The city of Rowlett, Texas, experienced an unauthorized wastewater ...
System Overview and Reservoir Data
Glendale (Calif.) Water & Power (GWP) operates and maintains a potable water system serving approximately 210,000 people with 380 miles of distribution system piping and 28 storage facilities. The potable storage facilities consist of in-ground reservoirs, aboveground steel tanks and partially buried reservoirs with storage capacities that range from 80,000 gal to 57 million gal. The tallest storage facility is a more-than-50-ft aboveground tank with difficult road access. Approximately 70% of the water supply is from Metropolitan Water District, which supplies water treated with chloramines for disinfection. The remaining 30% is supplied from groundwater. There are seven major pressure zones in the system, and typically, the lower zones operate in a chloraminated state and the upper zones in a chlorinated condition.
In order to provide sufficient reserves for fire suppression and maintain Glendale’s top insurance rating, storage facilities are large relative to potable demand. Storages are located at a wide range of elevations, and historically have experienced widely varying water age, which created challenges in maintaining disinfection residuals and preventing nitrification. Based on routine monitoring data, actions were taken to control nitrification, trim in the chloraminated areas and deep-cycle stored water to reduce water age. These actions maintained water quality, but also created taste and odor issues.
Typically, powdered HTH (or in some cases, liquid sodium hypochlorite) was applied through one or more dosing ports in the roof of a reservoir or tank. But because these disinfectants have a specific density greater than one, they would sink and create significant “slugs” of disinfectant at the lowest part of the storage area, which is also the location of the common inlet/outlet piping. Therefore, the chlorine disinfectant was not actually mixing with the stored water and instead high concentrations were drawn into the distribution system. This invariably resulted in numerous chlorine taste and odor complaints.
The primary objectives of the SolarBees were to thoroughly mix the tanks to prevent stratification and control nitrification from occurring. Other objectives included using the SolarBees to provide a more effective and efficient means of injecting disinfection chemicals when required. In May 2006, four units were installed in Glendale’s potable system. In December 2006, 34 additional SolarBees were installed to ensure that all tanks within the treatment system would have circulation and a means of controlled dosing. In this application, all models of SolarBees (from the SB1250v12-PW to the SB10000v12-PW) were installed in the various size tanks, including the SB1250v12-PW collapsible unit that fits through a 24-in.-diameter opening.
Results from the initial four SolarBees over the 2006 summer showed dramatic improvements in mixing, elimination of stratification, reduction in water age and temperature and overall water quality. Results were so positive that Glendale purchased 34 more SolarBees , and now its entire potable water storage system operates with SolarBees. Overall, the system is performing well, including tanks in the upper portion of the system that historically had difficulty maintaining uniform water age, residual and water quality. Since full implementation, GWP has found the highest residual retainage ever recorded system-wide. Circulation, together with a better control plan and increased monitoring, greatly reduced nitrification throughout 2007, resulting in a 20% reduction in chlorine use for trimming to tie up ammonia to maintain the desired residual. The combination of deep mixing and use of the chemical dosing rings for chlorination applications have eliminated the formation of slugs.
More significantly, Glendale has experienced a 50% reduction of chlorine use throughout its system since SolarBees were installed, and high chlorine complaints have been reduced to near zero. The SolarBee service crew also earned high marks from Glendale for diligence, professionalism and resourcefulness when faced with difficult installation challenges. Since the installations, all objectives are being met and Glendale is pleased with the improved, consistent water quality and the potential for economic and chemical savings.