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•Key principle problems for hindering anaerobic digestion efficiency are analyzed.•Two perspectives on enhancing anaerobic digestion efficiency are proposed.•The available strategies ...for enhancing anaerobic sludge digestion are reviewed.•Main knowledge gaps in enhancing anaerobic sludge digestion are identified.•Sludge’s structure and property responsible for poor biodegradability is emphasized.
Anaerobic digestion (AD) of waste activated sludge (WAS) is an important bio-energy strategy that has been hindered by low conversion efficiency. This paper presents a comprehensive review of research on the sludge’s property and enhancing AD of WAS, and proposes two perspectives of material structure and microbial activity on improving AD efficiency. In the first part of this review, the key principle problems for hindering AD efficiency are identified based on the concept of AD. Then, the possibility that the complex microstructure and composition of WAS are responsible for poor biodegradability is considered and main methods for enhancing AD are summarized. In the third part, according to the published works, the main knowledge gaps in research are recognized as the identification and specific activity adjustment of functional microbes, the understanding of key constituents of WAS and their interactions, the deciphering of complex structure of sludge organic substance, and the revealing of relationships between complex nature of WAS and biodegradability. Further discussions reveal that to enhance AD more studies should be centered on the sludge’s structure and properties in future. However, this review is expected to provide the clear and accurate research directions for enhancing AD efficiency of WAS.
Lanthanide-doped glasses and crystals are attractive for laser applications because the metastable energy levels of the trivalent lanthanide ions facilitate the establishment of population inversion ...and amplified stimulated emission at relatively low pump power. At the nanometre scale, lanthanide-doped upconversion nanoparticles (UCNPs) can now be made with precisely controlled phase, dimension and doping level. When excited in the near-infrared, these UCNPs emit stable, bright visible luminescence at a variety of selectable wavelengths, with single-nanoparticle sensitivity, which makes them suitable for advanced luminescence microscopy applications. Here we show that UCNPs doped with high concentrations of thulium ions (Tm
), excited at a wavelength of 980 nanometres, can readily establish a population inversion on their intermediate metastable
H
level: the reduced inter-emitter distance at high Tm
doping concentration leads to intense cross-relaxation, inducing a photon-avalanche-like effect that rapidly populates the metastable
H
level, resulting in population inversion relative to the
H
ground level within a single nanoparticle. As a result, illumination by a laser at 808 nanometres, matching the upconversion band of the
H
→
H
transition, can trigger amplified stimulated emission to discharge the
H
intermediate level, so that the upconversion pathway to generate blue luminescence can be optically inhibited. We harness these properties to realize low-power super-resolution stimulated emission depletion (STED) microscopy and achieve nanometre-scale optical resolution (nanoscopy), imaging single UCNPs; the resolution is 28 nanometres, that is, 1/36th of the wavelength. These engineered nanocrystals offer saturation intensity two orders of magnitude lower than those of fluorescent probes currently employed in stimulated emission depletion microscopy, suggesting a new way of alleviating the square-root law that typically limits the resolution that can be practically achieved by such techniques.
Lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 (BCTZ) piezoelectric ceramics were prepared by a conventional oxide-mixed method at various calcination and sintering temperatures. Both calcination and ...sintering temperatures had an effect on the density and grain size, which are closely related to piezoelectric and other properties of ceramics. The calcination temperature had a great influence on the grain boundary, which also played an important role in the piezoelectric properties. With increased calcination and sintering temperature, the ferroelectric and piezoelectric properties were enhanced. The BCTZ ceramics calcined at 1300 C and sintered at 1540 C exhibited optimal electrical properties: d33 = 650 pC/N, d31 = 74 pC/N, kp = 0.53, kt = 0.38, k31 = 0.309, S(E/11) = 14.0 x 10 exp(-12) m2/N, epsilonr = 4500, Pr = 11.69 microC/cm2, making it a promising lead-free piezoelectric.
A sludge structure perspective of the effects of humic matter (HM) on the anaerobic digestion (AD) of sewage sludge was proposed and investigated in this study. It was observed that the net ...cumulative methane production of sludge was significantly lower in the presence of HM. The fractal dimension values of sludge samples were increased by the addition of HM, whilst their total surface energy values were decreased, indicating that HM reinforced the stability of the sludge structure. Analyses of the physicochemical properties of different sludge samples revealed that HM enhanced the structural stability of sludge organic substances and restricted its organic solubility by interacting with the biopolymers to form a dense granular aggregate, thereby reducing the random-coil degree of extracellular organic substances and its active sites for enzymes, which suggested that HM could inhibit AD by changing the sludge structure. It was further confirmed by the biochemical methane potential (BMP) assay process. The BMP tests and corresponding kinetic analyses revealed that HM can restrict the potentials of sludge organic solubilisation, hydrolysis and acidification processes, but not necessarily the rates of these processes by enhancing the structural stability of high molecular weight readily biodegradable organic matter (RBOM) and restricting the mobility of low molecular weight RBOM (i.e., hydrolysis products). These findings can enrich understanding of the AD of sludge and may thus aid in the development of more effective methods to improve sludge treatment.
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•A sludge structural view of humic matter inhibiting methane production was proposed.•Humic matter can enhance the structural stability of sludge.•Humic matter can change the spatial configurations of biopolymer in sludge.•Humic matter can limit the biodegradation of readily biodegradable organic matter.
Selenium is an essential micronutrient that plays a crucial role in maintaining human health. Selenium deficiency is seriously associated with various diseases such as Keshan disease, Kashin–Beck ...disease, cataracts, and others. Conversely, selenium supplementation has been found to have multiple effects, including antioxidant, anti-inflammatory, and anticancer functions. Compared with inorganic selenium, organic selenium exhibits higher bioactivities and a wider range of safe concentrations. Consequently, there has been a significant development of selenium-enriched foods which contain large amounts of organic selenium in order to improve human health. This review summarizes the physiological role and metabolism of selenium, the development of selenium-enriched foods, the physiological functions of selenium-enriched foods, and provides an analysis of total selenium and its species in selenium-enriched foods, with a view to laying the foundation for selenium-enriched food development.
Sub-diffraction microscopy enables bio-imaging with unprecedented clarity. However, most super-resolution methods require complex, costly purpose-built systems, involve image post-processing and ...struggle with sub-diffraction imaging in 3D. Here, we realize a conceptually different super-resolution approach which circumvents these limitations and enables 3D sub-diffraction imaging on conventional confocal microscopes. We refer to it as super-linear excitation-emission (SEE) microscopy, as it relies on markers with super-linear dependence of the emission on the excitation power. Super-linear markers proposed here are upconversion nanoparticles of NaYF
, doped with 20% Yb and unconventionally high 8% Tm, which are conveniently excited in the near-infrared biological window. We develop a computational framework calculating the 3D resolution for any viable scanning beam shape and excitation-emission probe profile. Imaging of colominic acid-coated upconversion nanoparticles endocytosed by neuronal cells, at resolutions twice better than the diffraction limit both in lateral and axial directions, illustrates the applicability of SEE microscopy for sub-cellular biology.
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