Nanostone Membrane Matters 154 - Nanostone CM-151* - Pretreat Less and Recover More

Nanostone Membrane Matters 154 - Nanostone CM-151* - Pretreat Less and Recover More

Nanostone CM-151* - 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-151* UF module, ceramics are now a viable option in mainstream water treatment applications.

Figure 1: Nanostone CM-151* 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-151* module’s ability to operate at elevated recovery rates compared to conventional polymeric UF membranes:

Table 1: Key Reasons for Higher Recovery Rate

Three Key Reasons For Higher Recovery Rates
  • Higher total suspended solids tolerance
  • Higher pressure limits
  • Higher chemical resistance

Hydrophilicity and Fouling Resistance HYDROPHILIICITY and FOULING RESISTANCE

With the higher total suspended solids (TSS) tolerance 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-151* module is rated up to 100 psi ( 7 bar) of transmembrane pressure. 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-151* Module Profile

DOLLARS & CENTS of WATER RECOVERY

The higher ceramic recovery was validated in a comparative evaluation of Nanostone’s CM-151* 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-151* 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.

Table 2: Cost of Water vs. UF Recovery Rate

Flow (GPD, m3/hr) 2.3 MGD, 363 m3/hr
UF Recovery % 90% 97%
RO Recovery % 75% 75%
Overall Recovery % 68% 73%
Source Water Cost $1.58 USD / 1,000 Gal $0.42 USD / m3,
Annualized Water Costs $431, 130 USD $361,467 USD
Annual Water Consumption 273M Gal / Yr. 103M m3 / Yr. 229M Gal / Yr. 0.87M m3 / Yr.
Savings x 44M Gal. / Yr.17M m3 / Yr. $69,643 USD / Yr.

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 PRETREAMENT SYSTEM NEED PRETREATMENT?

A common tenet 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.

Table 3: Water Treatment Process Steps

Large Clarifier Small Clarifier
Multi-Media Filtration
polimetric Ultrafiltration Ceramic Ultrafiltration
Reverse Osmosis Reverse Osmosis

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.

Table 4: Pretreatment Recovery and Cost Analysis

MMF Recovery %
UF Recovery %
Overall Pretreatment Recovery %
95%
95%
90%
N/A
95%
95%
Specific Capital Cost Clarifier, MMF, UF $0.53 USD/GPD $0.49 USD/GPD

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-151* ceramic UF.

References