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The integrated process of ozonation coupled with ceramic membrane filtration has been actively utilized to alleviate membrane fouling in water/wastewater treatment, however, the effect of ozonation on protein-based ceramic membrane fouling is still contradictory. Herein, for the first time, we reported the severe protein-based ceramic membrane fouling at high ozone dosage in the integrated process of ozonation coupled with ceramic membrane filtration and the related fouling mechanism was systematically explored. Ozonation at low dosage slightly mitigated membrane fouling, whereas severe membrane fouling occurred at high ozone dosage (10 mg/L for pre-ozonation; 4 and 10 mg/L for in-situ ozonation). At high ozone dosage, the trans-membrane pressure (TMP) remarkably increased (> 40 kPa) within 90 min and both hydraulically reversible and irreversible fouling contributed to the total membrane fouling resistance. Electro kinetic potential and particle size of the bovine serum albumin (BSA) solution were not the key factors affecting the aggravated membrane fouling at high ozone dosage. The remarkably deteriorated membrane fouling at high ozone dosage can be accounted for the formation of BSA crosslinks ascribed to the oligomerization and agglomeration of BSA and the intermolecular disulfide bridge formation with the crosslinks progressively accumulating on the membrane surface and in the membrane pores during filtration. The modeling results confirmed that the BSA-based membrane fouling mechanism was changed from cake-intermediate to cake-standard with ozonation at high ozone dosage. Meanwhile, the cake layer and/or gel layer played a more important role for the aggravated membrane fouling at high ozone dosage even though the contribution of pore blocking was also significant. [ABSTRACT FROM AUTHOR]

Pre-ozonation or in-situ ozonation coupled with membrane filtration has been actively utilized for membrane fouling control in water treatment, however, the comparative analysis of these two ozonation processes on membrane fouling control has not been reported so far. In this study, the comparative effect of pre-ozonation and in-situ ozonation on mitigation of ceramic UF (ultrafiltration) membrane fouling caused by alginate was systematically investigated through characterization of TMP, fouling resistance, MW distribution, dissolved ozone concentration, the formation of hydroxyl radical and modeling. Results showed that both pre-ozonation and in-situ ozonation were effective in alleviating the cake layer fouling. Ozonation efficiently broke down the high molecular weight (MW) fractions (>150 kDa and 80–150 kDa) of alginate into the low MW fractions (6–80 kDa; 0.4–6 kDa and 0.1–0.4 kDa), reducing the membrane interception of alginate. Pre-ozonation achieved better fouling mitigation performance compared with in-situ ozonation at low ozone dosages of 2 and 4 mg/L. However, in-situ ozonation had better fouling control performance at high ozone dosage of 10 mg/L with the normalized TMP (ΔTMP) maintaining below 0.2 kPa after 60 min filtration. Besides, in-situ ozonation was more effective in hydraulically irreversible fouling control than pre-ozonation regardless of ozone dosage. Integration of in-situ ozonation and ceramic membrane filtration catalyzed ozone decomposition with the increased generation of hydroxyl radical, which further strengthened the oxidation of the accumulated foulants on the membrane surface and within the membrane pores and thus effectively alleviated the reversible and irreversible fouling. [ABSTRACT FROM AUTHOR]

The effect of mixed liquor properties changed by ozonation especially with high dosages on membrane fouling is very complex and remains unclear. In this study, the effect of mixed liquor properties changed by ozonation especially with high dosages on ceramic ultrafiltration (UF) membrane fouling in wastewater treatment and the corresponding mechanism were systematically studied by characterization of the mixed liquor properties, hydraulic performance, the fouling layers and modeling at different ozone dosages (0, 2, 5, 10 mg/L). The membrane filterability of the mixed liquor after pre-ozonation (⩽5 mg/L) was enhanced and the corresponding membrane fouling was mitigated. After pre-ozonation, activated sludge had the better settleability and larger floc size. Meanwhile, there was a remarkable reduction of dissolved organic carbon (DOC), soluble microbial products (SMP) and extractable extra-cellular polymeric substances (EPS) after pre-ozonation and the removed organics were mainly belonged to the high molecular weight (MW) (1–10 kDa) and very high MW (10–200 kDa) substances. Intermediate blocking was the main membrane fouling during the mixed liquor filtration process and the best fouling mitigation performance was achieved for the sample with an intermediate ozone dosage of 5 mg/L (1.7 mg-ozone/g-mixed liquor suspended solids (MLSS)). Meanwhile, the water quality of permeate was even better after pre-ozonation (⩽5 mg/L) with the lower DOC and total nitrogen (TN) concentrations. Severe cell lysis occurred with the significant increase of the released organics in the mixed liquor and the activated sludge had smaller floc size and worse settleability when the pre-ozonation dosage was above 10 mg/L, which in turn resulted in the deteriorated membrane fouling control performance. [ABSTRACT FROM AUTHOR]

Inorganic salts (e.g., FeCl 3 and FeSO 4) are typically added to membrane bioreactor (MBR) for achieving improved total phosphorus (TP) removal and hydraulic performance. However, at the iron dose (e.g., Fe to P molar ratio of 1–4) required for effective TP removal, severe irreversible membrane fouling could become a significant concern. In this context, intermittent in-situ ozonation was provided for the first time directly in the membrane tank of Fe(II)-dosed membrane bioreactor, and its effect on membrane fouling mitigation was assessed and elucidated. The basic effluent quality remained unaffected, indicating that in-situ ozonation had no detrimental effects. In addition, concentration of foulants and the relative abundance of biofilm-forming microbes were comparable in both the Fe-MBR and Fe/O 3 -MBR. Importantly, as compared to the Fe-MBR, a 33% reduction in membrane fouling was achieved in the Fe/O 3 -MBR. The enhanced filterability of mixed liquor and the scrubbing of the membrane surface by ozone with the direct/indirect oxidation of the deposited foulants contributed to membrane fouling mitigation in the Fe/O 3 -MBR. Meanwhile, trans -membrane pressure profiles of MBRs followed cake-intermediate fouling mechanism. This study demonstrates that provision of intermittent in-situ ozonation is a simple and attractive approach to extend the operation of iron-dosed MBR. [Display omitted] • Performance of in-situ ozonation combined with Fe-MBR (Fe/O 3 -MBR) was elucidated. • Abundance of biofilm-forming bacteria was comparable in both Fe- and Fe/O 3 -MBR. • Ozonation improved mixed liquor properties and delayed the onset of severe fouling. • Increased floc size and membrane scrubbing by ozone contributed to fouling control. • Cake-intermediate fouling was the fouling mechanism in both Fe- and Fe/O 3 -MBR. [ABSTRACT FROM AUTHOR]

• Long-term performance of MBRs with and without in-situ ozonation was investigated • in-situ ozonation achieved improved (up to 26%) micropollutant removal • in-situ ozonation increased microbial diversity and favoured the growth of PAOs • Denitrifying taxa reduced in Oz-MBR, but effluent quality remained unaffected • Cake-complete model was effective to explain the fouling mechanisms in Oz-MBR In this study, impacts of in-situ ozonation applied directly in the membrane tank of a ceramic MBR (Oz-MBR) were assessed to elucidate its implications on micropollutant removal, microbial taxa and membrane fouling. The basic effluent quality (i.e. , bulk organics and nutrients) of the MBR without and with in-situ ozonation was comparable. Importantly, pollutant-specific (10-26%) improvement in micropollutant removal was achieved by the Oz-MBR, which could be attributed to the increase in the abundance of microbial taxa responsible for the removal of structurally complex pollutants and/or ozone-assisted oxidation. In-situ ozonation affected the abundance of denitrifying bacteria and functional genes but total nitrogen removal by the Oz-MBR was comparable to that achieved by the control (C)-MBR. Improved mixed liquor properties, and the reduced accumulation of foulants on the membrane surface resulted in membrane fouling alleviation (53%) in the Oz-MBR. In addition, fouling models evaluated for the first time in the case of Oz-MBR indicated that the cake-complete model was suitable to explain membrane fouling mechanism. This comprehensive study demonstrates the performance of MBR coupled with in-situ ozonation, and the obtained results would serve as a useful reference for its implementation at pilot- and/or full-scale. [ABSTRACT FROM AUTHOR]