Constituents of Coliform Species Contained in the Permeate of Microfiltration Membranes in Wastewater Treatment
Abstract; Shuai Zhou, Taro Urase and Saki Goto. Water, 16(9), 1269. (2024). (DOI)
MBRs (Membrane bioreactors) have been increasingly employed for municipal and industrial wastewater treatment in the last decades for their small footprint and excellent effluent quality. However, microorganisms are often detected in the permeates of microfiltration (MF) membranes even with small pore sizes. Coliform bacteria are known for indicating the potential presence of pathogenic bacteria that cause infectious disease such as bacteremia, respiratory tract infections, and urinary tract infections. Thus, the retention of coliform bacteria by membrane processes is important when the membrane process is utilized in water reclamation. In this study, a microbial community of coliform bacteria in the permeates of MF membranes with different pore sizes (0.2, 0.4, and 0.8 µm) was identified. The results showed that the dominant coliform bacteria changed from Enterobacter spp. and Citrobacter spp. in the activated sludge to Enterobacter spp. and Klebsiella spp. in the permeate of MF membranes, while some pieces of membranes showed complete retention. The bacterial regrowth on the surface of the piping system on the permeate side could be a significant factor contributing to the frequent and exclusive detection of Enterobacter spp. and Klebsiella spp. in the case of membranes with small pore size (0.2 and 0.4 µm) after a long continuous filtration time. To indicate the public health-related risk of treated wastewater by MF, Escherichia coli may not be a suitable indicator species because E. coli is relatively retentive in MF compared to other coliforms.
Keywords: membrane bioreactor; Enterobacteriaceae; permeable bacteria
Bacterial Species Identified in the Filtrate of Microfiltration Membranes in the Separation of Activated Sludge
Abstract; Shuai ZHOU, Manae NINOSEKI, Asahi KUSABA, Kazuma NAKAGAWA, Taro URASE. Journal of Water and Environment Technology, Vol.19, No.6, Pages 294-301. (2021). (DOI)
Membrane bioreactor-reverse osmosis process (MBR-RO) is widely applied in wastewater treatment, especially when high-quality treated water is needed. Although MBR shows better performances in the removal of pathogens than the conventional activated sludge process, stable operation of RO process in the latter step of MBR-RO depends on residual bacteria in the filtrate of microfiltration membranes. Species and sizes of bacteria found in the filtrate of activated sludge with 0.2μm pore-size polycarbonate membranes were investigated in this study. Isolated bacterial species grown on R2A agar medium were identified based on the full length 16S rRNA gene sequences. The result showed that approximately 90% of the isolates found in the filtrates were members of phylum Proteobacteria in which Ralstonia spp., Achromobacter spp., Methylobacterium spp. and Methylorubrum spp. accounted for the largest proportions while other bacteria affiliated with phyla Actinobacteria and Firmicutes. The leakage of Ralstonia and Actinobacteria was probably due to their small sizes judging from microscopic observation, while a longer filtration time is needed for Methylobacterium and Methylorubrum to be detected in the filtrate.
Keywords: activated sludge, membrane bioreactor, ultra-small microorganism, filtrable bacteria, microbial community
Retention of Bacteria and DNA by Microfiltration Membranes in Wastewater Reclamation
Abstract; Hirofumi Tsutsui, Taro Urase. Journal of Water and Environment Technology, Vol. 17, No. 3: 194-202. (2019).(DOI)
16S rRNA gene copy numbers and bacterial counts in the permeate from different microfiltration membranes installed in membrane bioreactors (MBRs) were measured in order to provide information on the selection of suitable membrane for wastewater reclamation and reuse. 16S rRNA gene copy numbers in the MBR effluent (105 − 107 gene copies / mL) were 1/5 to 1/500 of those in the centrifugal supernatant of the mixed liquor. High bacterial counts and high gene copies were observed in the permeate of the membranes at the beginning of the filtration stage. The permeate contained bacteria without exceptions by using a 0.4 µm or larger pore size membrane, although the passage of bacteria was sporadic by the use of a membrane with cylindrical pores of 0.2 µm diameter. Acinetobacter junii and Microbacterium fluvii were identified in the permeate of the 0.2 µm pore size membrane based on the closest match of 16S rRNA gene sequence. The possibility of selective passage of small size bacteria in the mixed liquor of activated sludge through the membrane was suggested.
Keywords: microfiltration, membrane bioreactor, passage of DNA, pore size, leakage of bacteria
Effect of antimicrobials in feed wastewater on the performance of two-stage membrane bioreactor
Taro URASE, Hirofumi TSUTSUI, Takeshi INOU, Hao Yang CHEN. Journal of Japan Society on Water Environment, Vol.40, No.3, pp.107-114. (2017).
Removal of color from molasses wastewater using membrane bioreactor with acidic condition
Ahmad SHAHATA, Takumi OMATA, Taro URASE. Journal of Water and Environment Technology, Vol. 11, No.6, 539-546 (2013).
Treatment of Saline Wastewater by Thermophilic Membrane Bioreactor
Ahmad Shahata, Taro Urase. J. of Water and Environment Technology, Vol. 14, No. 2, pp. 76-81 (2016). (DOI)
Factors affecting removal of pharmaceutical substances and estrogens in membrane separation bioreactor
Taro Urase, Chie Kagawa and Tomoya Kikuta. Desalination, 178, 107-113.(2005)
