Removal of fouling species from brackish water reverse osmosis reject stream.

Brine disposal from reverse osmosis (RO) systems remains a major challenge for the desalination industry especially in inland areas where discharge options are very limited. Solutions will entail the introduction of economic treatment processes that will alleviate the brine's negative impact on the environment and reduce its discharge volume. Such processes could act as an intermediary treatment process for the recycling of the brine through an additional RO stage which, for brackish water (BW) desalination, could lead to saving valuable water while reducing the amount of brine discharge. In this context, the study at hand attempts to evaluate the effectiveness of a one-step chemical process for the treatment of BWRO brine. This study seeks to determine optimal operating conditions relative to type, ratio, and dosage of alkalizing chemicals, pH and temperature, for substantially reducing the concentrations of scaling parameters such as calcium, magnesium, silica, and strontium. The results indicate that precipitation softening at pH = 11.5 using combined chemical dosages of NaOH and Na2CO3 in a ratio of 2:1 leads to substantial removal of calcium and magnesium (>95%) and moderately high removal of strontium and silica (>71%).

Mullins effect in polyethylene and its dependency on crystal content: A network alteration model.

This contribution is focused on the Mullins effect in polyethylene. An ultra-low-density polyethylene with 0.15 crystal content, a low-density polyethylene with 0.3 crystal content and a high-density polyethylene with 0.72 crystal content are subjected to cyclic stretching over a large strain range. Experimental observations are first reported to examine how the crystal content influences the Mullins effect in polyethylene. It is found that the cyclic stretching is characterized by a stress-softening, a hysteresis and a residual strain, whose amounts depends on the crystal content and the applied strain. A unified viscohyperelastic-viscoelastic-viscoplastic constitutive model is proposed to capture the polyethylene response over a large strain range and its crystal-dependency. The macro-scale polyethylene response is decomposed into two physically distinct sources, a viscoelastic-viscoplastic intermolecular part and a viscohyperelastic network part. The local inelastic deformations of the rubbery amorphous and crystalline phases are considered by means of a micromechanical treatment using the volume fraction concept. Experimentally-based material kinetics are designed by considering the Mullins effect crystal-dependency and are introduced into the constitutive equations to capture the experimental observations. It is shown that the model is able to accurately reproduce the Mullins effect in polyethylene over a large strain range. The inherent deformation mechanisms are finally presented guided by the proposed constitutive model.

Vapor-induced transfer of bacteria in the absence of mechanical disturbances.

Transfer of bacteria through water vapor generated at moderate temperatures (30-50°C) in passive solar stills, has scarcely been reported. The objective of this research was to investigate whether bacteria in highly humid atmospheres can get transferred through water vapor in the absence of other transfer media to find their way to the distillate. To achieve this objective, passive solar reactors were chosen as the medium for experimentation, and distillation experiments were conducted by spiking a pure bacterial culture (Escherichia coli, Klebsiella pneumonia or Enterococcus faecalis) in low mineralized water vs. highly mineralized water in the dark under moderate temperatures ranges (30-35°C, 40-45°C and 50-55°C). Results showed that bacteria indeed get transferred with the vapor in stills when not exposed to solar U.V. radiation. The trends observed were adequately explained by a zero-modified Hurdle-Poisson model. The numbers of cultivable bacterial colonies transferred were bacterial size, water type and temperature dependent with highest transfers occurring in E. faecalis>E. coli>K. pneumonia at the 40°C range in low mineralized water. Proper management strategies are recommended to achieve complete disinfection in solar stills.

A two-phase hyperelastic-viscoplastic constitutive model for semi-crystalline polymers: application to polyethylene materials with a variable range of crystal fractions.

Polyethylene-based polymers as biomedical materials can contribute to a wide range of biomechanical applications. Therefore, it is important to identify, analyse, and predict with precision their mechanical behaviour. Polyethylene materials are semi-crystalline systems consisting of both amorphous and crystalline phases interacting in a rather complex manner. When the amorphous phase is in the rubbery state, the mechanical behaviour is strongly dependent on the crystal fraction, therefore leading to essentially thermoplastic or elastomeric responses. In this study, the finite deformation stress-strain response of polyethylene materials is modelled by considering these semi-crystalline polymers as two-phase heterogeneous media in order to provide insight into the role of crystalline and amorphous phases on the macro-behaviour and on the material deformation resistances, i.e. intermolecular and network resistances. A hyperelastic-viscoplastic model is developed in contemplation of representing the overall mechanical response of polyethylene materials under large deformation. An evolutionary optimization procedure based on a genetic algorithm is developed to identify the model parameters at different strain rates. The identification results show good agreement with experimental data, demonstrating the usefulness of the proposed approach: the constitutive model, with only one set of identified parameters, allows reproducing the stress-strain behaviour of polyethylene materials exhibiting a wide range of crystallinities, the crystal content becoming the only variable of the model.

Adsorption of arsenate on untreated dolomite powder.

Raw dolomite powder was evaluated for its efficiency in adsorbing As(V) from water. An experimental setup comprised of a fluidized dolomite powder bed was used to assess the impact of various test variables on the efficiency of removal of As(V). Test influents including distilled water (DW), synthetic groundwater (SGW) and filtered sewage effluent (FSE) were employed to assess the effect of influent parameters on the adsorption process and the quality of the effluent generated. Dolomite exhibited good As(V) removal levels for distilled water (>92%) and synthetic ground water (>84%) influents at all initial As(V) concentrations tested (0.055-0.600 ppm). Breakthrough of dolomite bed occurred after 45 bed volumes for DW and 20 bed volumes for SGW influents with complete breakthrough taking place at more than 300 bed volumes. As(V) removal from FSE influents was relatively unsuccessful as compared to the DW and SGW influents. Partial removal in the order of 32% from filtered sewage effluent at initial concentration of 0.6 mg/L started at 75 bed volumes and gradually stopped at 165 bed volumes. Varying degrees of As(V) adsorption capacities were observed by the different test influents employed, which indicate that the adsorption of As(V) is adversely affected by competing species, mainly sulfates and phosphates present in the influent. The adsorptive behavior of dolomite was described by fitting data generated from the study into the Langmuir and Freundlich isotherm models. Both models described well the adsorption of dolomite. The average isotherm adsorptive capacity was determined at 5.02 mug/g. Regeneration of the dolomite bed can be achieved with the use of caustic soda solution at a pH of 10.5.

An audit of bone densitometry practice with reference to ISCD, IOF and NOF guidelines.

INTRODUCTION: The impact of osteoporosis guidelines on clinical practice has not been fully evaluated. OBJECTIVES: To estimate the positive predictive value (PPV) of the National Osteoporosis Foundation (NOF), the International Osteoporosis Foundation (IOF) and the International Society for Clinical Densitometry (ISCD) guidelines for osteoporosis and compare it to the PPV of clinical judgement alone. METHODS: All subjects tested for bone mineral density during the fall of 2001 in three teaching hospitals in Beirut were invited to participate. The reference databases used for the calculation of the T-score were the NHANES database for the hip and the manufacturer's database for the spine. The impact of using guidelines was measured by the increment in PPV. Osteoporosis was defined as a T-score < or =-2.5 at either the spine or hip. RESULTS: A total of 307 post-menopausal women were tested with dual-energy X-ray absorptiometry (DXA). In current practice (clinical judgement alone), the PPV for osteoporosis was 42.4%; using NOF guidelines, 236 women would have been tested, and the PPV would have been 46.2%. Similarly, using IOF or ISCD guidelines, 236 women would have been tested, and the PPV would have been 47.1%. CONCLUSION: Compared to current clinical practice, application of the ISCD, IOF and NOF guidelines may increase the predictive value of a central DXA for osteoporosis.

The combined effect of step-feed and recycling on RBC performance.

The effect of step-feed and recycling on the efficiency of treatment in rotating biological contractors (RBCs) was investigated. Experiments were conducted on a RBC system consisting of two three-stage units. The two units were operated in parallel, one unit as a control with a single feed point and the other in a step-feed mode. Seven experimental runs were conducted, using a simple synthetic wastewater, in which hydraulic loading rates were maintained constant at about 0.094 m3/m2d and variable COD concentrations (800-1200 mg/L), NH3-N concentrations (104-116 mg/L), step-feed ratios (60/40 and 70/30), and recirculation modes. Results indicate that improvements in the treatment efficiencies of RBC systems may be attained by operating the system in a step feed mode as compared to a single point feed mode. Further improvements may also be obtained by inducing effluent recirculation to the inlet stage. In both cases, levels of improvement have shown to be more pronounced for NH3-N removals and DO residual concentrations as compared to COD removals. The combined effect of step feed and recirculation of system effluent on NH3-N removal efficiencies is appreciable. Comparing removal efficiencies between the control, step feed and the combined step-feed/recirculation modes shows an increase of about 26%. For COD removals, the effect is not that pronounced as the results for the combined modes of operation indicate a limited increase in overall removal efficiency of about 3%. Supplementing step feed by a recircutation system also markedly improved DO residuals in stages 1 and 2 and to a lower extent in stage 3 of the system. Changing the ratio in the step feed system from 60/40% to 70/30% exhibited a slight improvement in NH3-N removal efficiencies as well as improved residual DO concentrations but very limited effect on COD removals. The use of a simple synthetic wastewater in the experiments may limit extrapolation of the findings to actual operation.

An optimisation model for regional integrated solid waste management I. Model formulation.

Increased environmental concerns and the emphasis on material and energy recovery are gradually changing the orientation of MSW management and planning. In this context, the application of optimisation techniques have been introduced to design the least cost solid waste management systems, considering the variety of management processes. This study presents a model that was developed and applied to serve as a solid waste decision support system for MSW management taking into account both socio-economic and environmental considerations. The model accounts for solid waste generation rates, composition, collection, treatment, disposal as well as potential environmental impacts of various MSW management techniques. The model follows a linear programming formulation with the framework of dynamic optimisation. The model can serve as a tool to evaluate various MSW management alternatives and obtain the optimal combination of technologies for the handling, treatment and disposal of MSW in an economic and environmentally sustainable way. The sensitivity of various waste management policies will be also addressed. The work is presented in a series of two papers: (I) model formulation, and (II) model application and sensitivity analysis.

An optimisation model for regional integrated solid waste management II. Model application and sensitivity analyses.

Increased environmental concerns and the emphasis on material and energy recovery are gradually changing the orientation of MSW management and planning. In this context, the application of optimisation techniques have been introduced to design the least cost solid waste management systems, considering the variety of management processes (recycling, composting, anaerobic digestion, incineration, and landfilling), and the existence of uncertainties associated with the number of system components and their interrelations. This study presents a model that was developed and applied to serve as a solid waste decision support system for MSW management taking into account both socio-economic and environmental considerations. The model accounts for solid waste generation rates, composition, collection, treatment, disposal as well as potential environmental impacts of various MSW management techniques. The model follows a linear programming formulation with the framework of dynamic optimisation. The model can serve as a tool to evaluate various MSW management alternatives and obtain the optimal combination of technologies for the handling, treatment and disposal of MSW in an economic and environmentally sustainable way. The sensitivity of various waste management policies is also addressed. The work is presented in a series of two papers: (I) model formulation, and (II) model application and sensitivity analysis.

Imaging of glutamate release from the goldfish retinal slice.

A fluorometric procedure to image release of the neurotransmitter glutamate from living retinal slices is described. Patterns of endogenous glutamate efflux were imaged with a cooled CCD camera in goldfish retinal slices as NADH fluorescence produced by a cycling glutamate dehydrogenase (GDH). Basal and potassium evoked glutamate effluxes were strongly localized to the outer and inner plexiform layers, supporting the model that photoreceptors and bipolar cells release glutamate as their prime fast neurotransmitter.

Imaging of endogenous neurotransmitter release.

A method for imaging endogenous release of two common neurotransmitters from tissue slices is described. This detection employs fluorometric, enzymatic assays for glutamate and for GABA, the progress of which is directly monitored by a cooled CCD camera. The assays are highly specific for their substrate, allowing accurate determination of either glutamate or GABA release by tissues. The images captured allow visualization of the release of these transmitters, permitting a direct correlation of transmitter release with well localized regions of the tissue examined. This procedure is advantageous for studies on endogenous neurotransmission.

Transport-mediated release of endogenous glutamate in the vertebrate retina.

In the present study we measured calcium-dependent, vesicular glutamate release, and calcium-independent, transport-mediated glutamate release patterns in the vertebrate retina to better understand the sources of elevated glutamate in neural tissue under ischemic conditions. A potassium concentration of 40 mM, which mimics the extracellular potassium concentration in the central nervous system during ischemia, was applied to the bathing medium of a retinal slice prepared from zebrafish. High external potassium evoked release of endogenous glutamate that was measured using a glutamate-specific fluorometric assay applied to the bath. The slice was visualized under 668 nm light using Normarski optics and fluorescent images were captured using a cooled charge-coupled device (CCD) camera. Following the elevation of external potassium to 40 mM several bands of glutamate fluorescence, reflecting the spatial distribution of glutamate release, were observed. A calcium-dependent cloud of glutamate was observed in the inner plexiform layer, that was antagonized by bath-applied nifedipine. A relatively dense glutamate cloud (1-10 microM) was observed over the ganglion cell layer, which was blocked by dihydrokainate, a glutamate transport antagonist. In contrast, nifedipine, an inhibitor of calcium-dependent neurotransmitter release in the retina, failed to block the cloud of released glutamate in the ganglion cell layer. These data suggest that under pathological conditions in the eye where glutamate levels are elevated surrounding retinal ganglion cells, such as observed in some forms of glaucoma, a possible source of the elevated glutamate is through a glutamate transporter operating in a reversed direction. A likely candidate for mediating this reversed transport of glutamate is the retinal Muller cell.

Presynaptic inhibition by GABA is mediated via two distinct GABA receptors with novel pharmacology.

Mechanisms of presynaptic inhibition were examined in giant presynaptic terminals of retinal bipolar neurons, which receive GABAergic feedback synapses from amacrine cells. Two distinct inhibitory actions of GABA are present in the terminals: a GABAA-like Cl conductance and a GABAB-like inhibition of voltage-dependent Ca current. Both of the receptors underlying these actions have unusual pharmacology that fits neither GABAA nor GABAB classifications. The GABA-activated Cl conductance was not blocked by the classical GABAA antagonist bicuculline, while the inhibition of Ca current was neither mimicked by the GABAB agonist baclofen nor blocked by the GABAB antagonist 2-hydroxysaclofen. The "GABAC" agonist cis-4-aminocrotonic acid (CACA) both activated the Cl conductance and inhibited Ca current, but the inhibition of Ca current was observed at much lower concentrations of CACA (< 1 microM) than was the activation of the Cl conductance (K1/2 = 50 microM). Thus, by the criterion of being insensitive to both bicuculline and baclofen, both GABA receptors qualify as potential GABAC receptors. However, it is argued on functional grounds that the two GABA receptors coupled to Cl channels and to Ca channels are best regarded as members of the GABAA and GABAB families, respectively.

Substance P modulates calcium current in retinal bipolar neurons.

Retinal bipolar cells are non-spiking interneurons that relay information from photoreceptors to amacrine and ganglion cells. In turn, bipolar cells receive extensive synaptic feedback from amacrine cells, some of which contain neuropeptides, including substance P. We have examined the effect of substance P on single bipolar neurons isolated from goldfish retina and find that substance P (0.1-1 nM) produced a voltage-dependent inhibition of calcium current in these cells. The inhibition was strongest at negative potentials, with the peak suppression occurring at -20 to -30 mV; at potentials positive to 0 mV, there was little effect on calcium current. Thus, the net effect was to shift the voltage range of activation of calcium current toward more positive potentials. The inhibition of calcium current by substance P required GTP in the patch pipette and was blocked by internal GDP-beta-S. Similar effects on calcium current were observed with somatostatin and metenkephalin, which are also found in amacrine cells.

Conformational specificity of GABA binding to the presynaptic GABAA receptor.

GABAA receptors on the synaptic terminal of retinal bipolar neurons mediate the inhibition by GABA of presynaptic calcium influx in these non-spiking interneurons. To characterize the conformational specificity of GABA binding to the receptor underlying this presynaptic inhibition, we have recorded the conductance change induced in isolated bipolar cells by GABA and by two conformationally locked analogs of GABA, cis- and trans-4-aminocrotonic acid (ACA). Trans-ACA (the extended conformation) is more potent than GABA in activating the GABAA chloride conductance of the synaptic terminal, while cis-ACA (the folded conformation) is 20-fold less potent than GABA. These results show that the extended conformation of GABA is the preferred form for the presynaptic GABAA receptor.

Application of a fluorometric method to measure glutamate release from single retinal photoreceptors.

Release of the endogenous transmitter, glutamate, was measured from individual cone photoreceptors using a microfluorometric technique. The assay for glutamate was conducted within the lumen of a suction pipette, and was based on the fluorometric measure of the production of NADH from NAD+. This reaction was catalyzed by glutamate dehydrogenase contained in the pipette. Upon introduction of glutamate to the pipette, an increase in the NADH fluorescence was observed, representing the stoichiometric conversion of glutamate to NADH. The fluorescent signal was quantified, allowing an estimate of glutamate release from a single cone upon depolarization. The release observed was elicited upon depolarization of the cell with extrinsic current, and was detectable simultaneous with stimulation of the cell. Depolarization-induced release of endogenous glutamate was from the synaptic pedicle of the cell, and this release decreased with subsequent stimulations. The decrease in the release could be briefly reversed by an increase in the depolarization current used, or by allowing the cell to rest for several minutes.

Phorbol esters enhance transmitter release in rat hippocampal slices.

Phorbol esters enhance synaptic transmission in the rat hippocampal slice preparation most likely by acting at a presynaptic locus. To more directly examine the actions of phorbol esters on neurotransmitter release we have measured their effects on the occurrence of spontaneous postsynaptic potentials as well as on the potassium stimulated release of endogenous glutamate. Both measures of transmitter release were increased by phorbol esters suggesting a functional or regulatory role for protein kinase C in controlling the release of neurotransmitter in the mammalian CNS.