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Assessment of biomass functionalities in a biofilm membrane bioreactor (BF-MBR) targeting biological nutrient removal
Norwegian University of Science and Technology, Faculty of Natural Sciences and Technology, Department of Biotechnology.
2013 (English)MasteroppgaveStudent thesis
Abstract [en]

High concentrations of nutrients such as nitrogen, phosphorus and organic matter can cause serious eutrophication in receiving water bodies. In biological wastewater treatment microorganisms remove nutrients from the wastewater and ensure that these components in the final effluent stay at acceptable levels. A biofilm membrane bioreactor (BF-MBR) removing nitrogen, phosphorus and carbon from municipal wastewater was operated for 85 days. An assessment of the process focusing on the biomass in the various reactors was carried out. The amount of ammonium oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB), phosphate accumulating organisms (PAO) and glycogen accumulating organisms (GAO) was quantified. Fluorescence in situ hybridization (FISH), confocal laser scanning microscopy (CLSM) and digital image processing with the software daime were used for this purpose. Changes in the communities were compared to different operating conditions. The effect of a decrease in the hydraulic retention time (HRT) and diluted concentrations of nutrients in the influent were evaluated. The correlation between filamentous bacteria and the sludge volume index was studied. The viability of bacterial populations in a nitrifying biofilm was also investigated. The BF-MBR produced a high quality effluent in terms of chemical oxygen demand (COD), nitrogen and total suspended solids (TSS). The system handled well the reduction in the HRT. The removal of phosphorus was not satisfactory. The microbial communities investigated by FISH analysis were present in all samples, but their abundance varied. Substrate limitation due to reduced nutrient loading and the activity of denitrifying bacteria in the anaerobic reactor of the A/O bio-P process, affected the population of PAOs negatively. Results and observations from this study suggest that for the enrichment of PAOsin an A/O bio-P system it is crucial to have strictly anaerobic conditions in the reactor designated for this purpose and sufficient substrate available. When the abundance of PAOs increased, the phosphorus removal improved. A higher decay rate was observed for PAOsthan GAOs. It might be assumed that the high decay rate of PAOs was not caused by the substrate competition with GAOs, but rather with denitrifying bacteria. In this study, the abundance of GAOs and AOB seemed solely limited by the available substrate being carbon and ammonium, respectively. The abundance of NOB and the total nitrifying community increased despite of periods with ammonium limitations. A live/dead analysis of the nitrifying biofilm suggested limited diffusion rates in the deeper layers of the biofilm, leading to cell decay. The entire microbial community investigated handled the reduction in the HRT well. The microbial communities of the biomass were found to be more protected on the inside of a carrier, forming larger spherical clusters, than in the activated sludge. The abundance of PAOs on a carrier was found to be superior of the amount of PAOs detected in the activated sludge surrounding the carrier in an IFAS system. A difference in the amount of PAOs and GAOs in the two reactors of the A/O bio-P process was also found. Large amounts of filamentous bacteria were not observed in the A/O bio-P system despite the high sludge volume index.

Place, publisher, year, edition, pages
Institutt for bioteknologi , 2013. , 128 p.
URN: urn:nbn:no:ntnu:diva-21820Local ID: ntnudaim:9612OAI: diva2:644218
Available from: 2013-08-29 Created: 2013-08-29 Last updated: 2013-08-29Bibliographically approved

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