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Impact of biofilm layer on virus removal capacity and integrity testing of passive membrane systems

University of British Columbia

Passive membrane filtration is a self-sustained process where an ultra-low permeate flux is maintained by hydrostatic pressure (i.e. gravity) and little to no fouling control measures are used. Due to their ultra-low permeate flux and ease of operation, passive membrane systems are particularly suited for small scale applications, such as decentralized water treatment in small and remote communities. A key aspect of passive membrane filtration is the development of a structurally loose and permeable biofilm layer that enables a sustainable flux to be achieved. The biofilm layer of passive membrane systems has also been associated with improved removal of humic acids, polysaccharides, proteins, assimilable organic carbon and microcystins. The present study investigated the contribution of the biofilm layer to the virus removal capacity of passive membrane systems. Intact and breached passive membrane modules were studied. Breach sizes considered ranged from 20 to 180µm. Challenge tests (CTs) identified an increase of more than 2.0 log in the log removal value (LRV) for viruses of both intact and breached passive membranes when a biofilm layer was present. As a result, intact and breached passive membranes consistently achieved an LRV for viruses of more than 4.0 log. The use of pressure decay tests (PDTs) to estimate the LRVs of passive membrane systems was also studied. The LRVs estimated using the standard PDT approach did not reflect the increase in LRVs detected in the CTs. Results suggested that the biofilm layer grows on top of the breaches, acting as a secondary barrier to contaminants that would otherwise bypass treatment by flowing through the breach. The standard PDT approach failed to estimate the LRVs of passive membranes because it was not developed to take into account the additional removal provided by the biofilm layer. An alternative integrity testing protocol for passive membrane systems is provided, which includes a modified PDT approach for estimation of LRVs.

Text

2019-10-16

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/71930

Civil Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/