Greenhouse gas emission characteristics and influencing factors of agricultural waste composting process: A review.

China, being a major agricultural nation, employs aerobic composting as an efficient approach to handle agricultural solid waste. Nevertheless, the composting process is often accompanied by greenhouse gas emissions, which are known contributors to global warming. Therefore, it is urgent to control the formation and emission of greenhouse gases from composting. This study provides a comprehensive analysis of the mechanisms underlying the production of nitrous oxide, methane, and carbon dioxide during the composting process of agricultural wastes. Additionally, it proposes an overview of the variables that affect greenhouse gas emissions, including the types of agricultural wastes (straw, livestock manure), the specifications for compost (pile size, aeration). The key factors of greenhouse gas emissions during composting process like physicochemical parameters, additives, and specific composting techniques (reuse of mature compost products, ultra-high-temperature composting, and electric-field-assisted composting) are summarized. Finally, it suggests directions and perspectives for future research. This study establishes a theoretical foundation for achieving carbon neutrality and promoting environmentally-friendly composting practices.

Relative contribution of ammonia-oxidizing bacteria and denitrifying fungi to N2O production during rice straw composting with biochar and biogas residue amendments.

Nitrous oxide (N2O) production is associated with ammonia-oxidizing bacteria (amoA-AOB) and denitrifying fungi (nirK-fungi) during the incorporation of biochar and biogas residue composting. This research examined the relative contribution of alterations in the abundance, diversity and structure of amoA-AOB and nirK-fungi communities on N2O emission by real-time PCR and sequence processing. Results showed that N2O emissions showed an extreme relation with the abundance of amoA-AOB (rs = 0.584) while giving credit to nirK-fungi (rs = 0.500). Nitrosomonas and Nitrosospira emerged as the dominant genera driving ammoxidation process. Biogas residue changed the community structure of AOB by altering Nitrosomonadaceae proportion and physiological capacity. The denitrification process, primarily governed by nirK-fungi, served as a crucial pathway for N2O production, unveiling the pivotal mechanism of biochar to suppress N2O emissions. C/N and NH4+-N were identified as significant parameters influencing the distribution of nirK-fungi, especially Micromonospora, Halomonas and Mesorhizobium.

Response characteristics of antibiotic resistance genes and bacterial communities during agricultural waste composting: Focusing on biogas residue combined with biochar amendments.

This research investigated biogas residue and biochar addition on antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and changes in bacterial community during agricultural waste composting. Sequencing technique investigated bacterial community structure and ARGs, MGEs changes. Correlations among physicochemical factors, ARGs, MGEs, and bacterial community structure were determined using redundancy analysis. Results confirmed that biochar and biogas residue amendments effectively lowered the contents of ARGs and MGEs. The main ARGs detected was sul1. Proteobacteria and Firmicutes were the main host bacteria strongly associated with the dissemination of ARGs. The dynamic characteristics of the bacterial community were strongly correlated with pile temperature and pH (P < 0.05). Redundancy and network analysis revealed that nitrate, intI1, and Firmicutes mainly affected the in ARGs changes. Therefore, regulating these key variables would effectively suppress the ARGs spread and risk of compost use.

Characteristics of carbon, nitrogen, phosphorus and sulfur cycling genes, microbial community metabolism and key influencing factors during composting process supplemented with biochar and biogas residue.

Carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) cycling functional genes and bacterial and fungal communities during composting with biochar and biogas residue amendments were studied. Correlations between microbial community structure, functional genes and physicochemical properties were investigated by network analysis and redundancy analysis. It was shown that the gene of acsA abundance accounted for about 50% of the C-related genes. Biogas residue significantly decreased the abundance of denitrification gene nirK. Biogas residues can better promote the diversity of bacteria and fungi during composting. Biochar significantly increased the abundance of Humicola. Redundancy analysis indicated that pile temperature, pH, EC were the main physicochemical factors affecting the microbial community. WSC and NO3--N have significant correlation with C, N, P, S functional genes. The research provides a theoretical basis for clarifying the metabolic characteristics of microbial communities during composting and for the application of biochar and biogas residues in composting.

Evaluation of the synergistic effects of biochar and biogas residue on CO2 and CH4 emission, functional genes, and enzyme activity during straw composting.

This study examined the effects of biochar, biogas residue, and their combined amendments on CO2 and CH4 emission, enzyme activity, and related functional genes during rice straw composting. Results showed that the biogas residue increased CO2 and CH4 emissions by 13.07 % and 74.65 %, while biochar had more obvious inhibition. Biogas residue addition enhanced functional gene abundance more than biochar. Biogas residue raised the methanogens mcrA gene by 2.5 times. Biochar improved the Acetyl-CoA synthase and ß-glucosidase activities related to carbon fixation and decreased coenzyme activities related to methanogens. Biochar and biogas residue combined amendments enhanced the acsB gene abundance for CO2 assimilation process and decreased methyl-coenzyme M reductase α subunit activity. Pearson correlation analysis indicated that organic matter was the significant variable affecting CO2 and CH4 emissions (P < 0.01). These results indicated biochar played significant roles in carbon loss and greenhouse emissions caused by biogas residue incorporation during composting.

The characteristics of alkaline phosphatase activity and phoD gene community in heavy-metal contaminated soil remediated by biochar and compost.

This research was carried out to determine the influence of biochar and compost addition on the characteristics of potential alkaline phosphatase (ALP) activity and phoD gene community in heavy metal polluted soils. The ALP activity, the abundance and structure of phoD gene were systematically determined. Results showed that biochar and compost significantly changed soil properties, and promoted the microbial transformation of phosphorus. Compost addition significantly increased the ALP activity. Biochar and compost addition markedly increased the phoD gene abundance. The addition of biochar increased the proportion of Actinobacteria, Euryarchaeota, and Proteobacteria. By contrast, Betaproteobacteria, Deltaproteobacteria, and Gammaproteobacteria were the dominant taxa in soils with compost addition. Electrical conductivity critically controlled the expression of phoD and changed the structure of phoD-coding microbial communities in heavy-metal polluted soils that remediated by biochar and compost.

Fe-Mn Plaque Formation Mechanism Underlying the Inhibition of Cadmium Absorption by Rice Under Oxygation Conditions.

Oxygation (O) is a water-saving and energy-saving irrigation method that can also influence the absorption of cadmium (Cd) by rice, but the related mechanism is still unclear. In this study, the relationship between O method and Fe-Mn plaque formation was tested through pot experiments. The Fe-Mn plaque content and Cd concentration were measured during different rice growth periods, and the fitted models based on their correlation were established. The results show that, Fe-Mn plaque formation was the most significant factor affecting Cd accumulation in rice under O conditions. The content of rice root Fe-Mn plaque was higher after the application of O during the filling and maturity stages of rice growth, and Fe-Mn plaque inhibited Cd accumulation in the rice roots and grains and reduced the translocation factors (TFs) from the rice dithionite-citrate-bicarbonate extract (DCB) to the roots (TFDCB-R) and from the roots to the straw (TFStraw-G). O may influence the Fe-Mn plaque formation on the root surface to impede Cd absorption by rice. This research provides theoretical support for the Cd absorption under O conditions.

Comparisons of pollution characteristics, emission situations, and mass loads for heavy metals in the manures of different livestock and poultry in China.

The application of livestock and poultry manures was the predominant source of heavy metals in agricultural soils, particularly in China. It is important to systematically compare the pollution characteristics, emission situations and mass loads for heavy metals in the manures of different livestock and poultry in China. According to analysis and estimation based on the reported concentration levels of eight heavy metals (Zn, Cu, Pb, Cd, Cr, Hg, As, and Ni) and the feed quantities of livestock (pig, cattle, and sheep) and poultry in 2017, the concentrations of Zn and Cu and the over-standard frequencies of Zn, Cu, Cd, and As were much higher than those of other heavy metals, especially in pig manure. In 2017, the total emission of livestock and poultry manure in China was 1.64 × 109 t (FW), which was mainly excreted from cattle (45.77%); while the total emission of heavy metals sourced from manures was 2.86 × 105 t (DW), with the predominant contribution originating from pig manure (71.52%). The highest mass loads of manures and heavy metals were observed in Shandong, Tianjin, Henan, and Shanghai, where heavy metal contamination may be occurring (especially for Zn and Cu). The heavy metal concentrations in livestock and poultry manures of China were similar to other countries; however, more heavy metals were discharged into agricultural land through manure (especially for Zn and Cu). For many countries, abundant Zn and Cu exist in agricultural soils, principally contributed by livestock and poultry manures. These heavy metals originate from their addition to livestock and poultry feeds. Therefore, reducing the addition of Zn and Cu in feeds is an effective measure to lower their input into agricultural soils.

Concentrations and emissions of particulate matter and ammonia from extensive livestock farm in South China.

Atmospheric particulate matter (PM) and ammonia pollution from livestock feeding have gradually become the environmental concerns due to the spring up of livestock farms in worldwide. However, researches about the formation of atmospheric particulate matter related to ammonia are still limited. Therefore, a study to survey the total suspended particles (TSP), PM with the diameter less than 10 µm (PM10), PM4, PM2.5, PM1, and ammonia was conducted at four types of hog houses distinguished by its building design as well as manure handling methods in South China. Four hog houses were monitored during three fattening periods from 2016 to 2017. The emissions of NH3 per hog house averaged 210.42 µg s-1. The emissions of PM per hog house averaged 2.017 µg h-1 for PM1, 2.149 µg h-1 for PM2.5, 2.305 µg h-1 for PM4, 3.950 µg h-1 for PM10, and 9.317 µg h-1 for TSP. The emissions of PM per hog house average 2.017 µg h-1, 2.149 µg h-1, 2.305 µg h-1, 3.950 µg h-1, and 9.317 µg h-1, respectively for PM1, PM2.5, PM4, PM10, and PM10. In each hog house, while the quantity of manure determined the concentration of NH3, biological fermentation bed was able to control the ammonia volatilization compared with other three manure handling methods. The largest percentage of fine PM (< 10 µm) is produced by the manual waterless method for manure handling. When it came to the manual waterless method, largest amount of fine PM (< 10 µm) was founded to form. Among various contributions of secondary inorganic PM to PM1, the NH3 was a dominant factor. Based on our experiment, the absolute concentration of NH3 was inversely proportional to the concentration of PM1 when the background influence was removed.

Key environmental factors to variation of ammonia-oxidizing archaea community and potential ammonia oxidation rate during agricultural waste composting.

In this research, the abundance and structure of AOA amoA gene during agricultural waste composting were determined by quantitative PCR and sequencing techniques, respectively. Pairwise correlations between potential ammonia oxidation (PAO) rate, physicochemical parameters and the AOA abundance were evaluated using Pearson correlation coefficient. Relationships between these parameters, PAO rates and AOA community structure were evaluated by redundancy analysis. Results showed that 22 AOA gene OTUs were divided into the soil/sediment lineage by phylogenetic analyses. Significant positive correlations were obtained between AOA amoA gene abundance and moisture, ammonium, water soluble carbon (WSC) and organic matter (OM), respectively. Redundancy analysis showed OM, pH and nitrate significantly explained the AOA amoA gene structure. Pearson correlation revealed the PAO rate correlated positively to ammonium, AOA amoA gene abundance. These results indicated that AOA communities sense the fluctuations in surrounding environment, and ultimately react and influence the nitrogen transformation during agricultural waste composting.

Effects of bloom-forming cyanobacterial extracellular polymeric substances on the adsorption of cadmium onto kaolinite: behaviors and possible mechanisms.

Cyanobacterial blooms result in high level of cyanobacterial extracellular polymeric substances (EPS) in water. The effects of bloom-forming cyanobacterial EPS on the distribution of Cd(II) in the interface between sediment and water is unknown. Clay is a main component in sediment. The effects of EPS, originated from a typical bloom-forming cyanobacterium Microcystis aeruginosa, on the adsorption and desorption characteristics of Cd(II) by kaolinite were investigated in this study. Results of XRD analysis indicated that cyanobacterial EPS bound on the surface of kaolinite. The composite of kaolinite + EPS showed higher adsorption capacity toward Cd(II) than pure kaolinite, and hydroxyl groups were involved in the adsorption processes. The data for the adsorption of Cd(II) by kaolinite are well fitted by both Langmuir model and Freundlich model, whereas only Freundlich model well describes the adsorption data of Cd(II) by the composite of kaolinite + EPS. The adsorption of Cd(II) onto kaolinite was an exothermic process, but it became an endothermic process after EPS incorporation. Results of desorption showed that EPS incorporation increased the adsorption of kaolinite toward Cd(II) through physical adsorption, ion exchange and complexation.

Residual veterinary antibiotics in pig excreta after oral administration of sulfonamides.

Sulfonamides (SAs) are applied widely as feed additives in the farming of livestock and poultry. It can lead to the excretion of large amounts of SAs in manure and result in persistent environmental pollution. We evaluated the fate of four SAs, sulfamerazine (SM1), sulfachloropyridazine (SCP), sulfadimoxine (SDM') and sulfaquinoxaline (SQ), from oral administration to excretion in urine and feces in pigs. The four SAs were added to homemade feed to make them reach the required concentration gradient, which were 0, 50 and 100 mg/kg (low, normal and high concentrations, respectively). In different treatments, excretions of the four SAs were 35.68-86.88 %. With regard to total excretion, the order was SQ > SCP > SM1 > SDM' for all treatments. The concentration of SAs in the feed had significant effects on the amount of the four SAs excreted every day. The concentration of SAs in feces and in the urine for different treatments was 15.03-26.55 and 14.54-69.22 %, respectively. In each treatment, excretions of SCP, SDM' and SQ in feces were lower than that in urine. The four SAs remained longer in urine than in feces. Excretions in urine and feces were lower if SAs were administered orally rather than by injection.

Modification of cyanobacterial bloom-derived biomass using potassium permanganate enhanced the removal of microcystins and adsorption capacity toward cadmium (II).

Cyanobacterial biomass shows high adsorption capacity toward heavy metal ions. However, the cyanotoxins in the cyanobacterial biomass inhibit its application in heavy metals removal. In order to safely and effectively remove Cd(II) from water using cyanobacterial bloom-derived biomass (CBDB), KMnO4 was used to modify CBDB. The results indicated that the microcystins in the CBDB were successfully removed by KMnO4. Potassium permanganate oxidation caused the transformation of hydroxyl to carboxyl on the CBDB, and formed manganese dioxide on the surface of CBDB. The oxidized CBDB showed higher adsorption capacity toward Cd(II) than that of unoxidized treatment. The optimal KMnO4 concentration for increasing the adsorption capacity of CBDB toward Cd(II) was 0.2g/L. The adsorption isotherm of Cd(II) by oxidized- or unoxidized-CBDB was well fitted by Langmuir model, indicating that the adsorption of Cd(II) by CBDB was monolayer adsorption. The desorption ratio of Cd(II) from oxidized CBDB was higher than that from unoxidized CBDB in the desorption process using NH4NO3 and EDTA as desorbent. The results presented in this study suggest that KMnO4 modified CBDB may be used as a safe and high efficient adsorbent in Cd(II) removal from water.

Evaluation of agricultural nonpoint source pollution potential risk over China with a Transformed-Agricultural Nonpoint Pollution Potential Index method.

Agricultural nonpoint source (NPS) pollution has been the most important threat to water environment quality. Understanding the spatial distribution of NPS pollution potential risk is important for taking effective measures to control and reduce NPS pollution. A Transformed-Agricultural Nonpoint Pollution Potential Index (T-APPI) model was constructed for evaluating the national NPS pollution potential risk in this study; it was also combined with remote sensing and geographic information system techniques for evaluation on the large scale and at 1 km2 spatial resolution. This model considers many factors contributing to the NPS pollution as the original APPI model, summarized as four indicators of the runoff, sediment production, chemical use and the people and animal load. These four indicators were analysed in detail at 1 km2 spatial resolution throughout China. The T-APPI model distinguished the four indicators into pollution source factors and transport process factors; it also took their relationship into consideration. The studied results showed that T-APPI is a credible and convenient method for NPS pollution potential risk evaluation. The results also indicated that the highest NPS pollution potential risk is distributed in the middle-southern Jiangsu province. Several other regions, including the North China Plain, Chengdu Basin Plain, Jianghan Plain, cultivated lands in Guangdong and Guangxi provinces, also showed serious NPS pollution potential. This study can provide a scientific reference for predicting the future NPS pollution risk throughout China and may be helpful for taking reasonable and effective measures for preventing and controlling NPS pollution.

Modified granulation of red mud by weak gelling and its application to stabilization of Pb.

This study presents a novel modification of red mud (RM) with cementitious materials by rotary drum granulation under partial hydration. Admixtures and surfactants were applied to improve the microspore structure of red mud-based granules in order to stabilize Pb steadily. Through XRD and SEM-EDS analyses, it was demonstrated that calcite, the main alkali in RM, was partially concreted and coated. Compared to pH 12.47 for RM, the lowest pH of the granules was 10.66 implying that the release of OH(-) from hydrolysis and decomposition was decreased. Based on stabilization of Pb, influence on soil properties and forming qualities, composition of the optimum granule PSP was determined as 5% cement, 5% gypsum, 1% rice straw, and 0.1% emulsifier OP-10. Within a 90 d remediation, immobilization of ionic Pb in a 500 mg kg(-1) Pb-contaminated artificial soil was 9.85 mg kg(-1) at day 30 with 5% PSP2 as substitute. Furthermore, the reverse increase diminished as the final concentration was 11.13 mg kg(-1) while it was 14.25 mg kg(-1) by RM. The increase of residual Pb was 122.61%, which was better than the 83.92% of RM. Particularly, the highest pH in mine soil was 11.09 at day 1 with RM, but the decrease of ionic Pb was 46.26%. Meanwhile, a significant deviation from the control soil zeta-potential lasted longer and the recovery was more difficult, as compared to the granules. Therefore, a granulated modification of RM is shown to be very important when aiming at steady release of OH(-) to improve the later stabilization of Pb.