Drying of Activated Sludge Under Partial Vacuum Conditions—An Experimental Study

A typical wastewater treatment system in a pulp and paper mill in Finland treats wastewater both mechanically and biologically. Sludges resulting from these processes have to be disposed of. One possible way of doing this is to incinerate them with solid fuel in the power plant of the mill. To minimize the amount of sludge and to make the use of the sludge energy efficient, it has to be dried before incineration. Mechanical drying of the sludge from biological wastewater treatment is difficult to carry out. Using secondary energies may provide a competitive way of arranging drying: a method of doing this by using partial vacuum evaporation to utilize the low temperature secondary heat in sludge drying is under development. A laboratory study to examine the behavior of activated sludge under partial vacuum evaporation conditions was carried out using a laboratory rotating evaporator to analyze the drying of activated sludge from three mills at 40-80°C boiling temperatures. This article presents the results from the tests. These are promising; it was possible to reach high dry solids content. Also, no boiling point temperature rise was detected, fouling of the evaporator seemed low and easily avoidable, condensate from the evaporator weas relatively clean and returnable to the processes of the mill.     

Release of chlorhexidine digluconate and flexural properties of glass fibre reinforced provisional fixed partial denture polymer

The objective of this study was to determine the flexural properties and the release of chlorhexidine digluconate (CHX) of CHX laced unidirectional E-glass fibre reinforced provisional fixed partial denture polymer. Bar shaped test specimens (3.3 × 10.0 × 65.0 mm) were fabricated from provisional fixed partial denture polymer (mixture of poly[ethylmethacrylate] powder and n-poly[butyl methacrylate] monomer liquid) with E-glass fibre reinforcements. Poly(methyl methacrylate) preimpregnated continuous unidirectional glass fibre reinforcement was laced with CHX. The glass fibre reinforcements were incorporated into the polymer and the polymerised to the form of test specimens. In addition test specimens without CHX in glass fibre reinforcement were made for comparison. Control specimens did not contain glass fibres in the test specimens. Flexural strength and modulus of test specimens (n = 6) was tested with three-point bending test after storing the specimens dry or in water (two weeks). Released CHX was determined with high performance liquid chromatography during 180 days water immersion. In dry conditions, the flexural strength and the modulus of the polymer was 43 MPa and 1.7 GPa, and with glass fibre reinforcement 96 MPa and 3.5 GPa. With the reinforcement laced with CHX, the strength was 92 MPa and the modulus was 3.2 GPa. The water storage of test specimens did not weaken the reinforced polymer. The majority of the CHX released from the glass fibre reinforced polymer during the first days of storage in water. Flexural properties of provisional fixed partial denture polymer were increased using glass fibre reinforcement. The fibre reinforcement that was laced with CHX resulted in similar reinforcing effect.     

Antibacterial efficiency of Finnish spice essential oils against pathogenic and spoilage bacteria

The antibacterial properties of 13 essential oils, derived from spices grown in Finland, were examined with an agar diffusion method against 12 bacterial strains. The organisms tested included both spoilage and pathogenic bacteria. The gram-positive bacteria appeared to be more sensitive than the gram-negative organisms, Clostridium botulinum and Clostridium perfringens being the most sensitive. Oregano, savory, and thyme showed the broadest antibacterial activity by distinctly inhibiting the growth of all the organisms tested. By gas chromatography-mass spectrometry analysis, differences were noted in the composition of oregano and thyme oils in comparison to previous reports.     

Structural and Catalytic Properties of Alkyl-Substituted Phosphanes. Effect of Ortho-Modification on Rhodium-Catalyzed 1-Hexene Hydroformylation

The influence of the alkyl-substituted phosphanes (o-methylphenyl)diphenylphosphane (o-MeP), (o-ethylphenyl)diphenylphosphane (o-EtP), bis(o-methylphenyl)phenylphosphane (o-Me₂P), bis(o-ethylphenyl)phenylphosphane (o-Et₂P), and (2,4,5-trimethylphenyl)diphenylphosphane (2,4,5-MeP) was screened in model reaction of rhodium-catalyzed 1-hexene hydroformylation. Compared with PPh₃, the prepared phosphanes afforded lower chemoselectivity towards aldehydes, but increased the normal to branched ratio. Catalyst results are discussed in relation to stereoelectronic properties of the phosphane ligands. Electron donor capacity of the ligands was studied in terms of spectroscopic data of the trans-RhCl(CO)P₂ species, formed in reaction between Rh₂(-Cl)₂(CO)₄ and the ligands (P). Furthermore, steric attributes of free and bound phosphanes were investigated by Tolmans cone angle method. Crystal structures for ligands o-EtP, o-Me₂P, o-Et₂P, and complexes trans-Rh(CO)Cl(o-MeP)₂ and trans-Rh(CO)Cl(o-Et₂P) were solved as well.     

The transpassive dissolution mechanism of highly alloyed stainless steels: I. Experimental results and modelling procedure

The transpassive dissolution of austenitic stainless steels (AISI 316L, AISI 904L, 254SMO and 654SMO) in a 0.5 M sulphate solution with pH 2 was studied by conventional and rotating ring-disc voltammetry, as well as electrochemical impedance spectroscopy. The main process in the transpassive potential region was found to be the release of soluble Cr(VI), while small amounts of lower-valency Cr or Mo species are released as well. Secondary passivation readily occurs for AISI 316L, whereas the remaining highly alloyed steels dissolve at high current densities in the whole potential range studied. The dissolution rate was found to increase in the order AISI 904L<254SMO<654SMO. Thus it can be correlated to the increase in the Cr and especially Mo content of the steel substrate. The impedance spectra contain contributions from the transpassive dissolution of Cr and secondary passivation, probably due to enrichment of Fe in the outermost layer of the surface film. A kinetic model of the process is proposed, including a two-step transpassive dissolution of Cr via a Cr(VI) intermediate and the dissolution of Fe(III) through the anodic film. The model was found to be in quantitative agreement with steady state current vs. potential curves and electrochemical impedance spectra. The kinetic parameters of transpassive dissolution were determined and the relevance of their values is discussed.