CM-131 – Pretreat Less and Recover More

Background
Ceramic membranes are widely recognized to be more robust than polymeric membranes. Chemical resistance, temperature stability, mechanical strength and the inherently higher flux rates of ceramics all contribute to significant performance benefits. Combined with the polymeric cost parity offered by Nanostone’s innovative CM-131TM UF module, ceramics are now a viable option in mainstream water treatment applications.

FIGURE 1 - Nanostone CM-131 Membrane Module End View

Another key attribute of Nanostone’s ceramic membrane is it’s ability to achieve higher recovery rates. There are three reasons contributing to the CM-131 module’s ability to operate at elevated recovery rates compared to conventional polymeric UF membranes:

Hydrophilicity and Fouling Resistance
of the ceramic membranes, each filtration cycle can be extended, affording higher solids levels to accumulate on the membrane surface. Secondly, the higher pressure limits afforded by ceramics allow for more aggressive hydraulic cleaning methods with higher pressures and flow rates over shorter durations. Nanostone’s CM-131 module is rated up to 150 psi ( 10 bar). Lastly, the inherent higher chemical resistance of ceramics enables a wide range of chemical cleaning routines to ensure stable permeability. With a much wider operating envelope and more aggressive cleaning options, recovery rates of up to 99% have been observed in some cases.

FIGURE 2 - Nanostone CM-131 Module Profile

Dollars & Cents of Water Recovery
comparative evaluation of Nanostone’s CM-131 UF ceramic membrane and an existing polymeric UF system installed at an industrial waste water reuse facility. In effort to accommodate fluctuations in water quality resulting in periods of high suspended solids loading, the polymeric UF system is operated at an average recovery rate of 90%. Applying the same feed water to a pilot system with Nanostone’s CM- 131 membranes, a sustained recovery rate of 97% was observed. Table 2 reports the annual water cost savings realized with the ceramic UF considering the facility’s cost of source water and the 7% improvement in ceramic UF recovery compared to the polymeric UF.

As shown in Table 2, even a modest improvement in recovery translates to savings of nearly $70,000 and more that 40 million gallons less water consumed every year. Additional operating costs efficiencies afforded by the high recovery include reduction in waste water discharge costs.

Why Does My Pretreatment System Need Pretreatment?
A common tenant amongst water treatment engineers states that one of the keys to a successfully operating water treatment plant is proper pretreatment of critical processes. In fact, the root cause of poorly performing ultrafiltration, ion-exchange and reverse osmosis systems is often traced to inadequately designed or operated pretreatment processes. It is quite common for reverse osmosis to be pretreated with UF, and UF to be pretreated with a clarifier and multi-media filtration. Historically, the practice of pretreating polymeric UF membrane has been driven by TSS / turbidity limitations that are typically less than 100 NTU.

The inherent robustness of ceramic UF membranes offers much higher TSS tolerance and can often be operated without the pretreatment steps required with polymeric UF membranes. Given the water losses associated with each step of the process, early pretreatment steps need to be designed for significantly more throughput than the overall system. Consequently, elimination of UF pretreatment can result in substantial CAPEX and OPEX savings with significant reduction of the system footprint.

The example below compares the capital cost and water recovery impact of the pretreatment steps required by polymeric and ceramic UF systems in a typical industrial wastewater reuse system.

The less costly clarification system combined with the elimination of the multi-media filtration results in a CAPEX reduction of nearly 8% when using Nanostone’s CM-131 ceramic UF.