Spontaneous changes in dissolved organic matter affect the bio-removal of steroid estrogens

Microbial action is the main pathway removing steroid estrogens (SEs) from both aerobic and anaerobic natural waters. The rate is influenced by other active substances present, particularly dissolved organic matter (DOM). DOM in natural surface waters has unstable components which undergo spontaneous photochemical oxidation, biological oxidation, chemical oxidation changes. How these changes influence the biosorption and bio-removal of SEs was the subject of this research. Photo oxidation-induced DOM increased the proportion of the fluorescence in area V, but biological oxidation and chemical oxidation caused fluorescence area V to decrease. All three oxidation processes can reduce the proportions of molecular weight (MW) > 5 kg·mol^-1 and increase the proportions of MW < 5 kg·mol^-1. Both the electron transfer capacity decreased monotonically with photo oxidation and chemical oxidation ageing, but biological oxidation ageing increased them. 17β-estradiol (E2) was the SEs used in the experiments. In aerobic conditions, fresh river humic acids (RHA) and aged RHA had the stronger mediating effect on the rate of E2 bio-removal under aerobic conditions. Its greater effectiveness was probably related to its binding with E2. Binding, biosorption of E2 and bio-removal of E2 were strongly positively correlated with the elemental C (R > 0.8, p ≤ 0.01) and SUVA₂₅₄ (R > 0.8, p ≤ 0.01) by correlation matrix. Besides, fresh river fulvic acids (RFA) and aged RFA had the bigger mediating effect on E2 bio-removal under anaerobic conditions, and this imply that changes in aged DOM affected by other electron transfer groups in an anaerobic water environment. In anaerobic conditions, biosorption of E2 and binding action could cluster together with SUVA₂₅₄, p(v), and 1 kg·mol^-1 < MW < 5 kg·mol^-1 by redundancy analysis, and but bio-removal of E2 could be well polymerized with EAC, EDC, p(iv), and MW > 5 kg·mol^-1.