Operation of different membrane bioreactors : experimental results and physiological state of the micro-organisms

• Published in: Water science and technology 2000-01, Vol.41 (10-11), p.269-277
• Main Authors: ROSENBERGER, S, WITZIG, R, MANZ, W, SZEWZYK, U, KRAUME, M
• Format: Article
• Language: English
• Subjects: Activated sludge; Applied sciences; Bacteria; Biodegradation; Biological and medical sciences; Biological treatment of waters; Biomass; Bioreactors; Biotechnology; Cells; Chemical oxygen demand; Detection; Dry weight; Environment and pollution; Exact sciences and technology; Filamentous bacteria; Fluorescence; Fluorescence in situ hybridization; Fundamental and applied biological sciences. Psychology; General purification processes; Industrial applications and implications. Economical aspects; Membranes; Microfiltration; Molasses; Municipal wastewater; Oxygen consumption; Pollution; Protozoa; Ratios; Reactors; Sludge; Wastewater; Wastewaters; Water treatment and pollution
• ISSN: 0273-1223; 1996-9732
• DOI: 10.2166/wst.2000.0659

Lab-scale and pilot-scale activated sludge bioreactors with integrated microfiltration membranes were operated over a period of up to three years. During the entire operation period no excess sludge was removed from the bioreactors apart from sampling, resulting in highly concentrated biomass in the reactors. The dry weight of the sludge ranged from 15 to 23 g MLSS l–1 for a plant fed with municipal wastewater and up to 60 g ll–1 for a lab-scale plant fed with high strength molasses. Stable biomass concentrations were reached at F/M ratios as low as approximately 0.07 kg COD (kg MLSS)–1 d–1. The degradation performance of the analyzed reactors was high and stable. Direct microscopical studies revealed high amounts of free suspended cells and at various times also high numbers of filamentous bacteria. Surprisingly only low numbers of protozoa were observed during most of the time. By use of fluorescent in situ hybridization (FISH) only about 40% to 50% of all bacteria emitted probe conferred fluorescence signals sufficient for detection, compared to around 80% cells detectable in conventional activated sludge. Studies on oxygen consumption rates indicated that the biomass in the bioreactor was substrate limited. These data suggest that substrate is mainly oxidized and not used for growth purposes which offers the possibility to operate membrane bioreactors with significantly reduced secondary sludge production.