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CONTENTS
Volume 12, Number 6, November 2021
 


Abstract
As an efficient membrane separation technology, membrane distillation (MD) technology has broad application prospects in desalination of marine and high-salt wastewater. However, membrane fouling/wetting is still the main factor limiting the industrialization of MD technology. In this paper, a polyvinylidene fluoride (PVDF) micro/nano superhydrophobic membrane was prepared using Fenton pretreatment combined with a surface grafting method. Membrane surface hydrophobicity, chemistry and morphology were characterized using measurements of water contact angle (WCA) and liquid entry pressure (LEP), along with observations using attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The grafted fluorinated SiO2 nanoparticles reduced the surface energy of the PVDF base membrane while at the same time increasing the surface roughness. After modification, the WCA of the PVDF base membrane surface increased from 99° to 155° and the LEP was enhanced from 204 kPa to 235 kPa. Furthermore, the composite membrane revealed stable performance due to the pre-activation by the Fenton solution. The proposed superhydrophobic composite membrane has a great potential to solve the problems of complex membrane pretreatment and prevent damage to the base membrane. The simple method demonstrated here also reduces costs which opens up multiple opportunities for applications in industry.

Key Words
composite membrane; desalination; pre-activated grafting; surface modification; superhydrophobic

Address
Zheng Li, Jingdong Niu, Guangze He, Chuntao Zhu, Zicheng Chen, Lanhe Zhang, Jian Zhang, Lin Li and Jian Ming: School of Chemistry Engineering, Northeast Electric Power University, Jilin 132012, Jilin, P. R. China

Abstract
In this research, the performance of strong cationic Purolite C-100 Na+, Ambersep IR252 H+, Amberlite IR120 H+ ion exchange resins and an IRA402 OH- anionic resin have investigated to the reduction of hardness and TDS of drinking water in Bushehr, Iran. Also, to demonstrate the efficiency of these resins, the experimental variables affecting the ion exchange process such as contact time and adsorbent consumption were investigated. The results showed that the maximum adsorption capacity in the best operating condition was 48.01, 45 and 36.01 mg.g-1 for Purolite, Ambersep, and Amberlite resins, respectively. The maximum percentage of total hardness reduction parameters, calcium and magnesium ions reduction at best operating condition was 90.086%, 93.085%, 77.27% for Purolite ion exchange resins, 83.84%, 86.70%, 71.59% for Ambersep ion exchange resins and 69.83, 69.41, 69.32 for Amberlite ion exchange resins, respectively. Also, in the compound stage (the combination of cationic and anionic resins), at the best condition, 3 g/L of cationic resin and 12 g/L of anionic resin had the best efficiency in adjusting pH and reducing TDS. To study the adsorption kinetic process of calcium and magnesium ions by three strong cationic ion exchange resins, three pseudo-first-order, pseudo-second-order, and Morris-Weber models were employed. Among these models, the pseudo-second-order kinetic model had the best agreement with the experimental data. The models of Langmuir, Freundlich, Temkin, and Dobinin-Radskvich were utilized for the equilibrium study of hardened ions adsorption (calcium and magnesium). From the equilibrium study of the absorption process, it was founded that this process involves both chemical and physical absorption and the Langmuir model has the best agreement with the experimental data.

Key Words
hardness; ion exchange resins; scaling; TDS; water corrosion

Address
Shahla Sadeghi, Mohsen Abbasi, Shahriar Osfouri and Mohammad Javad Dianat: Department of Chemical Engineering, Faculty of Petroleum, Gas and Petrochemical Engineering, Persian Gulf University, 75169, Bushehr, Iran

Javad Khodaveisi: Water and Wastewater Company of Bushehr Province, Bushehr, Iran

Abstract
In the membrane processes, pretreatment of the hardness is an effective way to minimize membrane fouling, and to increase the quality of the permeate. Many pretreatment methods can be applied for hardness removal in way of individual or combined before membrane processes. In this study, effects of pretreatment, pH adjustment, caustic soda (NaOH) softening and soda ash (Na2CO3) + caustic soda softening, on desalination performance of the coal fired power plant cooling tower blowdown water (CTBD) by membrane distillation (MD) was investigated. By the MD system operated with hot feed (60°C) and cold permeate (20°C) sides of membrane, approximately 32 LMH permeate flux and more than 99.8% salt rejection were obtained in all experiments. While it was observed that the recovery rate of raw CTBD was 66.2%, recovery rate of pretreated CTBD with caustic soda was 79.4%. It was also found that pretreatment significantly reduces membrane scaling.

Key Words
cooling tower blowdown water; membrane distillation; pretreatment; scaling; softening

Address
Mahir İnce, Yasin Abdullah Uslu, Elif İnce and Handenur Yaşar: Department of Environmental Engineering, Gebze Technical University, Kocaeli, 41400, Turkey

Abstract
Mercury is a poisonous heavy metal that causes deleterious effects on public health and the ecosystem, even with a trace level of contamination. Selective separation of mercury ions in an aqueous environment is a challenging task, while supported liquid membrane poses to be a promising tool. In this research work, the removal of mercury ions using a porous PTFE membrane with TBP as a carrier has been studied. Batch experiments were carried out in an SLM reactor with feed phase and strip phase solution on either side of the membrane. Maximum removal of 97% of Hg2+ ions occurred under optimum conditions, namely, 0.5 M of HCl (feed), 0.4 M NaOH (strip), 90% of TBP, stirring speed at 300 rpm and 3 h of reaction time. SEM analysis of the membrane confirmed the formation of a complex between TBP and Hg2+ ions. SLM was found to be stable for 18 h. The high selectivity of the SLM towards Hg2+ ions was unaltered in the presence of Cd2+, Ni2+ and Zn2+ ions. The proposed SLM was used for the treatment of spiked seawater samples, wastewater from a thermal power plant, and contaminated lake water samples. The results indicated that the SLM system was highly efficient in removing Hg2+ ions from real contaminated samples.

Key Words
mercury; removal; supported liquid membrane; transport; tri n-butyl phosphate

Address
Ayyavoo Saravanan: Water Chemical Treatment Plant, TPS II Expansion, NLC India Ltd, Neyveli, Cuddalore-607 801, India/ University College of Engineering Villupuram, Anna University, Villupuram-605 103, India

Ramasamy Sankar: University College of Engineering Villupuram, Anna University, Villupuram-605 103, India

Kandasamy Palanivelu: Centre for Environmental Studies, Anna University, Chennai- 600 025, India

Abstract
A membrane technology is one of the basic categories of water purification technologies that are used to treat wide range of salinity water from brackish to sea water. Bipolar membrane (BPM) is a special type of catalytic ion exchange membrane (IEM) which involves water dissociation reaction in intermediate layer. Here monopolar and bipolar IEMs with Ru (water dissociation catalyst) as intermediate layer (IL) are prepared with resin and glass fiber reinforcements using functionalized polysulfone polymer (RBPM-Ru). The prepared RBPM-Ru was characterized using universal testing machine, thermo gravimetric analysis, contact angle and chemical stability through conductivity and water absorption studies. In addition the present study highlights the new method of characterizing RBPM-Ru especially through image segmentation technique as one of the prior characteristic technique before SEM analysis to confirm its bi-layer formation in a single membrane because of its advantages like no cost requirement and less time consumption method with the same quality of accuracy. The performance of RBPM-Ru in a two-compartment electrodialytic cell was evaluated using correlated parameters such as pH, concentration and conductivity studies in both compartments. By using current voltage graph (I-V) the importance of incorporating catalytic material in IL for enhancing BPM water dissociation reaction were identified. Finaly it can be concluded that RBPM-Ru was expected to have better process efficiency due to lower co-ion leakage capacity when compared with results of polystyrene–divinylbenzene (PSDVB) based BPM under similar experimental conditions.

Key Words
correlated parameters; image segmentation technique; lower co-ion leakage; performance comparison; RBPM-Ru; resin-fiber reinforcements; water dissociation reaction

Address
Kothandaraman D: School of Computer Science and Artificial Intelligence, SR University, Warangal, Telangana - 506371, India

Krishnaveni V: Department of Chemistry, Anna University, Chennai 600025, Tamil Nadu, India


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