Lubo Liu

Theoretical analysis of the influence of process parameters on the use of an encapsulated phosphate buffer to control pH in a soil column.

Abstract A one-dimensional mathematical model was developed to analyze the influence of different physical and chemical parameters on the performance of an encapsulated phosphate buffer for controlling pH and enhancing a pH-dependent process in a soil column. Three scenarios were investigated where base equivalents are produced through the degradation of the target compound (scenario I), through reactions in the matrix (scenario II), and a combination of both mechanisms (scenario III). In all three scenarios, the production of base equivalents is countered by the release of the acidic core of the encapsulated phosphate, resulting in an enhanced removal of the target compound. A sensitivity analysis on the model shows that under the conditions investigated, the removal of the target compound is dependent on the flowrate, porosity, dispersion coefficient, reaction rate constants, mass of added capsules, and the point of addition of the capsules. The approach can be used to analyze scenarios where encapsulated buffers can control pH and optimize pH-dependent processes in a soil column.

Modeling and Comparison of Electrolytic Aeration and ORC® Aeration of Anoxic Groundwater in a Simulated Laboratory Aquifer

This study investigated the electrolytic method of aerating anoxic groundwater, where the goal for aeration is to enhance in situ bioremediation by indigenous microbes. Experiments in a simulated aquifer were performed to study the electrolytic cell as an oxygen generating source, and its performance was compared to oxygen release compound (ORC®) with respect to aerating the anoxic aquifer. Two different flow rates and concentrations of a dissolved oxygen (DO) scavenger were tested. Sodium sulfite was used to simulate the presence of DO scavengers such as Fe2+. Electrolytic aeration is possible at a current of 100 mA, and is competitive with ORC® aeration. A higher flow rate resulted in lower dissolved DO levels in the simulated aquifer, and lower sulfite levels increased the DO levels. A mathematical model was developed to simulate the movement and dispersion of DO down-gradient of the oxygen delivery well. The model results confirmed that the two aeration technologies are comparable. The use of the mode...

Parametric Study of Fate and Transport Model of E. coli in the Nearshore Region of Southern Lake Michigan

AbstractForecasting the level of waterborne bacterial pathogens (E. coli as indicator) in recreational waters using a deterministic model has been a very effective tool for water quality prediction and management. The fate and transport of pathogens in water is a complex process controlled by various factors of hydrodynamics, hydrology, chemistry, and microbiology. To better understand the importance of these factors and their roles in the inactivation, transport, and removal of pathogens, it is extremely important to enhance the reliability and effectiveness of a model by increasing the accuracy of simulation and prediction. This paper reports the results of sensitivity analyses on each of these factors using a calibrated hydrodynamic model coupled with a water quality model for temperature variation and E. coli transport. A nearshore region in southern Lake Michigan was used as the modeling domain in this research. Based on the sensitivity analysis method of differential analyses coupled with one-at-a-t...

Simulation of wind-driven circulation and temperature in the near-shore region of southern Lake Michigan by using a channelized model

To enhance the efficiency of a pathogen forecasting model in the beach areas of southern Lake Michigan and to reduce the computation time, the near-shore current is approximated as a channelized flow parallel to the shorelines in clockwise or anti-clockwise direction within the accuracy tolerance range. A channelized model with a curvilinear boundary can significantly reduce the computation effort, and at the same time achieve a good agreement between the predicted and measured water surface elevations, currents, and water temperatures. The sensitivity analysis results show that the suitable channel width for the near-shore region of southern Lake Michigan should be no less than 10 km. The modeling results of the water temperature are much less sensitive to the channel width than those of the current velocity and the water surface elevation. The modeling results also show a close correlation between the speeds of the wind and the near-shore current. The current may fully respond the wind stress with a time lag of several hours. The correlation may provide an approximate estimation of the lake circulation under some wind conditions for a practical fore-casting purpose. More complex wind-current relationships need to be described with a more sophisticated hydrodynamic model. This verified model can be used for the pathogen forecasting in the near-shore regions of southern Lake Michigan in the future.