H. Carlsson

Calcium phosphate precipitation in biological phosphorus removal systems

Abstract Since the early days of the use of the excess biological phosphorus removal (EBPR) process, it has been discussed whether and to what extent, chemical precipitation contributes to the phosphorus removal that is seen in the process. In this study, calcium phosphate precipitation in EBPR systems was investigated. Four laboratory-scale fill and draw activated sludge systems operating in parallel, fed with natural Ca-rich wastewater, with additions of acetate and phosphate were studied. Two of the systems were operated as EBPR systems and the remaining two as aerobic systems. The results showed that calcium phosphate precipitation occurred in all the systems at sufficiently high concentrations of calcium and phosphate. Based on differences in the effluent water, the Ca/P molar ratio of the precipitate was found to be around 1–1.3. Redissolution occurred when the concentrations of calcium and phosphate had fallen below the saturation curve for Ca3(PO4)2 at neutral pH, and below the saturation curve for CaHPO4 at pH ≈ 8.5. The results also showed that the concentration of phosphate in the effluent from the EBPR system could be substantially lower than from the aerobic system, for the same effluent concentration of calcium. This indicates that there is an important time factor involved, which implies that simple equilibrium equations cannot be used alone to judge whether or to what extent, precipitation will take place. The results suggest that at neutral pH the phosphate concentration must be at least 50 mg P l−1 at a calcium concentration of 100 mg Ca l−1, and in soft water much higher, before precipitation starts. This, together with the fact that redissolution starts at phosphate concentrations far above 1 mg P l−1 indicates that in most cases calcium phosphate precipitation in EBPR processes with municipal wastewater does not constitute a significant phosphorus removal mechanism.

More than thirty bands in 177Re

Abstract The level scheme of 177Re has been extended extensively, with fragments of more than thirty bands, characterised by a given signature, observed. Alignments at low frequency in one-quasiparticle bands are interpreted as deformation effects and compared with the predictions of cranking calculations. The previously assigned one-quasiparticle π i 13 2 band is shown to be a mixture of three-quasiparticle and vibrational character. The non-observation of the one-quasiparticle π i 13 2 band is explained as being due to crossings of its s-band by competing bands. A number of high-K bands are also reported, including five- and seven-quasiparticle bands. Configuration assignments for these bands are aided by comparing experimental gκ values with “effective” gκ values, calculated with a semi-classical expression taking Coriolis mixing into account. The population of the yrast band was observed to oscillate with every four units of spin.

Superdeformed triaxial bands in Lu-163,165

An experimental investigation of the nucleus 165Lu, using the reactions 138Ba(31P,4n) 165Lu and 150Sm(19F,4n) 165Lu at beam energies of E = 155 and 95 MeV, respectively, has been performed. Among other additions to the existing level scheme, a new band, with transition energies almost identical to a strongly deformed (β2 0.42) πi13/2[660 1/2+] band recently discovered in 163Lu has been established. A theoretical analysis of the structure of the two Lu isotopes, 165Lu and 163Lu is carried out by detailed calculations of total potential energy surfaces for specific configurations. By a diabatic treatment of crossings specific proton configurations as πi13/2[660 1/2+] are identified throughout the deformation space and as a function of spin. It is found as a general feature that well deformed local minima of considerable nonaxial symmetry coexist with a normal deformed global minimum. The depth of these local minima depend on configuration. The structure of the different global and local minima found in these surfaces are analysed and discussed in terms of occupation of available basis configurations and their orientation relative to the rotation axis. The strongly deformed minima are found to belong to a group of superdeformed triaxial structures, expected to appear at low energies for certain favourable combinations of proton and neutron numbers.

Signature inversion in semi-decoupled bands: residual interaction between protons and neutrons ☆

Abstract Semi-decoupled bands based on the πh 9 2 ⊗ vi 13 2 configuration are observed in 162 Tm, 164 Tm and 174 Ta. Spins assigned to these bands imply an inversion of the expected signature splitting, which is interpreted as being the result of a residual proton-neutron interaction.

Interactions between wastewater quality and phosphorus release in the anaerobic reactor of the EBPR process

Abstract Studies on enhanced biological phosphorus removal (EBPR) operation in activated sludge processes have been conducted on a pilot plant at the Sjolunda wastewater treatment plant in Malmo, Sweden, since 1986. The plant receives wastewater from a combined sewer system. The aim of this study was to investigate interactions between variations in the wastewater quality and the effect on the EBPR operation. The paper focuses on the overall role of the concentration of volatile fatty acids (VFA) in the influent wastewater on the EBPR process. Firstly, the relation between VFA, COD and phosphorus in the influent wastewater at the plant is examined. Secondly, the effect of pH on phosphate release under anaerobic conditions is investigated. Finally, the observed relation between phosphate release in the anaerobic zone in relation to the concentration of VFA in the influent wastewater is discussed. The pilot plant consists of two parallel, activated sludge systems with EBPR, one system with a solids retention time (SRT) of 4 days, operated without nitrification-denitrification and one system with a SRT of 21 days, operated with nitrification-denitrification. Results derived from daily, composite samples taken over 3 yr have formed the basis of a general description of the water quality and the performance of the process. In addition, intensive field studies and laboratory studies have been used as ways of investigating certain phenomena in more detail. The results of the pilot plant study showed that the concentration of total phosphorus on average was low in the effluent, below 0.5 mg P/l. Increased phosphorus concentrations were, however, observed on a number of occasions. High concentrations of phosphorus in the effluent were observed every year in July, which is the holiday period at industrial plants in Sweden. Other instances of increased phosphorus concentrations in the secondary effluent were recorded after prolonged periods of rain. Increasing flow rates due to rain lead to a dilution and a change in the composition of the COD in the influent wastewater. A laboratory study showed that the ratio of phosphorus release/HAc uptake depends on pH in the range of 6–8. At neutral pH a ratio of 0.35-0.4 mg P/mg COD was found. The results of an intensive field study on the pilot plant suggested a relationship of 0.5 mg P/mg COD. Hydrolysis and/or fermentation processes have to be taken into account when describing phosphorus release in the anaerobic reactor. However, it was clearly demonstrated that it is primarily the VFA in the influent wastewater that affect the release of phosphorus in the systems studied.

Band structures and proton-neutron interactions in 174Ta

Abstract Six rotational bands in the odd-odd nucleus 174Ta have been populated with the 160Gd(19F,5n) reaction. High-spin states were identified using the NORDBALL array. Both signatures of the doubly decoupled π 1 2 − [541] ⊗ ν 1 2 − [521] band and semi-decoupled π 1 2 − [541] ⊗ ν 7 2 − [633] band are observed, in addition to the high-K couplings of the π 9 2 − [514] ⊗ ν 7 2 + [633] , π 9 2 − [514] ⊗ ν 5 2 − [512] , π 7 2 + [404] ⊗ ν 7 2 + [633] , and π 5 2 + [402] ⊗ ν 5 2 − [512] configurations. The signature splitting of the π 1 2 − [541] ⊗ ν 7 2 + [633] band is inverted from the expected splitting, and this is interpreted as being due to a residual proton-neutron interaction. It is shown empirically that this interaction, together with deformation changes, can account for the increased crossing frequency associated with the alignment of i 13 2 neutrons in the π 1 2 − [541] bands of odd-Z nuclei.

THE DISTRIBUTION OF THE ROTATIONAL TRANSITION STRENGTH IN WARM NUCLEI STUDIED THROUGH GAMMA-RAY CORRELATIONS

Abstract The study of damping of rotational motion applying te rotational plane mapping (RPM) method is presented and discussed. The aim of this technique is to extract the distribution of the rotational transition strength from an analysis of the shape of the “central valley” of two- and three-dimensional γ-ray spectra. The method is applied to a triple γ-coincidence data set of 162,163Tm nuclei formed in 37Cl+130Te reactions. The rotational transition strength is obtained as a function of rotational frequency for selected regions of entry states, and the width is found to be rather constant and approximately equal to 80 keV. This value is significantly smaller than the value predicted theoretically for the rotational damping width Γrot. Also the ratio between the observed depth and width of both the 2D and 3D valleys does not agree with the simple model adopted in the RPM method. These discrepancies point to the presence of both a wide and a narrow component in the distribution of rotational strength as extracted by the RPM method. The analysis of simulated spectra obtained on the basis of realistic band-mixing calculations, including residual interactions, confirms this behaviour.

Noisy equilibrium selection in coordination games

We analyse symmetric coordination games a la Bryant (1983) where a number of players simultaneously choose efforts from a compact interval and the lowest effort determines the output of a public good. Assuming that payoffs are concave in the public good and linear in effort, this game has a continuum of Pareto-ranked equilibria. In a noicy variant of the model an error term is added to each players choice before his effort is determined. An equilibrium of the original model is noise-proof if it can be approximated by equilibria of noisy games with vanishing noise. There is a unique noise-proof equilibrium and, as the noisy games are supermodular, this solution can be derived by an iterated dominance argument. Our results agree with the experimental findings in Van Huyck, Battalio and Beil (1990). We also show that the unperturbed game is a potential game and that the noise-proof equilibrium maximizes the potential.

Electromagnetic properties and high-spin states in 173Ta

Abstract High-spin properties of rotational bands are studied in 173Ta using the 160Gd(19F,6n) reaction at bombarding energies of 103–105 MeV. With the existing bands being extended, and new bands established, a total of 16 rotational sequences are interpreted in terms of their (multi) quasiparticle structure. Measurements of electromagnetic properties for these bands include E2 M1 mixing ratios, branching ratios and lifetimes of isomeric states close to band heads, for which all energies have now been determined. Particular emphasis is devoted to (i) the band structures related to the 1 2 − [541] intruder configuration, for which both favoured, and unfavoured partners as well as the extended g- and S-bands in the (delayed) crossing region have been established, (ii) the reduced E1 transition strength between the (new) 1 2 + [411] and 1 2 − [541] bands, which is strongly enhanced, most likely due to coupling to octupole degrees of freedom, and show a ΔI = 4 staggering, (iii) the observation of weak interband transitions between the two partners of a pseudo-spin doublet composed of the 5 2 + [402] and 7 2 + [404] bands together with accurately measured intraband mixing ratios enable an analysis of the mixing of these bands through comparisons to particle-rotor calculations, (iv) the observed three-quasiparticle bands which are assigned to specific configurations coupling the lowest protons to lowest two-quasineutrons with negative parity.

Interactions between a multitude of rotational bands in well deformed odd nuclei: A new method for spin and parity assignment

Abstract Using the ( 18 O,5n) 163 Er reaction a multitude of rotational bands have been established with firm spin and parity assignments in 163 Er. In 17 out of 24 band crossings E2 cross-band transitions have been observed. The interaction strength varies between ∼ 1 and ∼ 50 keV with many of the values in the range 10–15 keV. These interactions sample a variety of the lowest (multi) -quasiparticle configurations. For some bands, in particular those with high K -values, the configurations can be established rather well. Quite complicated changes in the wavefunctions must occur at these crossings, and to explain the observed interaction strengths coupling to various vibrational degrees of freedom, in addition to possible residual neutron-proton interactions, may be needed.