Assessing key microbial communities determining nitrogen transformation in composting of cow manure using illumina high-throughput sequencing

Dynamic changes in and correlations between microbial communities and physicochemical properties during the composting of cattle manure with Penicillium oxalicum

BACKGROUND

Penicillium oxalicum is an important fungal agent in the composting of cattle manure, but the changes that occur in the microbial community, physicochemical factors, and potential functions of microorganisms at different time points are still unclear. To this end, the dynamic changes occurring in the microbial community and physicochemical factors and their correlations during the composting of cattle manure with Penicillium oxalicum were analysed.

RESULTS

The results showed that the main phyla observed throughout the study period were Firmicutes, Actinobacteria, Proteobacteria, Bacteroidetes, Halanaerobiaeota, Apicomplexa and Ascomycota. Linear discriminant analysis effect size (LEfSe) illustrated that Chitinophagales and Eurotiomycetes were biomarker species of bacteria and eukaryote in samples from Days 40 and 35, respectively. Bacterial community composition was significantly correlated with temperature and pH, and eukaryotic microorganism community composition was significantly correlated with moisture content and NH4+-N according to redundancy analysis (RDA). The diversity of the microbial communities changed significantly, especially that of the main pathogenic microorganisms, which showed a decreasing trend or even disappeared after composting.

CONCLUSIONS

In conclusion, a combination of high-throughput sequencing and physicochemical analysis was used to identify the drivers of microbial community succession and the composition of functional microbiota during cattle manure composting with Penicillium oxalicum. The results offer a theoretical framework for explaining microecological assembly during cattle manure composting with Penicillium oxalicum.

Asynchronous characteristics of Feammox and iron reduction from paddy soils in Southern China

Recently, the newly discovered anaerobic ammonium oxidation coupled with iron reduction (i.e., Feammox) has been proven to be a widespread nitrogen (N) loss pathway in ecosystems and has an essential contribution to gaseous N loss in paddy soil. However, the mechanism of iron-nitrogen coupling transformation and the role of iron-reducing bacteria (IRB) in Feammox were poorly understood. This study investigated the Feammox and iron reduction changes and microbial community evolution in a long-term anaerobic incubation by 15N isotope labeling combined with molecular biological techniques. The average rates of Feammox and iron reduction during the whole incubation were 0.25 ± 0.04 μg N g-1 d-1 and 40.58 ± 3.28 μg Fe g-1 d-1, respectively. High iron oxide content increased the Feammox rate, but decreased the proportion of Feammox-N2 in three Feammox pathways. RBG-13-54-9, Brevundimonas, and Pelomonas played a vital role in the evolution of microbial communities. The characteristics of asynchronous changes between Feammox and iron reduction were found through long-term incubation. IRB might not be the key species directly driving Feammox, and it is necessary to reevaluate the role of IRB in Feammox process.

Control of nitrogen and odor emissions during chicken manure composting with a carbon-based microbial inoculant and a biotrickling filter

Although aerobic composting is usually utilized in livestock manure disposal, the emission of odorous gases from compost not only induces harm to the human body and the environment, but also causes loss of nitrogen, sulfur, and other essential elements, resulting in a decline in product quality. The impact of biotrickling filter (BTF) and insertion of carbon-based microbial agent (CBMA) on compost maturation, odor emissions, and microbial population during the chicken manure composting were assessed in the current experiment. Compared with the CK group, CBMA addition accelerated the increase in pile temperature (EG group reached maximum temperature 10 days earlier than CK group), increased compost maturation (GI showed the highest increase of 41.3% on day 14 in EG group), resulted in 36.59% and 14.60% increase in NO3--N content and the total nitrogen retention preservation rate after composting. The deodorization effect of biotrickling filter was stable, and the removal rates of NH3, H2S, and TVOCs reached more than 90%, 96%, and 56%, respectively. Furthermore, microbial sequencing showed that CBMA effectively changed the microbial community in compost, protected the ammonia-oxidizing microorganisms, and strengthened the nitrification of the compost. In addition, the nitrifying and denitrifying bacteria were more active in the cooling period than they were in the thermophilic period. Moreover, the abundance of denitrification genes containing nirS, nirK, and nosZ in EG group was lower than that in CK group. Thus, a large amount of nitrogen was retained under the combined drive of BTF and CBMA during composting. This study made significant contributions to our understanding of how to compost livestock manure while reducing releases of odors and raising compost quality.

Effect of simplified inoculum agent on performance and microbiome during cow manure-composting at industrial-scale

A simplified inoculum agent, only comprising Bacillus subtilis and Aspergillus niger, was utilized for industrial-scale cow-manure composting to investigate its impact on composting performance and microbiome. Inoculants elevated the average and peak temperatures by up to 7 and 10 °C, respectively, during the thermophilic stage, reduced organic matter content, and raised germination index. Inoculation also extended the period of composting above 50 °C from 12 to 26 days. Sequencing unveiled significant shifts in microbial diversity, composition, and function. Aspergillus thrived during the mesophilic phase, potentially initiating composting, whereas Bacillus, Lysinibacillus, and Clostridium were enriched during the thermophilic stage. Metagenomic sequencing revealed an increased abundance of carbohydrate-active enzymes and glycometabolism-related genes responsible for lignocellulose degradation and heat generation after inoculation. These enriched microbes and functional genes contributed to organic matter degradation and temperature maintenance during thermophilic stage, expediting composting. This suggests the effectiveness of this simplified inoculum in industrial-level cow-manure composting.

Disparities and mechanisms of carbon and nitrogen conversion during food waste composting with different bulking agents

The low C/N ratio, high moisture content, and low porosity of food waste require the addition of bulking agents for adjustment during the composting process. However, the effect and mechanism of different bulking agents on the reduction of carbon and nitrogen losses are unclear. Therefore, this study conducted experiments to evaluate and clarify the differences in carbon and nitrogen transformation between sawdust, rice husk and wheat bran in food waste composting. The results showed that the addition of bulking agents promoted the conversion of carbon and nitrogen into total organic carbon (TOC) and total organic nitrogen (TON) rather than CO2 and NH3. The carbon and nitrogen losses were reduced by 16.00-25.71% and 11.56-29.54%, respectively. Notably, the Sawdust group exhibited the highest carbon retention, whereas the Wheat_bran group demonstrated superior nitrogen retention. The succession of bacterial communities showed that sawdust enhanced the cellulolysis and xylanolysis functions while wheat bran promoted nitrogen fixation. Correlation analysis was further employed to speculate on potential interactions among carbon and nitrogen components. The incorporation of sawdust and rice husk improved humification partly due to the addition of lignocellulose and the accumulation of total dissolved nitrogen (DTN) in the substrate, respectively. In the process of ammonia assimilation, the addition of wheat bran promoted the accumulation of dissolved organic carbon (DOC), contributing to the synthesis of TON to a degree. These findings offer cost-effective strategies for conserving carbon and nitrogen from loss in food waste composting by selecting suitable bulking agents, ultimately producing high-quality fertilizer.

Treatment Options for Municipal Solid Waste by Composting and Its Challenges

Recovery and recycling of municipal solid waste biodegradable fraction (50-55%) are essential for attaining sustainability and a circular economy. Among organic waste treatment methods, composting is used to recycle organic fractions of waste. However, only 10-12% of municipal solid waste is utilized for composting treatment due to a lack of segregation practices and process challenges, including long process periods, odorous and greenhouse gas emissions, nitrogen loss, and low compost quality, which hinders large-scale practice. The current review paper discusses the challenges of composting treatment and its possible solutions. Various strategies were explored to address these challenges, such as utilizing microbial inoculum, additives, and optimization of physicochemical parameters. It also emphasizes the application of metagenomics for exploring key species. The knowledge about the microbial community and biochemical pathways (genome mining) can be exploited for the improvement of treatment efficiency.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-023-01087-4.

Investigation of underlying links between nitrogen transformation and microorganisms' network modularity in the novel static aerobic composting of dairy manure by "stepwise verification interaction analysis"

Conventional composting is a viable method treating agricultural solid waste, and microorganisms and nitrogen transformation are the two major components of this proces. Unfortunately, conventional composting is time-consuming and laborious, and limited efforts have been made to mitigate these problems. Herein, a novel static aerobic composting technology (NSACT) was developed and employed for the composting of cow manure and rice straw mixtures. During the composting process, physicochemical parameters were analyzed to evaluate the quality of compost products, and microbial abundance dynamics were determined using high-throughput sequencing technique. The results showed that NSACT achieved compost maturity within 17 days as the thermophilic stage (≥55 °C) lasted for 11 days. GI, pH, and C/N were 98.71 %, 8.38, and 19.67 in the top layer, 92.32 %, 8.24, and 22.38 in the middle layer, 102.08 %, 8.33, and 19.95 in the bottom layer. These observations indicate compost products maturated and met the requirements of current legislation. Compared with fungi, bacterial communities dominated NSACT composting system. Based on the stepwise verification interaction analysis (SVIA), the novel combination utilization of multiple statistical analyses (Spearman, RDA/CCA, Network modularity, and Path analyses), bacterial genera Norank Anaerolineaceae (-0.9279*), norank Gemmatimonadetes (1.1959*), norank Acidobacteria (0.6137**) and unclassified Proteobacteria (-0.7998*), and fungi genera Myriococcum thermophilum (-0.0445), unclassified Sordariales (-0.0828*), unclassified Lasiosphaeriaceae (-0.4174**), and Coprinopsis calospora (-0.3453*) were the identified key microbial taxa affecting NH₄⁺-N, NO₃^--N, TKN and C/N transformation in the NSACT composting matrix respectively. This work revealed that NSACT successfully managed cow manure-rice straw wastes and significantly shorten the composting period. Interestingly, most microorganisms observed in this composting matrix acted in a synergistic manner, promoting nitrogen transformation.

Response characteristics of denitrifying bacteria and denitrifying functional genes to woody peat during pig manure composting

This study aimed to explore the impacts of adding different proportions of woody peat (WP) (0%(CK), 5%(T1), and 15%(T2)) on denitrification during composting. The results demonstrated that compared with CK, T1 and T2 increased the total Kjeldahl nitrogen content (8% and 14%, respectively) and reduced the nitrate nitrogen (7% and 23%) content after composting. After composting, the abundances of nirK and nirS decreased by 4-9% and 33-35% under T1 and T2, respectively. Adding 15% WP reduced the abundances of key denitrifying bacteria such as Pseudomonas, Pusillimonas, Achromobacter, and Rhizobiales by 5-90%. The main factors that affected denitrification genes were the carbon content, nitrogen form (nitrite nitrogen and ammonium nitrogen), and denitrifying bacteria community. In summary, adding 15% WP has the best ability to reduce nitrogen loss by decreasing the abundances of denitrifying bacteria and denitrifying functional genes, thereby improving the agricultural value of composting products.

Co-composting of cattle manure and wheat straw covered with a semipermeable membrane: organic matter humification and bacterial community succession

Semipermeable membrane-covered composting is one of the most commonly used composting technologies in northeast China, but its humification process is not yet well understood. This study employed a semipermeable membrane-covered composting system to detect the organic matter humification and bacterial community evolution patterns over the course of agricultural waste composting. Variations in physicochemical properties, humus composition, and bacterial communities were studied. The results suggested that membrane covering improved humic acid (HA) content and degree of polymerization (DP) by 9.28% and 21.57%, respectively. Bacterial analysis indicated that membrane covering reduced bacterial richness and increased bacterial diversity. Membrane covering mainly affected the bacterial community structure during thermophilic period of composting. RDA analysis revealed that membrane covering may affect the bacterial community by altering the physicochemical properties such as moisture content. Correlation analysis showed that membrane covering activated the dominant genera Saccharomonospora and Planktosalinus to participate in the formation of HS and HA in composting, thus promoting HS formation and its structural complexity. Membrane covering significantly reduced microbial metabolism during the cooling phase of composting.

Indigenous cyanobacteria enhances remediation of arsenic-contaminated soils by regulating physicochemical properties, microbial community structure and function in soil microenvironment

Biocrust was widely used for the immobilization and removal of arsenic (As) in drainage systems of rice fields and mining areas. In this study, the role of an indigenous cyanobacteria (Leptolyngbya sp. XZMQ) was explored in the bioremediation of As-contaminated farmland and tailing soil. After 80 d of inoculation with cyanobacteria, total As (As(T)) accumulated in the cyanobacterial crust of farmland and tailing soil was 279.89 mg kg^-1 and 269.57 mg kg^-1, respectively, and non-EDTA exchangeable fraction was the major fraction of it. The As(T) in farmland and tailing soil of micro-environment decreased by 10.76% and 12.73%, respectively. Meanwhile, the available As (As(a)) decreased by 21.25% and 27.65%, respectively. The XRD results showed that hematite and SiO₂ existed in cyanobacterial crust of farmland and tailing soil. FTIR spectra indicated that the adsorption of As in cyanobacterial crust was mediated by OH and CO. After inoculation of Leptolyngbya sp. XZMQ, in subcrust soil, As biotransformation gene aioA was the most abundant, followed by arsM. The dominant phyla of soil biota were Proteobacteria, Cyanobacteria, Actinobacteria, and Bacteroiota, which could play critical roles in shaping aioA and arsM harboring microbe communities in soil. Redundancy analysis (RDA) showed that soil organic carbon (OC), pH, and chlorophyll a (Chl a) were the most important environmental factors in altering soil bacterial communities. Correlation analysis showed the Leptolyngbya had a positive correlation with Chl a, effective nitrogen (N(a)), electrical conductivity (EC), OC, pH in the soil, respectively, while it had a significant negative correlation with As(a), As(III) and As(T). These results emphasized on the significance of cyanobacteria in the behavior of As in mine soils and offered a promising strategy for bioremediation of As-contaminated soil in the mining area.

Deciphering biochar compost co-application impact on microbial communities mediating carbon and nitrogen transformation across different stages of corn development

Under current climatic conditions, developing eco-friendly and climate-smart fertilizers has become increasingly important.The co-application of biochar and compost on agricultural soils has received considerable attention recently.Unfortunately, little is known about its effects on specific microbial taxa involved in carbon and nitrogen transformation in the soil.Herein, we report the efficacy of applying biochar-based amendments on soil physicochemical indices, enzymatic activity, functional genes, bacterial community, and their network patterns in corn rhizosphere at seedling (SS), flowering (FS), and maturity (MS) stages.The applied treatments were: compost alone (COM), biochar alone (BIOC), composted biochar (CMB), fortified compost (CMWB), and the control (no fertilizer (CNTRL).The non-metric multidimensional scaling (NMDS) indicated total nitrogen (TN), pH, NO₃^--N, urease, protease, and microbial biomass C (MBC) as the dominant environmental factors driving soil bacteria in this study.The dominant N mediating genes belonged to nitrate reductase (narG) and nitronate monooxygenase (amo), while beta-galactosidase, catalase, and alpha-amylase were the dominant genes observed relating to C cycling.Interestingly, the abundance of these genes was higher in COM, CMWB, and CMB compared with the CNTRL and BIOC treatments.The bacteria network properties of CWMB and CMB indicated robust niche overlap associated with high cross-feeding between bacterial communities compared to other treatments.Path and stepwise regression analyses revealed norank_Reyranellaceae and Sphingopyxis in CMWB as the major bacterial genera and the major predictive indices mediating soil organic C (SOC), NH₄⁺-N, NO₃^--N, and TN transformation.Overall, biochar with compost amendments improved soil nutrient conditions, regulated the composition of the bacterial community, and benefited C/N cycling in the soil ecosystem.

Variations of microbiota in three types of typical military contaminated sites: Diversities, structures, influence factors, and co-occurrence patterns

Contamination with energetic compounds (ECs) is common in military sites and poses a great risk to the environment and human health. However, its effects on the soil bacterial communities remain unclear. This study assessed the variations of bacterial communities, co-occurrence patterns, and their influence factors in three types of typical military-contaminated sites (artillery range, military-industrial site, and ammunition destruction site). The results showed that the most polluted sites were ammunition destruction sites, followed by military-industrial sites, whereas pollution in the artillery ranges was minimal. The average concentrations of ECs including 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) in the study sites ranged 120-1.67 × 10⁵, 20-7.20 × 10⁴, and 180-2.38 × 10⁵ μg/kg, respectively. Bacterial diversity and community structure in military-industrial and ammunition destruction sites were significantly changed, but not in artillery ranges. TNT, pH, and soil moisture are the critical factors affecting bacterial communities in contaminated military sites. Co-occurrence network analysis indicated that the pressure of ECs affected bacterial interactions and microbiota function. Our findings provide new insights into the variations in bacterial communities in EC-contaminated military sites and references for the bioremediation of ECs.

Involvement of exogenous arsenic-reducing bacteria in root surface biofilm formation promoted phytoextraction of arsenic

Root surface biofilm (RSB) is the last window for pollutants entering plant roots and thus plays a critical role in the phytoextraction of pollutants. Exogenous arsenic-reducing bacteria (EARB) have been adopted to enhance the phytoextraction of arsenic (As). However, whether EARB would be involved in RSB formation together with indigenous bacteria and the role of EARB involvement in As phytoextraction are still unknown. Herein, two EARB strains and two phytoextractors (wheat and maize) were selected to investigate the involvement of EARB in RSB formation and its role in As phytoextraction. Results showed that EARB successfully participated in RSB formation together with indigenous bacteria, attributing to their strong chemotaxis and biofilm formation abilities induced by root exudates. The involvement of EARB in RSB formation significantly enhanced As accumulation in plant roots, since more arsenite (As(III)) caused by arsenate (As(V)) reduction in RSB was absorbed by roots. Its underlying mechanism was further elucidated. EARB involvement increased phylum Proteobacteria to produce more siderophores in RSB. Siderophores then improved photosynthesis by increasing catalase and peroxidase activities and decreasing the malondialdehyde of plants. These actions further raised the shoot fresh weight to enhance As accumulation in plant roots. Moreover, mesophyll cell in wheat has a stronger As(V) reduction ability than that in maize, resulting in opposite distribution patterns of As(III) and As(V) in wheat and maize shoots. This study provides a new understanding of phytoextraction enhanced by exogenous bacteria and fills the gap in the role of EARB in As phytoextraction from the perspective of the RSB microregion.

Food waste digestate composting enhancement by sodium polyacrylate addition: Effects on nitrogen transformation processes and bacterial community dynamics

The influences of sodium polyacrylate (PAAS) at the ratios of 0% (CK), 0.5% (F1), 1.0% (F2), 1.5% (F3), 2.0% (F4) and 2.5% (F5) on nitrogen transformation and bacterial community composition were investigated in the composting of food waste digestate (FWD) and corn straw (CS). PAAS addition increased the thermophilic temperature but had no significant effect on pH values. PAAS exerted significantly effects on the concentration of total nitrogen (TN), ammonia nitrogen (NH₄⁺-N), nitrite-nitrogen (NO₂^--N) and nitrate-nitrogen (NO₃^--N). The compost product in 1.0% PAAS treatment was more active in absorbing nutrients. Firmicutes (9.40-83.54%), Actinobacteriota (9.98-51.50%), Proteobacteria (0.20-27.87%) and Bacteroidota (0.11-34.69%) were the dominant phyla in FWD composting. Moreover, relative to CK, PAAS promoted the propagation of dominant bacterial phyla Firmicutes with increment of 30.05-102.06% in the thermophilic phase. Kroppenstedtia, Thermobifida and Saccharomonospora were observed to be dominant at the maturing phase and correlated with NH₄⁺-N, NO₂^--N, TN and NO₃^--N. Therefore, they might be regarded as probable biomarkers symbolic for the maturing phase during FWD composting. The compost product had the highest maturity degree in 1.0% PAAS treatment. These results indicated that PAAS addition improved the maturity and nutrient contents of the compost product as well as altered compost bacterial community dynamics.

Effects of sponge iron dosage on nitrogen removal performance and microbial community structure in sequencing batch reactors

The application of sponge iron (SI) carriers can improve the biochemical treatment performance of sequencing batch reactors (SBR) during wastewater treatment. This study used SBR reactors to explore the effects of SI dosage on the nitrogen removal performance and reactor stability and microbial community structure under low temperature and ultra-low load. In contrast to conventional SBR, the average removal rate of total nitrogen (TN) in the biological sponge iron system (BSIS) was increased by 5.38 % for 45 g/L, 18.93 % for 90 g/L, and 13.52 % for 135 g/L, respectively. The nitrogen removal performance and reactor stability showed the best performance under the SI dosage of 90 g/L. The addition of SI formed the anaerobic-anoxic-aerobic microenvironments, which facilitate the propagation of denitrifying bacteria (Saccharimonadales, Hydrogenophaga) and iron bacteria (Rhodoferax and Acinetobacter) in the BSIS. This study provides a new insight on the application of SI in the wastewater treatment.

Effects of di-n-butyl phthalate on aerobic composting process of agricultural waste: Mainly based on bacterial biomass and community dynamics analysis

Phthalic acid esters (PAEs) pollution has become a major environmental problem in agricultural waste composting. However, little information was available about the how the PAEs alter microbial processes during composting. This study investigated the effects of di-n-butyl phthalate (DBP) on bacterial biomass and community dynamics during composting. The results showed that a decreasing of DBP was observed from thermophilic phase and 43.26% of DBP was degraded after composting. The bacterial biomass and diversity during composting were reduced under DBP stress, so delaying the decomposition of organic matter. Moreover, the changes in bacterial community were observed since the thermophilic phase of DBP-contaminated composting. KEGG pathway analysis indicated that DBP stress decreased the relative abundance of the main metabolic pathways and inhibited compost maturation. Moreover, DBP stress had more significant correlation with the dominant bacteria. This work will expand the understanding of PAEs-contaminated organic waste composting and further control of PAEs pollutants.

Copiotrophic taxa in pig manure mitigate nitrogen limitation of soil microbial communities

Microbial nitrogen (N) limitation is a common problem in terrestrial ecosystems. Pig manure, a type of solid waste, is increasingly applied to improve soil N availability in agriculture through inputs of organic matter and inorganic N. Pig manure application also introduces a lot of exogenous microorganisms, which have distinctly different N requirements and metabolic properties, into the resident soil microbial community. However, the impacts of these manure-borne microorganisms on soil N cycling have not been well determined. Here, we investigated effects of manure-borne microorganisms on the N limitation of soil microorganisms using an ecoenzymatic stoichiometry analysis. We monitored microbial communities over a 90-day period in a laboratory-controlled experiment with four treatments: (1) non-sterilized soil mixed with non-sterilized manure (S-M), (2) non-sterilized soil mixed with sterilized manure (S-sM), (3) sterilized soil mixed with non-sterilized manure (sS-M), and (4) non-sterilized soil without manure addition (S, the control). The microbial N limitations were significantly mitigated in both S-M and sS-M. By contrast, the S-sM and S showed high levels of microbial N limitation, likely stemming from differences in the microbial functional composition. We found chitin-degrading bacteria were the dominant copiotrophic manure-borne bacteria associated with N mineralization, and they may improve soil N availability. We further identified several copiotrophic manure-borne bacteria in S-M and sS-M, and their abundances had significantly negative correlation with the level of N limitation and significantly positive correlation with the stoichiometric homeostasis. As these copiotrophic taxa can maintain homeostasis through regulating enzymatic activities, our results indicate that copiotrophic taxa in pig manure contribute to the mitigation of soil microbial N limitation. Our study also highlights the invasiveness capacity of manure-borne microorganisms in soil and evaluates the biotic effects of manure application on soil N cycling.

Understanding Responses of Soil Microbiome to the Nitrogen and Phosphorus Addition in Metasequoia glyptostroboides Plantations of Different Ages

Nitrogen (N) and phosphorus (P) have significant effects on soil microbial community diversity, composition, and function. Also, trees of different life stages have different fertilization requirements. In this study, we designed three N additions and three P levels (5 years of experimental treatment) at two Metasequoia glyptostroboides plantations of different ages (young, 6 years old; middle mature, 24 years old) to understand how different addition levels of N and P affect the soil microbiome. Here, the N fertilization of M. glyptostroboides plantation land (5 years of experimental treatment) significantly enriched microbes (e.g., Lysobacter, Luteimonas, and Rhodanobacter) involved in nitrification, denitrification, and P-starvation response regulation, which might further lead to the decreasing in alpha diversity (especially in 6YMP soil). The P addition could impact the genes involved in inorganic P-solubilization and organic P-mineralization by increasing soil AP and TP. Moreover, the functional differences in the soil microbiomes were identified between the 6YMP and 24YMP soil. This study provides valuable information that improves our understanding on the effects of N and P input on the belowground soil microbial community and functional characteristics in plantations of different stand ages.

The nitrogen cycle and mitigation strategies for nitrogen loss during organic waste composting: A review

Composting is a promising technology to decompose organic waste into humus-like high-quality compost, which can be used as organic fertilizer. However, greenhouse gases (N₂O, CO₂, CH₄) and odorous emissions (H₂S, NH₃) are major concerns as secondary pollutants, which may pose adverse environmental and health effects. During the composting process, nitrogen cycle plays an important role to the compost quality. This review aimed to (1) summarizes the nitrogen cycle of the composting, (2) examine the operational parameters, microbial activities, functions of enzymes and genes affecting the nitrogen cycle, and (3) discuss mitigation strategies for nitrogen loss. Operational parameters such as moisture, oxygen content, temperature, C/N ratio and pH play an essential role in the nitrogen cycle, and adjusting them is the most straightforward method to reduce nitrogen loss. Also, nitrification and denitrification are the most crucial processes of the nitrogen cycle, which strongly affect microbial community dynamics. The ammonia-oxidizing bacteria or archaea (AOB/AOA) and the nitrite-oxidizing bacteria (NOB), and heterotrophic and autotrophic denitrifiers play a vital role in nitrification and denitrification with the involvement of ammonia monooxygenase (amoA) gene, nitrate reductase genes (narG), and nitrous oxide reductase (nosZ). Furthermore, adding additives such as struvite salts (MgNH₄PO₄·6H₂O), biochar, and zeolites (clinoptilolite), and microbial inoculation, namely Bacillus cereus (ammonium strain), Pseudomonas donghuensis (nitrite strain), and Bacillus licheniformis (nitrogen fixer) can help control nitrogen loss. This review summarized critical issues of the nitrogen cycle and nitrogen loss in order to help future composting research with regard to compost quality and air pollution/odor control.

Analysis of the influence paths of land use and landscape pattern on organic matter decomposition in river ecosystems: Focusing on microbial groups

Organic matter decomposition (OMD) is one of the important river ecosystem functions. Changes in land use and landscape pattern (LULP) have a serious influence on the OMD in neighboring river ecosystems. However, there is limited information on the influence paths of LULP on organic matter decomposition in river ecosystems. In this study, cotton strip (CS) as a substitute for investigating OMD, was introduced to the delineated catchments in Luanhe River Basin in China, meanwhile combining with remote sensing interpretation, water quality analysis, microbial sequencing, and redundancy analysis (RDA) to identify the dominant LULP metrics, water quality parameters, and microbial groups controlling the OMD. Then the structural equation models (SEMs) were used to connect these dominant controlling factors to track the influence paths of LULP on OMD in river ecosystems. RDA results indicated that construction land (CON), farmland (FAR) and landscape shape index (LSI) in LULP, total nitrogen (TN), chemical oxygen demand (COD) and pH in water quality, bacterial phyla Planctomycetes and Firmicutes, as well as fungal phyla Chytridiomycota and Basidiomycota were the dominant factors controlling the OMD (quantified by tensile strength loss (TSL) and respiration (RES)). These four microbial phyla contributed significantly to OMD. SEMs further proposed three paths to explain the mechanism of LULP influencing on OMD, which were CON - TN - Firmicutes - TSL, CON - TN - Chytridiomycota - RES, and FAR - COD - Chytridiomycota - TSL. CON promoted OMD mainly through enhancing TN content in river water to increase Firmicutes and Chytridiomycota. FAR increased Chytridiomycota by decreasing COD in river water, promoting OMD. These results will deepen our understanding of the influence of LULP on river ecosystem functions and provide valuable information for policymakers and managers to carry out watershed land planning and river management in the future.

Bacteria in (vermi)composted organic wastes mostly survive when applied to an arable soil cultivated with wheat (Triticum sp. L.)

Composting and vermicomposting are an environmentally friendly way to reduce pathogens in organic wastes and generate a valuable product that provides nutrients for crops. However, how the bacterial community structure changes during these different processes and if the bacteria applied with the (vermi)composted products survive in an arable cultivated soil is still largely unknown. In this study, we monitored how the bacterial community structure changed during conditioning, composting with and without Eisenia fetida, and when the end-product was applied to arable soil cultivated with wheat Triticum sp. L. The organic wastes used were biosolid, cow manure, and a mixture of both. Large changes occurred in the relative abundance of some of the most abundant bacterial genera during conditioning, but the changes were much smaller during composting or vermicomposting. The bacterial community structure was significantly different in the organic wastes during conditioning and (vermi)composting but adding E. fetida had no significant effect on it. Changes in the relative abundance of the bacterial groups in the (vermi)composted waste applied to the arable soil cultivated with wheat were small, suggesting that most survived even after 140 days. As such, applying (vermi)composted organic wastes not only adds nutrients to a crop but also contributes to the survival of plant growth-promoting bacteria found in the (vermi)compost. However, putative human pathogens found in the biosolid also survived in the arable soil, and their relative abundance remained high but mixing the biosolid with cow manure reduced that risk. It was found that applying (vermi)composted organic wastes to an arable soil not only provides plant nutrients and adds bacteria with plant growth-promoting capacities, but some putative pathogens also survived.

Insights on dissolved organic matter and bacterial community succession during secondary composting in residue after black soldier fly larvae (Hermetia illucens L.) bioconversion for food waste treatment

Black soldier fly larvae (Hermetia illucens L. BSFL) bioconversion is a promising biotechnology for food waste treatment. However, the separated residues still do not meet criteria for use as land application biofertilizers. In this work, we investigated a full-scale BSFL bioconversion project to explore features of dissolved organic matter (DOM) and its associated responses of bacterial community succession in residue during secondary composting. Data showed that the concentrations of total nitrogen and ammonium nitrogen decreased by 11.8% and 22.6% during the secondary composting, respectively, while the nitrate nitrogen concentration increased 18.7 times. The DOM concentration decreased by 69.1%, in which protein-like, alcohol-phenol, and biodegradable aliphatic substances were metabolized by bacteria during the thermophilic phase together with the accumulation of humus-like substances, resulting in an increase in the relative concentration of aromatic compounds. The structure of the bacterial community varied at different stages of the bioprocess, in which Bacteroidetes, Actinobacteria, Proteobacteria, and Firmicutes were the dominant bacterial phyla. Lysinibacillus, Pusillimonas, and Caldicoprobacter were found to be key contributors in the degradation and formation of DOM. The DOM concentration (33.4%) and temperature (17.7%) were the prime environmental factors that promoted succession of the bacterial community. Through bacterial metabolism, the structural stability of DOM components was improved during the composting process, and the degrees of humification and aromaticity were also increased. This study depicted the dynamic features of DOM and the associated bacterial community succession in residue during secondary composting, which is conducive with the reuse of BSFL residue as biofertilizer for agriculture.

Microecological insight to fungal structure and key fungal communities regulating nitrogen transformation based on spatial heterogeneity during cow manure composting by multi-angle and multi-aspect analyses

Composting is the mainstream technology for the treatment of agricultural solid waste, but limited efforts were made to investigate fungal composition and its contributions to nitrogen transformation in different depths of compost. In this study, spatial distributions of fungi were analyzed using high throughput sequencing by multi-angle analyses, and the key fungal communities determining nitrogen transformation were quantified and identified by multi-aspect analyses during cow manure composting. Multi-angle analyses showed that fungal structure, biomarkers and trophic mode composition varied in different layers, revealing that spatial heterogeneity is the distinctive attribute of composting system. Ascomycota and Basidiomycota were dominant phyla during composting, the two phyla peaked in top and bottom layer respectively. At mesophilic stage, Tremellales, and unclassified Ascomycota (order) were biomarkers in top and middle layer respectively, and so were Remersonia, Pyrenochaetopsis, and Wallemia in bottom layer by LEfSe analysis. Based on multi-aspect analyses, Unclassified Dothideomycetes mainly affected NH₄⁺-N transformation both in top (1.2816***) and middle layers (1.1726*). Trichocladium asperum (0.9536***) and Zopfiella (-0.9484***) mainly affected TN transformation in top layer. Guehomyces pullulans (-0.9684**) and Preussia (-1.0508**) regulated NO₃^--N transformation in middle layer. Thermomyces lanuginosus (0.7127***) and Typhula sp. UW973129 (0.7298***) were the key species promoting TN and C/N transformation in bottom layer, respectively. Interestingly, different fungal communities showed a complex network interaction driving nitrogen transformation, and the abundance of microbial community could be conducive to characterizing nitrogen transformation in the vertical space of composting.

Producing high-quality cultivation substrates for cucumber production by in-situ composting of corn straw blocks amended with biochar and earthworm casts

In-situ composting is an efficient method for the dispose of crop residues. However, the high organic carbon content and low water-holding capacity of corn (Zea mays L.) straw can easily result in a slow composting process with high nutrient loss. In this study, compressed corn straw blocks was a control (S), straw mixed with earthworm casts (SE), straw mixed with biochar (SB), straw mixed with earthworm casts and biochar (SEB) were treatments to determine their effects on in-situ composting performance. In general, compared with S, the thermophilic period was extended by 14, 13 and 3 days in SE, SB and SEB, respectively, reduced nutrient loss, the water holding porosity of SE and SEB increased by 28.67% and 24.03%. Besides, the bacterial Shannon and Pielou's indices of SEB increased by 9.42% and 9.33%, respectively, and the relative abundance of Acinetobacter was increased in SB and SEB. Amino acid metabolism and carbohydrate metabolism were the most abundant metabolic processes in composts. SEB showed not only the highest cucumber yields, but also the highest OQI. The OQI of the CCSBs was significantly and positively correlated with cucumber yields (P < 0.001). These results indicated that the combination of earthworm casts and biochar was more effective than each single additive during in-situ composting of corn straw blocks, and emphasized that the overall quality of CCSBs played pivotal roles in determining the agronomic performance of CCSBs. In addition, the in-situ composting of corn straw blocks could be used to produce high-quality cultivation substrates.

Ventilation induced evolution pattern of archaea, fungi, bacteria and their potential roles during co-bioevaporation treatment of concentrated landfill leachate and food waste

To obtain a favorable aeration type in co-bioevaporation treatment of concentrated landfill leachate and food waste, and to deeply understand the co-bioevaporation mechanisms, the temporal evolution differences of archaea, fungi and bacteria as well as the related microbial metabolism genes and functional enzymes under intermittent ventilation (IV) and continuous ventilation (CV) were investigated. Results through metagenomics analysis showed that the less sufficient oxygen and longer thermophilic phase in IV stimulated the vigorous growth of archaea, while CV was beneficial for fungal growth. Even genes of carbohydrates and lipids metabolism and ATP-associated enzymes (enzyme 2.7.13.3 and 3.6.4.12), as well as peptidoglycan biosynthesis enzyme (enzyme 3.4.16.4), were more abundant in CV, IV hold better DNA repair ability, higher microbial viability, and less dehydrogenase sensitivity to temperatures due to the critical contribution of Pseudomonas (3.1-45.9%). Furthermore, IV consumed a similar amount of heat for water evaporation with nearly half of the ventilation of CV and was a favorable aeration type in the practical application of co-bioevaporation.

Nitrate and nitrite pathways and dynamic changes in bacterial communities during beet sugar processing

BACKGROUND

Bacterial community successions were surveyed during the processing stages of sugar production using high-throughput sequencing methods. Furthermore, the correlation between bacterial community and nitrate/nitrite content in beet sugar processing were investigated.

RESULTS

In an analysis of the V3-V4 region of the 16S rDNA gene, 254 122 effective sequences were obtained from samples, which included sugar beet, cossettes, diffusion juice, second-phase diffusion juice, light juice and thick juice. The results showed that dominant genera included Pantoea, Pseudomonas, Leuconostoc and Burkholderia. Moreover, significant changes in bacterial communities were observed in samples. Regarding the relevant nitrogen metabolic potential, this study revealed communities with the ability for nitrate and nitrite metabolism. Furthermore, a shaking experiment involving diffusion juice and second-phase diffusion juice was performed, and results showed that the nitrate level declined 73% and 98% in 36 h, respectively. These results suggested that the bacterial communities contribute to nitrate and nitrite transformation.

CONCLUSION

This study illustrated that the bacterial communities and their specific effects on the formation of nitrate and nitrite during beet sugar processing. The results presented the basic concept involving the nitrate- and nitrite-forming pathways directly related to the mechanism of bacterial community growth. This study could facilitate an understanding of the correlation between nitrite content and microorganisms to guide beet sugar manufacturers regarding the control of nitrite and nitrate content. © 2021 Society of Chemical Industry.

Effect of biochar combined with a biotrickling filter on deodorization, nitrogen retention, and microbial community succession during chicken manure composting

The high-nitrogen content and dense structure of poultry manure compost cause volatilization of N to ammonia (NH₃). This study evaluated the combined application of biochar and biotrickling filtration (BTF) to remove of odor in chicken manure mixed straw compost (w/w, 2.5:1). Adding of 10% biochar reduced NH₃, hydrogen sulfide (H₂S), and total volatile organic compounds (TVOCs) contents by 20.04%, 16.18%, and 17.55% respectively, and decreased the N loss rate by 8.27%, compared with those observed in control. The organic matter content decreased by 28.11% and germination index reached 97.36% in the experimental group. Meanwhile, the N-cycling microorganisms such as Pusillimonas and Pseudomonas became more active, and the relative abundance of sulfur-cycling microorganisms Hydrogenispora decreased in the experimental group. Following BTF application, the NH₃, H₂S, and TVOCs removal rates reached 95%, 97%, and 53%, respectively.

Different Effects of Thermophilic Microbiological Inoculation With and Without Biochar on Physicochemical Characteristics and Bacterial Communities in Pig Manure Composting

This study evaluated the effects of thermophilic microbiological inoculation alone (TA) and integrated with biochar (TB) on the physicochemical characteristics and bacterial communities in pig manure (PM) composting with wheat straw. Both TA and TB accelerated the rate of temperature increase during the PM composting. TA significantly reduced total nitrogen loss by 18.03% as opposed to TB which significantly accelerated total organic carbon degradation by 12.21% compared with the control. Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria were the major phyla in composting. Variation of the relative abundance of genera depended on the composting period and treatment. The genera Lactobacillus (26.88-46.71%) and Clostridium_sensu_stricto (9.03-31.69%) occupied a superior position in the temperature rise stage, and Bacillus (30.90-36.19%) was outstanding in the cooling stage. Temperature, total nitrogen (TN), and ammonium nitrogen significantly influenced the bacterial phyla composition. TN, water content, and nitrite nitrogen were the main drivers of the bacterial community genera. Furthermore, our results demonstrated that microbiological consortia were resistant to high temperatures and could fix nitrogen for enriched Pseudomonas; however, when interacted with biochar, total organic carbon (TOC) degradation was accelerated for higher bacterial richness and diversity as well as overrepresented Corynebacterium.

Bacterial Community Structure and Metabolic Function Succession During the Composting of Distilled Grain Waste

Distilled grain waste (DGW) can be converted to organic fertilizer via aerobic composting process without inoculating exogenous microorganisms. To illustrate the material conversion mechanism, this study investigated the dynamic changes of bacterial community structure and metabolic function involved in DGW composting. Results showed that a significant increase in microbial community alpha diversity was observed during DGW composting. Moreover, unique community structures occurred at each composting stage. The dominant phyla were Firmicutes, Proteobacteria, Actinobacteriota, Bacteroidota, Myxococcota, and Chloroflexi, whose abundance varied according to different composting stages. Keystone microbes can be selected as biomarkers for each stage, and Microbispora, Chryseolinea, Steroidobacter, Truepera, and Luteimonas indicating compost maturity. Co-occurrence network analysis revealed a significant relationship between keystone microbes and environmental factors. The carbohydrate and amino acid metabolism were confirmed as the primary metabolic pathways by metabolic function profiles. Furthermore, nitrogen metabolism pathway analysis indicated that denitrification and NH₃ volatilization induced higher nitrogen loss during DGW composting. This study can provide new understanding of the microbiota for organic matter and nitrogen conversion in the composting process of DGW.

Metagenomic analysis revealed the microbiota and metabolic function during co-composting of food waste and residual sludge for nitrogen and phosphorus transformation

This paper used bagasse as a composting additive and bulking agent in order to investigate the aerobic composting process of food waste and residual sludge. Accordingly, the variations of nitrogen and phosphorus nutrients, microbiota and metabolic function during the composting process were systematically explored. Three piles with residual sludge, food waste and bagasse mass ratios of 1:1:1, 2:1:1 and 4:1:1 were set. The ammonia nitrogen content in the three compost piles were 3.18 mg/g, 4.68 mg/g and 5.84 mg/g at the end of composting. The final available phosphorus content of the three piles were 3.42 mg/g, 6.70 mg/g and 11.21 mg/g, respectively. X-ray photoelectron spectroscopy (XPS) analysis showed that absorption peaks attributed to amines, amino acids and amides appeared in the 1:1:1 pile. Metagenomic analysis of the glycolysis and ammonia transformation pathways showed that the total relative abundance of key enzyme genes for the conversion of glucose to glucose-6-phosphate in the three plies were 0.326%, 0.213% and 0.248%, respectively. The total relative abundance of 2 glutamate dehydrogenase (GDH2), glud1-2 and E1,4,1,4 dehydrogenases in the three piles was 0.125%, 0.151% and 0.160%, respectively, as the main enzymes for the mutual conversion of ammonia and glutamate.

Effects of humic acid modified oyster shell addition on lignocellulose degradation and nitrogen transformation during digestate composting

The aim of this work was to investigate the performance of a novel humic acid modified oyster shell (MOS) bulking agent on the digestate composting. MOS was prepared by immobilizing humic acid onto oyster shell using solid phase grafting method, and then applied to the composting process. Results showed more obvious degradation of lignocellulose was observed in the MOS treatment, which was probably due to the high relative abundance of Actinobacteria. Moreover, the addition of MOS could significantly preserve NH₄⁺ and reduce the NO₃^- generation with the decreasing abundance of ammonia-oxidizing bacteria and archaea. Besides, adding MOS reduced the N₂O emission by 59.63% compared with the control. After composting, excitation-emission matrix fluorescence spectra demonstrated that the humification degree as well as compost maturity was enhanced with MOS added.

Challenges and Control Strategies of Odor Emission from Composting Operation

Composting is a biological decomposition process that occurs from microbial progression, which brings about the degradation and stabilization of various organic waste into compost. During composting, the emission of undesirable odor adversely affects compost quality and causes environmental deterioration. Also, odor emission from composting adversely affects human health and well-being. Ammonia (NH₃), volatile organic compounds (VOCs), and hydrogen sulfide (H₂S) are major components of odorous gases responsible for unpleasant odor. Physiological parameters such as pH, temperature, and aeration affect the pattern of odor emission during the composting process. The lack of techniques for the accurate identification and estimation of odor and control are some major challenges associated with composting. Therefore, the present review article concentrates on challenges and solutions to odor control. Biotrickling filter, optimization of process parameters, usage of additives, microbial inoculation, and pre-treatment techniques are practiced to lower odor emission during the process. The application of metagenomics may provide insight into the various biogeochemical pathways that can be explored in the future for odor control.

The degradation of organic matter coupled with the functional characteristics of microbial community during composting with different surfactants

The purpose of this study was to investigate the effects of anionic and cationic surfactants on the physico-chemical properties, organic matter (OM) degradation, bacterial community structure and metabolic function during composting of dairy manure and sugarcane bagasse. The results showed that the surfactant could optimize the composting conditions to promote the degradation of OM. The most OM degradation and humic substances (HS) synthesis were observed in SAS. Firmicutes and Proteobacteria were more abundant in SAS and CTAC, and Actinobacteria in CK. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) showed that SAS and CTAC are more abundant than CK in genes related to metabolism, environmental and genetic information processing. The correlation analysis showed that the dominant bacteria had more significant correlation with environmental factors. In general, the anionic surfactant could better promote the degradation of OM, change the structure of microbial community, and improve the quality of compost.

Thermal pretreatment enhances the degradation and humification of lignocellulose by stimulating thermophilic bacteria during dairy manure composting

This study investigated the effect of thermal pretreatment (TP) on the lignocellulose degradation and humification during dairy manure composting and the underlying microbial mechanism. The results showed that TP accelerated temperature rise and elevated composting temperature by increasing 26% initial content of simple organics. The degradation of cellulose, hemicellulose and lignin was 78, 10 and 109% higher in thermal pretreatment composting (TPC) than traditional composting (TC), respectively. Moreover, TP significantly improved the humification degree of composts, as indicated by 14 and 38% higher humus content and humification indexes in TPC, respectively. 16S rRNA sequencing showed that TP increased the relative abundance of thermophilic bacteria in TPC, of which Thermobifida, Planifilum, Truepera and Thermomonospora were potentially involved in lignocellulose biodegradation and humification. Canonical correspondence analysis revealed that TP changed the main factor determining the bacterial community evolution from dissolved organic carbon (DOC) in TC to temperature in TPC.

Manure pretreatments with black soldier fly Hermetia illucens L. (Diptera: Stratiomyidae): A study to reduce pathogen content

This study aim was to investigate the influence of black soldier fly larvae (BSFL) Hermetia illucens L. (Diptera: Stratiomyidae) on pathogenic bacteria (PB) survival in the chicken manure (CM), pig manure (PM), cow manure (COM) and sewage sludge (SS) compost. Three kinds of manure [chicken (T2), pig (T4) and cow (T6)] and SS (T8) were inoculated with BSFL (1.2:7 ratio on fresh weight basis) and without BSFL (T1, T3, T5 and T7) was used as control and experiment lasted for 9 days. The results indicated that BSFL amendment 90-93% of PB abundances (RAs) was significantly mitigate in CM and COM (T2 and T6), and 86-88% in PM and SS compost. However, relatively greater abundance of PB was recorded in the T4 and T8 treatments. Most of the PB belong to Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes phylum and their community composition varied from phylum to species levels among the all treatments. The PB composition was significantly altered by BSFL amendment and also important role play to enhance in compost quality. Interestingly, Bacillus and Clostridium were significantly very less abundant present in BSFL applied treatments, but considerably higher population of these bacterial genus and its associated species were identifies from control or without BSFL applied treatments. Overall, without BSFL blended-all three kinds of manure-composts have comparatively greater PB abundance than with BSFL applied treatments, as the PB species Listeria_monocytogenes_FSL_R2-503, Staphylococcus_aureus_M0406, Bacillus_anthracis, Listeria_ivanovii, Staphylococcus_aureus_C0673, Salmonella Bacillus_cereus_VD115, Mycobacterium_tuberculosis_FJ05194 and Pseudomonas_aeruginosa has relatively greater RAs, followed by Bartonella_bacilliformis_Ver075; Bordetella_pertussis_2356847; Brucella_melitensis_ADMAS-G1; Klebsiella_pneumoniae_LCT-KP182 and Corynebacterium_jeikeium_K411 respectively. Thus, chicken manure composting with BSFL addition is efficient technology for the organic waste recycling and conversion of sanitized matured compost with significantly less abundance of pathogenic bacteria.

Effects of exogenous N-acyl-homoserine lactones on nutrient removal, sludge properties and microbial community structures during activated sludge process

This study investigated the effects of exogenous N-acyl-homoserine lactone (AHL) signal molecules, N-hexanoyl-_l-homoserine lactone (C6-HSL) and N-octanoyl-_l-homoserine lactone (C8-HSL), on treatment performance, sludge properties and microbial community structures in activated sludge systems. Results showed that the nitrification and denitrification efficiencies were enhanced with the addition of signal molecules. The particle size, irregularity, and internal mass transfer resistance of activated sludge flocs (ASFs) increased, primarily because dosing AHLs led to a content increase and chemical composition variation of extracellular polymeric substances (EPS) in sludge. Microbial analysis indicated an increase in both the bacterial richness and diversity of the systems. The relative abundances of the key functional groups, including bacteria related to C and N removal and EPS production, varied correspondingly. This study presents an insight into the comprehensive understanding of the effects of AHL-based quorum sensing on activated sludge treatment process.

Denitrification performance and microbial diversity using starch-polycaprolactone blends as external solid carbon source and biofilm carriers for advanced treatment

Enhanced nitrate removal from the secondary effluent in municipal wastewater treatment plants (WWTPs) is essential for avoiding water eutrophication. To this end, a vertical baffled solid-phase denitrification reactor (VBSDR) was developed using a starch and polycaprolactone (PCL) blend plate (S-PCL) as a carbon source and biofilm carrier. In this study, we evaluated the denitrification performance and microbial diversity of the VBSDR. The results of the Fourier transform infrared spectroscopy (FTIR), carbon leaching experiment, and scanning electron microscopy (SEM) demonstrated that the S-PCL structure can be attached and degraded more rapidly. Furthermore, the denitrification performance under varied operational conditions, i.e., influent nitrate loading rate (NLR) and operating temperature, was also investigated. Herein, when treating low C/N ratio and low-strength wastewater, a high denitrification rate (DR) [0.33 gN/(L·d)] was achieved. The effect of temperature on DR can be described by the Arrhenius-type equation, which shows that low temperature has a negative influence on DR and nitrate removal efficiency. Furthermore, DR was simultaneously affected by the NLR and temperature. The microbial diversity and community structure were determined by Illumina high-throughput sequencing. The special carbon source led to Acidovorax (denitrifying bacteria) and Flavobacterium (hydrolysis acidifying bacteria) being the VBSDR biofilm's most predominant functional bacteria at the genus level.

Microbial community composition, co-occurrence network pattern and nitrogen transformation genera response to biochar addition in cattle manure-maize straw composting

A better understanding of the microbial group influencing nitrogen (N) dynamics and cycling in composting matrix is critical in achieving good management to alleviate N loss and improve final compost quality. This study investigated the bacterial composition, structure, co-occurrence network patterns and topological roles of N transformation in cattle manure-maize straw composting using high-throughput sequencing. The two treatments used in this experiment were cattle manure and maize straw mixture (CM) and CM with 10% biochar addition (CMB). In both treatments, the bacterial community composition varied during composting and the major phyla included Actinobacteria, Firmicutes, Proteobacteria, Bacteroidetes and Chloroflexi. The phyla Actinobacteria and Proteobacteria were more abundant in CMB treatment while Firmicutes was abundant in CM piles. The metabolic functional profiles of bacteria was predicted using the "phylogenetic investigation of communities by reconstruction of unobserved states" (PICRUSt) which revealed that except for cellular processes pathway, CMB had slight higher abundance in metabolism, genetic information processing and environmental information processing than the CM. Pearson correlation revealed more significant relationship between the important bacteria communities and N transformation in CMB piles compared with CM. Furthermore, network pattern analysis revealed that the bacterial networks in biochar amended piles are more complex and harbored more positive links than that of no biochar piles. Corresponding agreement of multivariate analyses (correlation heatmap, stepwise regression, Path and network analyses) revealed that Psychrobacter, Thermopolyspora and Thermobifida in CM while Corynebacterium_1, Thermomonospora and Streptomyces in CMB were key bacterial genera affecting NH₄⁺-N, NO₃^--N and total nitrogen (TN) transformation respectively during composting process. These results provide insight into nitrogen transformation and co-occurrence patterns mediating microbes and bacterial metabolism which could be useful in enhancing compost quality and mitigating N loss during composting.

Evaluation of biochar amendment on heavy metal resistant bacteria abundance in biosolids compost

The present investigation was design to evaluate the impact of different dosages of biochar on heavy metal resistant bacterial (HMRB) dynamic in biosolid (BS) compost. The bacterial abundance map was reveals that all the samples have 35 prominent genera and showed significant alteration of HMRB among the all biochar applied treatment. The main phyla identify in each treatments were Proteobacteria, Firmicutes and Chloroflexi, however, Pseudomonas, T78, Acinetobacter and Urebacillus were most abundant genera in all the treatment. The visualization of HMRB bio-diversity by bioinformatic tools and krona were clearly indicated a considerable difference in classification tree complexes and network analysis among the all biochar added treatments. Thus, in present study was found that HMRB like Paracoccus, Planomicrobium, Devosia and Agrobacterium viable hyper-thermo tolerant in BS compost. In addition, heat map analysis also confirmed that Proteobacteria, Firmicutes and Chloroflexi have significant correlation with physicochemical parameters.

Intensified nitrogen removal by heterotrophic nitrification aerobic denitrification bacteria in two pilot-scale tidal flow constructed wetlands: Influence of influent C/N ratios and tidal strategies

This study investigated the influence of C/N ratios and tidal strategies on nitrogen removal and bacterial communities in two pilot-scale tidal flow constructed wetlands (TFCWs) with simultaneous nitrification-denitrification process. Heterotrophic nitrification aerobic denitrification (HNAD) was the main nitrogen transformation pathway in both TFCWs. High C/N ratios and effluent circulation at low temperature promoted HNAD in TFCWs with high nitrogen removal efficiencies (72.6%-95.5% for NH₄⁺-N and 70.9%~91.8% for TN). Effluent circulation had more influence on bacterial community structure and diversity than C/N ratios. Among 16 detected genera related to nitrogen removal, HNAD bacteria (HNADB) were abundant. Especially, some dominant HNADB (e.g. Aeromonas, Hydrogenophage and Gemmobacter) were core genera, showing positive interactions with other genera related to nitrogen removal. Tidal strategies had more contribution to the shifts in these genera than C/N ratios. This study highlights the importance of HNADB in pilot-scale TFCWs and their responses to C/N ratios and tidal strategies.

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.

Odor emission and microbial community succession during biogas residue composting covered with a molecular membrane

A membrane-covered composting system was used to investigate the odor emission and microbial community succession during biogas residue composting. Results showed that in comparison with the control (CK) group, the NH₃ and H₂S emissions outside the membrane of the membrane-covered (CT) group decreased by 58.64% and 38.13%, respectively. The nitrogen preservation rate of the CT group was increased by 17.27% in comparison with the CK group. Moreover, the ammonium nitrogen and nitrate nitrogen contents of the CT group were 37.68% and 11.77% higher than those of the CK group, respectively. Microbial analysis showed that the average abundance and co-occurrence rate of ammonification bacteria dominated by Pseudomonas and Bacillus in the CT group were lower than those in the CK group, and the abundance of anaerobic sulfate-reducing bacteria (SRB) dominated by Desulfovibrio in the CT group was higher than that in the CK group.

Insight into the effects of sulfamethoxazole and norfloxacin on nitrogen transformation functional genes during swine manure composting

The effects of sulfamethoxazole and norfloxacin on nitrogen functional genes were investigated in four composting treatments of swine manure: CK (no antibiotics), SMZ (spiked with 5 mg kg^-1 dry weight (DW) sulfamethoxazole), NOR (spiked with 5 mg kg^-1DW norfloxacin), and SN (spiked with 5 mg kg^-1DW sulfamethoxazole and 5 mg kg^-1DW norfloxacin). Antibiotics decreased relative abundance of bacterial amoA and nxrA, while increased nosZ/nirK. The decline in amoA/16S rRNA increased the total NH₃ emission in SMZ and NOR from 1027.05 to 1144.39 and 1278.22 mg kg^-1DW. The decrease of nxrA/16S rRNA enhanced the NO₂^--N content and N₂O emission in SMZ in the initial composting. Additionally, the increase in nosZ/nirK probably was the main reason for the lower N₂O emission in SN than other treatments in the cooling phase. The inhibition on nitrification process and increase in NH₃ emission resulted from antibiotics is worthy of attention in the future.

Genetic associations as indices for assessing nitrogen transformation processes in co-composting of cattle manure and rice straw

In this study, mechanism of nitrogen transformation was investigated in terms of genetic associations (nitrogen-related gene groups) in co-composting of cattle manure and rice straw. Mutual validation among KEGG, Pearson correlation, stepwise regression, and Path analyses indicated that the functional genes synergistically affected on nitrogen transformation in composting process. NxrA/qnorB (0.9419 ± 0.0334) and (amoA + anammox)/Bacteria (0.7187 ± 0.0334) were the key functional gene groups mediating NH₄⁺-N transformation. AmoA/(narG + napA) (-0.8400 ± 0.0129), amoA/bacteria (0.8692 ± 0.0273), and (nirK + nirS)/nosZ (1.1652 ± 0.0089) determined NO₃^--N, NO₂^--N and N₂O transformation, respectively. AmoA/(napA + narG) mediated both NO₃^--N and NO₂^--N transformation. AmoA/anammox (-0.7172 ± 0.0591) and (nirK + nirS)/nosZ (-0.6626 ± 0.0825) served as predominant factors for total nitrogen removal. These results provided a molecular-level insight that nitrification, anaerobic ammonia oxidation and denitrification (SNAD) might simultaneously contribute to nitrogen transformation during composting, rather than sequentially.