Elsevier

Journal of Electroanalytical Chemistry

Volume 776, 1 September 2016, Pages 148-151
Journal of Electroanalytical Chemistry

Short Communication
Influence of solids on the removal of emerging pollutants in electrooxidation of municipal sludge with boron-doped diamond electrodes

https://doi.org/10.1016/j.jelechem.2016.07.018Get rights and content

Highlights

  • •

    Electrooxidation of sludge is limited by solid particles.

  • •

    Selected emerging pollutants are partially degraded using BDD electrodes (51–69%).

  • •

    Sorption of emerging pollutants (> 98%) reduces electrooxidation efficiency.

  • •

    Electrooxidation of soluble organic matter occurs faster than for particulate organics.

Abstract

Electrooxidation of waste activated sludge (WAS) was performed using boron-doped diamond (BDD) electrodes to evaluate the removal of emerging pollutants: 4-[2-(4-hydroxyphenyl) propan-2-yl]phenol (bisphenol A); nonylphenols (including isomers); and (5-chloro-2-(2,4-dichlorophenoxy)phenol) (triclosan). The applied current density was 28.5 mA cm− 2, and the treatment times evaluated were 60, 120, and 180 min. Partial degradation of selected emerging pollutants was obtained with efficiencies of 51% for bispenol A, 69% for nonylphenols, and 62% for triclosan. Organic matter was partially oxidized, mainly in the soluble phase. Most of the organic matter (78%) and emerging pollutants (> 98%) were found to associate with solid particles in WAS, which limited the efficiency of the process.

Introduction

Wastewater sludge management is a major concern for treatment facilities due to its potential impacts on public health and the environment, as well as the associated handling and disposal costs. Wastewater sludge contains > 90% water with the remainder consisting of organic matter, nutrients, and trace elements. It also concentrates pollutants and significant amounts of pathogens [1]– [3]. Recently, research has focused on the presence of emerging pollutants in sludge [2] as some of these may affect the endocrine system [4], [5]. Furthermore, some of these compounds may end up in soils where sludge is land applied [6].

The electrooxidation technique has proven to be a suitable treatment process because it offers advantages such as the environmental compatibility, versatility, energy efficiency, amenability to automation, and in particular it has high efficiency in destroying persistent organic pollutants in water, wastewater, and sludge [7]. The process may oxidize organic compounds through two main routes: (i) a direct process, in which the organic molecules are oxidized after adsorption onto the electrode surface; or (ii) an indirect process, in which the oxidation is carried out in the bulk solution by electrogenerated oxidants [8], [9]. Among these various oxidants, the hydroxyl radical (radical dotOH) is one of the most powerful, and is produced by the oxidation of water on certain anodes, such as boron-doped diamond electrodes [7].

Based on the above, this work focused on the electrooxidation of municipal sludge with boron-doped diamond (BDD) anodes to evaluate the removal of organic matter, including three emerging pollutants (triclosan, bisphenol A, and nonylphenols), and provide information on the influence of sludge solids on their degradation.

Section snippets

Collection and characterization of sludge samples

Waste activated sludge (WAS) was obtained from a 2 m3/s activated sludge wastewater treatment plant in Mexico City. Samples were collected in glass containers and cooled to 4 °C before transportation to a certified laboratory for characterization and treatment. Sludge was characterized for pH, conductivity, total and volatile solids, as well as total and soluble chemical oxygen demand (COD), all of which were determined according to the Standard Methods for the Examination of Water and Wastewater

Results and discussion

Waste activated sludge used in the electrooxidation tests exhibited slight variations in pH, as well as in total and volatile solids since it was sampled on different dates Table 1. However, in all samples, > 99% of the volume was water, while the rest was composed of solid particles (total solids: 0.80%). Volatile solids, an indicator of the amount of organic matter in the sludge, were 80.7% of the total solids since the sludge is mostly biomass. Values of total COD (10,440 mg/L) reflect the

Conclusions

Electrooxidation of sludge using boron-doped diamond electrodes reduced the concentration of emerging pollutants by 51, 69, and 63% for bisphenol A, nonylphenols, and triclosan, respectively. These compounds were partially degraded due to their association (adsorption) to solid particles in sludge (> 98%) which limited mass transfer and thus contact with hydroxyl radicals. Total organic matter was partially oxidized (between 5 and 31% of total COD) and most of this oxidation was for soluble

Acknowledgements

This project was funded by the Institute of Engineering UNAM Research Fund 2013.

References (27)

  • Y.H. Cui et al.

    Electrochemical degradation of bisphenol A on different anodes

    Water Res.

    (2009)
  • K. Kimura et al.

    Removal of pharmaceutical compounds by submerged membrane bioreactors (MBRs)

    Desalination

    (2005)
  • J. Stevens-Garmon et al.

    Sorption of emerging trace organic compounds onto wastewater sludge solids

    Water Res.

    (2011)

    • Cited by (0)

    View full text
    © 2016 Elsevier B.V. All rights reserved.