When it comes to ceramic membranes for microfiltration projects, the jury is still out — but keeping an open mind. In fact, some membrane technology experts see growing acceptance of ceramics versus polymeric membranes in larger-scale water and wastewater treatment facilities. 

Ceramic membrane filtration is a mild, highly selective process. The medium to be filtered — raw water, for example — flows through the channels of the membrane carrier. Particles are trapped if their size exceeds the radius of the membranes pores, while the filtered material permeates through the pores on its way to continued processing. Polymeric membranes are microporous films, which come in different pore sizes and filter by retaining particles larger than their pore size. They are ideal for both microfiltration (MF) and ultrafiltration (UF) applications. 

Focus on overseas use cited 

Ceramic membranes have been used for roughly 20 years, mostly in smaller-scale industrial projects, including pharmaceuticals, chemicals and food and beverage applications. It’s been only in the past five or six years that people in the United States have started seriously looking at them for water and wastewater treatment; much of their use has been overseas, primarily in Japan. 

“The Japanese started using ceramics in the 1970s when big water regulations first came out,” says Tony Wachinski, senior vice president and technical director of Water Processing at Pall Corporation, which offers a line of ceramic membranes. “With the way the water industry in Japan is structured, they are more likely to use ceramic membranes. This is primarily because of large-scale government funding, which allows companies to move a technology along even though it might not be the most competitive. That’s something we’re not doing here in America yet.” 

Stability, durability seen as major advantages 

Wachinski points to many advantages in using ceramic membranes for water and wastewater treatment versus polymeric membranes. For one thing, ceramic membranes are generally very stable chemically, thermally and mechanically, and are frequently bio inert; no additives are necessary and process temperature is not limited. They’re ideal for removing silt, suspended solids, oil and grease, metal oxides and some dissolved organic matter. For another, they’re highly durable, bacteria resistant and operate effectively even with high flow rates. 

“They’re built like a tank,” says Scott Freeman, membrane technology leader for the global water business of Black & Veatch, of ceramic membranes. “Because they’re so strong, you can clean them with harsher chemicals and backwash them at much higher pressure. Also, unlike at polymeric membrane plants, you don’t have broken fibers to deal with. We’ve heard of ceramic membrane plants that have run for 10 years without any imperfections resulting in leaks. That can happen with a well-designed and properly maintained polymeric membrane plant, but to a lesser extent.” 

In terms of filtration, pore size is essentially the same for both kinds of membranes. With MF or UF filters, whether they’re ceramic or polymeric, it’s a matter of exclusion, filtering out particles that are too big to pass through the pores. Often, that includes Giardia and Cryptosporidium, disease-causing bacteria which are trapped in the submicron pores of the membranes, thereby ensuring clean and safe water. Still, there are 400 to 500 multi-mgd polymeric plants worldwide compared with only about 10 ceramic membrane facilities. Why? 

Higher costs limit widespread use 

Wachinski and Freeman agree the answer is cost. 

“The initial cost of a ceramic membrane plant is much higher than a polymeric plant, and that’s what has limited their use,” says Freeman, whose company, Black & Veatch, has been involved in the design, engineering and construction of municipal water projects for decades. “They also have a shorter installation record, which is an issue for some utilities that don’t want to use something until a lot of other people do.” 

One example of a pioneering effort to develop a larger-scale ceramic membrane project is in Andijk, the Netherlands, an innovative 32 mgd pretreatment plant currently under construction. PWN Technologies, the Dutch company building the facility, has pioneered ways to make the ceramic membranes more cost competitive with polymeric membranes. PWN says the new treatment process not only will produce water of a better quality but will also have a 30 percent less energy consumption and lower environmental load. 

Future bright, if things work well 

What, then, is the future of ceramic membranes? 

With lower-cost products being developed, Freeman is “cautiously optimistic” that ceramic membrane use will grow. In fact, Black & Veatch has done successful piloting of ceramic membranes at a variety of facilities and assisted PWN’s ceramic design for Andijk. 

“If technology breakthroughs bring the cost down and make them competitive, they’ll be a force to reckon with,” adds Wachinski. “And if somebody wants to take the risk and install a large ceramic membrane plant and show that they can work as advertised and last as long as they’re supposed to, then they’ll gain acceptance. Only time will tell.”