Degradation of endocrine-disrupting chemicals during activated sludge reduction by ozone

Ozonation has been considered to be an effective means for the reduction of excess sludge in recent years. However, it remains largely unknown whether hydrophobic organic micro-pollutants, which are originally adsorbed on activated sludge, will be released into wastewater upon ozonation because of sludge solubilization. This study investigated the degradation efficiencies of several typical endocrine-disrupting chemicals (EDCs) during sludge ozonation, including estrone (E1), estriol (E3), 17α-ethynylestradiol (EE2), bisphenol A (BPA), and 4-nonylphenol (NP). Results indicate that the EDCs present in activated sludge could be effectively removed by O3 even though the apparent rate constants in sludge were 3–4 orders of magnitude lower than those in water. However, the applied O3 dose should be prudently controlled because a low dose (e.g., 29 mg O3 g−1 SS) may lead to an increase of BPA and NP concentrations in the liquid phase of activated sludge. Furthermore, H2O2 addition or pH adjustment could improve the removal of most studied EDCs, but exert a negative effect on the more hydrophobic and refractory compound, NP.

Figure optionsDownload as PowerPoint slideHighlights
► Ozonation was an effective means for excess sludge reduction.
► Sludge-bound EDCs were effectively removed during sludge ozonation.
► The adsorption of EDCs on sludge greatly retarded their degradation by O3.
► EDCs degradation kinetics could be expressed by the pseudo-first-order model.
► Either H2O2 addition or pH adjustment enhanced the removal of most EDCs.