What were your first experiences with reverse osmosis membrane technology for drinking water treatment?
In the 1980s, as a doctorial student, I participated in a U.S. Environmental Protection Agency research study on relatively low-pressure nanofiltration membranes. This project was instrumental for the future of low-pressure membranes—it confirmed the technology’s ability to remove disinfection by-products and improve the quality of water that is high in color, dissolved organic carbon, and hardness.
My first significant nanofiltration membrane projects with CDM Smith were in Southeast Florida. The technology was a breakthrough for this area, where utilities struggled with removing color from the water. We designed a 40-million-gallon-per-day nanofiltration plant in Boca Raton, which is the largest facility to combine nanofiltration with traditional lime softening. In Palm Beach County, we implemented CDM Smith’s first standalone low-pressure nanofiltration treatment plant. These projects established our expertise concerning technical and cost issues relating to foulant identification, fouling control, process performance, design issues, and cost optimization.
Over the years, what have you learned about membrane technology?
It comes down to research and pilot testing. CDM Smith is heavily invested in understanding how to maximize membrane performance. Early on, we realized the importance of pretreatment to reduce fouling potential. Now we are skilled at taking a raw water supply and using pretreatment and post-treatment to optimize membrane efficiency—from process and cost perspectives.
Concentrate disposal in inland areas presents challenges for membrane treatment facilities. We use deep well injection when possible, but have to be creative when this is not an option. In Ormond Beach, Florida, membrane concentrate is mixed with wastewater effluent to greatly expand the reuse water supply. We are also studying the beneficial use of salts recovered from concentrate, zero liquid discharge techniques, and a patented very high membrane product water recovery technology to minimize the need for concentrate disposal.
What’s in the future for CDM Smith and membrane drinking water treatment?
We are taking what we have learned in the United States and applying that knowledge to projects in the Middle East, North Africa, and Southeast Asia—where there are similar water challenges. Membrane treatment will drive the creation of alternative water supplies in arid areas that have degraded or limited supplies and become crucial to indirect potable reuse projects globally.
In coming years, we will see membranes used increasingly for the treatment of highly mineralized groundwater, as well as for indirect potable reuse using under-utilized wastewater effluents. Also, the treatment technology itself will be transforming. We will be practicing techniques including membrane distillation, carbon nanotube distillation, and forward osmosis—which uses osmotic pressure to separate feed water from its solutes, rather than hydraulic pressure, as used in reverse osmosis. Forward osmosis will require less energy, remove more contaminants, and will be less prone to fouling than reverse osmosis.
Why are you excited to be in this field?
Membrane technology can essentially turn any water source into a clean, safe supply. This allows us to provide potable water—the most basic human need—to all areas of the world. And, the technology provides the challenges and opportunities that my colleagues and I thrive on. We are removing contaminants at the atomic level, making this technology useful for all types of constituents. It reduces chemical needs, provides an absolute barrier to pathogens and toxins, and makes subsequent treatment easier.
CDM Smith is staying at the forefront of research, leveraging young minds and cutting edge experts to discover new membrane applications. It is extremely rewarding to use an advanced technology to help clients all over the world solve their water treatment challenges, in economical and energy-efficient ways.
Don Thompson, Ph.D., PE, is a senior vice president at CDM Smith. He is an environmental engineer with more than 30 years of experience in water and wastewater treatment process and design, with a focus on membrane technologies.