Characterization of persistent dissolved organic matter in municipal effluents after ozonation and soil aquifer treatment

The removal of dissolved organic matter (DOM) was investigated for municipal effluent treated by ozonation and soil aquifer treatment (SAT). The apparent molecular weight (AMW) distribution of DOM was characterized using high-pressure size exclusion chromatography with organic carbon detector (OCD), ultraviolet (UV) and fluorescent detectors. Using OCD, the DOM in secondary effluent (SE) was mainly humic substance (50.2 %) and low AMW acids (45.4 %). Ozonation removed 55 % of low AMW acids, while SAT removed 58 % humic substances. Using UV detector, the aromatic DOM in SE was mainly medium AMW 1.2–5.5 kDa (60.8 %) and low AMW 0.4–1.2 kDa (38.5 %). Ozonation removed 65 % of medium AMW fraction, while SAT removed 17 % medium AMW and 29 % low AMW. Fulvic acids and soluble microbial products (SMPs) were monitored using fluorescent detector. Fulvic acids in SE were mainly AMW 0.7–4.6 kDa (76.5 %) and AMW < 0.5 kDa (19.5 %). SMPs in SE were mainly AMW 0.8–4.1 kDa (52.1 %) and AMW 0.4–0.8 kDa (33.8 %). Ozonation effectively removed most fractions (AMW > 0.4 kDa) by 76–100 %, while SAT could only remove less than 30 % of small AMW (0.2–0.8 kDa) fraction. For the whole system, the reductions of total peak areas were 78.6, 66.3, 81.3 and 85.1 % for OCD signals, aromatic DOM, fulvic acids and SMPs, respectively. Compared with SE, the percents of total humic substances, aromatic low AMW acids (0.4–1.2 kDa), SMPs with AMW of 0.4–1.1 kDa and fulvic acids with AMW of 0.5–4.6 kDa increased in the final effluent, indicating such DOM was more resistant during the treatments.