Membrane aging in water treatment plants

Membrane filtration is a rapidly expanding option for drinking water treatment. Unfortunately, as membranes age, there is limited data on long-term changes in membrane performance. This study investigated the changes in performance factors and chemical properties of hollow fiber ultrafiltration membranes in eight large drinking water treatment plants.

Plant operators regularly harvest the membrane and perform analysis using standardized laboratory tests. About half of the membranes are new PVDF-based chemicals. Since the start of the run, it has been observed that these have no significant changes in performance factors and chemical properties. However, since these membranes are relatively new, only the data for the first 5 years of operation is provided.

The other half of the membrane was observed to have older PVDF-based chemistries until its behavior was stable after approximately 5 years of operation. Thereafter, the performance factors and chemical properties of the film began to change significantly. For these membranes, the water-resistance and fouling rate were improved after 5 years of operation. The mechanical properties of these films also deteriorated after 5 years of operation, indicating that they are more susceptible to cracking after prolonged use. These changes in performance factors are parallel to, and possibly caused by, the removal of hydrophilic additives from the membrane material.

Clean water resistance was identified as a good benchmark for all study parameters, and this finding is useful for water treatment facilities to quickly assess the state of their membranes. Finally, although the cumulative exposure dose (C*t) was not used as an indicator of age, we observed that when higher doses of hypochlorite were used, all indicators changed faster than surgery alone. expected. Therefore, limiting the size of the cumulative hypochlorite dose is critical to controlling membrane deterioration.

This study reveals the knowledge gap between bench-scale aging research and operational water treatment plants.

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