A generalized methodology for optimal configurations of hybrid distillation-pervaporation processes

The aim of this work is to illustrate the structural and parametric optimization of continuous hybrid distillation-pervaporation process with different configurations such as series, parallel, and series-parallel arrangement of pervaporation modules in the pervaporation network, and to propose a generalized methodology for difficult separations. A superstructure representation of hybrid process is considered and the process is modeled and optimized using an MINLP approach. The optimization strategy is to obtain the desired degree of either the retentate or the distillate purity without violating the composition constraints of products and heat exchange policy which minimizes the required membrane area by increasing the flux through the membrane. The structural and operating parameters such as number of trays required, feed tray location, reflux ratio, retentate recycle location, permeate recycle location, membrane feed location, number of pervaporation modules required, target composition (which is directly related to membrane area), and membrane selectivity are optimized for each configuration by minimizing the total annual cost (TAC) for the separation system. The optimization studies have been carried out with General Algebraic Modeling System software (GAMS/SBB/CONOPT) and the results of different configurations have been compared on the basis of TAC required for the separation. A total of three industrial case studies have been dealt with. The separation of isopropanol-water as an azeotropic mixture, propylene-propane as a close boiling mixture (system with a low relative volatility) and acetone-water as a tangent pinch mixture have been studied as representative examples.     

X-ray absorption and micro X-ray fluorescence spectroscopy investigation of copper and zinc speciation in biosolids

Despite its pivotal role in determining the risks and time frames associated with contaminant release, metal speciation remains a poorly understood aspect of biosolids chemistry. The work reported here used synchrotron-based spectroscopy techniques to investigate the speciation of copper and zinc in a range of Australian biosolids. High resolution element mapping of biosolids samples using micro X-ray fluorescence spectroscopy revealed considerable heterogeneity in key element associations, and a combination of both organic and inorganic copper and zinc binding environments. Linear combination fitting of K-edge X-ray absorption spectra indicated consistent differences in metal speciation between freshly produced and stockpiled biosolids. While sulfide minerals play a dominant role in metal binding in freshly dewatered biosolids, they are of lesser importance in dried biosolids that have been stockpiled. A degree of metal binding with iron oxide minerals was apparent but the results did not support the hypothesis that biosolids metals are chiefly associated with iron minerals. This work has potential implications for the long-term stability of metals in biosolids and their eventual fate following land application.     

Synthesis and photovoltaic properties of novel PPV-derivatives tethered with spiro-bifluorene unit for polymer solar cells

New thermally robust photoactive arylenevinylene-based conjugated polymers, poly[3,6-bis(3,7-dimethyloctyloxy)-9,9-spirobifluorenyl-2,7-vinylene] [(OC₁₀)₂-spiro-PFV] and poly[{3,6-bis(3,7-dimethyloctyloxy)-9,9-spirobifluorenyl-2,7-vinylene}-co-2-{methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene}] [(OC₁₀)₂-spiro-PFV-co-MEH-PPV], were synthesized and used to fabricate polymer solar cells. Bulk heterojunction solar cells fabricated by blending the new copolymers, spiro-PFV and (OC₁₀)₂-spiro-PFV-co-MEH-PPV, as an electron donor with the fullerene derivative, [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) as an electron acceptor. The effects of electron donor to acceptor ratio, thickness of photoactive layer, and the cathode structures on the power conversion efficiency (PCE) in polymer solar cells were studied. The copolymer feed ratio was found to have a considerable effect on the PCE. The maximum PCE of 1.30% was achieved with (OC₁₀)₂-spiro-PFV-co-MEH-PPV.     

Application of the singular perturbation method to a steam power system

A fifth-order steam power system with reheat unit is considered. The discrete model of the continuous system is cast in the singularity perturbed form. A perturbation method is applied to the discrete model. The important features of singular perturbations in discrete systems are clearly illustrated. The numerical values represent a typical set of real data. The results show a new avenue for the application of the singular perturbation method to discrete models of large-scale power systems.     

Fast reduction of potential fields measured over an uneven surfaceto a plane surface

The present work is aimed at rapid reduction of the gravity and magnetic fields observed over an uneven surface to a horizontal plane. The approach suggested is to estimate the Fourier transform of the potential field over an imaginary horizontal plane lying entirely above the ground surface and impose boundary conditions; namely, the solution must satisfy the observed field over the ground surface and vanish over an infinite hemisphere. The desired Fourier transform is obtained in an iterating manner. A 2D FFT algorithm can considerably reduce the computational burden. The FFT approach cannot be used unless the discrete data is available on a rectangular grid. If the observations are scattered, interpolation to the nearest grid point will have to be carried out. Interpolation introduces marginal increase in the rms error. The iterating approach is about 10 times faster than the least squares approach     

Variation of surface flashover voltage in SF6 withpressure

Surface flashover characteristics of solid spacers in a rod-plane configuration have been investigated in SF₆, at pressures to 400 kPa, for switching impulse voltages to determine the effect of spacer, spacer materials and polarity of applied impulses. The effect of spacer material on the flashover voltage is not significant. For negative polarity impulses, the influence of the spacer is also insignificant. But for positive polarity impulses, at pressures <200 kPa, the spacer efficiency becomes >1.0. On the other hand, at pressures >200 kPa, the presence of the spacer drastically reduces the flashover voltage of the system. At about atmospheric pressure also, the spacer efficiency in air has been found to be >1.0, with the same electrode geometry     

Orderly oriented wire mesh: a novel porous coating

As an alternative to commercially available porous beads and fiber metal mesh, a new porous coating, orderly oriented wire mesh (OOWM), was developed. Rectangular plugs, 10 x 5 x 5 mm with porous-coated beads, and four different OOWM configurations were inserted into bilateral femoral condyles of adult beagles. Dogs were sacrificed immediately after implantation, and at 4 weeks, 8 weeks, and 12 weeks postimplantation. Mechanical pullout strength of plugs revealed that porous beads are equivalent to the simplest OOWM at 12 weeks postimplantation. Of the four OOWMs tested, the 25 x 25 single layer was significantly more stable than others at 4 weeks postimplantation. These results indicate that in an in vivo unloaded model, OOWM is just as effective as the porous beads in achieving early bone ingrowth and stability.     

Heterogeneous Bifunctional Catalysts for the Synthesis of Chiral Vicinal Diols

Heterogeneous bifunctional catalysts consisting of palladate–osmate and osmate–tungstate developed by the ion exchange on quaternary ammonium salts covalently bound to resin, and their homogeneous bimetallic analogs are evaluated for the synthesis of chiral vicinal diols. The heterogeneous bifunctional catalyst (resin-PdOs) and its homogeneous analog are used in the tandem Heck-asymmetric dihydroxylation (AD) to afford diols with excellent yields and enantiomeric excesses (ee's) in the presence of various co-oxidants. The other bifunctional catalyst (resin-OsW) and its homogeneous analog are used in a simultaneous asymmetric dihydroxylation-N-oxidation of a wide range of olefins to obtain chiral vicinal diols with higher yields and ee's using H₂O₂ as terminal oxidant. The bifunctional resin catalysts are recovered quantitatively by a simple filtration and reused for a number of cycles with consistent activity.     

Pathways to scaling-up in community based rehabilitation agencies

Scaling-up is the expansion or development of organizational activities to achieve a greater impact. Scaling-up among non-government organizations (NGOs) involved in community based rehabilitation (CBR) is a recent phenomenon. Case study materials from NGOs in India, Canada, and Indonesia are used to illustrate four pathways to scaling-up in CBR and the use of collaboration strategies in these efforts. Discussion focuses on differences between scaling-up in industrialized and less developed countries and on structural characteristics of organizations which influence their pathways.     

Removal of sulfide in integrated anaerobic–aerobic wastewater treatment system

In recent years, the stipulations fixed by regulatory bodies have become stringent to keep environmental pollution under control. Normally COD and BOD are the parameters monitored to determine the efficiency of any treatment system. But in many cases, industrial wastewater may contain sulfate along with other organic constituents. Sulfate, if present in the wastewater, will be converted to H₂S under anaerobic conditions and this is hazardous. Subsequently, if the same wastewater is treated under aerobic conditions, a part of the air supplied will be utilized for oxidation of sulfide back to sulfate which leads to reduced efficiency of the aerobic treatment. The released wastewater with high sulfate levels will be going into the environment, which is undesirable. Methods are reported in the literature for the removal of sulfate and sulfide before and after anaerobic treatment respectively. Most of these methods are chemical which are either costly or impracticable. Therefore, a novel approach for removing sulfate or sulfide in the treatment scheme is required. In the present communication, studies are undertaken by designing an innovative stripper system where sulfide is removed to the extent of 60 to 70% before aerobic treatment. The parameters involved in design and operation of the stripper, such as airflow rate, liquid flow rate, liquid to air ratio, and pH profile, are optimized. It is a physical system in which air and waste water are passed as counter currents. The treated wastewater from the stripper, which contains less sulfide, may be post-treated in the aerobic system before final discharge. Hydrogen sulfide can be efficiently removed by coupling this type of stripper to existing anaerobic systems. The system can be efficiently used in existing treatment plants or in new designs to control sulfide (free sulfide generated in an anaerobic reactor in the case of wastewaters having high sulfate inhibits methanogenesis, resulting in reduced performance of the anaerobic process) generated in anaerobic reactors and to optimize the air and oxygen requirements in the aerobic system.