In an effort to provide safer drinking water for customers and keep a step ahead of inevitable future compliance regulations, the Johnston County Water Treatment Plant (JCWTP) in North Carolina took a proactive stance and initiated a completely new state-of-the-art treatment process aimed at reducing total organic carbon (TOC). The new facility included an ion exchange process, PVC piping, pneumatically actuated valves and conductivity instrumentation, as well as a host of pumps, tanks and compressors.
JCWTP treats surface water from the Neuse River to provide drinking water to its customers. The treatment facility and intake are both located on the south bank of the Neuse River about one mile east of Wilson’s Mills, N.C., providing drinking water to Johnston County. The plant operates at 8.5 to 10 million gal per day (mgd) with a capacity of 12 mgd; it serves about 30,000 retail customers, including local industry, and provides primary or bulk water service to most towns within the county and two private water providers.
DOC Levels
Dissolved organic carbon (DOC) comes from natural organic matter that is found in potable water sources and is part of the TOC content in raw water. Maintaining an acceptable level of DOC in potable water is important to ensure safe drinking water and keep in compliance with federally mandated disinfection byproduct (DBP) regulations. Because DOC contributes to the formation of DBPs, managing a proper DOC level has become an ongoing challenge for water treatment plants.
To better meet this challenge, the JCWTP installed an ion exchange raw water pretreatment system that removes DOC prior to coagulation and conventional water treatment processes in the plant. The system uses a fluidized bed ion exchange reactor to remove DOC while allowing turbidity to pass through the reactor for downstream removal. A resin, designed specifically for the ion exchange process, is removed from the reactor for regeneration and is replaced by regenerated resin to remove DOC.
To integrate the system into the plant, a vertical pipe and valve network array was provided on a skid approximately 35 ft long and 15 ft high using PVC pipe, fittings and valves from GF Piping Systems (Irvine, Calif.). The piping system included approximately 25 Type 546 and Type 233 series manual and pneumatic actuated ball valves ranging in size from ½ to 2 in., and another 15 Type 567 and Type 240 series manual and pneumatic actuated butterfly valves ranging in size from 3 to 6 in.
The valves are responsible for directing water with spent resin and with regenerated resin throughout the ion exchange system. The raw water coming into the system and treated water going out—and the many process steps in between—are controlled by the pipe and valve system.
All of the actuated valves were equipped with pneumatic actuators and limit switches to achieve a fully automated system that could be remotely operated. This is accomplished with a control system that monitors pH and conductivity readings remotely, and automatically signals the valve to turn on and off to change direction of the fluid flow as needed. A signal transmits to the solenoid switch that turns the air on, which in turn forces the valve to cycle open or closed. To confirm that the valve has opened and closed properly, limit switches—which are located between the valve and the actuator, inside a multifunction module—provide a contact signal back to the controller, verifying the valve operation is in the open or closed position.
Custom Solution
After the complete installation, although all products were working properly, there was no visible indication on the valve that the limit switch contacts had indeed made full contact. Also, there was no easy access to the limit switches, which are located inside the multifunction module between the actuator and valve body, thus making it more difficult to verify when a missed signal was detected after the valve had cycled, due to possible sticking of the ball or disc that could occur if solids were to build up inside the valve. JCWTP staff required a more positive visual indication that the limit switches had indeed made contact; plus, they wanted easier access to the limit switch contacts from a service and adjustment standpoint.
To solve this, external limit switches were added to the top of the pneumatic actuator. This addressed all needs and provided the staff with more confidence and comfort that the valves were actually performing up to their full potential.
Because the plant staff also wanted a visual confirmation of the contact, the new switches were installed with a large clear dome, so the contact and the position of the valve are clearly visible to operators as they walk up to the valve.
Serviceability was another important factor for the staff. With the switches now installed on top, there was no need to disassemble the valve to service the relays. Four screws with the standard NAMUR mounting pull off easily, and the GF Piping Systems’ pneumatic actuator can adapt to any manufacturer’s relay that meets the NAMUR pattern and will fit. The upgraded valve offered more flexibility, better serviceability, a visual indication, and stronger relay contacts than the original valve configuration.
“The valves from GF Piping Systems have proved to be top-of-the line and gave us no recurring leaks due to worn O-rings or cracks in the ball valves,” said Steve Beale, chief operator at JCWTP. “The ion exchange process has done a great job in reducing TOCs by 30% to 50% compared with other areas of the plant that don’t use this system. We have also reduced DBPs by keeping pH and Cl2 residuals lower in storage prior to sending it out to the ion exchange treated part of the distribution system.”
An added bonus of obtaining proper DOC levels also means that DBP standards are within the U.S. Environmental Protection Agency regulatory compliance limits.
Currently, JCWTP has a split system that includes ion exchange treated water and finished water
without the ion exchange pretreatment. Given the successful installation, an all-ion exchange plant may be in the foreseeable future for the JCWTP process facilities.
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