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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]

The combined pretreatment of coagulation and ozonation is extensively adopted for water quality enhancement and membrane fouling reduction in wastewater reclamation. Herein, the integrated treatment of ferrate pretreatment and in-situ ozonation/ceramic membrane filtration on water quality improvement and fouling reduction of ceramic membrane in secondary wastewater effluent treatment was reported for the first time. The results showed that the hybrid treatment of ferrate pretreatment and in-situ ozonation greatly inhibited the generation of N-dimethyl nitrosamine (NDMA) and did not generate bromate. Meanwhile, the best removal efficiencies of low molecular weight (MW) organics (32.3%), humic-like substances (17.8%) and biopolymers (87.5%) in effluent were achieved by the combination of ferrate (0.15 mM) pretreatment and in-situ ozonation (10 mg/L). Moreover, the control sample (without any treatment) had a fouling transmembrane pressure (TMP) of 30.5 kPa after 7.0 h filtration under a constant flux of 90 L/(m2·h) while that was only 1.0 kPa by the hybrid treatment of ferrate (0.15 mM) pretreatment and in-situ ozonation (10 mg/L). Soluble microbial products (SMP)-like substances with high molecular weight (MW) of 20–2000 kDa were the main foulants and intermediate-standard fouling mechanism played a principal role during the membrane filtration process. Statistical analysis showed that dissolved organic carbon (DOC), UV 254 and protein had the greatest positive correlation (above 0.92) to the total fouling resistance, whilst turbidity displayed the greatest negative correlation (around −0.61) to the total fouling resistance. The remarkable fouling alleviation was due to the improved water quality and in-situ cleaning, which were contributed to the coagulation and oxidation by ferrate and in-situ ozonation. Image 1 • Ferrate pretreatment- in-situ ozonation greatly reduces ceramic membrane fouling. • NDMA and bromate are remarkably reduced by ferrate pretreatment- in-situ ozonation. • Intermediate-standard fouling is the main fouling mechanism. • DOC, UV 254 and protein are the most important positive factors to R t. • Fouling alleviation is due to the improved water quality and in-situ cleaning. [ABSTRACT FROM AUTHOR]