Research Article

Environmental Science and Pollution Research

, Volume 20, Issue 5, pp 3024-3033

First online:

Open Access This content is freely available online to anyone, anywhere at any time.

Removal mechanisms and kinetics of trace tetracycline by two types of activated sludge treating freshwater sewage and saline sewage

  • Bing LiAffiliated withEnvironmental Biotechnology Laboratory, Department of Civil Engineering, The University of Hong Kong
  • , Tong ZhangAffiliated withEnvironmental Biotechnology Laboratory, Department of Civil Engineering, The University of Hong Kong Email author 

Abstract

Understanding the removal mechanisms and kinetics of trace tetracycline by activated sludge is critical to both evaluation of tetracycline elimination in sewage treatment plants and risk assessment/management of tetracycline released to soil environment due to the application of biosolids as fertilizer. Adsorption is found to be the primary removal mechanism while biodegradation, volatilization, and hydrolysis can be ignored in this study. Adsorption kinetics was well described by pseudo-second-order model. Faster adsorption rate (k 2 = 2.04 × 10−2 g min−1 μg−1) and greater adsorption capacity (q e = 38.8 μg g−1) were found in activated sludge treating freshwater sewage. Different adsorption rate and adsorption capacity resulted from chemical properties of sewage matrix rather than activated sludge surface characteristics. The decrease of tetracycline adsorption in saline sewage was mainly due to Mg2+ which significantly reduced adsorption distribution coefficient (K d) from 12,990 ± 260 to 4,690 ± 180 L kg−1. Species-specific adsorption distribution coefficients followed the order of \( K_{\mathrm{d}}^{{ + 00}} \gg K_{\mathrm{d}}^{{ + - 0}} > K_{\mathrm{d}}^{{ + - - }} \). Contribution of zwitterionic tetracycline to the overall adsorption was >90 % in the actual pH range in aeration tank. Adsorption of tetracycline in a wide range of temperature (10 to 35 °C) followed the Freundlich adsorption isotherm well.

Keywords

Trace antibiotics Activated sludge Removal mechanisms Sewage Adsorption kinetics Adsorption isotherm