Jia-Ming Chern

Adsorption of nitrophenol onto activated carbon: isotherms and breakthrough curves

The adsorption isotherm of p-nitrophenol onto granular activated carbon in 25 degrees C aqueous solution was experimentally determined by batch tests. Both the Freundlich and the Redlich-Peterson models were found to fit the adsorption isotherm data well. A series of column tests were performed to determine the breakthrough curves with varying bed depths (3-6 cm) and water flow rates (21.6-86.4 cm3/h). Explicit equations for the breakthrough curves of the fixed-bed adsorption processes with the Langmuir and the Freundlich adsorption isotherms were developed by the constant-pattern wave approach using a constant driving force model in the liquid phase. The results show that the half breakthrough time increases proportionally with increasing bed depth but decreases inverse proportionally with increasing water flow rate. The constant-pattern wave approach using the Freundlich isotherm model fits the experimental breakthrough curves quite satisfactorily. A correlation was proposed to predict the volumetric mass-transfer coefficient in the liquid phase successfully. The effects of solution temperature and pH on the adsorption isotherm were also studied and the Tóth model was found to fit the isotherm data well at varying solution temperatures and pHs.

DESORPTION OF DYE FROM ACTIVATED CARBON BEDS: EFFECTS OF TEMPERATURE, pH, AND ALCOHOL

The adsorption isotherms of yellow and red dye solutions onto granular activated carbon at varying solution pHs (2-8). temperatures (15-50 degrees C), and alcohol concentrations (0-20%) were experimentally determined by batch tests and the Tóth model was found to best fit the adsorption isotherm data for varying solution pHs. temperatures, and alcohol concentrations. The maximum adsorption capacity was found to decrease with increasing solution pH and alcohol concentration and could be predicted by the correlation equations obtained in this study. A correlation equation was also obtained to account for the effects of solution temperature on the adsorption equilibrium constant. The 25 degrees C water was found to be a very poor regenerant for the carbon bed presaturated with the yellow dye compared with 20% alcohol solution. A simple equation was derived, based on non-linear wave propagation theory, to predict the desorption curves of activated carbon bed. Given presaturation concentration, bed density and void fraction, and adsorption isotherm, the wave propagation theory predicted the desorption curves quite satisfactorily.

Competitive adsorption of benzoic acid and p-nitrophenol onto activated carbon: isotherm and breakthrough curves

Three series of batch tests at 25 degrees C were performed to determine the benzoic acid and p-nitrophenol (PNP) binary adsorption isotherms onto GAC in the aqueous solutions and the experimental data were fitted to the extended Langmuir isotherm model successfully. The experimental data and the isotherm model parameters showed that the GAC used in this study had a higher affinity to PNP than benzoic acid. Three column tests were performed to determine the breakthrough curves and effluent solution pH with varying feed compositions. According to the experimental results, the weakly adsorbed BA exhibited an intermediate zone of effluent concentration higher than its feed one; the effluent solution pH could serve as a good indicator for breakthrough. The breakthrough curves with varying feed compositions could be predicted by the non-linear wave propagation theory satisfactorily. Only the adsorption isotherm models were required to construct the composition path diagram with which the breakthrough curves could be predicted.

Effects of impurities on oxygen transfer rates in diffused aeration systems

A series of unsteady-state reaeration tests were performed in a 500-L tank at 0.81-4.58 m3/h diffused-air flow rate and 288-302 K water temperature. Three different types of impurities: soybean oil, surfactant, and diatomaceous earth were doped to simulate the impurities in wastewaters and the effects of the impurities on the oxygen transfer rate were investigated. The ASCE and the two-zone oxygen mass-transfer models were used to analyze the unsteady-state reaeration data and the volumetric mass-transfer coefficients determined from the unsteady-state reaeration data were correlated as a function of the diffused-air flow rate, water temperature, and impurity concentration. The results showed that the alpha factors based on the ASCE model are less sensitive to the impurity concentration while the presence of the impurities significantly reduces the alpha factors in the gas bubble zone. The saturation DO concentration and volumetric oxygen mass-transfer rate can be predicted by the two-zone model along with the correlation obtained in this study.

Heavy metal extraction from PCB wastewater treatment sludge by sulfuric acid

Heavy metals contaminated wastewater sludge is classified as hazardous solid waste and needs to be properly treated to prevent releasing heavy metals to the environment. In this study, the wastewater treatment sludge from a printed circuit board manufacturing plant was treated in a batch reactor by sulfuric acid to remove the contained heavy metals. The effects of sulfuric acid concentration and solid to liquid ratio on the heavy metal removal efficiencies were investigated. The experimental results showed that the total and individual heavy metal removal efficiencies increased with increasing sulfuric acid concentration, but decreased with increasing solid to liquid ratio. A mathematical model was developed to predict the residual sludge weights at varying sulfuric concentrations and solid to liquid ratios. The trivalent heavy metal ions, iron and chromium were more difficult to be removed than the divalent ions, copper, zinc, nickel, and cadmium. For 5 g/L solid to liquid ratio, more than 99.9% of heavy metals can be removed from the sludge by treating with 0.5M sulfuric acid in 2h.

Kinetics of pulp mill effluent treatment by ozone-based processes

The wastewaters generated from wood pulping and paper production processes are traditionally treated by biological and physicochemical processes. In order to reduce chemical oxygen demand (COD) and color to meet increasingly strict discharge standards, advanced oxidation processes (AOPs) are being adapted as polishing treatment units. Various ozone-based processes were used in this study to treat simulated wastewaters prepared from black liquor from a hardwood Kraft pulp mill in Taiwan. The experimental results showed that the COD and color were primarily removed by direct ozone oxidation and activated carbon adsorption. While the addition of activated carbon could enhance the COD and color removal during ozonation, the addition of hydrogen peroxide improved the color removal only. For the various ozone-based treatment processes, kinetic models were developed to satisfactorily predict the COD and color removal rates. According to the kinetic parameters obtained from the various ozone-based processes, the enhanced COD and color removal of ozonation in the presence of activated carbon was attributed to the regeneration of the activated carbon by ozonation. These kinetic models can be used for reactor design and process design to treat pulping wastewater using ozone-based processes.

Adsorption of copper-citrate complexes on chitosan: equilibrium modeling.

The effects of complexes on the adsorption of copper from citrate solutions using chitosan were investigated. Various copper to citrate ratios and solution pHs were used to determine the copper adsorption capacity on the chitosan and a mathematical model was developed to simulate the copper adsorption process. According to the model, the three parameters influencing the copper adsorption capacity are the fraction of protonated amine groups (RNH(3)(+)), the fraction of anionic copper-citrate complexes (CuL(-) and CuL(2)(4-)), and the fraction of anionic citrate complexes (HL(2-), H(2)L(-), and L(3-)). The copper adsorption capacities onto chitosan at varying copper-citrate ratios and solution pHs can be predicted by the mathematical model. With such a model to facilitate understand the copper adsorption mechanisms at varying copper-citrate ratios and solution pHs, the copper adsorption efficiency can be increased by the adjustment of the copper-citrate ratio and solution pH.

General rate equations and their applications for cyclic reaction networks: multi-cycle systems

Many chemical reactions of industrial importance involve complex reaction pathways and networks; and the determinations of the reaction rate laws are very difficult. The accurate or proper rate expression is the most desired information in design phase however. In this study, the network reduction technique and the Bodenstein approximation of quasi-stationary behavior of reaction intermediates were systematically applied to derive general rate and instantaneous rate ratio equations for multi-pathway reaction networks in homogeneous catalysis or enzyme system. Multiple small reaction cycles in a main cycle, and multiple-pathways stemming from an intermediate and ending at different nodes in a cycle were considered. The general rate and rate ratio equations derived in this study are applicable for most homogeneous catalytic reactions and enzymatic reactions. Two examples of multi-pathway cyclic enzyme reaction were used to illustrate the applications of the general rate and rate ratio equations for network elucidation.

Study of Nonlinear Wave Propagation Theory. II. Interference Phenomena of Single-Component Dye Adsorption Waves

Yellow acid dye was adsorbed from aqueous solution by granular activated carbon packed in a column. The feed concentration was kept constant for a period of time and then switched to another level to simulate the concentration variation in wastewater treatment processes. The resulting breakthrough curves were experimentally measured and theoretically predicted. Explicit equations and an algorithm were developed based on the wave interference theory to predict the column breakthrough curves of single-component adsorption processes with step change in the feed concentration. The experimental results show that the wave interference theory predicts the column breakthrough curves satisfactorily.

General rate equations and their applications for cyclic reaction networks: pyramidal systems

The King-Altman-Hill graphic method has been widely used to derive the rate laws of enzymatic reactions, but the compilation of all the possible pathways is very time-consuming and the reaction rates are not given explicitly. In this study, the network reduction and Y-to-delta transformation techniques were systematically used to derive the general rate equations for pyramidal reaction networks in homogeneous catalysis. The enzymatic reaction of 7,8-dihydrofolate and NADPH to form 5,6,6,8-tetrahydrofolate and NADP, catalyzed by dihydrofolate reductase was taken as an example to illustrate the application of the general reaction rate equations. The calculated overall reaction rate was compared with that obtained from the exact solution by matrix algebra and those obtained from the King-Altman-Hill graphic method.