Drought conditions, rising water costs and effluent restrictions are forcing plant operators to consider more sustainable technologies for treating facility water. In the case of cooling water treatment, chemical solutions have traditionally been used to control scale, corrosion and bacteria. But a number of non-chemical solutions have emerged as viable alternatives.
The role of chemicals in water treatment is to impart energy into the water to induce a change in the water’s chemistry. This chemical energy can be replaced by other sources that create different, but equally useful, reactions. For example, chemicals keep solids dissolved in solution until saturation occurs, at which point they are purged from the system. On the other hand, some non-chemical technologies cause the scale particles to drop from the solution, allowing them to be filtered from the water.
Processes using magnetic fields, AC induction, electric fields or pulses, ultrasonic waves and ultraviolet disinfection are available to address various water treatment issues, each of which has had varying levels of success. In recent years, a new non-chemical technique has emerged, capable of performing a robust set of water purification tasks while being cost-effective and environmentally friendly.
Controlled hydrodynamic cavitation (CHC) sounds impressive, and it is. Cavitation is the process of forming microscopic bubbles in a fluid, which expand and then collapse, creating extremely high temperatures, light and intense pressure waves. VRTX is harnessing the energy produced in the cavitation process to treat water in an environmentally friendly, chemical-free manner.
The company has developed a chamber that induces cavitation by forcing streams of water to collide at high velocity. The streams collide at the mid-point of the chamber, creating high-shear forces and a region of near total vacuum. These conditions result in hydrodynamic cavitation and cause the calcium carbonate scale in the water to form a precipitate, which can then be filtered out. The rapid change in pressure ruptures the cell walls of bacteria and the vacuum degasses the water, reducing CO2 levels and buffering pH to a non-corrosive level.
Case studies performed by VRTX have determined that the cycles of concentration—the number of times the solids in a particular volume of water are concentrated—can dramatically increase when CHC is used in place of chemical treatments, resulting in substantial water savings. Also, if chemicals are not used, the blowdown can be reused for non-potable applications such as landscaping.
Electric pulse systems are the biggest non-chemical competitor for CHC technology due to their effectiveness in smaller systems with softer water, but as systems increase in size, the pulse has difficulty transmitting efficiently through thicker circulation line piping. Systems that use mechanical energy—such as CHC—can be scaled up without diminishing performance.
According to VRTX’s CEO David Nicholas, cavitation technology has its challenges, but holds a lot of potential. “There is a reluctance for customers and traditional chemical treatment companies to use new technologies. The failure of a few led to a tarnished view of non-chemical water treatment devices. But cavitation technology is a relatively under-developed science. I believe that the key will be to create controlled cavitation in a non-destructive manner for a variety of treatment applications.”
New applications currently being researched by VRTX include the treatment of sludge to reduce solids disposal in wastewater treatment plants, the destruction of organics in contaminated groundwater and enhancing yield in biodiesel plants.
Revenue Streams Removing phosphorus from water is a basic function of wastewater treatment plants, but American Water has figured out a cost-effective way to turn the phosphorous into fertilizer, which can then be sold. In what sounds like a relatively simple process, magnesium is added to phosphorous-rich water to produce struvite, a commercial fertilizer.
Dr Yanjin Liu, an environmental engineer at American Water, sees wastewater as a commodity of the future. “People will think of wastewater as a kind of natural resource, like oil and gas. Wastewater treatment technologies will become highly advanced and the operation will be highly automated in a cost-effective manner. The final products, treated water and recovered nutrients and energy, will be clean and ready to use for various purposes.”