Degradation behavior of effluent organic matter and comparison of different oxidation processes during ozonation, UVC/H₂O₂ and UVC/persulfate revealed by fluorescence

This paper reports a new insight into the evolution of Effluent organic matters (EfOM) during ozonation and advanced oxidation process (AOPs), such as UV/H₂O₂ and UV/PS, revealed by fluorescence-PARAFAC. EfOM posed risks to receiving aquatic environments due to the complex compositions [1]. Based on previous reports, ozonation and advanced oxidation processes showed excellent performance during organic micropollutants removal and biotoxicity reduction. The principal reactions during ozonation and AOPs were shown in Table 1. However, it was lack of knowledge on evolution of EfOM during ozonation and AOP. Fluorescence coupled with PARAFAC was a useful tool to trace the EfOM [2]. So this study introduced a new insight into the EfOM transformation and oxidant kinetics during different oxidation processes.

Methods

All experiments were performed under batch test. DOC was determined using a TOC -VCPH analyser. UV absorbance was measured with a UV-VISIBLE Spectrophotometer. Fluorescence EEMs were created using a fluorescence Spectrophotometer. PARAFAC was modeled with DOMfluor Toolbox.

Results and Discussion

The water quality of secondary effluent was shown in Table 2. Four components were identified based on fluorescence-PARAFAC, including three humic-like substances (C1，C2 and C4) and a tryptophan-like substances (C3) (Fig. 1). C1, C2 and C4were related to the humic-like substances, and C3 was related to protein-like substances. These components were commonly found in secondary effluent [2]. The degradation of UV₂₅₄, DOC and PARAFAC components during all processes fitted well with pseudo-first-order kinetic. The degradation of PARAFAC components during ozonation was faster than that during AOP. With higher oxidants dosage, indicators removal rates and oxidants decline rates were both increased. This made a new insight into the use of oxidants during AOP.

Conclusion

Fluorescence components were more sensitive indicators than UV₂₅₄ and DOC in indicating the evolution of EfOM. Ozonation was an outstanding pretreatment process for AOP for its higher apparent reaction rate with fluorescence indicators. Moreover, efficiencies of ozonation and AOP could be observed by monitoring the change of fluorescence components, thus controlling the oxidants dosage dynamically.