Abstract
Graphene oxide (GO) membranes have attracted extensive attention in water treatment and related fields. However, GO films are unstable and have low permeability, which have hindered their further development. In this paper, a simple and effective method was used in which GO and single-layer graphene (GN) were mixed, and the layer spacing was effectively controlled by accurately controlling the ratio of GO to GN. GO-GN composite membranes have excellent stability, salt rejection (95.4%), and water flux (26 L m-2 h-1 bar-1). This unique design structure can be used for precise and effective regulation of the layer spacing in GO, improving the rejection rate, and increasing water flux via the enhancement of low-friction capillary action. The rational development and use of this unique composite membrane provides a reference for the water treatment field.
Key Words
composite membranes; graphene oxide; interlayer spacing; water treatment
Address
Xuan Liu, Zhu Zhou, Hengzhang Dai and Kuang Ma: College of Engineering, Shanghai Ocean University, 999 Huchenghuan Road, Pudong New Area District Shanghai, P.R.China
Yafei Zhang: Ministry of Education Key Laboratory for Thin Membrane and Microfabrication Technology, Research Institute
of Micro/Nanometer Science and Technology, Shanghai Jiao Tong University, 800 Dongchuan Road, Minxing District, Shanghai, P.R.China
Bin Li: Research Center for Photovoltaics, Shanghai Institute of Space Power-Sources, 2952 Dongchuan Road, Minhang District, Shanghai, 200245, China
Abstract
The design theory for nanoporous filtration membranes needs to be established. The present study shows that the performance and technical advancement of nanoporous filtration membranes are determined by the fundamental parameter I (in the unit Watt1/2) which is formulated as a function of the shear strength of the liquid-pore wall interface, the radius of the filtration pore, the membrane thickness, and the bulk dynamic viscosity of the flowing liquid. This parameter determines the critical power loss on a single filtration pore for initiating the wall slippage, which is important for the flux of the membrane. It also relates the membrane permeability to the power cost by the filtration pore. It is shown that for biological cellular membranes its values are on the scale 1.0E-8Watt1/2, for mono-layer graphene membranes its values are on the scale 1.0E-9Watt1/2, and for nanoporous membranes made of silica, silicon nitride or silicon carbonized its values are on the scale 1.0E-5Watt1/2. The scale of the value of this parameter directly measures the level of the performance of a nanoporous filtration membrane. The carbon nanotube membrane has the similar performance with biological cellular membranes, as it also has the value of I on the scale 1.0E-8Watt1/2.
Key Words
filtration; membrane; nanopore; permeability; power loss; water
Address
Wei Li and Xiaoxu Huang: School of Mechanical Technology, Wuxi Institute of Technology, Wuxi, Jiangsu Province, China
Yongbin Zhang: College of Mechanical Engineering, Changzhou University, Changzhou, Jiangsu Province, China
Abstract
This study introduces a NaOH/Zn-assisted hydrothermal method for the synthesis of zeolites derived from coal ash (CA). A zeolite/Zn adsorbent is successfully prepared by the activation of CA with NaOH and Zn; it is characterized by a high surface area and a negative surface charge. Methylene blue (MB) and methyl orange (MO) are selected as dye pollutants, and their adsorption onto the zeolite/Zn adsorbent is investigated. Results show the high adsorption capacities of MB and MO and that the negative surface charge facilitates electrostatic interactions between the adsorbates and adsorbents. The zeolite/Zn adsorbents shows the selective adsorption of positively charged dye MB via electrostatic interactions between the =NH+ group (positive dipole) and the oxygen functional group of the adsorbents (negative dipole). The selectivity for the positively charged dye is sufficiently high, with the removal efficiency reaching 99.41% within 10 min. By contrast, the negatively charged dye MO exhibits negligible absorption. These findings confirm the role of electrostatic interactions in the adsorption of MB, in addition to the effect of a large surface area. The results of this study are expected to facilitate the development of simple, eco-friendly, and cost-effective zeolite-based adsorptive composites from CA residuals for the selective removal of dye pollutants from CA waste.
Address
Chatchai Rodwihok, Mayulee Suwannakaew, Sang Woo Han, Siyu Chen and Han S. Kim: Civil and Environmental Engineering, Konkuk University, 120 Neungdong-ro, Gwangjin-gu, Seoul 05029, Republic of Korea
Duangmanee Wongratanaphisan: Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand
Abstract
The appropriate injection of H2O2 is essential to produce hydroxyl radicals (OH·) by mixing H2O2 quickly and exposing the resulting H2O2 solution to UV irradiation. This study focused on evaluating mixing device of H2O2 as a design factor of UV/H2O2 AOP pilot plant using a surface water. The experimental investigation involved both experimental and model-based analyses to evaluate the mixing effect of different devices available for the H2O2 injection of a tubular hollow pipe, elliptical type of inline mixer, and nozzle-type injection mixer. Computational fluid dynamics analysis was employed to model and simulate the mixing devices. The results showed that the elliptical type of inline mixer showed the highest uniformity of 95%, followed by the nozzle mixer with 83%, and the hollow pipe with only 18%, after passing through each mixing device. These results indicated that the elliptical type of inline mixer was the most effective in mixing H2O2 in a bulk. Regarding the pressure drops between the inlet and outlet of pipe, the elliptical-type inline mixer exhibited the highest pressure drop of 15.8 kPa, which was unfavorable for operation. On the other hand, the nozzle mixer and hollow pipe showed similar pressure drops of 0.4 kPa and 0.3 kPa, respectively. Experimental study showed that the elliptical type of inline and nozzle-type injection mixers worked well for low concentration (less than 5mg/L) of H2O2 injection within 10% of the input value, indicating that both mixers were appropriate for required H2O2 concentration and mixing intensity of UV/ H2O2 AOP process. Additionally, the elliptical-type inline mixer proved to be more stable than the nozzle-type injection mixer when dealing with highly concentrated pollutants entering the UV/H2O2 AOP process. It is recommended to use a suitable mixing device to meet the desired range of H2O2 concentration in AOP process.
Address
Heekyong Oh, Jinseok Hyung and Jayong Koo: Department of Environmental Engineering, University of Seoul, 163 Seoulsiripdaero, Dongdaemun-gu, Seoul 02504, Republic of Korea
Pyonghwa Jang: R&D Center, OCI, R&D Center, OCI, 61 Sagimakgol-ro 62beon-gil, Jungwon-gu, Seongnam-si, Gyeonggi-do, 13212, Republic of Korea
SungKyu Maeng: Department of Civil and Environmental Engineering, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul 05006, Republic of Korea
Abstract
Algal organic matters (AOMs) are challenging to remove using traditional water treatment methods. Additionally, they are recognized as disinfection by product (DBP) precursors during the chlorination process. These compounds have the potential to seriously harm aquatic creatures. Despite the fact that AOMs and DBPs formed from algae can harm aquatic species by impairing their cognitive function and causing behavioral problems, only a few studies on the effects of AOMs and associated DBPs have been conducted. To assess the impact of extracellular organic materials (EOMs) produced by three different hazardous algal species and the chlorinated EOMs on zebrafish, this study used fish acute embryo toxicity (FET) and cognitive function tests. With rising EOM concentrations, the embryo's survival rate and mental capacity both declined. Of the three algal species, the embryo exposed to Microcystis aeruginosa EOM exhibited the lowest survival rate. On the other hand, the embryo exposed to EOMs following chlorination demonstrated a drop in CT values in both the survival rate and cognitive ability. These findings imply that EOMs and EOMs treated with chlorine may have detrimental effects on aquatic life. Therefore, an effective EOM management is needed in aquatic environment.
Key Words
algal organic matter(AOM); aquatic ecosystem; FET test; toxicity
Address
Se-Hyun Oh and Yunchul Cho: Department of Civil and Environmental Engineering, Daejeon University, 62 Daehak-ro, Dong-gu, Daejeon 34520, Republic of Korea
Jing Wang: Research and Development Department, CanFit Resource Technologies Inc., 65 Fushi-Ro, Haidian District, Beijing, China
ung Rae Kim: School of Chemical Engineering, Pusan National University, 2, Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan 46241, Republic of Korea
