Ick-Tae Yeom

Removal of ions in nickel electroplating rinse water using low-pressure nanofiltration

Abstract This study investigated the performance of nanofiltration (NF), which is more economic than reverse osmosis (RO) and requires lower pressure for the removal of cations and anions in simulated nickel electroplating rinse water environments. Removal rates according to changes in basic parameters such as pressure, crossflow velocity, pH, ion types and ion concentrations were observed. In single-salt system experiments NF removed more Ni2+ in NiSO4 solution than in NiCl2 solution. As concentration increased in single-salt systems, removal rate of sulfate salts and some chloride salts (in the system with cations of +1 valency) decreased, whereas chloride salts with cations of +2 valency increased. In the experiment with multi-salt systems, the removal rate of ions showed a logarithmic increase with pressure until 3 kgf/cm2 (0.294 MPa), and beyond this value the removal rate stabilized. Change in crossflow velocity did not affect the ion removal, but change in pH was a significant factor for Cl− removal rate. Furthermore, the removal rate of Cl− was heavily dependent on the amount of SO42− present in the same system. In experiments using simulated nickel electroplating rinse water below a pressure of 3 kgf/cm2, the removal efficiencies of ions increased greatly with increased influent salt concentration and pressure, whereas beyond 3 kgf/cm2, the removal efficiency stabilized. This result indicated that 3 kgf/cm2 is the optimum pressure for NF application against nickel electroplating rinse water.

Treatment of household wastewater using an intermittently aerated membrane bioreactor

Abstract An intermittently aerated membrane bioreactor using a submerged hollow fiber membrane was applied in laboratory scale to treat household wastewater including toilet flushing water. Nitrogen removal was optimized with intermittent aeration of the reactor and adjusting the time lengths of anoxic and aerobic phases of a cycle. Membrane filtration occurred during the aeration period to take advantage of the air bubbles for fouling control. With 8–15 h HRT and a very long SRT, 96% of TCOD and 100% SS could be removed. On average, the removal efficiency for TN was 83%. No significant accumulation of inert matter was observed after 4 and 5 months of operations without sludge wasting. Fast and complete nitrification was accomplished regardless of the operation cycle mode, and denitrification appears to be the rate-limiting step. Results from track studies revealed that the specific denitrification rate (SDNR) varied between 0.6 and 1.8 mg/gVSS·h. Endogenous SDNR was determined in a separate batch experiment and found to be 0.56 mg/gVSS·h. A linear relationship between the measured SDNR and the influent BOD/TN value was found. Based on this relationship, a rule-of-thumb method to determine the optimum time length for the anoxic phase was proposed. Intermittently aerated MBR appears to have advantages over other biological nitrogen removal processes in that denitrification can be enhanced under high MLVSS conditions. Endogenous denitrification may play a significant role, making the system more robust to the fluctuation or the limitation of external carbon supply.

Application of nanofiltration for recycling of paper regeneration wastewater and characterization of filtration resistance

Abstract The potential of using nanofiltration (NF) membranes in purification of the effluent from paper regeneration wastewater treatment plant was investigated. The change of filtration resistance for various NF membranes and the mechanisms responsible for the resistance were identified. The mahyority of the pollutants remaining in the wastewater were mostly nonbiodegradable and ware less than MWCO 3000 in size, indicating micro- or ultrafiltration may not be applicable. Among the five NF membranes used in this study, NTR-759HR showed the highest rejection efficiency; 98.5% and 99.5% for TOC and color, respectively. The TOC concentration of the permeate could be maintained at less than 0.7 mg/L regardless of the concentration of the feed solution. However, the permeate flux steadily decreased with time up to 50% of the initial value at the recovery rate of 89%. To investigate the possible mechanisms responsible for the reduction of permeate flux, the observed total filtration resistance was divided into three categories; (1) the intrinsic membrane resistance for pure water (Rm), (2) resistance due to concentration polarization (Rcp), and (3) resistance due to membrane fouling (Rf). The increase of filtration resistance for NTR 7410 could be explained by membrane fouling while those for NTR-759HR and NTR-7250 are attributed to the osmotic pressure build-up due to concentration polarization. The different mechanisms for the flux reduction were studied.

Nitrogen Removal in Household Wastewater Treatment Using an Intermittently Aerated Membrane Bioreactor

Membrane bioreactor using a submerged hollow fiber membrane was applied in laboratory scale conditions to treat household wastewater including toilet-flushing water. The bioreactor was aerated intermittently to alternate anoxic/oxic conditions while membrane filtration occurred during the aeration period to take advantage of the air bubbles for fouling control. After being operated for about 150 days, the initial flux and suction pressure were maintained almost constant at 0.01m hr−1 and 4-6 kPa, respectively, indicating fouling control by air bubbling was very effective. With 10-15 hour hydraulic retention time (HRT), and a very long solid retention time (SRT), 97% of Total chemical oxygen demand (TCOD) and 100% suspended solids (SS) could be removed. On average, removal efficiencies for total nitrogen (TN) and total phosphorus (TP) were 83% and 55% respectively. Ammonia and coliform bacteria were completely removed. Due to the long SRT and sufficient oxygen supply, fast and complete nitrification was accomplished regardless of operational mode, and denitrification was the rate-limiting step. Results from track study revealed that the initial specific denitrification rate (SDNR) varied between 0.6 and 1.8 mg g−1VSS hr−1. Endogenous SDNR was found to be 0.35-0.51 mg g−1VSS hr−1. Nitrogen removal was controlled mainly by the value of BOD/TN of the influent. However, the role of endogenous denitrification was relatively significant under the high mixed liquor volatile suspended solid (MLVSS) condition, making the system more robust to the fluctuation of external carbon supply. The anoxic/oxic cycle of 60/90 minutes with an hydraulic retentin time (HRT) of 10 hrs appears to be an appropriate choice for the process.

Enhancement of Sludge Dewaterability by Ozone Treatment

The effects of ozone treatment on the dewaterability of activated sludge wasted from a sewage treatment plant were investigated in this study. Following ozone treatment, sludge was dewatered using a pressure filter. The sludge filterability evaluated by SRF deteriorated with ozone dosage at relatively low ozone doses. However, at ozone doses higher than 0.6gO3/gSS, the SRF of the ozone treated sludge became comparable with the value for the sludge without ozone treatment. It is suggested that the oxidation of the viscous, high molecule organics attached at cell surface reduces the surface charge of sludge particle and promotes flocculation at relatively high ozone doses. Ozone treatment also cause the release of bound water trapped inside cells or floes, resulting in significant reduction of cake water content after dewatering. In terms of cake volume, more than 55 % reduction was obtained at 0.4gO3/gSS. These observations suggest that ozone treatment has potential to significantly enhance sludge dewaterability and to produce a more compact cake without severe deterioration of its filterability.

A simplified model approach for mass transfer of a complex liquid mixture during soil venting

A simplified model approach for multi-component mass transfer of a complex liquid mixture in porous media was proposed and experimentally evaluated. The method includes grouping of individual components of a complex mixture based on its gas chromatographic (GC) profile and treating each group as a pseudo-single compound. Soil venting experiments were conducted using soil artificially contaminated with gasoline. It was found that the predicted concentrations of individual gasoline components in the effluent air by the simplified approach are almost identical to the values estimated from the method that considers all the components of gasoline as independent variables. In general, the model predictions for the removal of both total gasoline and individual compounds agree well with the experimental data. However, in the later phase of venting, the estimated concentrations were somewhat higher than the measured values. It was suggested that grouping different compounds in complex mixtures based on their GC profiles and treating the groups as pseudo-single compounds be a very useful tool, saving greatly the analytical and computational efforts without sacrificing accuracy of the model.

Analysis of the contributions of pollution to industrial discharge categories in Korea using the Modified Toxic Weighting Factor

In 2007, 45,163 domestic industrial direct/indirect discharge sources were registered in Korea, which have been categorized into 82 divisions based on the characteristics of their products, raw materials and wastewaters. The purpose of this study was to set priorities using a risk assessment of pollutants toxic weighting for each industrial category with respect to pollution prevention and control. This study developed the upgraded Modified Toxic Weighting Factors (MTWFs) rather than the Toxic Weighting Factors (TWFs) suggested by the United States Environmental Protection Agency (USEPA) with respect to domestic environmental regulations, and the assessment of existing databases of domestic industrial wastewater characteristics for the 82 categorized industries in Korea. Finally, priority of industrial categories and pollutants were established to determine the target industries and pollutants requiring controls. High contributing categories in order of their pollution loads were pulp, paper and paper products manufacturing, dyeing and processing facilities, etc. The top 10 industrial category loads accounted for 76.0% of the total effluent equivalent kilograms of pollution. High contributing categories, in order of their toxic level were synthetic resins and other plastics manufacturing, leather and fur processing and manufacturing.