Double-win effects of in-situ ozonation on improved filterability of mixed liquor and ceramic UF membrane fouling mitigation in wastewater treatment?

The effects of in-situ ozonation on mixed liquor filterability and ceramic membrane fouling in wastewater treatment were systematically studied by evaluating the mixed liquor filterability with a factor analysis method, modeling the membrane fouling process with nine fouling models, and analyzing the mechanism of membrane fouling mitigation with a redundancy analysis method. In-situ ozonation had trade-off effects on the filterability of mixed liquor. On one hand, the filterability of mixed liquor was improved as a result of the remarkable reduction of mixed liquid suspended solids (MLSS), sludge volume after 30 min sedimentation (SV30) and extractable extra-cellular polymeric substances (EPS). On the other hand, the filterability of mixed liquor deteriorated as a result of the obvious increase of dissolved organic carbon (DOC) and soluble microbial products (SMP). The contribution of sludge properties (MLSS, SV30, EPS) to the filterability of mixed liquor was nearly doubled compared with that of the supernatant properties (DOC, SMP). The filterability of mixed liquor was effectively improved with increase of ozone dosage (≤5 mg/L). Meanwhile, membrane fouling was effectively mitigated by in-situ ozonation with the maximum normalized TMP (ΔTMP) reduction of 55.6% achieved at ozone dosage of 5 mg/L (1.3 mg-ozone/g-MLSS). The combined intermediate-standard model excellently fitted the experimental data at different ozone dosages and the alleviation of intermediate blocking mainly contributed to the fouling mitigation by in-situ ozonation (≤5 mg/L). The cake layer resistance was maximally reduced by 61.5% at ozone dosage of 5 mg/L mainly as a result of the significantly improved filterability of mixed liquor. The gel layer resistance was maximally reduced by 32.3% at ozone dosage of 5 mg/L mainly as a result of the direct oxidation of organic foulants deposited on membrane surface.