Ceramic Membrane Pilot Plant for Drinking Water Treatment

Emma Cross, Andreas Fischer, Louis Ortenzio (Lutra)

Together with Waipā District Council, Lutra operated a 3,600 Liters per hour silicon carbide (SiC) ceramic membrane pilot plant for several months at one of their river source water treatment plants drawing from the Waikato River. The objective was to gather in-situ operational and performance data, such as sustainable flux rates (L/m2 /h) and trans-membrane pressure (TMP) development, specific fluxes (L/m2 /h/bar), water efficiency (fraction treated of total volume abstracted), cleaning chemicals consumption, as well as general operational experience. 

Ceramic membranes are used for liquid/solids separation in water treatment processes. Typical ceramic membranes manufacturing materials include alumina, silica, titania, and zirconia. While some characteristics between materials differ, in general ceramic membranes offer several benefits compared to polymeric membranes. These include higher flux rates (L/m2 /h, or LMH), pH resistance, temperature resistance, chemical resistance, oil resistance, and longer service life. 

The higher flux rates of ceramic membranes (L/m2 /h) result in less membrane area (m2) required for the same flow (L/h). Where polymeric membranes may need frequent replacements of individual membrane units due to failure, ceramic membranes are much more durable. Their general resistance allows for more thorough and frequent cleaning and restoring the membranes to original performance. The principal downside is that ceramic membranes are more expensive than polymeric membranes. However, the higher flux rates and increased durability makes ceramic membranes likely an economically viable option, based on whole-of-life costs.

Ceramic membranes are used widely in industrial wastewater applications due to their resistance and durability. In drinking water treatment, their use is more prevalent in Asia (e.g., Japan, China, Singapore), but installations are increasing globally. There is widespread interest and research into drinking water applications, and manufacturing costs are decreasing.

The trial results can be summarized as below:
▪ The ceramic membranes were able to meet the turbidity requirements of the Drinking Water Quality Assurance Rules (DWQAR).
▪ The membranes proved resilient and were restored to original performance multiple times despite heavy buildup of sludge in the filtration tank.
▪ The sustainable flux rates during the trial were found to be 200 LMH and up to 220 LMH. Bench-scale results with actual raw water from the membrane supplier indicated even higher sustainable flux rates of 250 LMH and more.
▪ The trial results indicate that pre-treatment plays a significant role in achieving optimum performance, similar to polymeric membranes. The pilot plant received pre-dosed water, with reliance on in-line mixing and flocculation. We expect that with a dedicated pre-treatment infrastructure (such as a rapid mix and flocculation tank, pH and possibly ORP correction), the performance of the ceramic membrane system will increase.
▪ To mitigate the performance risks, the supplier of a ceramic membrane system should be responsible to ensure adequate pre-treatment to their specifications and provide performance guarantees. 

In conclusion, we found that ceramic membranes are a viable alternative to polymeric membrane systems for drinking water treatment.