Elsevier

Chemosphere

Volume 125, April 2015, Pages 139-146
Chemosphere

Evaluation of potential for reuse of industrial wastewater using metal-immobilized catalysts and reverse osmosis

https://doi.org/10.1016/j.chemosphere.2014.12.021Get rights and content

Highlights

  • Display wastewater can be achieved economically using catalyst and membrane.

  • Metal-immobilized catalyst was preferential to remove low-molecular-weight organic compounds.

  • Operational factors such as acid, pH, and H2O2 was optimized for practical application.

  • With regard to water quality and operating costs, the proposed system was superior to existing systems.

Abstract

This report describes a novel technology of reusing the wastewater discharged from the display manufacturing industry through an advanced oxidation process (AOP) with a metal-immobilized catalyst and reverse osmosis (RO) in the pilot scale. The reclaimed water generated from the etching and cleaning processes in display manufacturing facilities was low-strength organic wastewater and was required to be recycled to secure a water source. For the reuse of reclaimed water to ultrapure water (UPW), a combination of solid-phase AOP and RO was implemented. The removal efficiency of TOC by solid-phase AOP and RO was 92%. Specifically, the optimal acid, pH, and H2O2 concentrations in the solid-phase AOP were determined. With regard to water quality and operating costs, the combination of solid-phase AOP and RO was superior to activated carbon/RO and ultraviolet AOP/anion polisher/coal carbon.

Introduction

Of the latest-generation display panels, the active-matrix organic light-emitting diode (AMOLED) is a self-luminous element that does not need a backlight, unlike liquid crystal display (LCD). The AMOLED manufacturing industry is growing rapidly, because AMOLED has a simpler structure and better image quality than LCD. However, the fast development of the electronics industry has accelerated its water use, causing such problems as a lack of water and a increasing amount of pollutant discharged into river into rivers (Chen et al., 2003, Chen and Chen, 2004). To address these problems, over 40% of wastewater that is discharged from AMOLED manufacturing is reused (reclamation) as raw water for the production of ultrapure water (UPW).

In general, industries consuming a large volume of water obviously have greater potential for reusing wastewater. If the wastewater is reused for activities such as washing floors and cooling in power station, the reusing water quality is easily achieved by additional simple physical and chemical treatments (Rebhun and Engel, 1988, Mohsen and Jaber, 2002, Mohammadnejad et al., 2011). However, more specific and complicated treatment for reusing wastewater in the electronics industry is necessary to produce high purity water which is supplied to UPW production process (Victoria University and CSIRO, 2008, Gutterres and de Aquim, 2013).

The wastewater discharged to reclamation process from manufacturing facility was containing less than 3000 μg L−1 as total organic carbon (TOC). The reclaiming water with a TOC of less than 1000 μg L−1 is considered as low-strength wastewater, and a TOC between 1000 and 3000 μg L−1 reflects high-strength wastewater. Especially, main components in low-strength wastewater are acetone, isopropyl alcohol, acetaldehyde, and methanol. Among these compounds, isopropyl alcohol, which utilized in etching and washing the surface of panel in the display manufacturing process, is toxic to humans and relatively resistant to biodegradation (Ruiz, 2004, Kim et al., 2012).

In actual facility, the reclamation of low-strength wastewater has been achieved by a combination of activated carbon and reverse osmosis (RO), whereas high-strength wastewater has been treated with ultraviolet advanced oxidation process (UV-AOP), anion exchange resin, and coal carbon. However, the combination of activated carbon and RO are not applicable for wastewater containing high TOC, and UV-AOP and ion exchange is considered to be uncompetitive due to large footprint requirement. Therefore, an innovative reclamation method is necessary to satisfy the water quality standards and minimize the footprint for the installation of facilities due to continuous expansion of AMOLED production lines.

The homogeneous Fenton reaction was one of representative advanced oxidation processes (AOPs) which was mainly used in industrial waste water purification (Centi et al., 2000). Recently, there were many researches using solid phase Fe instead of liquid phase Fe as Fenton’s catalysts which is called heterogeneous Fenton reaction. Fe on carbon, SiO2 and zeolite, clay mineral containing copper or iron, and iron bearing minerals were studied to evaluated the possibility of effectively producing hydroxyl radical in the reaction with H2O2 on removing various organic chemicals in solution (Abdellaoui et al., 1999, Barrault et al., 2000, Centi et al., 2000, Huling et al., 2000, Chou et al., 2001, Pirkanniemi and Sillanpää, 2002, Zazo et al., 2006, Ramirez et al., 2007). The heterogeneous Fenton reaction has an advantage in reducing the chemical usage and sludge production compared to homogeneous Fenton reaction which was considered as an obstacle when Fenton reaction was applied in low strength waste water treatment. Therefore, authors were developed and evaluated the metal-immobilized catalyst based on activated carbon (Choi et al., 2013).

In this study, we examined the possibility of reusing reclaimed water as raw water for UPW production by applying practically a metal-immobilized catalyst (solid-phase advanced oxidation process; solid-phase AOP) to oxidize the large amounts of low-molecular-weight organic compounds in reclaimed water. Specifically, the effects of operational factors such as pH, hydrogen peroxide concentration, and various acids were determined through a batch and a column test. Finally, the TOC removal efficiency and operational cost of S-AOP + RO were compared with those of existing (activated carbon + RO and UV-AOP + anion resin + coal carbon) for the same reclaimed water in the pilot scale experiment.

Section snippets

Characteristics of reclaimed water

Reclaimed water was generated by etching and washing the surface of a glass plate from the display manufacturing process. The main components of the reclaimed water were acetone, isopropyl alcohol, tetramethyl ammonium hydroxide (TMAH), acetaldehyde, methanol, and ethanol. The average TOC concentration of the reclaimed water was 1691 ± 528 μg L−1 (max. 3312; min. 366 μg L−1), and the conductivity was 4–5 μS cm−1 (see Fig. 1a). As shown in Fig. 1b, the isopropyl alcohol, acetone, acetaldehyde, methanol,

Effect of acids

Because the pH of the reclaimed water discharged from display manufacturing facilities was approximately 4.5, the pH had to be decreased by adding the appropriate acids to initiate the AOP reaction. Inorganic acids, such as, persulfuric acid, nitric acid, hydrochloric acid, and perchloric acid, could be considered as possible candidate for acid. Perchloric acid can be considered in recycling reclaimed water, because ClO4 ions have less of a OH radical scavenger effect than chloride ions from

Conclusions

To reuse organic wastewater that is generated from the display manufacturing industry, we developed a hybrid process that combines solid-phase AOP and RO. For the solid-phase AOP, the applicable and practicable acid was hydrochloric acid. The optimal pH and H2O2 concentration in the AOP using catalysts were below 3.2 and 3.5 mg L−1, respectively. For RO, sodium bisulfate was selected to remove the residual H2O2. TOC concentration (<200 μg L−1) and conductivity (<5 μS cm−1) in the solid-phase AOP + RO

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