Solubilisation of sludge by combined chemical and enzymatic treatment

In this study, the effects of cation-binding agents used alone and/or in combination with enzymes on solubilisation of municipal sludge and structure changes were investigated. Formic acid, citric acid,tartaric acid, EDTA, sodium tripolyphosphate (STPP), Zeolite A, sodium fluoride, sodium thiosulphate or sodium silicate were added to both biological and digested sludges. Citric acid (50 mmol/l) released thehighest COD, amounting to 8 g/l from bio-sludge and 3 g/l from digested sludge. The highest specific dissolution rate was 0.5 g COD per mmol citric acid. COD released by STPP (50 mmol/l) was 3.3 g/l from bio-sludge and 2 g/l from digested sludge. STPP acted most efficiently to reduce suspended solids, 20% for digested and 40% for bio-sludge. The pre-treatment by the sequestering agents was followed by addition of three glycosidic enzymes. The used enzymes were more effective in hydrolysis of bio-sludge than in hydrolysis of the digested sludge. Additionally, after 4 h of incubation the remained enzymesactivities in enzyme treated sludges were improved by up to 20%, indicating high stability of added enzymes

Interplay of Stimulated Emission and Fluorescence Resonance Energy Transfer in Electrospun Light-Emitting Fibers

Concomitant amplified spontaneous emission (ASE) and F\"orster resonance energy transfer (FRET) are investigated in electrospun light-emitting fibers. Upon dye-doping with a proper FRET couple system, free-standing fibrous mats exhibit tunable FRET efficiency and, more importantly, tailorable threshold conditions for stimulated emission. In addition, effective scattering of light is found in the fibrous material by measuring the transport mean free path of photons by coherent backscattering experiments. The interplay of ASE and FRET leads to high control in designing optical properties from electrospun fibers, including the occurrence of simultaneous stimulated emission from both donor and acceptor components. All tunable-optical properties are highly interesting in view of applying electrospun light-emitting materials in lightening, display, and sensing technologies.Comment: 32 pages, 13 figure

Electronic structure, charge transfer, and intrinsic luminescence of gadolinium oxide nanoparticles: Experiment and theory

The cubic (c) and monoclinic (m) polymorphs of Gd2O3 were studied using the combined analysis of several materials science techniques - X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. Density functional theory (DFT) based calculations for the samples under study were performed as well. The cubic phase of gadolinium oxide (c-Gd2O3) synthesized using a precipitation method exhibits spheroidal-like nanoclusters with well-defined edges assembled from primary nanoparticles with an average size of 50 nm, whereas the monoclinic phase of gadolinium oxide (m-Gd2O3) deposited using explosive pyrolysis has a denser structure compared with natural gadolinia. This phase also has a structure composed of three-dimensional complex agglomerates without clear-edged boundaries that are ~21 nm in size plus a cubic phase admixture of only 2 at. % composed of primary edge-boundary nanoparticles ~15 nm in size. These atomic features appear in the electronic structure as different defects ([Gd...O-OH] and [Gd...O-O]) and have dissimilar contributions to the charge-transfer processes among the appropriate electronic states with ambiguous contributions in the Gd 5p - O 2s core-like levels in the valence band structures. The origin of [Gd...O-OH] defects found by XPS was well-supported by PL analysis. The electronic and atomic structures of the synthesized gadolinias calculated using DFT were compared and discussed on the basis of the well-known joint OKT-van der Laan model, and good agreement was established.Comment: 27 pages, 10 figures, accepted in Appl. Surf. Sc

Nonlinear absorption and nonlinear refraction: Maximizing the merit factors

Both nonlinear absorption and nonlinear refraction are effects that are potentially useful for a plethora of applications in photonics, nanophotonics and biophotonics. Despite substantial attention given to these phenomena by researchers studying the merits of disparate systems such as organic materials, hybrid materials, metal-containing molecules and nanostructures, it is virtually impossible to compare the results obtained on different materials when varying parameters of the light beams and different techniques are employed. We have attempted to address the problem by studying the properties of various systems in a systematic way, within a wide range of wavelengths, and including the regions of onephoton, two-photon and three-photon absorption. The objects of our studies have been typical nonlinear chromophores, such as π-conjugated molecules, oligomers and polymers, organometallics and coordination complexes containing transition metals, organometallic dendrimers, small metal-containing clusters, and nanoparticles of various kinds, including semiconductor quantum dots, plasmonic particles and rare-earth doped nanocrystals. We discuss herein procedures to quantify the nonlinear response of all of these systems, by defining and comparing the merit factors relevant for various applications

Luminescent thermometer based on Eu3+/Tb3+-organic-functionalized mesoporous silica

In this work we investigate a mesoporous silica (MS) decorated with dipyridyl-pyridazine (dppz) ligands and further grafted with a mixture of Eu3+/Tb3+ ions (28.45%:71.55%), which was investigated as a potential thermometer in the 10-360K temperature range. The MS material was prepared employing a hetero Diels-Alder reaction: 3,6-di(2-pyridyl)-1,2,4,5-tetrazine was reacted with the double bonds of vinyl-silica (vSilica) followed by an oxidation procedure. We explore using the dppz-vSilica material to obtain visible emitting luminescent materials and for obtaining a luminescent thermometer when grafted with Eu3+/Tb3+ ions. For the dppz-vSilica@Eu,Tb material absolute sensitivityS(a) of 0.011K(-1) (210K) and relative sensitivityS(r) of 1.32 %K-1 (260K) were calculated showing good sensing capability of the material. Upon temperature change from 10K to 360K the emission color of the material changed gradually from yellow to red

Enzymatic treatment of wastewater sludge. Sludge solubilisation, improvement of anaerobic digestion and extraction of extracellular polymeric substances.

The processing and disposal of sludge from wastewater treatment plants is an important topic of increasing environmental, ecological, technological, economic and social concern. The large amounts of sludge produced represent an urgent problem today, new treatment methods being very much needed. Reducing the volume of sludge can be achieved either by decreasing the amounts of it produced during the wastewater treatment process or by reducing the volume of sludge once it has been produced. The thesis considers different methods of the latter sort involving biological and chemical disintegration of municipal wastewater sludge prior to or during anaerobic digestion of it. Municipal wastewater sludge contains such valuable and renewable resources as (i) carbon, which can be converted to biogas, and (ii) phosphorus and nitrogen, which can be utilized as fertilizers. These valuable components accumulate in sludge in polymeric form. The biological disintegration of sludge by hydrolytic enzymes was studied here. The effects of enzymatic hydrolysis were tested, the following factors being varied: total solids (TS), type of enzymes, enzyme dose, dosing point, reaction time, temperature, pH, the ratio of TS to enzyme concentration, the volume of sludge treated and the operating conditions. In batch laboratory tests, 20% to 40% mass solubilisation of sludge was found after treatment. The reduction obtained depended upon the enzyme dose and the operational conditions during treatment. Enzyme treatment was found to increase methane production by 60%. This was confirmed in both pilot- and full-scale continuous digestion experiments, the addition of the enzyme mixture resulting in an improvement in both biogas production and the dewatering properties of the digested sludge. Furthermore, the enzymes added were found to be partially entrapped by, bound or adsorbed to the sludge structure, reducing the activity of the enzymes that were added. To counteract adsorption and reduce the enzyme dose, the sludge was pre-treated by several organic and inorganic cation-binding agents. The cation-binding agents used either alone or in combination with the enzymes disrupted the formation of sludge flocs and improved solubilisation of the sludge. Citric acid was the most effective agent tested. Additionally, the level of activity of the residual enzymes increased by up to 20% in the presence of the cation-binding agents, indicating the stabilizing effect these additives had on the enzymes that were added. Hydrolytic enzymes were also used for the extraction and characterization of extracellular polymeric substances (EPS) from sludge, in efforts to predict the bio-digestibility of the sludge. EPS have been found to be partly responsible for the formation, the structure and the settling of sludge flocs in particular. Wastewater-activated sludges were also treated by selected enzymes, the polysaccharides and glycoconjugates released being characterized by use of a lectin panel