Demonstration of Ice Pigging Technology to Remove Biofilms in Water Distribution Systems
Mr. Steven Fann | Naval Facilities Engineering Services Center
Excessive buildup of biofilm and sediment in Department of Defense (DoD) water distribution systems can lead to loss of residual disinfectant as well as generation of elevated levels of disinfection byproducts such as nitrite/nitrate and trihalomethanes (THMs), which could trigger Safe Drinking Water Act (SDWA) violations. Water system operators commonly address these water quality concerns by implementing extensive hydrant flushing programs to discard water that no longer has adequate residual disinfectant, and continue flushing until adequate residual is restored. This project will demonstrate removal of biofilms and sediment buildup in drinking water distribution systems at Naval Air Station Lemoore, California, using a new pipe cleaning technology known as ice pigging. Effective removal of biofilms will reduce the need for water system flushing, which wastes significant quantities of water.
Ice pigging uses an ice and water slurry that is introduced into the pipe network, and gets propelled through pipes using the distribution system’s own pressure to achieve cleaning and removal of loose materials on pipe walls with minimal impact on water system operation. The ice plug forms a compact durable mass that very effectively scrapes pipe surfaces without the risk of permanently blocking choke points in the system. Unlike the conventional pig, the ice-water slurry is able to maneuver itself through pipes having different sizes, bends, valves, and fittings without risking system blockage or damages. The ice pigging waste is collected through downstream hydrants for disposal. To evaluate the technology’s performance, benefits, and costs, the project will monitor hydrant flushing frequency and volumes, and system water quality for pre- and post-pigging to validate improvement in system operations.
Key benefits of the ice pigging technology include water savings through reduction in hydrant flushing, ability to maintain adequate chlorine residuals, reduction in chlorine injection rates, and lower THM concentrations to improve compliance with the SDWA.
Although proper operation of distribution systems require periodic pigging or swabbing in addition to regular flushing, DoD facilities rarely perform these services due to fear of potential damages to valves and pipes from conventional pigging techniques. This fear is justified considering the age and condition of most of our piping systems. Without performing proper water main cleaning, facility managers have resorted to a more aggressive flushing program that has resulted in excessive flushing of sections of distribution systems and dead-end pipes in order to maintain mandated chlorine residuals in the distribution system. A typical medium size military base might use up to about 20 million gallons per year for routine water flushing operations. The need for flushing such large amounts of water can be primarily attributed to the old and dirty piping network, which typically has an accumulation of sediment and biofilm on the pipe walls. Biofilm forms when bacteria excrete a slimy and sticky substance that allows them to adhere to surfaces. Once formed, the biofilm is resistant to chlorine and is difficult to remove. Mechanical means such as pigging or swabbing are needed to remove biofilms and sediments. The presence of biofilms and sediments will require increased chlorine dosages to compensate for the loss of disinfectants from reaction with the biofilms. The higher chlorine concentrations will lead to higher THM concentrations, which are regulated under the disinfection byproducts regulations. Water system operators struggle to maintain minimum residual chlorine levels while limiting the generation of THMs in the delivered water.
Ice pigging has minimum adverse impacts on distribution systems, and could be a viable technology for including in routine operations and maintenance (O&M) protocols for the maintenance of water quality in water mains. Proper O&M will restore distribution systems to good working condition, which equates to water savings from reduced flushing and better compliance with water quality standards. (Anticipated Project Completion - 2017)
Points of Contact
Mr. Steven Fann
Naval Facilities Engineering Services Center
Energy and Water
SERDP and ESTCP