillimonas, Ignatzschineria, Alcanivorax, Cerasibacillus, Truepera and Erysipelothrix. C/N ratio of 30:1 yielded the least C/N losses in the composting process, indicating that adjustment to the initial C/N ratio could affect nitrogen transforming bacteria to reduce the total losses of N and C and improve compost quality.

Beneficial effects of bacterial agent/bentonite on nitrogen transformation and microbial community dynamics during aerobic composting of pig manure

This study investigated the effects of adding a bacterial agent (B) and bentonite (BT) on nitrogen transformation, nitrogen functional genes, and the microbial community dynamics during the aerobic composting of pig manure, as well as their contributions to NH₃ and N₂O emissions. Treatments B, BT, and BT + B reduced the NH₃ emissions by 31.34%, 18.82%, and 23.67%, respectively, and the N₂O emissions by 53.16%, 72.56%, and 63.41%. N₂O and NH₃ emissions were strongly related to the functional genes. Adding bacterial agent promoted the ammonia oxidation process to reduce NH₃ emissions, whereas the influence of bentonite on nitrogen conversion was mostly related to nirS and nirK in denitrification processes. Nitrification and denitrification were dominated by different functional microorganisms in various stages of composting, where Proteobacteria comprised the most important denitrifying microorganisms. Thus, the additives reduced NH₃ and N₂O emissions by regulating nitrification and denitrification processes, and adding both was highly advantageous.

Compost supplementation with nitrogen loss and greenhouse gas emissions during pig manure composting

This research investigated the influence of biochar (B) and bean dregs (BD) amendments on carbon and nitrogen losses through greenhouse gas (GHG) emissions during pig manure (PM) composting. The treatments included 15% BD, 10% B and 15% BD+10% B (w/w dry basis of PM) amendments in the compost, whereas the CK (control) lacked any additives. The NH₄⁺-N, C/N and germination index (GI) of the end products ensured compost maturity. Compared with the CK, the 15% BD amendment increased the total nitrogen content (TKN) of the final product by 8.05% but also increased NH₃ (54.98%) and GHG emissions (40.35%) as well as nitrogen loss (25.62%). Furthermore, the combined treatment of 15% BD+10% B improved the TKN (2.83%) of the end product and controlled NH₃ emissions (33.71%), GHG emissions (29.56%) and nitrogen loss (24.26%) while increasing CO₂ only with the 15% BD amendment. Therefore, the combination of BD+B was recommended.

Nitrification plays a key role in N2O emission in electric-field assisted aerobic composting

Nitrous oxide (N₂O) emission is a serious environmental problem in composting. Previous studies have indicated that electric field assistance results in lower N₂O emissions in aerobic composting; however, the exact mechanisms involved in electric-field assisted aerobic composting (EAAC) are not clear. In this study, the biological N transformation processes and the N-associated genes were investigated. The results demonstrated that electric field application inhibited nitrification, weakened the nitrifying functional genes (the hao and nxrA genes declined maximally by 86% and 86.8%, respectively), and increased the N₂O consumption-related gene (nosZ) by a maximum factor of 2.76 compared with that in CAC. The correlation analysis demonstrated that nitrification was the main source of N₂O emission in EAAC. The findings imply that EAAC is a promising process for mitigating N₂O emission at the source during aerobic composting.

Role of NH3 recycling on nitrogen fractions during sludge composting

The aim of this study is to reduce nitrogen (N) loss and investigate the role of ammonia (NH₃) recycling on N fractions, environmental factors and bacterial communities. In this study, collected NH₃ from composting and recycled in it. The results showed that NH₃ recycling affected N-cycling processes such as nitrification. Redundancy Analyses (RDA) showed that NH₄⁺-N had significantly negative correlation with denitrifying bacteria in treatment group (p < 0.05), demonstrating that NH₃ recycling have influenced on the bacterial community structure. Furthermore, Structural Equation Model (SEM) revealed causal relationships between visual variables. Based on these results, we concluded that NH₃ recycling is a novel method to reduce N loss.

Effects of macroporous adsorption resin on antibiotic resistance genes and the bacterial community during composting

Swine manure is considered a reservoir for antibiotic resistance genes (ARGs), which may enter the soil and then the food chain to endanger human health. This study investigated the effects of adding 0%, 5%, and 15% (w/w) macroporous adsorption resin (MAR) on ARGs and the bacterial community during composting. The results showed that the addition of MAR reduced the abundances of ARGs (14.14-99.44%) and mobile genetic elements (MGEs) (47.83-99.48%) after swine manure composting. Significant positive correlations were detected between ARGs and MGEs, and thus the variations in MGEs may have led to the changes in ARGs. Redundancy analysis showed that MGEs had stronger effects on ARGs than environmental factors and the bacterial community. Network analysis suggested that ARGs and MGEs co-existed in common host bacteria. In conclusion, the results showed that adding 5% MAR can reduce the risk of ARG transmission.

Impact of pine leaf biochar amendment on bacterial dynamics and correlation of environmental factors during pig manure composting

The influence of pine leaf biochar (PLB) amendment on bacterial community succession and its correlation with physic-chemical parameters during pig manure (PM) composting was evaluated. The five different dosages of PLB [at 0% (T1), 2.5% (T2), 5% (T3), 10% (T4) and 15% (T5)] mixed with initial composting mass were conducted to composting for 50 days. The present study indicated that bacterial diversity was significantly (p < 0.05) higher in PLB amended treatments than the control, but T4 treatment showed the highest among the all PLB applied treatment. Firmicutes, Actinobacteria, Proteobacteria and Bacteroidete were four most abundant phyla of all the treatments. Furthermore, redundancy analysis showed that the bacterial community were significantly (p < 0.05) positively correlated with temperature, pH, TOC, CO₂ and NH₃ emissions, while they were negatively correlated with the N₂O and CH₄ emission. Overall, the results suggested that the addition of 10% PLB (T4 treatment) was a potential option to enhance the composting efficiency with significantly greater abundance of bacterial community and finally improved the compost quality.

Effects of four additives in pig manure composting on greenhouse gas emission reduction and bacterial community change

Four different additives of Medical stone (MS), Zeolite (ZL), Bamboo biochar (BC), and Wood vinegar (WV) were investigated in pig manure composting. The four additives reduced the peak CH₄ emission from 54% to 74%, while reduced N₂O loss from 36% to 69%, compared with control (CK). WV and ZL showed better ability in N₂O loss reduction, yet MS with the efficient inhibition both on CH₄ and NH₃ emissions. The bacterial community analysis indicated that bacterial diversity in the maturity phase was higher than that in the thermophilic phase, especially with treatments of ZL, BC and WV. The selected factors of pH, temperature, TOC and DOC could influence the thermophilic phase, while EC and TKN related closely with maturity phase in pig manure composting.

Evaluation of integrated biochar with bacterial consortium on gaseous emissions mitigation and nutrients sequestration during pig manure composting

This study focused on evaluate the effectiveness of biochar alone compare integrated with bacterial consortium amendment on the gaseous emissions mitigation as well as carbon and nitrogen sequestration during pig manure composting. Six additive treatments were performed based on uniform mixing pig manure with wheat straw [bacterial consortium (T2), 12%wood biochar (T3), 12%wood biochar + bacterial consortium (T4), 12%wheat straw biochar (T5), 12%wheat straw biochar + bacterial consortium (T6), while T1 without any additive]. The results obviously indicated that integrated use of biochar and bacterial consortium could remarkably relieved gaseous emissions, improved carbon and nitrogen conservation as well as accelerated maturity of composting. Notably the optimum combination was existed in T6 owing to lowest nutrient losses (nitrogen and carbon losses were 9.91 g/kg and 189.54 g/kg) and gas emissions (30.16 g/kg) as well as supreme maturity (germination index > 100%); it's an economic-practical and environmental protection novel disposal approach for solid waste.

Microbial inoculation influences bacterial community succession and physicochemical characteristics during pig manure composting with corn straw

This study determined the physicochemical changes and bacterial community succession in the pig manure composting process with microbial inoculant. Microbial inoculant could prolong the thermophilic stage by 2 days and increased the germination index (GI). Analysis with 16S rDNA showed that the Chao1 and Shannon indices increased at the thermophilic stage in the treatment (T), while those of the control (C) decreased. Microbial inoculant increased the relative abundance of Flavobacterium and Solibacillus in 4-12 and 12-24 days, respectively. Acinetobacter was reduced at 4-12 days. The key physicochemical factors affecting microbial successions were revealed by canonical correspondence analysis (CCA) and correlation analysis. Linear discriminant analysis (LDA) effect size (LEfse) analysis showed that there were 78 biomarkers, while in piles T and C, there were 35 and 43 biomarkers, respectively. These results indicated the addition of microbial inoculant improved the maturity and fertility, as well as significantly regulating the microbial community structure.

Impact of Composting Methods on Nitrogen Retention and Losses during Dairy Manure Composting

Currently, composting is one of the most effective methods for treating fecal waste on large-scale livestock and poultry farms, but the quality effects of different composting methods are different. In this study, we implemented four composting methods, including farmer compost (FC), anaerobic compost (AnC), mixed compost (MC), and aerobic compost (AC), to study the effects of different composting methods on nitrogen (N) losses while composting dairy manure. Our results showed that the germination indexes (GIs) of three of the composting treatments (AnC, MC, and AC) exceeded 80%, which met the maturity requirements for composted products. Ammonia (NH₃) emissions were the main contributor to nitrogen losses, while accumulated nitrous oxide (N₂O) emissions accounted for the lowest proportion of nitrogen losses. The cumulative N losses via the leachate of the AC treatment were the lowest and accounted for 0.38% of the initial total nitrogen (TN). The accumulated N losses of the AC, FC, AnC, and MC treatments accounted for 13.13% 15.98%, 15.08%, and 19.75%, respectively, of the initial TN. Overall, the AC method significantly reduced N losses via leachates, further reducing TN losses. This observation suggests that AC might be an appropriate method for highly efficient nitrogen management during dairy manure composting.

Effect of bean dregs on nitrogen transformation and bacterial dynamics during pig manure composting

This work studied the nitrogen transformation and bacterial dynamics in the co-composting of bean dregs (BD) and pig manure (PM). Four treatments were performed with BD at 0% (CK), 5%, 10% and 15% (w/w dry basis of PM) amended for 49-days aerobic compost. Results revealed that the temperature, NH₄⁺-N and pH of end product all met the maturity requirement. The BD-amendment increased nitrogen losses (8.55%-55.92%) during composting compared to CK. However, this amendment also enhanced total nitrogen content (TKN) of end products (1.86%-12%). The highest content of TKN was in 10%BD-amended treatment with relatively lower nitrogen loss compared to 15%BD. Furthermore, the results of 16S rDNA showed that BD-amended changed the bacterial community composition compared with CK. Especially, 10%BD-amended was the optimum in promoting the diversity and abundance of bacteria. Additionally, Firmicutes, Actinobacteria, Proteobacteria, Bacteroidetes and Chloroflexi were dominant phyla and Bacilli was dominant class in BD-amended compost.

Exploring the mechanisms of organic matter degradation and methane emission during sewage sludge composting with added vesuvianite: Insights into the prediction of microbial metabolic function and enzymatic activity

Effect mechanisms of organic matter (OM) degradation and methane (CH₄) emission during sewage sludge (SS) composting with added vesuvianite (V) were studied by high-throughput sequencing (HTS) and phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt). Results show that the addition of V accelerated the OM degradation and decreased the cumulative CH₄ emissions by 33.6% relative to the control. In addition, V significantly decreased the mcrA gene abundance and the methanogen community richness at the genus level. PICRUSt also indicated that V strengthens the microbial metabolic function and enzymatic activity related to OM degradation, and reduced the enzymatic activity related to CH₄ production. Methanogens community variation analysis proved the ratio of carbon and nitrogen and moisture content are the significant variables affecting CH₄ emissions. Thus, optimizing the ratio of carbon and nitrogen and moisture content will decrease CH₄ emission during SS composting.

Effect of Different Proportions of Three Microbial Agents on Ammonia Mitigation during the Composting of Layer Manure

Odor emissions represent one of the important issues of aerobic composting. The addition of microbial agents to compost is an important method for solving this problem, but this process is often unstable when a single microbial agent is added to the compost. Therefore, in this study, five treatments comprising different proportions of Bacillus stearothermophilus, Candida utilis, and Bacillus subtilis were tested to determine the best combination of the three microbial agents for ammonia reduction, as follows: control group (CK), 2:1:1 (A), 1:1:2 (B), 1:2:1 (C), and 1:1:1 (D). Compared with the CK group, the A, B, C, and D groups reduced ammonia emissions by 17.02, 9.68, 53.11, and 46.23%, respectively. The total ammonia emissions were significantly lower in C and D than in CK (p < 0.05). These two treatment groups had significantly increased nitrate nitrogen concentrations and decreased pH values and ammonium nitrogen concentrations (p < 0.05). Throughout the composting process, the total bacterial number was significantly higher in C and D than in CK (p < 0.05). Therefore, it is likely that B. stearothermophilus, C. utilis, and B. subtilis compounded from 1:2:1 (C) to 1:1:1 (D) reduced the ammonia emissions due to (1) a reduction in the pH and (2) the promotion of the growth of ammonia-oxidizing bacteria and the conversion of ammonium nitrogen to nitrate nitrogen. This study provides a theoretical basis and technical support for the odor problem of layer manure compost and promotes the development of composting technology.

Positive impact of biochar alone and combined with bacterial consortium amendment on improvement of bacterial community during cow manure composting

The present work studied to evaluate the effectiveness under the interaction of bacterial consortium and biochar applied to give impetus to bacterial community activities among cow manure composting. High-throughput sequencing technique and six treatments were carried out: T2, T3 and T6 were single apply of bacteria culture (C), 12%wood biochar (12%WB) and 12%wheat straw biochar (12%WSB), respectively, while T4 and T5 were bacterial consortium combined with 12%WB and 12%WSB respectively, and T1 was used as control. The conclusion shows that the richness of bacterial community were most prosperity in T5 and T4 that in line with the statistical analysis angle of curves and cluster. The dominate phyla of Firmicutes, Proteobacteria and Bacteroidetes were accounted to 31.36%, 34.79% and 33.85%, the superior genera were Dysgonomonas (16.55%), Empedobater (9.39%), Atopostipes (13.42%), Tissierella (8.25%), Marinimicrobium (14.45%) and Pseudomonas (9%). Overall, bacterial consortium combined with biochar could stimulate microbe activity to accelerate degradation, enhance richness and alter specific selection of bacterial community.

A systematic review of biochar use in animal waste composting

The animal production industry in the United States is currently undergoing a phase of growth; however, such growth brings certain challenges. One of the most prominent concerns in this regard is the increasing amounts of animal waste produced as a natural consequence of stock population growth. For decades, composting, including that of manure and animal mortalities, has been utilized to manage animal waste. Recently, in an effort to enhance the composting process, biochar has been proposed for use as a compost amendment, and over the last few years, an increasing number of papers on composting with biochar have been published. However, although there have been a few review papers that have summarized the literature regarding biochar use in composting, none of these has focused on animal waste composting. Accordingly, the purpose of this review is to critically analyze the role of biochar in livestock and poultry waste composting, identify gaps in our current knowledge, and propose future research directions. On the basis of the studies analyzed, biochar has the potential to improve animal waste composting processes at application rates of 5-10%. Biochar can extend the thermophilic phase of the composting process, lower the pH of compost material, prevent leachate formation, and reduce ammonia, methane, and nitrous oxide emissions. Given that the feedstock used to produce biochar and the pyrolysis conditions employed in its production affect the performance of biochar, it is important to report the physicochemical properties of the biochars used to enable comparison of the results of different studies. Moreover, there is a need for further research to gain a better understanding of the impact of biochar regarding the elimination of antibiotic-resistant genes and animal mortality composting.

Beneficial influences of pelelith and dicyandiamide on gaseous emissions and the fungal community during sewage sludge composting

Reducing the emissions of NH₃ and greenhouse gases (GHGs) during composting is essential for improving compost quality and controlling environmental pollution. This paper investigates the effects of pelelith (P) combined with dicyandiamide (DCD) on gaseous emissions and the fungal community diversity during sewage sludge (SS) composting. Results showed that the P and P + DCD treatments decreased the cumulative gaseous emissions by 41% and 22% for NH₃, 21% and 34% for N₂O, and 31.5% and 33.0% for CH₄, respectively. The evolution of the fungal community analysis showed that Ascomycota and unclassified fungi dominated during the thermophilic stage, while only Ascomycota was the dominant fungal phylum during the maturity stage, composing 62%, 66%, and 73% of the total fungal community in the control, P, and P + DCD, respectively. The P and P + DCD significantly increased the fungal community richness at the genus level. Fungal community abundance was found to be significantly related to temperature, pH, organic matter, and total Kjeldahl nitrogen, which also influence the gaseous emissions during SS composting. It suggested that the combined addition of pelelith and dicyandiamide (DCD) was an effective method for reducing the emissions of NH₃ and greenhouse gases during SS composting.

A comprehensive mitigation strategy for heavy metal contamination of farmland around mining areas - Screening of low accumulated cultivars, soil remediation and risk assessment

A three-year field test was conducted in an area surrounding past mining activity (mining area) to investigate the value of a novel comprehensive remediation strategy for Cd and Pb contamination, which included screening of low accumulated vegetable cultivars that take up Cd and Pb less than normal cultivars, in situ soil remediation using different soil amendments, and health risk assessment that evaluates the possibility of safe consumption for the vegetables. Results showed that cultivar Huoqing 91-5C of which vegetable was selected as a low accumulator of Cd and Pb in a soil contaminated with 0.5 mg kg^-1 and 8180 mg kg^-1 total Cd and Pb concentrations, respectively. Addition of 20 t ha^-1 of biochar with 2 t ha^-1 of calcium superphosphate in 10 cm depth could decrease available Cd and Pb by 70% and 85% after 1 year, respectively. Following treatments, hazard quotients for adults and children were below 1, indicating that the vegetables grown were safe for human consumption. The total cost of remediation was $3885 ha^-1, so the cost of the remediation of the combination of Cd and Pb was economic in this mining area.

Microbial community responses to biochar addition when a green waste and manure mix are composted: A molecular ecological network analysis

High-throughput sequencing and network analysis were used to investigate the dynamic changes and the effects on bacterial community structures in green waste compost after biochar addition. Biochar addition led to higher thermophilic temperatures and total nitrogen (TN) concentrations and a longer thermophilic period compared with no biochar addition. Biochar also greatly influenced the composition of the bacterial community. Nitriliruptoraceae and Bacillaceae abundances increased in the poultry manure after biochar treatment, and Alcaligenaceae, Rhodispirillaceae and Xanthomonadaceae were more abundant in the cattle manure. Dissolved organic carbon (DOC) and TN emerged as the key determinants of bacterial community composition. Network analysis revealed that DOC had strong positive associations with some taxa (e.g. Comamonas, Leucobacter and Acidimicrobiales), whereas TN had negative associations with other taxa (e.g. Microbacteriaceae and Aeromicrobium). This study has revealed the key taxa related to the carbon and nitrogen cycle during composting with biochar.

Effects of different composting strategies on methane, nitrous oxide, and carbon dioxide emissions and nutrient loss during small-scale anaerobic composting

Composting is considered as one of the main sustainable methods for the treatment of livestock manure. In this study we investigated the effects of additives (urea and rice straw) on methane (CH₄), nitrous oxide (N₂O), and carbon dioxide (CO₂) emissions using a traditional Chinese pig slurry composting method over an 81-day period, as well as examining total organic carbon and total nitrogen loss. Four common treatment strategies were examined in this study: a control (MC), urea nitrogen addition (MN), composting using rice straw cover (MS_cover), and compost mixed with rice straw (MS_mix). Our results indicate that the addition of urea resulted in the lowest total CH₄ emissions and the highest N₂O emissions. MS_cover treatment had the highest and most significant effect on CH₄ emissions, while MS_mix treatment had the lowest CO₂ emissions. Carbon lost through CH₄ and CO₂ released during the experiment was 0.1-0.9 and 2.4-3.9% of total carbon loss, respectively, and nitrogen lost through N₂O release was 11.1-17.9% of total nitrogen. In general, although MS_mix, MS_cover, and MN treatments increased global warming potential by 21.4, 41.6, and 50.9% per kg of pig slurry, respectively, no statistical differences between the four treatments were recorded. By considering carbon and nitrogen conservation, as well as the improvement of the quality of compost and the mitigation of greenhouse gases (GHGs), the small-scale composting method of pig slurry alone is an acceptable environmentally friendly strategy for use in China.

Effects of biochar size and type on gaseous emissions during pig manure/wheat straw aerobic composting: Insights into multivariate-microscale characterization and microbial mechanism

Greenhouse gas and ammonia emissions during composting with different biochar types and particle sizes were investigated. Compared with powder-biochar, granular-biochar improved pore connectivity and was benefit to methanotrophs activities, like Methylococcaceae, reducing CH₄ emissions. At the same particle size, bamboo biochar (BB) had a higher pore volume and more aerobic microenvironment within the compost than rice straw biochar (RSB), reducing GHG emissions. Bamboo biochar had high aromatic compound and NO₃^- concentrations and therefore surface π-π electron donor/acceptor interactions, causing low N₂O emissions and inhibiting denitrifying bacteria (e.g., Bacteroidales). More CO and CO bonds in rice straw biochar than bamboo biochar caused lower NH₃ emissions using rice straw than bamboo biochar. Powdered biochar had more exposed reactive functional groups and decreased NH₃ production better than granular biochar. Powdered bamboo biochar controls gaseous emissions better than other biochars during aerobic pig manure/wheat straw composting.

Effects of biochar on the microbial activity and community structure during sewage sludge composting

To explore the contributions of functional bacterial community in composting, we performed medium-scale composting of sewage sludge and sawdust mixtures amended with rice straw biochar at different dosages (5, 10, and 20% of fresh mixture weight) in 400 L bioreactor systems. The dynamics of enzyme activity and bacterial community composition were monitored during the composting. The addition of biochar above 10% inhibited the activity of protease but promoted the activities of cellulase and peroxidase, which also increased the fluctuation of bacterial diversity during the composting. The relationship between the activity of most enzymes and bacterial community was strengthened by the addition of biochar (10% and 20%), which further enhanced the contributions of the functional bacterial communities to composting. Therefore, the study provides evidence for the promoting effects of biochar on the functions of bacterial community.

Comparative evaluation of the use of acidic additives on sewage sludge composting quality improvement, nitrogen conservation, and greenhouse gas reduction

The aim of this study was investigated the effects of acidic additives apple pomace (AP), citric acid (CA), elemental sulphur (ES), phosphoric acid (PA), magnesium hydrogen phosphate (PM), and calcium superphosphate (CP)) on N conservation and greenhouse gas (GHG) emissions during sewage sludge composting. Results showed that adding the additives have no negative effects on compost hygienisation, but could improve the N conservation. Treatments with additives showed 2.56-5.48% N loss of initial N, which is lower than the control (9.73%). Compared to other compost products, ES- and PA-treatments had the lower NH₃ volatilizations (0.80% and 0.98% of initial N, respectively) and germination index values (0.52 and 0.74, respectively), while the higher N₂O emissions (2.48% and 2.29% of initial N, respectively) and salinities. Comprehensive evolution of N loss, GHG emissions and compost maturity in this study, the feasibility of using AP, CA, and PM in high-quality compost production is promising.

Succession of organics metabolic function of bacterial community in swine manure composting

Organics metabolic function of bacterial communities was evaluated in 60 days composting of swine manure and pumice by using MiSeq sequencing, PICRUSt and Biolog tools. The diversity of bacterial communities significantly decreased during the first 10 days, and gradually increased in the cooling and curing phase. The PICRUSt and Biolog analysis indicated that carbohydrate, lipid and amino acids metabolisms were relatively higher in the thermophilic phases. Xenobiotics biodegradation and metabolism, lipid metabolism, terpenoids and polyketides and biosynthesis of other secondary metabolites were mainly detected in the curing phases. Canonical correspondence analysis (CCA) indicated that the succession of bacterial community and organics utilization characteristics were highly affected by the temperature, moisture and oxidation reduction potential (ORP) in the swine composting system.

Influence of clay as additive on greenhouse gases emission and maturity evaluation during chicken manure composting

To assess the impact of clay as additive on compost maturity and reduction of greenhouse gases (GHGs) as well as ammonia emission during chicken manure composting. Six treatments with different dosages of clay (0%, 2%, 4%, 6%, 8% and 10% clay added by dry weight basis of chicken manure and wheat straw) were designed to conduct an aerobic composting experiment for 50 days. The results showed that the clay amendment could prolong the thermophilic phase and reduced the maturity period of composting. In addition, the GHGs (N₂O and CH₄) and ammonia emission of clay added treatments were reduced by 25.3-63.4%, 26.01-50.24% and 8.5-70.5%, respectively. But CO₂ emission was significantly higher in 10% clay amended treatment. Furthermore, the redundancy analysis showed that C/N ratio and total organic matter among all physiochemical properties had significant relationship with GHGs and ammonia emission. Therefore, this study shown that clay addition can promote maturity, reduced GHGs emission and improve the quality of product.