Worldwide water scarcity, combined with an increase in population growth, is leading to the realization that water production and reuse must become more efficient. Industries that use large amounts of water, including food and energy, are increasingly on the lookout for sustainable filtration solutions that improve industrial water reuse efficiencies.
While the vast majority of applications use either polymer or ceramic tubular membranes, new high quality porous ceramic membranes are being developed as part of an innovative filtration system with the aim of improving filtration efficiency, reducing the amount of maintenance downtime and decreasing energy usage. These operational benefits can also result in reduced operating costs.
Filtration system basics
Polymer or ceramic tubular membranes are currently used to clean, conserve and reuse water in a variety of industrial and communal wastewater applications, including wastewater plants, buildings and even cruise ships. Currently, polymer membranes account for around 75 percent of the membrane filtration market, with ceramics accounting for the majority of the remaining 25 percent, along with a small number of other materials such as metallic membranes making up the rest. Figure 1 illustrates the variety of filtration separation processes available and provides an overview of their use in particular applications.
The use of ceramic membranes is common in dairy production and they are widely used for fruit juice clarification, whereas polymers currently dominate the wastewater treatment sector.
Due to their lower purchase price, systems using polymer membranes are widespread in the wastewater filtration market. However, while polymer membranes are cheaper to manufacture than their ceramic equivalents, polymer systems require more frequent filter replacements.
The low resistance properties of polymer membranes, compared to ceramic, limit the number of applications in which they can be used. In general, the ceramic membrane system filtration module housing, which is often metallic, sets the limitations for processing aggressive media, rather than the filter itself. Inversely, when polymer membranes are used in harsh environments, the filter material will wear first. In addition, the flow rate through ceramic membranes can be greater than through polymer membranes for a given pore diameter. A ceramic filtration unit also requires a lower pressure (and less energy) to circulate fluid.
As water reuse becomes a more important issue, some extremely demanding industrial applications are faced with the need to filtrate increasing challenging media. Due to the ceramic materials’ superior chemical resistance, and resistance to abrasion, their use is preferred over polymer membranes for some applications. An example is the separation of oil, water and sand in the oil industry, a process that is both chemically aggressive and abrasive.
While ceramics can withstand pH values ranging from 0 to 14, polymer membranes can withstand a much narrower pH range. They can be tailored to resist neutral, acid or basic pHs, but generally not all three ranges with the same material. Ceramic membranes are also better for high temperature applications. They can be sterilized or steam-cleaned for specific applications, such as in the medical industry, something not possible with polymers.
Moreover, ceramic has more strength and rigidity, giving it better dimensional stability under pressure than polymer. In the filtration of water containing oils or fatty acids, for example surfactant, emulsion-breaking chemical dispersants are often required to limit the formation of an organic fouling layer on the surface of polymer membranes. High quality ceramic membranes have been found to be more resistant to fouling without the need for dispersant additives.
While fouling of both ceramics and polymers is inevitable, ceramics can enable a wider range of options when it comes to systems with a Clean-In-Place (CIP) process. In some applications, membranes have to be cleaned with harsh chemicals and be able to withstand high pressure from two directions. This is especially necessary during back-flushing to prevent the formation of a fouling layer onto the membrane’s surface or in the pores, leading to a reduction in the membrane’s filtration capability.
For example, peroxide chemical cleaners or high temperature steam cleaning is acceptable for ceramics, but can be an issue for polymers. A combusting high temperature air cleaning treatment can be used for ceramics, but would be likely to melt a polymer membrane. CIP operations can be performed automatically without interrupting the filtration process when ceramic membranes are used, but this is more difficult with polymeric membranes.
At the same time as industries are adopting water reuse and conservation methods, they are trying to reduce the footprint of such activities on their facilities. Membrane selection and design plays a part in reducing the facility footprint in the businesses or communal buildings using these systems. Newly developed ceramic membranes can achieve a great compactness (increased surface area of membrane per volume unit) due to the versatility of their design and geometry. Compactness and improved design of ceramic filtration modules also contributes in increasing the energy efficiency of such systems.
Improving water reuse efficiency now a key global issue
Energy and water are inextricably related. Energy is required for producing water (for extraction, treatment and transportation), and water is required for producing energy (hydropower, steam to turn turbines or as coolants in industrial processes). Producing the energy needed to produce water and vice versa is already becoming a key issue worldwide. Fossil fuel shortages and water demand will also increase due to population increases, energy demand and effects of climate change.
As a result of pressures from an increase in water demand, there is now a greater likelihood that manufacturing plants and industries that use large amounts of water in their processes will be faced with legislation that charges them for both withdrawal and discharge of water.
In the future, businesses are likely to adapt by developing their own water filtration systems; this might even include the use of modular or local filtration systems rather than sending wastewater to a central system. And, such filtration systems will need more sustainable membranes. What this means is that innovations to increase efficiency are needed, and will be scrutinized more closely in the near future.
According to Global Water Intelligence, scarcity is driving water reuse policies. In China, agricultural use of water has been reduced from 86 percent in 1980 to 65 percent in 2005 — it is targeted to be 50 percent in 2050. Population growth and economic factors as well as the physical scarcity of water have driven China’s water treatment and reuse efforts. China’s target is to increase water reuse from its current 14 to 25 percent by 2015. Other examples include Saudi Arabia, whose goal is to increase water reuse from 11 to 65 percent by 2016, and Spain, which aims to increase water reuse from 11 to 40 percent by 2015.
Government intervention will become more prevalent as the need for drinking water increases pressures for industrial water reuse. For example, the state government in São Paulo, Brazil has introduced initiatives to protect drinking water for the region’s inhabitants, issuing regulations to restrict the industrial use of potable water. This is forcing businesses to look for ways to reuse their wastewater or obtain recycled water from another source. Filtration facilities have already been proposed and built to meet São Paulo’s water needs. In Japan, an early adopter of water reuse strategies, there are currently more than 90 ceramic membrane water filtration plants.
In the U.S., treated water reuse is currently at about 11 percent. No official targets have been set, but the National Resources Defence Council (NRDC) states that 10 of the U.S.’s largest cities are in severe danger of water shortages in the relatively near future. The top three listed are: Los Angeles, California, which imports water from Colorado; Houston, Texas, located in a high drought area; and San Antonio, Texas, identified by the NRDC as having a non-sustainable water supply. There is a great probability that regulations will eventually be imposed to respond to these shortages.
To address specific areas, several U.S. pilot plants are using ceramic membranes with ultrafiltration for industrial water reuse. A pilot ceramic membrane treatment system was developed by the Parker Water and Sanitation District (PWSD) for one of its water treatment plants, which treats water from the local reservoir. Since 2011, the plant has helped address the area’s long-term water shortage problems; the water is used by residents for everyday water needs to replenish the underground aquifer and as a reserve for better water management during a drought.
Sustainable solutions for industrial water reuse
In response to these trends, new ceramic water filtration and purification membranes are being developed for use in an innovative filtration system for industrial waste treatment processes. These systems will be more energy efficient to clean and circulate fluid than conventional systems with ceramic tubular membranes. The reliability of the high quality ceramic membranes being developed will enable businesses to reduce maintenance and energy usage and make associated cost savings.
These membranes are robust and offer high performance in high temperature environments, in the presence of harsh cleaning chemicals or where chemically aggressive or high viscosity fluids need filtering. They can withstand the harsh environments found in wastewater treatment facilities and do not need replacement as frequently as many plastic alternatives.
Moreover, the ceramic membranes can be manufactured to highly complex geometries and tight tolerances, facilitating more flexible innovative designs that make filtration modules more energy efficient. This means that businesses can save energy and costs associated with pumping water through the filtration system. Sustainability is becoming increasingly important in businesses and the environmental benefits of water filtration are well recognized. New ceramic water filtration membranes aim to help businesses operate more efficiently, save money and conserve water.
Morgan Technical Ceramics manufactures components and sub-assemblies using an extensive range of materials, including structural and piezoelectric ceramics, dielectrics, braze alloys and specialist coatings. It works with manufacturers’ design and R&D teams at local, national and international levels on projects from concept and feasibility studies through prototype development to full production. The business employs some 2,500 people and has 23 manufacturing sites worldwide across Europe, the U.S., Mexico, China and Australia.
