Nonylphenol polyethoxylate in hospital wastewater: A study of the subproducts of electrocoagulation

Abstract

Chromatographic procedures such as solid phase extraction and high performance liquid chromatography coupled with a fluorescence detector (SPE-HPLC-FLD), were carried out to determine the concentrations of the surfactant nonylphenol ethoxylate (9 ethylene oxide units, NP9EO) and its biodegradation product, 4-nonylphenol (NP), in samples collected from the wastewater treatment system at the University Hospital (HUSM) of the Federal University of Santa Maria. The results showed a high concentration of NP9EO in all the collected samples (0.075 – 4.12 mg L⁻¹) and an almost complete absence of NP. In addition, electrocoagulation (EC) of NP9EO was carried out in aqueous solution and in the HUSM effluent. A NP9EO removal rate of 95 % was achieved from the aqueous solution, following a pseudo-first-order kinetics. Through LC-MS measurements in aqueous solutions, it was possible to determine the formation of short-chain nonylphenol ethoxylate (NPEO), such as nonyl-phenoxy acetic acid (NP1EC), after 30 min of EC. In the case of the HUSM wastewater, the NP9EO removal was 89 %, and the chemical oxygen demand (COD) abatement was 26 %. A respirometric test was conducted to measure the increase of biodegradability during the EC and the aqueous samples were found to be less readily biodegradable before the 30-min period of electrocoagulation than after it had been completed.

Keywords:

• Nonylphenol ethoxylate
• nonylphenol
• hospital wastewater
• electrocoagulation
• LC-MS
• respirometry

Acknowledgments

The authors would like to express their gratitude to the Brazilian Council of Scientific and Technological Development (CNPq) and the German Academic Exchange Service (DAAD) for their sponsorship and financial support. The authors have declared no conflict of interest.