From Primary Treatment to Discharge
CPVC pipe proves effective in lowering total cost of ownership
Water and wastewater infrastructure in the U.S. continues to deteriorate as repairs stay on the back burner due to economic uncertainty and lack of funds. To address costly repairs, engineers and end users must think beyond what was good enough in the past and adopt innovative technologies that offer more economical installation, higher durability and reduced total lifecycle costs.
Carbon steel and stainless steel have traditionally been the go-to piping materials for water and wastewater applications due to their perceived strength. After years of field use, however, issues with corrosion, pitting, scaling and gradual pressure loss are leading to extensive repair costs for underfunded facilities.
As a result, chlorinated polyvinyl chloride (CPVC) is emerging as a material of choice for pipe and fittings in water and wastewater applications, with an increasing number of engineers adding it to their in-house specs. They are finding that CPVC not only is resistant to microbes and chemicals used in treatment processes, but it also boasts lower installation costs and durability and pressure ratings that do not diminish over time—providing a lower total cost of ownership.
With its corrosion resistance, CPVC has proven to be reliable in primary, secondary and advanced wastewater treatment, as well as in ancillary equipment, scrubbers, desalination processes, dual-containment applications, and water treatment and distribution. Because of its versatility, CPVC offers efficiencies in inventory control, because only one material needs to be stocked for a wide array of uses.
CPVC in Primary Treatment
CPVC can be used throughout the primary treatment process as effluent utility piping and also to connect treatment stations, including bar screens, scum/grit removal, filtering equipment, anaerobic digesters and chemical addition tanks. At this point, piping may be exposed to the harshness of microorganisms, ferrous chloride, alum, alkaline lime slurry and other clarifying and thickening chemicals.
With some piping, these corrosives will gradually impact the integrity of the system, whereas CPVC will continue to perform. For example, 316 stainless steel has a Hazen Williams C-factor of 120 when it is new. The Hazen Williams C-factor represents the interior smoothness of the pipe—the higher the C-factor, the smoother the pipe. Over time, pitting and scaling will cause the pipe’s interior to become less smooth, reducing the C-factor and increasing the pressure loss as liquid flows through the system. When this happens, facilities often must install larger pumps—and use more energy—to achieve the needed output of treated water.
On the other hand, CPVC starts with a C-factor of 150 and maintains that interior surface smoothness throughout its life by resisting the effects of corrosives found in the wastewater treatment process. This leads to greater efficiency and reduced costs to facilities, because smaller pipes, smaller pumps and less energy can be used to move fluids at the same rate. This is true in primary treatment and at every subsequent stage in the treatment process.
CPVC in Secondary Treatment
In secondary wastewater treatment processes, piping is exposed to high concentrations of microorganisms when excessive biological growth washes out and collects in a clarifier. Byproducts of these microbes, including acids such as hydrogen sulfide, along with disinfectants and dechlorination chemicals, contribute to the corrosion of some piping systems.
CPVC’s corrosion resistance makes it ideal for everything from carrying concentrated acids and caustics used in pH control, to carrying sludge and chemically treated water through aeration and filter equipment, to sodium hypochlorite feed and generation piping.
CPVC in Advanced Treatment
As in the preceding processes, CPVC piping meets the demands of advanced treatment by performing reliably even in cooling tower applications and when handling the nominal concentrations of methanol used in biological denitrification. CPVC pipe is pressure rated at operating temperatures up to 200°F. The high temperature and corrosion-resistant properties of CPVC make it an ideal material in advanced treatment for carrying treated water and chemicals through phosphorus removal, nitrogen removal, filtration and chlorine disinfection.
Additionally, CPVC’s inherent abrasion resistance, resistance to corrosive soil conditions and ease of installation make it ideally suited for situations when dual-containment piping is required for carrying chemicals, including sodium hypochlorite and sodium hydroxide.
Because a large amount of piping in a treatment facility can be installed outdoors, the effect of direct sunlight on the material must be taken into account.
Direct sunlight causes degradation to many nonmetallic piping systems. Gray CPVC, however, contains ultraviolet (UV)-protective levels of both carbon black and titanium dioxide (TiO2). Both carbon black and TiO2 are widely recognized as UV blocking agents that help protect the polymer backbone from the effects of UV radiation.
The combination of ambient temperatures and radiant solar heat can raise the surface temperature of piping materials to levels that exceed the limits of the materials.
Other CPVC Uses
With today’s long list of odor control mandates, CPVC is a proven material used in both the traditional wastewater applications mentioned above and in scrubbers and ancillary equipment. Whether a plant is using sodium hydroxide and sodium hypochlorite in its wet air scrubbers at temperatures as high as 200°F, or using metal chelating agents in a liquid redox process, advanced CPVC offers the chemical resistance and superior high temperature performance that wastewater odor control processes require.
Further, in desalination applications, CPVC can handle the chemical feeds for reverse osmosis processes. Because it is not susceptible to corrosion from high chloride levels, there is no need to pickle or passivate the piping system or provide expensive cathodic protection against corrosion—reducing the cost and complexity of installation.
Not All CPVC Is Equivalent
Considering the aforementioned benefits of CPVC piping systems, budget-strapped water treatment facilities are turning to this material for improved reliability, lower installation costs and lower lifecycle costs. But buyer beware: Not all CPVC is the same. To gain maximum benefits, look for CPVC pipe and fittings that exhibit:
• The highest drop impact strength—some systems are up to three times stronger than competitive systems;
• The highest heat deflection temperature, especially in outdoor installations where surface temperatures might go above the system’s maximum rated temperature;
• Excellent creep resistance and ability to withstand long-term pressure at high temperatures; and
• NSF Intl. approvals for potable water.
Even when budgets are a concern, the right CPVC pipe and fitting supplier can help users design an entire system or retrofit solution that will stand up to the high demands of the wastewater treatment process—and help users reduce their maintenance costs in the long run.
http://www.wwdmag.com/sites/default/files/imagecache/article_slider_big/Image_2.jpgCPVC is a material that can be installed in a variety of applications.
http://www.wwdmag.com/sites/default/files/imagecache/article_slider_big/Image_3.jpgCPVC piping resists corrosion when carrying acids and chemically treated water.