UBC Theses and Dissertations
Full-scale implementation of passive gravity driven membrane filtration for drinking water treatment Wei, Yixin
Passive gravity driven membrane filtration (PGDMF) uses a low hydrostatic pressure for filtration and fouling control, without mechanical pumps and chemical systems. In PGDMF, fouling controls are also achieved with hydrostatic pressure, referred to as Passive Fouling Controls. With promising results from laboratory and pilot-scale studies, a full-scale PGDMF drinking water treatment plant including four membrane systems, was implemented for a small First Nation community in British Columbia, Canada. The present study investigated the operational performance of PGDMF systems which could also be operated as GDMF systems (i.e., no passive fouling controls). The performance was assessed based on the permeability and treated water quality. At present, over 2 years of operational data has been collected. The present study focuses on the data of the first 16 months. In Stage 1 and Stage 2 of the performance monitoring, both GDMF and PGDMF operation were considered, respectively. Stage 1 and Stage 2a confirmed the effectiveness of passive fouling controls. Stage 2b considered the impact of variations in feed water characteristics on PGDMF systems. Increases in feed water temperature (i.e., above 16.5 degrees threshold) resulted in a significantly higher rate of decline in permeability. Increases in organic carbon content (i.e., from 1.10±0.12 to 2.20±0.32 mg.L⁻¹) did not impact the permeability. Stage 2b also considered the impact of the operational set-points. Changing one operational set-point (i.e., higher frequency of passive fouling controls, or lower hydrostatic pressure) did not have a significant impact on the permeability. However, changing both operational set-points simultaneously (i.e., higher frequency of passive fouling controls and lower hydrostatic pressure), resulted in a greater rate of decline in permeability. It was hypothesized that microbial communities in the biofilm could not readily adapt to the added stress induced by the simultaneous change in both operational set-points, which requires further research. The results demonstrated the long-term feasibility (beyond 1 year) of PGDMF systems. The treated water quality met all regulatory requirements. Flow throughput declined slowly over 13 months of operation. Positive feedback was also obtained from the operator and the support staff. Moreover, an unexpected 10-day no flow period did not impact the permeability.
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