The Southern Ontario Water Consortium’s (SOWC) cutting-edge equipment is enabling a group of top water experts at the University of Waterloo to conduct innovative research aimed at improving how we clean our drinking water.
Professor Peter Huck, the Natural Sciences and Engineering Research Council of Canada (NSERC) Industrial Research Chair holder in water treatment, and his team of researchers are investigating ways to optimize the use of membranes in drinking water filtration.
“Membranes are increasingly used in upgrading conventional plants or constructing new ones throughout the world and they are becoming more popular here,” says Huck. “Recent refinements in materials and improvements in energy efficient modes of operating these systems have made them cost competitive compared to conventional water treatment technologies.”
In some cases, membranes can also be less complex to operate and use less space and chemicals compared to conventional treatment processes, adds Huck.
“In order to advance this technology, we are interested in solving problems associated with membrane operations in a sustainable way,” says Huck. “The SOWC equipment has greatly enhanced what we could do with membranes.”
With the help of SOWC’s unique mobile membrane pilot plants and high-tech lab equipment, the group of about 20 researchers is working towards using biofiltration as a pretreatment to membranes in municipal drinking water treatment plants.
Membranes are sheets with tiny holes or pores that can range in size which, when appropriately selected, target the removal of various types of contaminants. They are classified based on pore size and the smaller the pore, the more energy is required to push or pull water through it. In the treatment of drinking water, reverse osmosis, which uses the smallest pore size, leaves behind virtually all but the smallest molecules, however requires the greatest amount of energy. One of the main problems with using membrane filtration for this process is that the holes in the membrane can get plugged.
As the water is filtered, the membrane plugs up, or fouls, with larger particles and organics as well as inorganics, in the case of reverse osmosis, that are naturally present in the source water. The membrane is regularly flushed by reversing the flow to remove many of these foulants that can cause plugging, but some still stick to the membrane.
When a membrane gets plugged up, water passing through it slows down and the water pressure must be increased to maintain the same flow. There are different chemical cleaning strategies that can be done to completely clear the membrane of foulants, but they require taking the membranes out of service so the cleaning agents don’t get into the drinking water. This process must then be followed by flushing the membrane to remove the cleaning agents before placing the membrane back into service for drinking water production. It can be a costly and time-consuming process.
Cleaning can also damage the membrane over time requiring them to be replaced more regularly, says Sigrid Peldszus, research associate professor with the NSERC Chair research team.
“Ultimately, it is beneficial to remove the foulants that stick to the membrane before they reach the membrane so that the membrane plants can run more efficiently in terms of energy consumption and cost.”
The research team is testing the effectiveness of removing the foulants using biofiltration. Biofiltration is a technique that uses living bacteria to biologically degrade organics. A biofilter is a basin or concrete tank typically containing sand, anthracite, granular activated carbon, or some combination of these. As bacteria normally present in the water pass through the biofilter, they attach to the sand or other filter media and once a population of bacteria has accumulated, the biofilter begins to function as a pretreatment process.
“The water flows through and the bacteria growing in the biofilter consume the organics coming in with the water,” says Peldszus. “The filters also remove larger particles that can plug up the membrane. This is a novel process that is not normally used with membranes so we are testing the effectiveness of this type of pretreatment.”
Biofiltration is an ideal way of removing the foulants from the water before it reaches the membrane because it does not require any chemicals, adds Peldszus.
“Membranes currently employed in drinking water treatment plants use the addition of chemicals to form flocs to pretreat the water. Since biofiltration does not involve the addition of these chemicals, it is a more sustainable process.”
SOWC’s mobile membrane pilot plants are key components to this research project. The NSERC team has 18 municipal partners and because the equipment is skid-mounted and can be transported to field sites, the researchers are able to test membranes at actual municipal treatment plants.
“It is extremely beneficial to be able to bring the testing equipment to the plants,” says Peldszus. “We need to work with the same water the utility gets so we can determine how this method will work in the real world.”
The mobility of the membrane pilot plants also allows the researchers to work with existing plants looking to improve their current membrane filtration systems, she adds.
“Just like industry, municipalities have to be efficient and produce drinking water cost-effectively,” she says. “The key to working with plants is that we can go to them and be in their environment. We can do trial tests and simulate different cleaning regimes to see how effective they are without disrupting the operations of the plant.”
The mobile membrane pilot plants have parallel treatment trains that can employ up to three different types of membranes including microfiltration, ultrafiltration and nanofiltration, to either mimic current treatment practice or evaluate new technologies or designs.
“Having two sets of membranes allows us to have a control stream,” says Peldszus. “We keep the conditions the same on the one side and change the conditions on the other side. It’s important to have a control stream because the quality of the water coming into the utility plant can change quickly.”
“We vary the treatment by testing different types of membranes with different biofilter parameters such as changing the filter depth or the amount of time the water has contact with the biofilter. Essentially we are testing for ways to advance the treatment process.”
Another key component to the group’s research is the ability to analyze the results of the various performance tests conducted with the mobilemembrane pilot plant, and this is where the SOWC’s lab equipment comes in. Set up at the University of Waterloo, the lab equipment entails a total organic carbon (TOC) analyzer, UV VIS spectrophotometer, fluorescence spectrophotometer, biological monitoring equipment, and liquid chromatography – organic carbon detection (LC-OCD) technology.
The lab’s LC-OCD technology in particular has provided the researchers with the ability to examine the TOC constituents in water in greater detail. This piece of equipment, which is one of only two in North America, can separate the organic molecules in the water by size and then measure them using an ultraviolet detector, organic carbon detector and a nitrogen organic detector.
In examining the effectiveness of using a biofilter as a pretreatment to membrane filtration, the LC-OCD can be used to measure the amount and type of foulants that are being removed by the biofilter. Having the ability to measure the amount of each class of foulant enables the researchers to determine which treatment process parameters lead to the most efficient filtration process.
The NSERC Industrial Research Chair in Water Treatment group has been working on this project for several years. So far they have demonstrated at bench- and at pilot-scale that biofiltration protects the membrane by removing these foulants before they reach the membrane. The next step is to prove the effectiveness of biofiltration as a pretreatment process on a large scale.
“The equipment provided by SOWC has not only made this research possible, but it is helping us to advance our projects beyond what we had planned. We are pleased SOWC fits in so well with what we are doing.”
In addition to Drs. Huck and Peldszus, other senior members of the NSERC Industrial Research Chair in Water Treatment team are Drs. Michele Van Dyke and Bill Anderson, and Dana Herriman.