John A. Pierson

Effect of didecyl dimethyl ammonium chloride on nitrate reduction in a mixed methanogenic culture.

The effect of the quaternary ammonium compound, didecyl dimethyl ammonium chloride (DDAC), on nitrate reduction was investigated at concentrations up to 100 mg/L in a batch assay using a mixed, mesophilic (35 degrees C) methanogenic culture. Glucose was used as the carbon and energy source and the initial nitrate concentration was 70 mg N/L. Dissimilatory nitrate reduction to ammonia (DNRA) and to dinitrogen (denitrification) were observed at DDAC concentrations up to 25 mg/L. At and above 50 mg DDAC/L, DNRA was inhibited and denitrification was incomplete resulting in accumulation of nitrous oxide. At DDAC concentrations above 10 mg/L, production of nitrous oxide, even transiently, resulted in complete, long-term inhibition of methanogenesis and accumulation of volatile fatty acids. Fermentation was inhibited at and above 75 mg DDAC/L. DDAC suppressed microbial growth and caused cell lysis at a concentration 50 mg/L or higher. Most of the added DDAC was adsorbed on the biomass. Over 96% of the added DDAC was recovered from all cultures at the end of the 100-days incubation period, indicating that DDAC did not degrade in the mixed methanogenic culture under the conditions of this study.

The Comparison of Membrane Blocking Process and Yeast Membrane Filtration Data

Membrane filtration systems are used in a variety of processing industries where their performance meet and exceed the requirements in cost and quality. However, it is a challenge to design a small pore-size membrane system that treats very concentrated, large-volume streams within a reasonable time period. In the processing industries, several membrane technologies are used to separate various fluid streams where the concentrate or filtrate contains high-value products. Nevertheless, pore blocking is one of the major factors determining the applicability, efficiency and performance of the membrane filtration and separation system. Inside and outside membrane pore blockages lead to concentration polarization and cake buildup that reduces the flux rate and increases losses in system efficiency. There are four pore blocking mechanisms identified and modeled (complete, standard, intermediate and cake). Several experimental and theoretical works exist that describe the pore flow and blocking process. Depending on the processing fluid and membrane characteristics, all or some of the blocking mechanisms will be exhibited during the filtration process. Understanding the fluid and membrane size and characteristics in addition to pore blocking mechanisms is very important to designing effective membrane filtration systems that overcome the drawbacks associated with membrane performance. Furthermore, developing a membrane filtration system with a target cleaning process that controls membrane performance declines and maintains a reasonable flux for an extended period of time requires understanding and identifying the cause of membrane blocking. In this study, the membrane blocking during the filtration process was investigated experimentally. The experiment was designed to simulate the characteristics of a fluid stream encountered in food processing. The higher concentration was selected to manage the experiment time as well as to address worst-case scenarios, while the lower concentrations were selected to manage the filter area reduction. Dead-end filtration of two yeast solution concentrations were filtered through two different filter areas. In addition, the dynamic tests were conducted with shear generated using an impeller operated at various rotational speeds. Several tests were performed and the filtrate volume, time, pressure and agitation rate were recorded. The volume was measured with a graduated cylinder and the time measured in seconds. The results show the membrane blocking process is significantly affected by the membrane and fluid characteristics. The plots of pore blocking models and the experimental membrane filtrate data show the dominant pore blocking observed for both filters and flow process is cake filtration. The side-by-side comparison also indicates that the dominant pore blocking mechanisms depend on time. Thus, the initial and final pore blocking may not be attributed to the same pore blocking mechanism. Although it cannot be clearly shown from the current study, some part of the experimental flux profile may also be shaped by the combined pore blocking effects.Copyright

Modeling and CFD Simulation of Membrane Flow Process

In the processing industries several membrane technologies are used to separate and concentrate various fluid stream where the concentrate or/filtrate has high value products. Nevertheless, pore blocking is one of the major factors determining the applicability, efficiency and performance of the membrane filtration and separation system. Inside and outside membrane pore blockage leads to concentration polarization and cake buildup that reduces the flux rate and increases losses in system efficiency. Several experimental and theoretical works exist that describe the pore flow and blocking process. However, a limited amount of published work integrates the pore blocking with computational fluid dynamics (CFD). The change in the fluid stream and membrane characteristics during the process are the major challenges in CFD modeling. This paper presents the initial simulations of two-dimensional CFD models that directly model the actual micro pore flow and the porous medium flow (Darcy flow). Various pressure and pore sizes (porosity and permeability) were simulated. For the first model, pore flow model, simplified two-dimensional micro pores were modeled and the continuity and Navier-Stokes equations were solved in all regions including pores. Appling various inlet pressures, the velocity and pressure in all fluid regions are simulated. In second model, the membrane region is modeled as porous medium and the flow field is simulated by using porous medium characteristics. The porous medium characteristics, porosity and permeability, were estimated from pore flow average outlet velocity. The result indicates that both models with equivalent values can be used to predict the overall flow fields. However, both models have to overcome challenges to be widely used. With the direct pore flow (pores flow) simulation, mesh generation becomes a challenge since the membrane pores are very small as compared to the inlet and outlet regions. The pore flow simulation results indicate that CFD can be used to understand the membrane flow characteristics and fluid mechanics. It also can be used to design and / or select a membrane system. For the simulation of membrane as porous medium, the detail of flow through the porous medium including the inlet and outlet effects becomes obscured. However, the system overall performance can be simulated using CFD model for porous medium.Copyright

Experiment and 2D Numerical Simulation of Cooking Process of Chicken Breast

In this work, we presented the experimental and numerical work of the cooking process of chicken breast muscles. The experimental cooking process was done in a convection oven where the chicken breast was placed on top of the plate. The experimental thermal history of the cooking and cooling process was measured using thermal probes at six locations. The measured temperature is used to evaluate the numerical model and define the heat transfer coefficient. Indeed, the result illustrates that the surface irregularity and the shape have a significant effect on the local temperature profile. In addition, the two-dimensional model illustrates the significance of the product variation in thickness. Although the computational simulation can generate detailed local data, there is no new method developed to quantify and evaluate the efficiency of cooking. Therefore, quantitiave estimation of the degree of cooking process (over- or undercooking) is attempted. Based on the cooking requirement (critical temperature), cooking process, and product shape, the two-dimensional analysis allows quantification of the shape factors that can lead to over and/or undercooking. Furthermore, knowing the cooking profile effect and the product shape and variations, the cooking process may be adjusted and optimized. In addition, the result of the numerical work shows that it is possible to realistically simulate the cooking process of a complicated shape like a chicken breast.Copyright