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This study investigates chemical cleaning mechanisms of a tubular ceramic UF membrane. The effect of cleaner type (ozone (O 3), sodium hypochlorite (NaOCl) and sodium hydroxide (NaOH)), clean in place (CIP) pH (11 vs. 12), and cleaning sequence on the removal of irreversible fouling of hydrophobic (humic acids) and hydrophilic (alginate with and without calcium (alginate + Ca+2 and alginate - Ca+2, respectively)) NOM fractions were investigated. Results showed that different NOM types responded differently to chemical cleaning. Alginate-Ca+2 and humic acids were equivalently removed by NaOCl or NaOH whereas a lower cleaning efficiency of alginate + Ca+2 was observed. Increasing the pH of NaOCl and NaOH CIP increased the removal of the chemically reversible fouling index (UMFI cr). The efficiency of NaOCl was always lower than that of NaOH at the same pH, which was attributed to surface tension (λ) differences in the CIP water and potential differences in cleaning mechanism. The ceramic UF CIP cleaning using O 3 (0.50 mg O 3 /mgC) for 1 h demonstrated higher cleaning efficiency for humic acids and alginate ± Ca+2, (%UMFI cr > 98%), than NaOCl or NaOH alone (%UMFI cr >80%). The O 3 CIP was as effective as 4 h cleaning using a sequential NaOH/NaOCl or combined NaOCl + NaOH CIP. • O 3 CIP (0.50 mgO 3 /mgC) is an effective cleaning method for ceramic membranes. • O 3 CIP is effective at removing hydrophilic and hydrophobic NOM fractions. • NaOCl and NaOH are more sensitive to water quality conditions for cleaning than O 3. • 1 h of O 3 CIP is equivalent to 4 h of combined NaOCl and NaOH cleaning. • Measuring the optimal ozonation conditions (time vs. O 3 dose) are required. [ABSTRACT FROM AUTHOR]

Highlights • Ceramic and polymeric UF fouling experiments were performed using five NOM models. • NOM fouling order was a NOM mixture ≈ BSA > sodium alginate ±Ca+2 > humic acids. • Backwash efficiency was 2× higher for the ceramic UF compared to the polymeric UF. • Hydraulic irreversibility was the dominant fouling resistance during NOM filtration. • Chemical cleaning was found to be effective for both membrane types. Abstract This research examines the effect of various NOM fractions on ceramic and polymeric UF membranes performance in terms of fouling and cleaning. Fouling experiments were performed using five model solutions, humic acid, protein as bovine serum albumin (BSA), alginate with and without calcium, and a combined NOM mixture. Two chemical agents were selected: an oxidant (NaOCl) and caustic (NaOH). Fouling and cleaning behavior were assessed using the resistance in series (RIS) model, membrane permeability, carbon mass balance, and fluorescence excitation and emission matrix (FEEM) analysis. The results demonstrated that NOM fouling order of the ceramic UF was similar to polymeric UF with the following trend: NOM mixture ≈BSA > alginate ±Ca+2 > humic acid. However, the backwash efficiency was 1.5×–2× higher for the ceramic UF in comparison to the polymeric UF, indicating a much higher hydraulic reversibility for the ceramic UF. A carbon mass balance in compliment with FEEM plots determined that NOM removal by the ceramic UF was ≈ 10% higher than the polymeric UF. Chemical cleaning was found to be effective for both membrane types. Thus, it was not possible to conclude, that the ceramic membrane demonstrated an advantage for chemical cleaning under the conditions studied. [ABSTRACT FROM AUTHOR]

• Water temperature demonstrated impacts on ceramic UF permeability and fouling. • The impact of temperature on fouling was over and beyond simple viscosity changes. • Cold water temperature 5 °C resulted in higher irreversible fouling compared to 20 °C. • At 5 °C condition fouling transitioned from standard to intermediate pore blocking. • Cleaning strategies with NOM impacted water must be altered at cold water condition. Ceramic ultrafiltration (UF) is an emerging technology for drinking water production, but the interplay and influence of water temperature on fouling is lacking. This research investigates temperatures from 5 to 35 °C and explored the fouling impacts of humic, protein, and polysaccharide substances on a ceramic UF membrane. Water temperature not only affected water viscosity but also altered the fouling behavior of organics. At 5 °C, while approximately 50 % of the change in the unified membrane fouling index (UMFI) was attributed to the change in water viscosity the remaining 50 % was due to change in organic fouling behavior. Conversely, at 35 °C, the overall UMFI decreased relative to the 20 °C standard, of which 36–53 % of the decrease was associated with changes in fouling behavior. Constant flux blocking models determined that standard pore blocking dominated the first filtration cycle for all temperature cases, suggesting that material accumulation inside the pores was responsible for fouling during the initial stages of filtration. The standard blocking continued throughout filtration for 20 and 35 °C suggesting that fouling was mostly reversible. In contrast, at 5 °C condition, fouling transitioned to intermediate blocking, suggesting deposition inside the pores causing irreversible fouling. UMFI and carbon analysis showed lower backwash and chemical cleaning efficiencies at the 5 °C condition indicating higher irreversible fouling mass, while better cleaning was observed at the warmer water temperatures. The exacerbated fouling at low temperatures demonstrates that changes in membrane backwash and chemical cleaning should be implemented under fluctuating water temperature conditions. [ABSTRACT FROM AUTHOR]