Membrane regeneration for wastewater reclamation using reverse osmosis

One of the major problems in applying reverse osmosis to wastewater reclamation is the potential plugging and simultaneous product flux-decline of the membranes. At present two techniques are prevalently used to minimize these deleterious effects. These are periodic clearing and extensive pretreatment. A third, and as yet untried, technique is presented here. It involves the in situ replacement of degraded membranes at projected replacement costs far below those for spirally wound units.Results presented here demonstrate that in situ replacement of cellulose acetate reverse osmosis membranes is technically sound. The membrane replacement cycle was repeated six times with average water fluxes of about 13 gal ft⁻² day⁻¹ and salt rejections of between 78 and 85 per cent. The regenerable unit was also tested on primary and secondary sewage effluent. Average water fluxes were between 3 and 10 gal ft⁻² day⁻¹, respectively, while salt rejections were between 66 and 73 per cent. Projected membrane costs are reduced from $4.06 ft⁻² for a 6-in. dia. module to $0.08 ft⁻² for a 72-in. dia. module. Thus, large diameter units become economically very attractive. Design and cost computer parametrization is also presented.     

Bayesian assessment of uncertainty in aerosol size distributions and index of refraction retrieved from multiwavelength lidar measurements

We investigate the assessment of uncertainty in the inference of aerosol size distributions from backscatter and extinction measurements that can be obtained from a modern elastic/Raman lidar system with a Nd:YAG laser transmitter. To calculate the uncertainty, an analytic formula for the correlated probability density function (PDF) describing the error for an optical coefficient ratio is derived based on a normally distributed fractional error in the optical coefficients. Assuming a monomodal lognormal particle size distribution of spherical, homogeneous particles with a known index of refraction, we compare the assessment of uncertainty using a more conventional forward Monte Carlo method with that obtained from a Bayesian posterior PDF assuming a uniform prior PDF and show that substantial differences between the two methods exist. In addition, we use the posterior PDF formalism, which was extended to include an unknown refractive index, to find credible sets for a variety of optical measurement scenarios. We find the uncertainty is greatly reduced with the addition of suitable extinction measurements in contrast to the inclusion of extra backscatter coefficients, which we show to have a minimal effect and strengthens similar observations based on numerical regularization methods.     

Theoretical aspects of the internal element connectivity parameterization approach for topology optimization

The internal element connectivity parameterization (I‐ECP) method is an alternative approach to overcome numerical instabilities associated with low‐stiffness element states in non‐linear problems. In I‐ECP, elements are connected by zero‐length links while their link stiffness values are varied. Therefore, it is important to interpolate link stiffness properly to obtain stably converging results. The main objective of this work is two‐fold (1) the investigation of the relationship between the link stiffness and the stiffness of a domain‐discretizing patch by using a discrete model and a homogenized model and (2) the suggestion of link stiffness interpolation functions. The effects of link stiffness penalization on solution convergence are then tested with several numerical examples. The developed homogenized I‐ECP model can also be used to physically interpret an intermediate design variable state. Copyright © 2008 John Wiley & Sons, Ltd.     

Model Sensitivity Analysis for Biotrickling Filter Treatment of Graywater Simulant and Waste Gas. II

A detailed sensitivity analysis was conducted to identify key parameters for a biotrickling filter simultaneously treating graywater and waste gas containing ammonia and hydrogen sulfide contaminants. Sampling-based approaches were applied to quantitatively assess the sensitivity of both design and intrinsic model parameters. Specifically, the sensitivity of contaminant removal rates under system conditions was investigated. Results suggested that contaminant removal rates can be substantially improved by increasing the fraction of wetted area in a biotrickling filter. Although recirculation flow rate is insensitive when considering liquid contaminant removal, increasing this parameter improves gas removal efficiency and also increases wetted area within the biotrickling filter. Reactor performance can also be improved by increasing gas and liquid residence times. Contaminant diffusivity through the biofilm is an important parameter and should be accurately assessed. This study differentiated key from insignificant biotrickling filter reactor design parameters for the biotrickling filter and provides guidance for similar research applications.     

Evaluation of Uplift Interpretation Criteria for Drilled Shaft Capacity

Representative interpretation criteria are examined to evaluate the capacity of drilled shaft foundations under axial uplift loading. A wide variety of uplift load test data are used, and these data are divided into drained and undrained databases. The interpretation criteria are applied to these load test data to establish a consistent uplift interpretation criterion. The results are comparable for both drained and undrained loading. In general, the undrained load test results show somewhat less variability than the drained results. Based on these analyses, the QL2, Q0.5in, and slope tangent methods are the more reliable and consistent, and specific design recommendations for the interpretation of uplift drilled shaft load test are given, in terms of both capacity and displacement.     

Early structural evolution of native cytochrome c after solvent removal

Electrospray ionization transfers thermally labile biomolecules, such as proteins, from solution into the gas phase, where they can be studied by mass spectrometry. Covalent bonds are generally preserved during and after the phase transition, but it is less clear to what extent noncovalent interactions are affected by the new gaseous environment. Here, we present atomic-level computational data on the structural rearrangement of native cytochrome c immediately after solvent removal. The first structural changes after desolvation occur surprisingly early, on a timescale of picoseconds. For the time segment of up to 4.2 ns investigated here, we observed no significant breaking of native noncovalent bonds; instead, we found formation of new noncovalent bonds. This generally involves charged residues on the protein surface, resulting in transiently stabilized intermediate structures with a global fold that is essentially the same as that in solution. Comparison with data from native electron capture dissociation experiments corroborates both its mechanistic postulations and our computational predictions, and suggests that global structural changes take place on a millisecond timescale not covered by our simulations.     

Tobit analysis of vehicle accident rates on interstate highways

There has been an abundance of research that has used Poisson models and its variants (negative binomial and zero-inflated models) to improve our understanding of the factors that affect accident frequencies on roadway segments. This study explores the application of an alternate method, tobit regression, by viewing vehicle accident rates directly (instead of frequencies) as a continuous variable that is left-censored at zero. Using data from vehicle accidents on Indiana interstates, the estimation results show that many factors relating to pavement condition, roadway geometrics and traffic characteristics significantly affect vehicle accident rates.     

Organochlorine insecticides and PCB in the sediments of Lake Huron (1969) and Georgian Bay and North Channel (1973).

Surficial and core sediments were collected from the main body of Lake Huron in 1969 and Georgian Bay and North Channel in 1973. These were analysed for organochlorine insecticides and PCB. Residues of organochlorines were higher in the twelve depositional basins in Lake Huron and Georgian Bay than in sediment in the non-depositional zones. PCB was present at similar concentrations to sigma DDT; with mean levels of 13 and 10 ng/g for PCB and sigma DDT in the main body of Lake Huron and 11 and 5 ng/g for PCB and sibma DDT in Georgian Bay. Residues of PCB varied from 9--33 ng/g in the 12 basins. With respect to sigma DDT, both parent DDT and its two metabolites were present in sediment at a mean residue of 7.8 ng/g for the whole lake. The main lake had residues of 10.2 ng/g while Georgian Bay had 5.8 ng/g and North Channel 4.1 ng/g in keeping with use pattenrs since 1943. HEOD was present in only 5.7% of sediment samples from main Lake Huron, 30% from Georgian Bay and 15% from North Channel. The highest residues 1.7 ng/g occurred in the North Channel. No chlordane was detected, however, heptachlor epoxide was identified in 8.5% of sediments collected in Lake Huron, 23% from Georgian Bay and 14% in North Channel. Endosulfan appeared in 4% of samples from both Georgian Bay and North Channel.