A Standardized Test Protocol for Evaluation of Scale Reduction Technologies

Abstract

Precipitation of calcium carbonate (i.e., scaling) can occur in both traditional tank (electric and gas) and “green” tankless hot water systems that have implications for public health, water and energy sustainability, infrastructure damage, and consumer esthetics. There are many scale reduction devices and technologies that aim to reduce or eliminate such problems, and several standardized methods have been proposed to research their performance with scientific rigor. All of the existing approaches were inherently nonreproducible or could not quantify important aspects of scale deposition, including quantity, location, and deposit durability. Here we develop and vet a Standardized Scaling Test Protocol that overcomes many of these deficiencies, using a laboratory-scale model premise plumbing system and a synthesized synthetic scaling water that could be reproduced in any laboratory. This approach produced 25.1 g of calcium carbonate scaling (95% confidence interval of 20.3–29.8 g, n = 3) in ∼5 days. Illustrative scale reduction for a range of representative technologies, including cation exchange, electrochemical deionization, magnetism, electric field generator, media-induced precipitation, phosphate sacrificial media, and citric acid sacrificial media, ranged from 0% to 100% using the standardized protocol. The general approach was also applied to suitable local natural water with high scaling potential, and similar capabilities were observed.

Phosphate Chemical Use for Sequestration, Scale Inhibition, and Corrosion Control

“…Lower water heater temperatures are often used to save money in heating costs and reduce scaling, while high temperatures are often targeted to discourage opportunistic pathogen growth. Calcium carbonate precipitation may increasingly become an issue with the use of higher temperatures to control emerging problems with Legionella …”

“…In homes, calcium carbonate can block drains and destroy appliances; stain dishes, sinks, and toilets; inhibit heat transfer in water heaters; increase soap demand; and cause pipe leaks (Figure 4). 68 There are no federal health regulations that require control of scaling, but the above consequences can be so devastating that some kind of treatment is necessary. Consumers may choose to remove calcium in their own buildings by installing in-home water softeners, or large systems can choose to soften all treated water at high pH (i.e., addition of lime or soda ash) followed by sedimentation and filtration.…”

“…92 While no water heaters are immune to problems with scaling, on-demand water heaters tend to be the most susceptible to precipitation due to the increased watt density and decreased diameter of tubes in the water heater. 68,94 In fact, on-demand water heaters can be rendered useless in a matter of months in some hard waters. 92,95 Tank heaters have similar but less severe problems due to the lower watt density.…”

“…In homes, calcium carbonate can block drains and destroy appliances; stain dishes, sinks, and toilets; inhibit heat transfer in water heaters; increase soap demand; and cause pipe leaks (Figure ). There are no federal health regulations that require control of scaling, but the above consequences can be so devastating that some kind of treatment is necessary.…”

“…While no water heaters are immune to problems with scaling, on-demand water heaters tend to be the most susceptible to precipitation due to the increased watt density and decreased diameter of tubes in the water heater. , In fact, on-demand water heaters can be rendered useless in a matter of months in some hard waters. , Tank heaters have similar but less severe problems due to the lower watt density. Scale forms on the bottoms of gas water heaters or on electric heating elements where it can be self-cleaned by spalling due to expansion and contraction of the heating element . Large quantities of scale can accumulate at the bottom of a tank before flow is blocked.…”