The bacterial community drive the humification and greenhouse gas emissions during plant residues composting under different aeration rates.

This study investigated the effects of different aeration intensities on organic matter (OM) degradation, greenhouse gas emissions (GHG) as well as humification during plant residue composting. Three intermittent aeration intensities of 0.084 (Tlow), 0.19 (Tmedium) and 0.34 (Thigh) L min-1kg-1 DM with 30 min on/30 min off were conducted on a lab-scale composting experiment. Results showed that OM mineralization in Thigh was more evident than Tlow and Tmedium, resulting in the highest humic acid content. Humic acid content in Tmedium and Thigh was 15.7% and 18.5% higher than that in Tlow. The average O2 concentration was 4.9%, 9.5% and 13.6% for Tlow, Tmedium and Thigh. Compared with Tmedium and Thigh, Tlow reduced CO2 and N2O emissions by 18.3%-39.6% and 72.4%-63.9%, but the CH4 emission was highest in Tlow. But the total GHG emission was the lowest in Thigh. Linear Discriminant Analysis Effect Size analysis showed that the core bacteria within Tlow mainly belonged to Anaerolineaceae, which was significantly negatively correlated to the emission of CH4. Thermostaphylospora, Unclassified_Vicinamibacteraceae and Sulfurifustis were identified as core bacteria in Tmedium and Thigh, and these genus were significantly postively correlated to CO2 and N2O emissions. Redundancy analysis showed that total orgnic carbon, O2 and electrical conductivity were the key factors affecting the evolution of bacterial community.

Reduced pH is the primary factor promoting humic acid formation during hyperthermophilic pretreatment composting.

Hyperthermophilic pretreatment composting (HPC) has the advantages of enhanced composting efficiency and accelerated humic substance (HS) over conventional composting (CC). However, the mechanisms towards the accelerated humification process by HPC are still not clear. By means of sterilization technology, the roles of abiotic and biotic components on the formation of HS can be distinguished. The study investigated the humification degree and the succession of microbial community during HPC of pig manure. The mechanisms underlying the accelerated humification by HPC was identified using gamma sterilization. Results showed that HS content increased significantly by 13.72% in HPC and 29.93% in sterilized HPC inoculated with 1% CC (HPC_I), compared with 8.76% increase in CC and 7.12% increase in sterilized CC inoculated with 1% HPC during composting (CC_I). Compared with CC and CC_I, stronger intensities of HA-like and fulvic acid-like components were observed in HPC and HPC_I. Results showed that physicochemical properties, especially pH, were the key factors in accelerating the humification in HPC, while both physicochemical properties and microbial community contributed to the HA formation in CC. The study contributed to a better understanding of the mechanism towards the accelerated humification degree in HPC.

Spectroscopic evidence for hyperthermophilic pretreatment intensifying humification during pig manure and rice straw composting.

Hyperthermophilic pretreatment composting (HPC) is superior to traditional composting (CK) with shortened maturity period and enhanced humification degree. However, the chemical and structural evolution of humic substances (HS) at the molecular level is not known. In this study, the impact of hyperthermophilic pretreatment (90 °C, 4 h) on the content and chemical composition of HS during composting were investigated. The HS content of the final compost was 87.8 g/kg and 76.7 g/kg in HPC and CK, respectively. Significantly higher humic acid/fulvic acid ratio (1.27 in HPC v.s. 0.77 in CK) was observed in HPC. 13C NMR spectroscopic data showed a higher aromatics percentage and earlier enrichment of aromatic structures in HS extracted from HPC than CK. Intensified humification of HPC was related to the increased levels of HS precursors and degradation of lignocellulose. Redundancy analysis demonstrated that aromatic C, phenolic C and O-alkyl C can be used for evaluation of the humification degree.

Hyperthermophilic pretreatment composting significantly accelerates humic substances formation by regulating precursors production and microbial communities.

Hyperthermophilic pretreatment composting (HPC) is superior to traditional composting (TC) with enhanced compost maturity and accelerated humic substances (HS) formation. However, the regulators affecting HS formation, which is of great importance in evaluating the compost maturity, are still unclear. This study aimed to examine and compare the effects of HPC and TC on (i) HS formations under varying precursors, (ii) bacterial and fungal dynamics, and (iii) factors affecting HS formations. Results revealed that HS formation was accelerated in the heating, thermophilic and maturity phases for HPC, whereas the synthesis of HS was observed in the maturity phase for TC. Particularly, concentrations of humic acid, polyphenols, amino acids, polysaccharides and reducing sugar were increased in compost by 50, 60, 52, 44 and 92%, respectively after the hyperthermophilic pretreatment. These increased precursors could stimulate the activity of Planococcaceae that possessed a high degradation capacity on D-mannitol in the heating stage. Additionally, the thermophilic microbes Solibacillus and Aspergillus with high degradation capacity on lignocelluloses and lignin, respectively dominated in the thermophilic stage. These microorganisms may promote the formation of precursors and thus accelerated synthesis of HS in HPC. Finally, structural equation model (SEM) showed polyphenol and reducing sugar were the key precursors to directly or indirectly promote HS formation in HPC and the higher temperature rise as well as the higher N content provided advantages over TC in improving HS formation. This study provides the stability to the accelerated humification process in HPC and reveals its potential applicability in improving HS formation.

Green Preparation of Straw Fiber Reinforced Hydrolyzed Soy Protein Isolate/Urea/Formaldehyde Composites for Biocomposite Flower Pots Application.

The effects of soil burial on the biodegradation of biocomposite flower pots (BFP) made from straw fiber (SF) and hydrolyzed soy protein isolate/urea/formaldehyde (HSPI/U/F) copolymer resin were studied in detail. The microstructure, crystallinity, functional groups, mechanical, degradation and thermal property of the prepared SF with HSPI/U/F copolymer resin have been studied, and the degradation mechanism was also elucidated. XRD results showed that the bond breakage between SF and HSPI/U/F copolymer resin induced a decrease in relative degradation-resistant crystal structures. FTIR spectra showed that the methylolated HSPI units could form a cross-linking network with U/F and SF. The BFP degradation after soil burial was mainly attributed to the effects of microorganisms. The degradation products were environmentally friendly, because they were degradable and could fertilize the soil. In addition, the U/F adhesives were slightly degraded by the microorganisms due to the HSPI in the pots. The TG and DSC results showed that the molecular motion of the BFP matrix could be restricted by the degradation action and the content of HSPI, resulting in decreased crystallization enthalpy and showing good thermal property. The tensile strength of different reinforced samples was not significantly reduced in comparison to U/F resin, and still kept good mechanical performance. Thus, the prepared SF reinforced HSPI/U/F copolymer resins could have good potential for use in the field of biodegradable flower pots because of their good thermal property, mechanical property, biodegradability, and relatively low cost.

[Degradation Characteristics of Spectral Analysis of Straw Nursery Containers in Situ Soil Culture].

This paper aimed to reveal the degradation behavior of a new type of biodegradable containers. The biodegradable containers, which was made of modified soybean adhesive and straw, was processed in situ biodegradation under natural condition. The physicochemical property and microstructure of straw nursery containers treated and untreated were characterized with Cellulose Tester, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope - Energy Dispersive X-ray Spectroscopy (SEM-EDS), and Thermo-gravimetry Analysis (TGA), respectively. The results indicated that the content of cellulose, hemicellulose and lignin of treated specimen decreased to 21.43%, 21.41% and 9.54% from 29.03%, 30.44% and 12.52%, respectively, comparing with those of untreated straw nursery container. FTIR analysis revealed that the ester and fat bond have been ruptured, and the aromatic characteristic peak became weakened. SEM-EDS spectrum showed the microfibril chain in the container has been fragmentation, and the soybean adhesive was also degradation. The surface of container appeared oxidization degradation. TGA analysis showed that a large number of small molecules have been produced in the process of degradation and the thermo-stability of treated samples improved.

Distribution of sulfonamides in liquid and solid anaerobic digestates: effects of hydraulic retention time and swine manure to rice straw ratio.

The effects of hydraulic retention time (20 and 15 days) and swine manure to rice straw ratios on distribution of sulfonamides (SAs) in liquid and solid anaerobic digestates were studied using bench-scale completely stirred tank reactors at (37 ± 1) °C. Results showed that anaerobic digestion (AD) treatment exhibited a good removal effect on sulfadiazine (SDZ), sulfadimidine (SM2) and sulfachloropyridazine (SCP), especially at HRT = 20 days and co-digestion with swine manure and rice straw. The removal rates of SDZ and SM2 were more than 90%, but only 72.8% for SCP. The residual SAs were mainly remained in solid digestates, with residual rates ranging from 28.8% to 71.3%, 40.6% to 88.0, and 82.7% to 97.0% for SDZ, SM2 and SCP, respectively. Due to lower pKa and higher log K ow of SCP, its residue in solid digestates was far more than SDZ and SM2. Higher HRT and co-digestion could improve the degradation of SAs, which can also be put down to the occurrence of cometabolism of SAs and COD.

Biochar pyrolytically produced from municipal solid wastes for aqueous As(V) removal: adsorption property and its improvement with KOH activation.

Biochar converted from waste products is being considered as an alternative adsorbent for removal of aqueous heavy metal(loid)s. In this work, experimental and modeling investigations were conducted to examine the effect of biochars pyrolytically produced from municipal solid wastes on removing aqueous As(V) before and after activated by 2M KOH solution. Results showed that the highest adsorption capacity of pristine biochars was 24.49 mg/g. The pseudo-second-order model and Langmuir adsorption isotherm model can preferably describe the adsorption process. The activated biochar showed enhanced As(V) adsorption ability with an adsorption capacity of 30.98 mg/g, which was more than 1.3 times of pristine biochars, and 2-10 times of modified biochars reported by other literatures. Increase of surface area and changes of porous texture, especially the functional groups on the surface of activated biochars are the major contributors to its more efficient adsorption of As(V).

[Methane production by anaerobic co-digestion of chicken manure and Spartina alterniflora residue after producing methane].

The characteristics of Spartina alterniflora residue after producing methane (SAR) digested alone and co-digestion of various proportions of chicken manure and SAR were investigated by batch model at 35 degrees C +/- 1 degrees C. The initial total solid (TS) loading of all treatments was 8.0%. The results indicated that there was still some biogas produced by SAR with TS biogas yield of 107.25 mL x g(-1) and average methane content of 76.92%. The cellulose crystallinity of re-digested SAR was destructed by anaerobic microorganisms, and the destruction rate was 5.55%. Co-digestion meliorated the environment where microorganisms lived in and increased the cumulative biogas yield. When the ratio of chicken manure to SAR was 4 : 1, the cumulative biogas yield was highest while the cumulative biogas yield of T1 (the rate of chicken manure to SAR is 5 : 0 based on TS), T3-T6 (the rate of chicken manure to SAR are 3 : 2, 2 : 3, 1 :4 and 0 : 5 based on TS, respectively) were 61.31%, 62.09%, 52.15%, 39.74% and 31.67% of it. The anaerobic fermentation type of co-digestion is mix acid type fermentation. Co-digested with chicken manure promoted the destruction of cellulous crystallinity by 1.13% - 21.61% and especially when the rate of chicken manure to SAR was 4 : 1.