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

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

Effects of semi-permeable membrane covering coupled with intermittent aeration on gas emissions during aerobic composting from the solid fraction of dairy manure at industrial scale.

In this study, the effects of covering the compost pile with a semi-permeable membrane in combination with intermittent aeration on the gas emissions during aerobic composting from the solid fraction of dairy manure at industrial scale were investigated. A large-scale composting experiment was carried out to compare a membrane-covered (CT) group with a control (CK) group. The results indicated that the CT group could maintain a suitable aerobic and positive micro-pressure environment. The carbon dioxide, methane, nitrous oxide, and ammonia emissions outside the membrane during the aeration interval were reduced by 64.23%, 70.07%, 54.87%, and 11.32%, respectively, compared with that inside the membrane. It was also determined that the methane and nitrous oxide emissions from the CT group were reduced by 99.89% and 60.48% relative to the CK group, confirming that the combined process represented a novel strategy for reducing gas emissions during dairy manure composting.

Metagenomic and q-PCR analysis reveals the effect of powder bamboo biochar on nitrous oxide and ammonia emissions during aerobic composting.

To investigate the emission mechanism of ammonia (NH3) and nitrous oxide (N2O) during aerobic composting and the influence of powder bamboo biochar (PBB) on this process, this paper conducted a systematic study on the nitrogen-transforming functional microbial community, including functional genes, microbial structure and metabolism pathways. PBB reduced N2O and NH3 emissions by 1.25%-8.72% and 10.4%-11.8%, respectively. The quantitative PCR results indicated that the reduced N2O emission by PBB were mainly related to denitrifying genes (nirS, nirK, nosZ, and narG). The metagenome results demonstrated that Nitrosococcus was the main genus that could oxidize ammonia to nitrite decreased by PBB. The PBB significantly affected the nitrogen metabolism pathway, reduced the activity of glutamate dehydrogenase to inhibit the formation of NH4+ to reduce NH3 emission. The higher N2O emission in the control group was also related to the higher relative contents of hydroxylamine reductase and nitrite reductase.

Electric dipole of InN/InGaN quantum dots and holes and giant surface photovoltage directly measured by Kelvin probe force microscopy.

We directly measure the electric dipole of InN quantum dots (QDs) grown on In-rich InGaN layers by Kelvin probe force microscopy. This significantly advances the understanding of the superior catalytic performance of InN/InGaN QDs in ion- and biosensing and in photoelectrochemical hydrogen generation by water splitting and the understanding of the important third-generation InGaN semiconductor surface in general. The positive surface photovoltage (SPV) gives an outward QD dipole with dipole potential of the order of 150 mV, in agreement with previous calculations. After HCl-etching, to complement the determination of the electric dipole, a giant negative SPV of -2.4 V, significantly larger than the InGaN bandgap energy, is discovered. This giant SPV is assigned to a large inward electric dipole, associated with the appearance of holes, matching the original QD lateral size and density. Such surprising result points towards unique photovoltaic effects and photosensitivity.

Multi-wavelength light emission from InGaN nanowires on pyramid-textured Si(100) substrate grown by stationary plasma-assisted molecular beam epitaxy.

We demonstrate multi-wavelength light emission from InGaN nanowires (NWs) monolithically grown on pyramid-textured Si(100) substrates by plasma-assisted molecular beam epitaxy (MBE) under stationary conditions. Taking advantage of the highly unidirectional source material beam fluxes, the In content of the NWs is tuned on the different pyramid facets due to varied incidence angle. This is confirmed by distinct NW morphologies observed by scanning electron microscopy (SEM) and by energy-dispersive X-ray (EDX) element mapping. Photoluminescence and cathodoluminescence (CL) reveal multiple lines originating from InGaN NWs on the different pyramid facets. The anomalous temperature dependence of the emission wavelength results from carrier redistribution between localized or confined states, spontaneously formed within the NWs due to composition fluctuations, verified by high-resolution EDX elemental analysis. First-principles calculations show that the pyramid facet edges act as a barrier for atom migration and enhance atom incorporation. This leads to uniform composition within the facets for not too high a growth temperature, consistent with the SEM, EDX and CL results. At elevated temperature, InGaN decomposition and In desorption are enhanced on facets with low growth rate, accompanied by Ga inter-facet migration, leading to non-uniform composition over the Ga migration length which is deduced to be around 580 nm. Our study presents a method for the fabrication of multi-wavelength light sources by highly unidirectional MBE on textured Si substrates towards color temperature-tunable solid-state lighting and RGB light-emitting diode displays.

Spatial Surface Charge Engineering for Electrochemical Electrodes.

We introduce a novel concept for the design of functional surfaces of materials: Spatial surface charge engineering. We exploit the concept for an all-solid-state, epitaxial InN/InGaN-on-Si reference electrode to replace the inconvenient liquid-filled reference electrodes, such as Ag/AgCl. Reference electrodes are universal components of electrochemical sensors, ubiquitous in electrochemistry to set a constant potential. For subtle interrelation of structure design, surface morphology and the unique surface charge properties of InGaN, the reference electrode has less than 10 mV/decade sensitivity over a wide concentration range, evaluated for KCl aqueous solutions and less than 2 mV/hour long-time drift over 12 hours. Key is a nanoscale charge balanced surface for the right InGaN composition, InN amount and InGaN surface morphology, depending on growth conditions and layer thickness, which is underpinned by the surface potential measured by Kelvin probe force microscopy. When paired with the InN/InGaN quantum dot sensing electrode with super-Nernstian sensitivity, where only structure design and surface morphology are changed, this completes an all-InGaN-based electrochemical sensor with unprecedented performance.

New insights into the kinetics of bacterial growth and decay in pig manure-wheat straw aerobic composting based on an optimized PMA-qPCR method.

Aerobic composting is a bacteria-driven process to degrade and recycle wastes. This study quantified the kinetics of bacterial growth and decay during pig manure-wheat straw composting, which may provide insights into microbial reaction mechanisms and composting operations. First, a propidium monoazide-quantitative polymerase chain reaction (PMA-qPCR) method was developed to quantify the viable bacteria concentration of composting samples. The optimal PMA concentration and light exposure time were 100 µM and 8 min respectively. Subsequently, the concentrations of total and decayed bacteria were quantified. Viable and decayed bacteria coexisted during the entire composting period (experiments A and B), and the proportion of viable bacteria finally fell to only 35.1%. At the beginning, bacteria grew logarithmically and decayed rapidly. Later, the bacterial growth in experiment A remained stable, while that of experiment B was stable at first and then decomposed. The duration of the stable stage was positively related to the soluble sugar content of composting materials. The logarithmic growth and rapid decay of bacteria followed Monod equations with a specific growth (0.0317 ± 0.0033 h-1 ) and decay rate (0.0019 ± 0.0000 h-1 ). The findings better identified the bacterial growth stages and might enable better prediction of composting temperatures and the degree of maturation.

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

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

Effects of amoxicillin on nitrogen transformation and bacterial community succession during aerobic composting.

This study systematically analyzed the effects of amoxicillin (AMX) on the nitrogen transformation and its corresponding functional bacterial communities by conducting two aerobic composting experiments, and AMX impact on bacterial community succession was also evaluated. It provides theoretical and methodological support for harmless composting treatment of large quantities of manure containing AMX in China and for the high-quality compost products. The results showed that AMX exerted several effects on basic physicochemical and biological compost parameters. Notably, temperature changes typically accompanying compost maturation were delayed in AMX compost, reflecting altered compost maturation kinetics and bacterial community structure. Moreover, relative to control, AMX inhibited growth and reproduction of dominant bacterial phyla Firmicutes and Bacteroidetes, with respective reductions of 17.8-26.1% and 0-7.76% in relative abundance (RA) and significantly increased Proteobacteria RA by 1.9-24.8%. Thus, AMX altered both compost bacterial community structure and succession. From the perspective of various nitrogen content changes, AMX has a significant effect on nitrogen conversion and release. Simultaneously, AMX may inhibit ammoniated and ammonia-oxidizing bacterial activity, while significantly increasing the RA of denitrifying bacteria. Indeed, during early composting with AMX, the RA of denitrifying bacteria was 1361.9-1435.0% of control, highlighting differences in nitrogen transformation and release between groups.

Effect of different particle-size biochar on methane emissions during pig manure/wheat straw aerobic composting: Insights into pore characterization and microbial mechanisms.

This study explored the effects of different particle sizes of rice straw biochar (RSB) on the methane emissions of pig manure/wheat straw aerobic composting experiments to provide a theoretical suggestion for biochar application. The experiments were conducted with a control group, powder (<1 mm) group, and granular (4 mm-1 cm) group. Methane emissions increased by 56.84% in the powder group but decreased by 22.15% in the granular group during the aerobic composting. Methane was generated by methanogens and methanotrophs in the specific anaerobic micro-environment characterized by X-ray micro-computed tomography (micro-CT). The porosity of initial composting samples increased by 4.02% in the granular group but decreased by 3.88% in the powder group. RSB additives typically reduced the mcrA/pmoA ratio and increased the diversity of Bacteria and Archaea. Conclusively, granular biochar benefits to aerobic composting to alleviate the CH4 emissions.

Variations in the fate and risk analysis of amoxicillin and its degradation products during pig manure aerobic composting.

In this study, 100 mg/kg of amoxicillin (AMX) was added to pig manure during aerobic composting using a laboratory-scale reactor system, for better understanding the degradation of AMX and its potential risks. Qualitative and quantitative analysis of AMX and its main degradation products (DPs) were then conducted using solid phase extraction combined with high performance liquid chromatography-tandem mass spectrometry. Additionally, hydrolysis testing was performed to monitor DPs produced from AMX degradation under various controlled conditions. The results showed that AMX was unstable in compost and rapidly degraded into AMX penicilloic acid, AMX penilloic acid and AMX diketopiperazine, which all eventually degraded, leaving a structurally simple and stable end product, 3-(4-hydroxyphenyl) pyrazin-2-ol, which appeared to be nonallergenic and less toxic than DPs generated earlier in the composting process. Besides, AMX was more unstable and more apt to generate multiple DPs in alkaline conditions than in acidic or neutral conditions or in ultrapure water, while pH exerted a larger effect on AMX degradation than did divalent metal ions (Cu2+ and Zn2+). This study provides technical and methodological support to better achieve AMX residual treatment and to evaluate the safety of AMX DPs produced in huge quantities in compost in China.

Effect of aeration interval on oxygen consumption and GHG emission during pig manure composting.

To verify the optimal aeration interval for oxygen supply and consumption and investigate the effect of aeration interval on GHG emission, reactor-scale composting was conducted with different aeration intervals (0, 10, 30 and 50 min). Although O2 was sufficiently supplied during aeration period, it could be consumed to <10 vol% only when the aeration interval was 50 min, indicating that an aeration interval more than 50 min would be inadvisable. Compared to continuous aeration, reductions of the total CH4 and N2O emissions as well as the total GHG emission equivalent by 22.26-61.36%, 8.24-49.80% and 12.36-53.20%, respectively, was achieved through intermittent aeration. Specifically, both the total CH4 and N2O emissions as well as the total GHG emission equivalent were inversely proportional to the duration of aeration interval (R2 > 0.902), suggesting that lengthening the duration of aeration interval to some extent could effectively reduce GHG emission.

An Exploration of the Calcium-Binding Mode of Egg White Peptide, Asp-His-Thr-Lys-Glu, and In Vitro Calcium Absorption Studies of Peptide-Calcium Complex.

The binding mode between the pentapeptide (DHTKE) from egg white hydrolysates and calcium ions was elucidated upon its structural and thermodynamics characteristics. The present study demonstrated that the DHTKE peptide could spontaneously bind calcium with a 1:1 stoichiometry, and that the calcium-binding site corresponded to the carboxyl oxygen, amino nitrogen, and imidazole nitrogen atoms of the DHTKE peptide. Moreover, the effect of the DHTKE-calcium complex on improving the calcium absorption was investigated in vitro using Caco-2 cells. Results showed that the DHTKE-calcium complex could facilitate the calcium influx into the cytosol and further improve calcium absorption across Caco-2 cell monolayers by more than 7 times when compared to calcium-free control. This study facilitates the understanding about the binding mechanism between peptides and calcium ions as well as suggests a potential application of egg white peptides as nutraceuticals to improve calcium absorption.

Evaluation of biochar powder on oxygen supply efficiency and global warming potential during mainstream large-scale aerobic composting.

This study investigated the effects of biochar powder on oxygen supply efficiency and global warming potential (GWP) in the large-scale aerobic composting pattern which includes cyclical forced-turning with aeration at the bottom of composting tanks in China. A 55-day large-scale aerobic composting experiment was conducted in two different groups without and with 10% biochar powder addition (by weight). The results show that biochar powder improves the holding ability of oxygen, and the duration time (O2>5%) is around 80%. The composting process with above pattern significantly reduce CH4 and N2O emissions compared to the static or turning-only styles. Considering the average GWP of the BC group was 19.82% lower than that of the CK group, it suggests that rational addition of biochar powder has the potential to reduce the energy consumption of turning, improve effectiveness of the oxygen supply, and reduce comprehensive greenhouse effects.