Intensive monitoring of sludge filterability of a pilot-scale membrane bioreactor treating municipal wastewater for better interpretation of fouling

• Published in: Journal of water process engineering Vol. 40; p. 101970
• Main Authors: Kakuda, Takayuki, Iwasaki, Hiroyuki, Huang, Xia, Kimura, Katsuki
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2021
• Subjects: Capillary suction time; Colloidal matter; Irreversible fouling; Lipopolysaccharides; Reversible fouling; Reversible fouling; Irreversible fouling; Capillary suction time; Colloidal matter; Lipopolysaccharides
• ISSN: 2214-7144; 2214-7144
• DOI: 10.1016/j.jwpe.2021.101970

[Display omitted] •Monitoring frequency needs to be high to obtain useful information.•A method facilitating frequent and separate assessment of colloids is proposed.•Deterioration of sludge filterability was related to temperature and ion balance.•Importance of a specific fraction of polysaccharides was suggested. In this study, a pilot-scale membrane bioreactor (MBR) treating municipal wastewater was operated over 600 d. Intensive monitoring of sludge filterability with high frequency, which is rarely reported in previous studies, was performed. Detailed information on sludge filterability obtained in this study makes the advanced interpretation of membrane fouling possible and allows to take effective countermeasures. Two methods (batch membrane filtration and measurement of capillary suction time (CST)) were used to assess sludge filterability, which significantly varies during the long-term operation. Although these two methods generated similar data, the CST measurement is easier than batch-filtration and is therefore recommended for intensive monitoring of sludge filterability in MBRs. Using the data obtained in this study, the evolution of reversible and irreversible fouling was distinguished. The importance of separately assessing the impact of colloidal matter on sludge filterability was also demonstrated: colloidal matter caused the deterioration of sludge filterability. To detect such impacts, the frequency of the assessment should be sufficiently high. A new method (modification of CST measurement) proposed in this study could be used for such frequent assessments. Temperature in the reactor and ion balance in raw wastewater were identified as key factors in the deterioration of sludge filterability. A specific fraction of polysaccharides (lipopolysaccharides) exhibited a significant correlation with the deterioration of sludge filterability. This study can provide important information for the operation and maintenance of large-scale MBRs treating municipal wastewater.