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).
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).
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
Abstract; Taro URASE, Hirofumi TSUTSUI, Takeshi INOU, Hao Yang CHEN. Journal of Japan Society on Water Environment, Vol.40, No.3, pp.107-114. (2017).
The effect of antimicrobials in wastewater on the effectiveness of small-scale wastewater treatment is of concern, although the usual concentrations of pharmaceuticals and personal care products (PPCPs) are lower than those that might induce inhibitory effects in large-scale wastewater treatment. The effect of antimicrobials on the operation of a newly designed two-stage membrane bioreactor, which is advantageous for the removal of micropollutants, was investigated. Levofloxacin (5 mg L-1) and/or clarithromycin (2 mg L-1) in the feed wastewater decreased the nitrification rate by at least 40% and promoted membrane fouling. The accumulation of antimicrobials in the sludge phase in the reactors would be the reason for the retardant adverse effects even after stopping the addition of the antimicrobials. Keywords:
Keywords: Antimicrobials; Membrane bioreactor; Levofloxacin; Inhibitory effects on nitrification; Membrane fouling
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: 10.2965/jwet.15-044
Factors affecting removal of pharmaceutical substances and estrogens in membrane separation bioreactor
Abstract; Taro Urase, Chie Kagawa and Tomoya Kikuta. Desalination, 178, 107-113.(2005)
The degradation of three estrogens, two endocrine disruptors and ten pharmaceutical substances in a membrane separation bioreactor was experimentally examined. Higher removal of acidic pharmaceutical substances was obtained in the case of lower pH operation because of the increased tendency of adsorption to the sludge particles. The target substances attached to the sludge were not accumulated in the reactor and they were biologically degraded. The membrane used in this study was a microfiltration membrane which has much larger pores than target substances. However, the permeate concentration was lower than the water phase concentration in the reactor probably due to activated sludge deposition onto membrane surface. The additional removal by the membrane was increased with the time elapsed, though the removal was not significantly high for the relatively hydrophilic compounds.
Keywords: Pharmaceuticals, membrane separation bioreactor, activated sludge, microfiltration