Environ. Sci. Technol. 2008, 42, 7411–7416
Efficient Removal of Aromatic Sulfonates from Wastewater by a Recyclable Polymer: 2-Naphthalene Sulfonate as a Representative Pollutant BINGJUN PAN, WEIMING ZHANG, BINGCAI PAN,* HUI QIU, QINGRUI ZHANG, QUANXING ZHANG, AND SHOURONG ZHENG State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210093, P.R. China
Received May 18, 2008. Revised manuscript received June 25, 2008. Accepted July 18, 2008.
As a family of hydrophobic ionizable organic compounds, aromatic sulfonates can be present at high levels in industrial wastewaters. They tend to exist as anions over a wide range of pH and cannot be effectively trapped by conventional adsorbents. In the current study, a recyclable acrylic ester polymer (NDA-801) was synthesized for effective removal of aromatic sulfonates from wastewater of high acidity (e.g., pH < 1) and inorganic salts (e.g., ∼5-10% Na2SO4 in mass), for which sodium 2-naphthalene sulfonate (2-NS) was chosen as a representative target contaminant. 2-NS uptake onto NDA801 increased with the increasing acidity of the solution. The ζ potential of NDA-801 measured at different pH levels as well as batch 2-NS adsorption from methanol/water binary systems demonstrated the favorable roles of electrostatic and hydrophobic interaction in 2-NS adsorption. As compared to a granular activated carbon GAC-1, NDA-801 exhibited much higher removal efficiency and capacity of 2-NS in fixed-bed adsorption. Moreover, the exhausted NDA-801 beads by 2-NS can be completely regenerated by water wash for repeated use, which is more economically desirable than by other regenerants, such as NaOH solution. Continuous column adsorption-regeneration cycles indicated negligible capacity loss of NDA-801 during operation and further validated its feasibility for potential application in associated wastewater treatment.
Introduction Many environmentally significant synthetic aromatic compounds (namely, aromatic carboxylic acids, naphthalene and benzene sulfonic acids) and quaternary benzylammonium compounds exist as ions in the aqueous phase over a wide range of pH. They are often referred to as hydrophobic ionizable organic compounds (HIOCs) (1, 2). As an important family of HIOCs, aromatic sulfonates (ASs), which are widely used in the chemical, pharmaceutical, tannery, paper, and textile industries, are of high water solubility and often present in industrial wastewaters at high levels (3, 4). Due to their highly sulfonated nature, ASs are resistant to microbial * Corresponding author phone: +86-25-8368-5736; fax: +86-258370-7304; e-mail:
[email protected]. 10.1021/es801370n CCC: $40.75
Published on Web 08/20/2008
2008 American Chemical Society
breakdown and have been described as nonbiodegradable or poorly biodegradable (5, 6). Adsorption is one of the most effective physical processes for removal of organic pollutants from contaminated waters, and activated carbon is the most commonly used adsorbent. Contrary to nonionized organic solutes, activated carbon was proved to be unsuitable for ASs removal in terms of the elevated height of the mass transfer zone in the column and low breakthrough volumes (7). In addition, thermal regeneration of activated carbon is energy-intensive and relatively expensive (8), and the spent adsorbent also presents a disposal problem (9). Previous studies have demonstrated effective ASs sorption onto polymeric anion exchangers (10, 11). Unfortunately, because of high sorption affinity between ASs and strong base anion exchangers (11), regeneration of spent exchanger becomes a particularly challenging and costly task. A satisfactory regeneration process for these exchangers requires large volumes of concentrated brine or alkaline solution or even organic solvent (11). In our earlier study (12), we prepared an aminated hyper-cross-linked polymer M-101 for effective AS removal from industrial wastewaters in the presence of low acidity (pH 2∼3) and low salinity (e.g.,
