Eung-Bai Shin

Decolorization of disperse and reactive dyes by continuous electrocoagulation process

The electrocoagulation process was developed to overcome the drawbacks of conventional wastewater treatment technologies. This process is very effective in removing organic pollutants including dyestuff wastewater and allows for the reduction of sludge generation. The purposes of this study were to investigate the effects of the operating parameters, such as current density, electrode number, electrolyte concentration, electrode gap, dyestuff concentration, pH of solution and inlet flow rate, on decolorization by continuous electrocoagulation. The dye removal efficiencies and reaction rate constants from the curves following the first-order relationship of electrocoagulation were calculated. In addition, from the points of power consumption, the effects of the operating parameters were also searched. Finally, the behaviors of decolorization according to dyestuff types, i.e., disperse dye and reactive dye, were also examined.

Pilot scale treatment of textile wastewater by combined process (fluidized biofilm process-chemical coagulation- electrochemical oxidation)

The performance of pilot scale combined process of fluidized biofilm process, chemical coagulation and electrochemical oxidation for textile wastewater treatment was studied. In order to enhance biological treatment efficiency, two species of microbes, which can degrade textile wastewater pollutants efficiently, were isolated and applied to the system with supporting media. FeCl3 x 6H2O, pH 6 and 3.25 x 10(-3) mol/l were determined as optimal chemical coagulation condition and 25 mM NaCl of electrolyte concentration, 2.1 mA/cm2 of current density and 0.71/min of flow rate were chosen for the most efficient electrochemical oxidation at pilot scale treatment. The fluidized biofilm process showed 68.8% of chemical oxygen demand (COD) and 54.5% of color removal efficiency, even though using relatively low MLSS concentration and short sludge retention time. COD and color removals of 95.4% and 98.5% were achieved by overall combined process. The contribution of fluidized biofilm process to the overall combined process was increased over 25.7% of COD reduction and 20.5% of color reduction by adopting support media in biological treatment. It can be thought that the fluidized biofilm process was effective, and pollutant loading on post-treatment was pretty much decreased by this system. This combined process was highly competitive in comparison to the other similar combined systems. It was concluded that this combined process was successfully employed and much effectively decreased pollutant loading on post-treatment for textile wastewater treatment at pilot scale.

A continuous fibrous-bed bioreactor for BTEX biodegradation by a co-culture of Pseudomonas putida and Pseudomonas fluorescens

A co-culture of Pseudomonas putida and P. fluorescens immobilized in a fibrous-bed bioreactor was used to degrade benzene, toluene, ethylbenzene and xylenes (collectively known as BTEX), present as sole carbon sources in contaminated water. The kinetics of BTEX biodegradation in the fibrous-bed bioreactor operated under the liquid-continuous condition was studied. Biodegradation rates of BTEX increased with increasing BTEX concentration and reactor loading rate. For benzene, the maximum biodegradation rate was 38 mg/l/h at a loading rate of 265 mg/l/h. For toluene, the rate was 45 mg/l/h at a 100 mg/l/h loading rate. Aeration was not used in the process and the addition of hydrogen peroxide (H2O2) as an additional oxygen source improved benzene and toluene biodegradation for the high strength synthetic wastewater feeds. When benzene, toluene, ethylbenzene and para-xylene were present as a mixture in the feed, they were concurrently and completely biodegraded under hypoxic conditions (no addition of air or H2O2). The total BTEX biodegradation rate was as high as 600 mg/l/h at the highest BTEX loading rate, 1000 mg/l/h, studied. Individual BTEX compounds were efficiently and concurrently degraded at a retention time of less than 15 h. Immobilized cells adapted in the bioreactor showed no preferential degradation of BTEX present as mixtures. The bioreactor also had a stable long-term performance, maintaining its ability for efficient BTEX degradation without requiring additional nutrients (e.g. glucose) for more than 1 year. The good performance of the fibrous-bed bioreactor was attributed to the high cell density and unique cell immobilization process provided by the fibrous matrix, which allowed use of the reactor for continued regeneration, adaptation and selection of efficient BTEX degraders in the bioreactor environment.

Decolorization of disperse and reactive dye solutions using ferric chloride

Abstract The composition of wastewater from dyeing and textile processes is highly variable depending on the dyestuff type; typically it has a high chemical oxygen demand. This study examined the decolorization of some of the most commonly used disperse and reactive dyestuffs by destabilization using ferric chloride as a coagulant. Dye removal, distributions of zeta potential, concentration of suspended solids, changes of the SCOD/TCOD ratio and distributions of SV and SVI values were investigated in this work. Compared to reactive dyes, disperse dyes have lower solubility, higher suspended solids concentrations and lower SCOD/TCOD ratios. It was concluded that disperse dye solutions are more easily decolorized by chemical coagulation than reactive dye solutions.

Electrochemical oxidation of polyvinyl alcohol using a RuO2/Ti anode

Abstract Polyvinyl alcohol (PVA), known as the dominant contributor of chemical oxygen demand (COD) in textile wastewater, is very difficult to decompose by conventional treatment technologies. In this study, electrochemical oxidation using a RuO 2 /Ti anode was applied to treat a PVA solution. The mechanisms of PVA degradation and COD destruction were investigated, while the operating parameters affecting the mechanisms were also studied. The parameters investigated included current density, PVA concentration in waste stream, the rate of electrolyte consumption of sodium chloride, and the feed rate of wastewater. The overall mass transport behavior of electrochemical oxidation of PVA was explained by the mathematical relationship of dimensionless numbers such as the Reynolds, Schmidt and Sherwood numbers.

Effects of Cl-based chemical coagulants on electrochemical oxidation of textile wastewater

As a supporting electrolyte and the source of chloride reactant, NaCl is generally added for the electrochemical oxidation process. In this study, Cl-based chemical coagulation was employed as the pretreatment step for the preremoval of suspended and colloidal solids which impede electrochemical oxidation. It was adopted for the purpose of providing the source of the chloride reactant for the electrochemical oxidation. It was ultimately intended to omit the artificial addition of electrolyte solution and to decrease the pollutant loading efficiently on the post electrochemical oxidation process in order to improve the performance of organics removal. PAC and FeCl3, Cl-based chemical coagulants, were successfully employed as the pretreatment step of electrochemical oxidation. PAC and FeCl3, were able to achieve sufficient removal efficiency of organics as well as to exclude the artificial addition of a supporting electrolyte and the source of a chloride reactant.

Effect of intermittent back ozonation for membrane fouling reduction in microfiltration using a metal membrane

Abstract In a microfiltration system using a metal membrane for municipal raw sewage reclamation, the following research points were mainly investigated: 1) Effect of intermittent back ozonation for membrane fouling reduction, 2) effect of operational parameters for permeation flux, and 3) the estimation of optimal operational conditions using an empirical model in the case of back ozonation. Intermittent back ozonation dramatically improved the membrane fouling. The permeation flux was recovered up to 90% of initial flux with dosage of 0.27 (mgO3/cm3/cycle). Among operational parameters, we found that ozone concentration was the most influential parameter for membrane fouling reduction. In the case of back ozonation, the optimal values of each operational parameter with respect to ozone concentration, ozone gas flow rate and injection time to satisfy 90% recovery of initial flux were 20.2 (mgO3/L), 3.1 (L/min) and 2.1 (min), respectively. Intermittent back ozonation is believed to be an innovative and feasible technology for fouling reduction and high permeation flux in case inorganic membrane material is being used.

A mechanical pretreatment of waste-activated sludge for HS decrease on anaerobic digestion

To decrease the HS and induce effective anaerobic digestion of waste-activated sludge (WAS), the micro-organisms concentration within the sludge were ruptured by a mechanical jet stream and smashed under a pressure of 30 bar. Using this procedure, the HS concentration was decreased from 30-50 mg/l of intact WAS to 27-240 μg/l.

Characteristics of contaminant release from lake sediment under different salinity and redox conditions

A laboratory-scale reactor containing the lake sediment obtained from two regional sites, mainly affected by live-stock wastewater and industrial wastewater, respectively, was tested for the amount of contaminants (i.e., organics, nutrients, and heavy metals) released from the sediment, under different salinity (freshwater vs. seawater) and redox (oxic vs. anoxic) conditions. Results showed that the amounts of released contaminants in freshwater were higher (e.g., up to 11.6-fold for Cd) than those in seawater, resulting from the increased saturation concentration toward the overlying water due to the relatively lower ionic strength in freshwater. On the other hand, the released amounts under the anoxic condition were higher (e.g., up to 2.9-fold for NH4+−N in livestock wastewater affecting regions) than those under the oxic condition, due to the increased amount resulted from the formation of reduced environment in overlying water under the anoxic condition. A the contaminant release proceeds through pore water in sediment under this reduced condition, the sediment it self can act as an area pollution source, resulting in a gradual deterioration of water quality pollution in lower water layers. In general, the release rates of organics and nutrients were higher than those of heavy metals. In addition, the livestock waste-water affecting regions showed high amounts of organics and nutrients released, whereas the industrial wastewater affecting regions showed high amounts of heavy metals released, due to the regional characteristics such as high content of specific components within pore water. In case of heavy metals, the release rates were in the order of Mn>Zn>Cu>Pb>Cd. Among all the conditions tested, the anoxic/freshwater condition showed the highest release of contaminants, whereas the anoxic/seawater condition showed the lowest release.

Simultaneous biological removal of nitrogen and phosphorus using the sbr process for a bench‐scale test

Abstract A bench‐scale reactor using the SBR process was experimented with synthetic wastewater. The main purpose of this investigation was to evaluate applicability in the field and process removal efficiencies in terms of BOD, TN and TP and its corresponding kinetic parameters. The removal rate of nitrogen was 71% in terms of total nitrogen and that of phosphorus was 77% in terms of total phosphorus. Effluent concentrations were 9.8mg/L BOD, 11.2mg/L TN, and 1.1mg/L TP. Effluent quality was maintained consistently stable by controlling decant volume and operating cycles. Denitrification/nitrification were accomplished during anaerobic/aerobic processes and the conversion rates were 4.8mg/kgMLSS/hr and 1.6mg/kgMLSS/hr, respectively. During the anaerobic phase, corresponding to the end of denitrification, the pH profile showed a maximum due to alkalinity production during the reactions. During the aerobic phase, pH showed a rapid increase due to CO2 stripping and pH started to increase again when ammonia ...