Removal of surfactants nonylphenol ethoxylates from municipal sewage-comparison of an A/O process and biological aerated filters

Abstract

The concentrations of nonylphenol ethoxylates (NPnEO, n=1 to 2) and nonylphenol (NP) in water and sludge samples were measured from a full scale sewage treatment plant (STP) with an Anaerobic/Oxic (A/O) and a Biological Aerated Filter (BAF) process. The A/O process was found to exhibit improved performance in comparison to the BAF process. Mean values of NP, NP1EO and NP2EO concentrations in influents from the STP were similar, ranging from 1.8 to 2.0×10(3)ngL(-1). In the A/O process, the removal efficiency of NP, NP1EO and NP2EO from the aqueous phase was 78%, 84%, and 89%, respectively. In contrast, the removal efficiencies of NP, NP1EO, and NP2EO were relatively lower for the BAF process, at 55%, 76%, and 79%, respectively. High concentrations of NP, NP1EO and NP2EO detected in the sludge samples had a maximum value of 2.7μgg(-1) dw, which indicates that improvement in the overall elimination of NP, NP1EO and NP2EO may be associated with adsorption by the sludge. To further investigate the fate of NP, NP1EO and NP2EO in the STP, our research assessed the degradation characteristics of NP by calculating its transformational loss in the STP. The results demonstrate that the quantity of NP measured in the effluent from the oxic unit increased by 32%, which indicates that NP1EO and NP2EO may undergo degradation in the oxic conditions.

Keywords: A/O process; BAF process; Nonylphenol ethoxylates; Wastewater treatment plant.