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Reducing operational costs in membrane bioreactors using slug bubbles

University of British Columbia

Membrane bioreactors (MBRs) are commonly used in wastewater treatment processes. In fact, the demand is expected to increase with more than double digit growth annually over the next decade [5]. However, operational costs of MBRs are still higher compared to operational costs of conventional treatment plants due to the additional aeration and pumping required in MBRs. This study examines the feasibility of using excess air that was used to clean the membrane for water conveyance (known as airlift pump), for a minimized energy use in MBR processes. In order to meet the objective, prototypes of airlift pumps were built with different dimensions. The experimental results of each prototype were comprehensively compared to existing models in the literature. The models were modified for a better fit of the experimental data. It was determined whether a new apparatus, where many riser tubes were bundled together, would behave like many individual riser tubes. While the air was injected at the bottom of the individual riser tube previously, the bundled riser tubes of the new apparatus would be attached to a rubber sheet; this, was attached to a frame. The rubber sheet was added to the apparatus in order to trap the air in the tank and lead it to the bundle of riser tubes. Different collector angles of the rubber as well as different water heights were investigated. The experimental results were compared to the previously modified models. The last step was to design a system that redirects the pumped water so that it can be transported back to the head of the MBR plant. The results suggest that air exiting to the atmosphere from an MBR can be used to transport the water. However, the models are only able to predict water flows for individual airlift pumps that consist of a single riser tube, where the air is injected at its bottom. Further research needs to be done in order to be able to predict water flows that can be achieved in systems, such as the one proposed in this present study, which uses a bundle of riser tubes.

Text

2015-01-15

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/51914

Civil Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/