Biological phosphorus removal from dairy wastewater by alternating anaerobic and aerobic conditions

In this study, the possibility of applying the enhanced biological phosphorus removal (EBPR) process for Algiers dairy wastewater which can have phosphorus contents up to 130 mg/L was examined. EBPR is conventionally performed by an anaerobic-aerobic process. The objectives of this work were to determine an optimal hydraulic retention time (HRT) in aerobic conditions and to study the effect of short chain fatty acids (SCFA) (acetic and propionic acids) addition on the phosphorus release in anaerobic conditions. The tests were performed in a batch reactor operating with an aerobic/anaerobic sequence of phases. Batch tests have been carried out at 3 HRTs in aerobic conditions (1, 2 and 3 h) while the anaerobic retention time was fixed at 4 h, to examine the effect of stress related to changes of aerobic HRT. Main results show that the most favorable aerobic retention time was found to be 2 h. The amount of P released in anaerobic phase increases from 2.25 to 2.48 mgP/gVSS with increasing aerobic HRT from 1 to 2 h and decreases to 1.28 mgP/g VSS for a time of 3 h using acetic acid. Similarly, this amount increases from 1.62 to 4.38 mgP/gVSS for 1 to 2 h and decreases to 1.41 mgP/gVSS for a time of 3 h using propionic acid. The initial release rate was directly proportional to the amount of added substrate. Propionate may be a more effective carbon source for biological phosphorus removal than acetate. Based on the results presented herein, we can confirm the possibility of phosphorus removal from dairy wastewater in the aerobic-anaerobic biological process.Keywords: Dairy wastewater, biological phosphorus removal, aerobic, anaerobic, release, acetic acid, propionic aci

Temperature effects on dislocation core energies in silicon and germanium

Temperature effects on the energetics of the 90-degree partial dislocation in silicon and germanium are investigated, using non-equilibrium methods to estimate free energies, coupled with Monte Carlo simulations. Atomic interactions are described by Tersoff and EDIP interatomic potentials. Our results indicate that the vibrational entropy has the effect of increasing the difference in free energy between the two possible reconstructions of the 90-degree partial, namely, the single-period and the double-period geometries. This effect further increases the energetic stability of the double-period reconstruction at high temperatures. The results also indicate that anharmonic effects may play an important role in determining the structural properties of these defects in the high-temperature regime.Comment: 8 pages in two-column physical-review format with six figure

Thermodynamic Behavior of a Model Covalent Material Described by the Environment-Dependent Interatomic Potential

Using molecular dynamics simulations we study the thermodynamic behavior of a single-component covalent material described by the recently proposed Environment-Dependent Interatomic Potential (EDIP). The parameterization of EDIP for silicon exhibits a range of unusual properties typically found in more complex materials, such as the existence of two structurally distinct disordered phases, a density decrease upon melting of the low-temperature amorphous phase, and negative thermal expansion coefficients for both the crystal (at high temperatures) and the amorphous phase (at all temperatures). Structural differences between the two disordered phases also lead to a first-order transition between them, which suggests the existence of a second critical point, as is believed to exist for amorphous forms of frozen water. For EDIP-Si, however, the unusual behavior is associated not only with the open nature of tetrahedral bonding but also with a competition between four-fold (covalent) and five-fold (metallic) coordination. The unusual behavior of the model and its unique ability to simulation the liquid/amorphous transition on molecular-dynamics time scales make it a suitable prototype for fundamental studies of anomalous thermodynamics in disordeered systems.Comment: 48 pages (double-spaced), 13 figure