Multi-objective Optimization Models for Distributing Biosolids to Reuse Fields: A Case Study for the Blue Plains Wastewater Treatment Plant

This paper presents multi-objective optimization models that simultaneously minimize biosolids odors as well as wastewater treatment and biosolids distribution costs and can be proactively used by biosolids managers at advanced wastewater treatment plants. The computational aspects of these models are daunting, typically involving over 200,000 constraints and about 145,000 variables and are thus difficult to solve. Also, some of the mathematical terms involve bilinear, nonconvex pieces which need to be approximated. This paper presents both a numerical approximation scheme to linearize these nonconvex terms using Schur’s decomposition and SOS2 variables as well as a Dantzig–Wolfe decomposition method to improve the computational times. The computational results as well as a sensitivity analysis are performed using data from the Blue Plains advanced wastewater treatment plant in Washington, DC.     

A residual-based a posteriori error estimator for a fully-mixed formulation of the Stokes–Darcy coupled problem

In this paper we develop an a posteriori error analysis of a new fully mixed finite element method for the coupling of fluid flow with porous media flow in 2D. Flows are governed by the Stokes and Darcy equations, respectively, and the corresponding transmission conditions are given by mass conservation, balance of normal forces, and the Beavers–Joseph–Saffman law. We consider dual-mixed formulations in both media, which yields the pseudostress and the velocity in the fluid, together with the velocity and the pressure in the porous medium, and the traces of the porous media pressure and the fluid velocity on the interface, as the resulting unknowns. The set of feasible finite element subspaces includes Raviart–Thomas elements of lowest order and piecewise constants for the velocities and pressures, respectively, in both domains, together with continuous piecewise linear elements for the traces. We derive a reliable and efficient residual-based a posteriori error estimator for the coupled problem. The proof of reliability makes use of the global inf–sup condition, Helmholtz decompositions in both media, and local approximation properties of the Clément interpolant and Raviart–Thomas operator. On the other hand, inverse inequalities, the localization technique based on element-bubble and edge-bubble functions, and known results from previous works, are the main tools for proving the efficiency of the estimator. Finally, some numerical results confirming the theoretical properties of this estimator, and illustrating the capability of the corresponding adaptive algorithm to localize the singularities of the solution, are reported.     

Long-term fairness with bounded worst-case losses

How does one repeatedly choose actions so as to be fairest to the multiple beneficiaries of those actions? We examine approaches to discovering sequences of actions for which the worst-off beneficiaries are treated maximally well, then secondarily the second-worst-off, and so on. We formulate the problem for the situation where the sequence of action choices continues forever; this problem may be reduced to a set of linear programs. We then extend the problem to situations where the game ends at some unknown finite time in the future. We demonstrate that an optimal solution is intractable, and present two good approximation algorithms.     

Theoretical and Experimental Analysis of a Laser Textured Thrust Bearing

In this article, a laser partially textured thrust bearing is theoretically and experimentally analyzed. An adiabatic model is developed in order to theoretically investigate the performances of the bearing. The bearing sample is partially textured both in radial and circumferential direction using the laser texturing process. The performance of the bearing (fluid film thickness and friction torque) is evaluated on a specially adapted test rig and the experimental results are compared with the theoretical model. A good agreement is found between the theoretical model and the experimental data. Also a comparison between a laser textured bearing and a bearing textured using the photolithographic method is presented.     

Influence of water type and maturation time on the properties of kaolinite–saponite peloids

We studied the effects of maturation time and water type on the properties of peloids. The peloids were prepared artificially by mixing the same amount of solid phase of kaolin and bentonite (9:1, m:m) with hypersaline mineral water (sodium potassium chloride water) from a spring in La Malahá (Granada, Spain) and bidistilled water (oligometallic water). The liquid/solid ratio was 2:1, m:m, with periodic manual homogenization and maturation time of one to three months. The water content of the peloids was maintained constant during the entire period of maturation.The peloid properties considered were the composition of the liquid phase, the thermal behaviour, the amount of defects in the structure of the main minerals present in the solid phase (kaolinite and saponite) and the ultramicroscopic fabric of the material, determined by scanning electron microscopy (SEM) and image analysis (IA). To date, the latter aspect has been very little studied.The composition of the liquid phases changed with maturation time. Most of the parameters measured showed a tendency to increase with increasing maturation time, as a consequence of releasing ions from the clay minerals into the liquid phase. Thus, the bidistilled water became mineral water. The initial differences between the two waters employed in the mixture were maintained in the liquid phases.The investigation of the thermal behaviour of the peloid revealed that the decrease in temperature followed, with time, a fitted logarithmic curve where R² > 0.9. The maximum change occurred in the first stage, later cooling being slower. A statistic relationship was found between the cooling kinetic and pore size and the size of the particle aggregates measured by SEM-IA. The peloids cooled more rapidly with increasing maturation time, as in the case of saline water.Both the Hinckley index of kaolinite and Integral Breadth index of saponite changed with the maturation time of the peloid. At the end of the maturation process similar values were reached regardless of the water employed.The main effect of maturation time was the increase in the size of the particle aggregates, the formation of a fabric with a more reticular morphology, and the increase in the area occupied by the pores in the SEM micrographs.     

The Effect of External Electrostatic Field Orientation on Aerosol Filtration by Granular Filters

The separation of fine aerosol particles by a packed granular-bed filter, enhanced by external electrostatic fields, was studied experimentally and theoretically. The filtration efficiencies of charged and neutralized aerosols were measured for external fields aligned with the air flow, transverse to the flow, and opposite to the flow. Theoretical models of electrostatically enhanced granular-bed filtration of micrometer and submicrometer particles were developed. Experimental results which demonstrate the relative merit of each configuration were presented and compared with the theory. The parallel-field configuration yielded the best filtration efficiency followed by the transverse configuration.     

Evolution of carbohydrate fraction in carbonated fermented milks as affected by beta-galactosidase activity of starter strains

The influence of carbonation on the evolution of lactose, galactose and glucose in fermented milks with added probiotic bacteria (Lactobacillus casei, Lactobacillus acidophilus and/or Bifidobacterium bifidum) was evaluated and related to beta-galactosidase activity of starter strains. During incubation and first days of refrigeration, lactose hydrolysis resulting in the liberation of galactose and glucose occurred in CT (Streptococcus thermophilus/Lb. casei), AT (Str. thermophilus/Lb. acidophilus) and ABT fermented milks (Str. thermophilus/Lb. acidophilus/Bifid. bifidum). Levels of galactose were higher than those of glucose and could be related to the preferential consumption of glucose by actively growing bacteria. Through the incubation, lactose and monosaccharide levels were not affected by milk carbonation. However, during refrigerated storage the presence of this gas was associated with slightly lower content of lactose and higher levels of galactose and glucose in AT and ABT products but not in CT fermented milks. Through the refrigeration galactose was moderately utilised by Lb. acidophilus in AT products whereas the presence of Bifid. bifidum seems to prevent the consumption of this sugar in ABT fermented milks. Glucose remained constant, with minor variations in CT products but a continuous increase of this sugar occurred in carbonated AT and ABT fermented milks during storage. Beta-galactosidase activity displayed by Str. thermophilus strains was similar at pH 6.5 (initial pH of non-carbonated samples) and pH 6.3 (initial pH of carbonated samples) whereas Lb. acidophilus LaA3 showed greater beta-galactosidase activity at pH 6.3 than at higher pH values. Thus, the enhanced metabolic activity of Lb. acidophilus caused by the low initial pH of carbonated milk also promoted higher cellular beta-galactosidase activity that could have released greater amounts of galactose and glucose from lactose in AT and ABT fermented milks through the refrigerated period. In CT fermented milks, similar beta-galactosidase activity levels of Str. thermophilus at pH 6.5 and 6.3 together with the absence of beta-galactosidase activity in Lb. casei could explain the lack of differences on glucose and galactose content between carbonated and non-carbonated samples.