Sook-Hyun Nam

Occurrence of disinfectant by-products during the sequential disinfection process

Abstract Sequential disinfection is considered a viable treatment option for the effective inactivation of pathogenic micro-organisms such as oocysts of protozoan parasites (e.g. Cryptosporidium parvum etc.) and spores of vegetative bacteria (e.g. Bacillus subtilis and Bacillus anthracis) that cannot be treated by the single-step application of chlorine-based disinfectants and for viruses (e.g. Adenovirus) that cannot be easily treated by the single-step application of UV irradiation. The aim of this research was to investigate the inactivation of B. subtilis spore and formation of disinfection by-products (DBPs) during sequential disinfection using a combination of chlorine dioxide and chlorine (ClO2/HOCl) or UV and chlorine (UV/HOCl) sequential disinfection. B. subtilis spores have been widely used as an indicator micro-organism for C. parvum oocysts. Trihalomethanes (THMs) and haloacetic acids have been used as indicator for DBPs. This study evaluates the effect of operating parameters (e.g. chemical d...

Organic fouling and osmotic backwashing in PRO

AbstractThe pressure-retarded osmosis process is the next generation seawater desalination technology and is considered as eco-friendly and economic renewable energy. As such, there are active studies of means of efficient cleaning to restore the membrane performance degraded due to the reversible membrane fouling that inevitably occurs after prolonged operation. This study evaluated the fouling rate by organic alginate, humic, and BSA (bovine serum albumin). Also, we focused on the comparison of cleaning methods which are physical flushing and osmotic backwashing (OB). For the comparison of the cleaning efficiency, we used alginate compound as a model substances representative of natural organic matter. Physical cleaning (PC) is the flushing method by flowing the distilled water on the membrane active and support layer in high velocity to remove the accumulated foulants on the membrane surface. OB is the method of backflow generated by osmosis to remove the accumulated foulants on/in the membrane active ...

Analyses of the current market trend and research status of indoor air quality control to develop an electrostatic force-based dust control technique

Abstract This study examined the current and future Indoor Air Quality (IAQ) control device markets and analyzed the recent studies on indoor air pollutantr emoval to develop a new technology for fine dust control. Currently, the mechanical filter technique occupies the bulk of the IAQ control market but the electronic technique is emerging as an alternative to control fine dust efficiently. Among the gaseous VOCs and fine dust particles contaminating the indoor air quality, fine dust particles are more problematic because they threaten human health by penetrating deep into the body and producing secondary contaminants by chemical reaction with VOCs. The electronic IAQ control device using dielectrophoretic and electrostatic forces is a good option for public spaces where many people pass, and at the same time, it needs to consider temperature, humidity, and the particle properties of specific areas to highlight the control efficiency. Electronic-related technology is expected to be used widely in many public/private spaces wherever a dust-free environment is required.

Photocatalytic disinfection of indoor suspended microorganisms (Escherichia coli and Bacillus subtilis spore) with ultraviolet light

New control methods are proposed for indoor air quality by removing fine airborne dust-particles. As suspended fine dust-particles contain inorganic dust as well as fine organic bacteria, studies for simultaneous control of these contaminants are required. In this study, photocatalytic disinfection of indoor suspended microorganisms such as E. coli and Bacillus subtilis is performed by three types of photocatalysts with UVA irradiation. The UVA irradiation strength was controlled to the minimum 3 ㎼/㎠, and ZnO, TiO2, and ZnO/Laponite ball were used as the catalysts. The results indicate that E. coli was removed over 80 % after about 2 hours of reaction with UVA and all three types of photocatalysts, whereas only with UVA, around 50 % E. coli removal was obtained. Among the catalysts, ZnO/Laponite composite ball was found to have similar sterilizing capacity to TiO2. However, in case of B. subtilis, which has thick cell wall in its spore state, disinfection was not effective under the low UVA irradiation condition, even with the catalysts. Further studies need to figure out the optimal UVA irradiation ranges as well as photocatalysts doses to control airborne dust, to provide healthy clean air environment.

Comparative evaluation of physical cleaning method for organic and inorganic foulants mitigation in pressure retarded osmosis (PRO)

Membrane fouling is one of the major problems to be solved to sustain stable pressure-retarded osmosis (PRO) performance. This phenomenon caused diminished water flux productivity. So an effective cleaning method for fouled membrane is necessary. This study was carried out to compare applicable cleaning methods to mitigate organic and inorganic foulants on the PRO membrane. Fouling experiments were divided into two types: organic fouling and inorganic–organic fouling. Humic substance and calcium carbonate were used as model compounds. The fouled PRO membranes were cleaned by seven types of cleaning methods namely: (i) physical flushing, (ii) pressure-assisted physical flushing at feed side, (iii) pressure-assisted physical flushing at draw side, (iv) osmotic backwashing, (v) reverse osmosis flushing, (vi) pressure-assisted osmotic backwashing with low pressure (PAOB-I), (vii) pressure-assisted osmotic backwashing with high pressure. PAOB-I was a more effective method to mitigate foulants on the PRO membrane compared with the other cleaning methods in this study.