Drinking water systems depend on consistent water quality from treatment through storage and distribution. But potable water tanks are typically maintained at more than 70% full to preserve pressure and meet peak demand. Because daily volume levels rarely fluctuate more than 10%, water can become stagnant and thermally stratified.
When water remains unmixed, disinfectant residuals can decay, creating conditions that support microbial regrowth, nitrification, taste and odor issues, and the formation of disinfection byproducts (DBPs). Stratification, sediment accumulation, and corrosion can further compromise water quality and tank performance.
Potable water storage challenges
Unmixed potable water storage tanks can experience a range of chemical, biological, and physical water quality issues.
- Chemical issues include disinfectant decay, chemical contaminants, DBP formation, and taste and odor problems.
- Biological issues include microbial regrowth, nitrification, pathogen contamination, and taste and odor problems.
- Physical issues include corrosion, temperature stratification, and sediment accumulation.
Drinking water mixing applications
Powdered activated carbon (PAC) contactors
Powdered activated carbon (PAC) is widely used in the treatment of drinking water to remove and control undesirable taste and odor compounds. PAC is typically added to the raw water upstream of the flocculation basins to provide adequate contact time for the taste and odor compounds to adsorb to the PAC.
Effective mixing in PAC contactors helps maximize contact between PAC and the compounds responsible for taste and odor issues. This improves removal efficiency while keeping PAC suspended and preventing deposition.
Potable water storage tanks
Potable water storage tanks are kept mostly full (greater than 70%) in order to provide enough water for maintaining desired pressure, meeting peak demand, fighting fires, and meeting supply needs for other emergencies. Daily volume levels rarely fluctuate more than 5-10%, creating stagnant water and thermally stratified layers. Over time, stagnant water can lose disinfectant residuals, increasing the risk of bacterial regrowth and waterborne illness.
In potable water storage applications, mixing provides complete homogenization of tank contents while slowing disinfection depletion and reducing the need for tank flushing and batch chlorination dosing. Proper mixing also helps reduce DBP formation, minimize taste and odor issues, eliminate thermal stratification, and prevent freezing or ice-related damage.
Water plant sludge tanks
Surface water treatment processes to produce drinking water often include flocculation, sedimentation, filtration, and disinfection to meet state and federal regulations and water quality requirements. Flocculation and sedimentation frequently generate sludge containing aluminum sulfate (alum) or ferric chloride solids. This settled sludge is pumped to sludge holding tanks prior to dewatering and disposal. In these applications, mixing helps fluidize the sludge and maintain a more uniform consistency for downstream handling.
Solutions for mixing drinking water
Xylem works closely with consulting engineers and municipalities to address drinking water treatment and storage challenges. With a comprehensive portfolio and experienced applications specialists, Xylem helps customers identify the best options for new treatment plants, retrofits, and system upgrades.
AquaBlend potable water mixing systems
EnviroMix’s AquaBlend potable water mixing systems are designed to mix water treatment process basins and blend water in storage tanks using programmed short-duration bursts of impurity-free compressed air. These bursts are delivered through patented, engineered nozzles located near the tank floor. Mixing parameters can be adjusted through operator input or automated process feedback to optimize both performance and energy use.
In potable water storage tanks, AquaBlend helps support regulatory compliance by improving control of microbial contaminants and reducing disinfection byproducts (DBPs). AquaBlend can also be applied in sludge holding tanks to maintain homogeneity and in PAC contactors to improve removal efficiency of unpleasant taste and odor compounds.