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CONTENTS
Volume 8, Number 2, March 2017
 

Abstract
This study investigated effects of physical and chemical cleaning methods on the initial flux recovery of fouled membrane in membrane distillation process. A laboratory scale direct contact membrane distillation (DCMD) experiment was performed to treat digested livestock wastewater with 3.89 mg/L suspended solids, 874.7 mg/L COD, 543.7 mg/L nitrogen, 15.6 mg/L total phosphorus, and pH of 8.6. A hydrophobic PVDF membrane with an average pore size of 0.22 um and a porosity of 75 % was installed inside a direct contact type membrane distillation module. The temperature difference between feed and permeate side was maintained at 40oC with the feed and permeate stream velocity of 0.18 m/s. The results showed that the permeate flux decreased from 22.1 L*m-2*hr-1 to 19.0 L*m-2*hr-1 after 75 hours of distillation. The fouled membrane was cleaned first by physical flushing and consecutively by chemicals with NaOCl and citric acid. After the physical cleaning the flux was recovered to 92 % as compared with the initial clean water flux of the virgin membrane. Then 94 % of the flux was recovered after cleaning by 2,000 ppm NaOCl for 90 minutes and finally 97 % of flux recovered after 3 % citric acid for 90 minutes. SEM-EDS and FT-IR analysis results presented that the foulants on the membrane surface were removed effectively after each cleaning step. The contact angle measurement showed that the hydrophobicity of the membrane surface was also restored gradually after each cleaning step to reach nearly the same hydrophobicity level as the virgin membrane.

Key Words
membrane distillation; wastewater treatment; membrane cleaning; flux recovery rate

Address
Sewoon Kim and Jinwoo Cho : Department of Environment and Energy, Sejong University,
209 Neungdong-ro, Gwangjin-gu, Seoul 143-747, Republic of Korea
Ki Young Park : Department of Civil and Environmental System Engineering, Konkuk University,
120 Neungdong-ro, Gwangjin-gu, Seoul 05029, Republic of Korea

Abstract
Reverse osmosis technology is being used on large scale for treatment of ground water, brackish water, wastewater and sea water. The most challenging issue in RO process is carbonate scaling which is directly linked with the efficiency and economy. Considering the natural phenomena of carbonate scaling different adaptations have been made to control scaling on the surface of RO membrane including acid dosage and antiscalant addition. As carbonate scaling is directly related with pH level of feed water, present study describes an experimental approach to reduce scaling on RO membrane by lowering the feed water pH by purging CO2. In this comparative study four different conditions including control process (without any scale inhibitor), with dosage of antiscalant, with purging of CO2 and with co addition of antiscalant and CO2 in a feed stream line; it was established that CO2 is a better appliance to reduce carbonate scaling on the membrane surface by reduce pH of feed stream. It was also observed that CO2 and antiscalant mutually function better for scale control.

Key Words
CaCO3; transmembrane pressure (TMP); RO; membrane fouling; CO2 purging; antiscalant

Address
Muhammad Kashif Shahid, Minsu Pyo and Young-Gyun Choi : Department of Environmental Engineering, Daegu University,
201 Daehak-ro, Gyeongsan 712-714, Republic of Korea

Abstract
A water treatment utility in South Korea operates a large system of pressurized hollow fiber membrane (PHFM) modules. The optimal selection of membrane module for the full scale plant was critical issue and carried out using Risk-based Life Cycle Cost (RbLCC) analysis based on the historical data of operation and maintenance. The RbLCC analysis was used in the process of decision-making for replacing aged modules. The initial purchasing cost and the value at risk during operation were considered together. The failure of modules occurs stochastically depending on the physical deterioration with usage over time. The life span of module was used as a factor for the failure of Poisson‟s probability model, which was used to obtain the probability of failure during the operation. The RbLCC was calculated by combining the initial cost and the value at risk without its warranty term. Additionally, the properties of membrane were considered to select the optimum product. Results showed that the module‟s life span in the system was ten years (120 month) with safety factor. The optimum product was selected from six candidates membrane for a full scale water treatment facility. This method could be used to make the optimum and rational decision for the operation of membrane water purification facility.

Key Words
asset management; pressurized hollow fiber membrane; risk-based life cycle cost (RbLCC); pin-repairing data; poisson‟s probability model

Address
Chul-sung Lee, Young-wook Nam and Doo-il Kim : Department of Civil and Environmental Engineering, Dankook University,
251 Jukeonro Sujigu Yonginsi Gyunggido, 16890, South Korea

Abstract
This study investigated effects of NaOH cleaning on the intrinsic permeability of polyvinylidene fluoride (PVDF) membranes and flux recoveries and membrane resistances under various conditions encountered during ultrafiltration in water treatment plants. The NaOH cleaning using 10,000 mg/L NaOH led to discoloration of PVDF membranes and had little effect on water flux. The NaOH cleaning was efficient in removing the fouling layer caused by humic water. However, long filtration induced a fouling layer that was not removed easily by NaOH cleaning. The lower temperature during filtration yielded rapid increases in transmembrane pressure and decreases in NaOH cleaning efficiency. The alkaline cleaning of PVDF changed the membrane properties such as the hydrophobicity and morphology. Foulant properties, operational conditions such as temperature, and chemical agents should be considered for cleaning strategies for PVDF applied in water treatment.

Key Words
NaOH cleaning; PVDF; ultrafiltration; flux recovery; resistance

Address
Yoon-sung Jang and Jungsu Park : Hanwha Eco Institute, 6 Shinsung-dong, Yusung-gu, Taejon 305-345, Republic of Korea
Yoon-sung Jang, JiHyang Kweon, Min-goo Kang, Jae Hyun Jung and JunHee Ryu : Department of Environmental Engineering, Konkuk University, #1 Hwayang-dong, Gwangjin-gu, Seoul, Korea

Abstract
The adsorption of phosphate onto mesoporous TiO2 was investigated in order to reduce phosphorus concentrations in wastewater and provide a potential mode of phosphorus recovery. Three equilibrium isotherms were used to optimize and properly describe phosphate adsorption (R2>0.95). The maximum capacity of phosphate on the adsorbent was found to be 50.4 mg/g, which indicated that mesoporous TiO2 could be an alternative to mesoporous ZrO2 as an adsorbent. A pseudo-second order model was appropriately fitted with experimental data (R2>0.93). Furthermore, the suitable pH for phosphate removal by TiO2 was observed to be in the range of pH 3-7 in accordance with ion dissociation. In contrast, increasing the pH to produce more basic conditions noticeably disturbed the adsorption process. Moreover, the kinetics of the conducted temperature study revealed that phosphate adsorption onto the TiO2 adsorbent is an exothermic process that could have spontaneously occurred and resulted in a higher randomness of the system. In this study, the maximum adsorption using real wastewater was observed at 30 C.

Key Words
equilibrium isotherm; kinetics; mesoporous TiO2 adsorbent; phosphate adsorption; wastewater

Address
Kwanyong Lee, Seokwon Lee and Ki Young Park : Department of Civil and Environmental System Engineering, Konkuk University, Seoul 05029, Korea
Warangkana Jutidamrongphan : Faculty of Environmental Management, Prince of Songkla University, Hatyai, Songkhla, Thailand

Abstract
This study presents the effect of hydraulic retention time (HRT) on the characteristics of emission of three major greenhouse gases (GHGs) including CH4, CO2 and N2O during operation of a sequencing batch reactor for aerobic oxidation of methane with denitrification (AeOM-D SBR). Dissolved N2O concentration increased, leveled-off and slightly decreased as the HRT increased from 0.25 to 1d. Concentration of the dissolved N2O was higher at the shorter HRT, which was highly associated with the lowered C/N ratio. A longer HRT resulted in a higher C/N ratio with a sufficient carbon source produced by methanotrophs via methane oxidation, which provided a favorable condition for reducing N2O formation. With a less formation of the dissolved N2O, N2O emission rate was lower at a longer HRT condition due to the lower C/N ratio. Opposite to the N2O emission, emission rates of CH4 and CO2 were higher at a longer HRT. Longer HRT resulted in the greater total GHGs emission as CO2 equivalent which was doubled when the HRT increased from 0.5d to 1.0 d. Contribution of CH4 onto the total GHGs emission was most dominant accounting for 98 - 99% compared to that of N2O (< 2%).

Key Words
aerobic oxidation of methane with denitrification (AeOM-D); hydraulic retention time (HRT); methane (CH4); carbon dioxide (CO2); nitrous oxide (N2O); greenhouse gases (GHGs)

Address
Kwanhyoung Lee : Department of Environmental Engineering, Korea University, 2511 Sejong-Ro, Sejong City 339-700, Korea
Oh Kyung Choi : Program of Environmental Technology and Policy, Korea University, 2511 Sejong-Ro, Sejong City 339-700, Korea
Jae Woo Lee : Department of Environmental Engineering, Korea University, 2511 Sejong-Ro, Sejong City 339-700, Korea/ Program of Environmental Technology and Policy, Korea University,
2511 Sejong-Ro, Sejong City 339-700, Korea

Abstract
Low-pressure membrane filtration is increasingly used for tertiary treatment of wastewater effluent organic matter (EfOM), mainly comprising organic base/neutral compounds. In-line coagulation with underdosing, charge neutralization, and sweep floc conditions prior to ultrafiltration (UF) was studied to determine removals of the EfOM components and consequent reduction of fouling using polyethersulfone membranes. Coagulation and UF substantially reduced fouling for all coagulation conditions while removing from 7 to 38% of EfOM organic acids. From 7 to 16% of EfOM organic base/neutrals were removed at neutral pH but there was no significant removal for slightly acid coagulation conditions even though fouling was substantially reduced. Sweep floc produced the lowest resistance to filtration but may be inappropriate for in-line use due to the large added volume of solids. Charge-neutralization resulted in poor recovery of the initial flux with hydraulic cleaning. Under-dosing paralleled sweep floc in reducing hydraulic resistance to filtration (for sub-critical flux) and the initial flux was also easily recovered with hydraulic cleaning. Hydrophobic and hydrophilic base/neutrals were identified on the fouled membranes but as previously reported the extent of fouling was not correlated with accumulation of organic base/neutrals.

Key Words
effluent organic matter; in-line coagulation; ultrafiltration; fouling; membrane autopsy

Address
Sung Kyu Maeng : Department of Civil & Environmental Engineering, Sejong University, Seoul 143-747, Republic of Korea
Thomas C. Timmes : US Army Center for Environmental Health Research, Fort Detrick, MD 21702, USA
Hyun-Chul Kim : Water Resources Research Institute, Sejong University, Seoul 143-747, Republic of Korea

Abstract
We investigated the effect of applied voltage and electrolyte concentration on the nitrate removal and its energy/current efficiency during the electrodialysis. The current increased as the applied voltage increased up to 30 V showing the limiting current density around 20 V. The nitrate removal efficiency (31 to 71% in 240 min) and energy consumption (11 to 77 W∙h/L) gradually increased as the applied voltage increased from 10 to 30 V. The highest current efficiency was obtained at 20 V. The increase in electrolyte concentration from 100 to 500 mM led to the dramatic increase of nitrate removal efficiency with much faster removal kinetics (100 % in 10 min).

Key Words
electrodialysis; nitrate removal; applied voltage; current efficiency; energy efficiency

Address
Ki Young Park, Ho Young Cha, Phrompol Chantrasakdakul and Kwanyong Lee : Department of Civil and Environmental System Engineering, Konkuk University, 120 Neungdong-ro, Gwangjin-gu, Seoul 05029, Republic of Korea
Ji Hyang Kweon and Sungjun Bae : Department of Environmental Engineering, Konkuk University,
120 Neungdong-ro, Gwangjin-gu, Seoul 05029, Republic of Korea


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