In my first article, “Traditional Treatment Methods” (June 2014), I touched on traditional methods of residential water treatment and conditioning such as water softeners, reverse osmosis and ultraviolet systems. As a water treatment professional living in one of the developed world’s worst consumers of water — Canada (amongst other studies that show excessive water use, one conducted by the Organization for Economic Co-operation and Development found that Canada’s water consumption is more than double that of the top 16 participating developed nations) — I felt that my second installment should focus on the alternative and emerging technologies that are making their way into the mainstream due to their comparative energy and cost-efficiency.
Combatting Scale
For many years, ion exchange water softeners were the only proven method for residential scale protection. In the past decade or so, some new technologies have been introduced.
Homeowners, property managers, chief engineers and facility maintenance personnel all face the same challenges in battling the ill effects of hard water. Protecting a commercial plumbing system from damaging scale buildup can bring considerable expenses, both up front and ongoing, to any commercial property.
Neglecting scale control is never a smart option, because eventually the cost of repairs or replacement will offset the initial savings. For many years, the installation of commercial-grade water softeners was the only proven technology for scale protection.
Water softeners, however, present their own set of challenges. They require electricity to operate, and they take up precious space in already cramped mechanical rooms. They demand, and then waste, hundreds of gallons of water to drain during backwash and regeneration cycles. They require regenerants like salt or potassium chloride to maintain performance. Clean water bears considerable cost coming in, and then also must be paid for as it makes its way into the waste treatment stream.
A Study of Alternatives
Results from a multi-phase, impartial study recently conducted by Arizona State University (ASU) in conjunction with the WateReuse Foundation have shed new light on the controversial subject of alternative water conditioning devices. Using the same source water, heating coils and identical testing rigs (including an untreated control rig), the study tested the effectiveness of four alternative technologies plus traditional ion exchange:
- Template-assisted crystallization (TAC) for residential and commercial use;
- Electrically induced precipitation (EIP) for residential and commercial use;
- Magnetic water treatment (MWT) for residential and commercial use;
- Capacitive deionization (CDI) for commercial use only; and
- Traditional ion exchange (IX).
Physical water treatment (PWT) technologies work by changing the physical characteristics of the solution being treated, but with little or no change in the solution’s chemical composition. It is chiefly used to reduce the negative effects of water hardness in plumbing systems, appliances, valves, equipment (boilers, water heaters, dishwashers, automotive and process wash equipment, etc.) and other components that generate or use heated water.
The vast majority of PWT devices work to promote hardness crystallization (mostly CaCO3) in the bulk solution so that it is not available to scale on downstream surfaces. The following are brief overviews of each technology tested.
TAC. TAC is a technology that influences the water solution at localized sites on the media surface such that hardness ions and their counter-ions (bicarbonate) combine to form inert nanometer-size “seed crystals.” Called nucleation, this occurs when dissolved molecules or ions dispersed throughout a solution start to gather to create clusters in the sub-micron size range. When the remaining dissolved ions reach their solubility shift, they attach to the seed crystals and continue harmlessly downstream, eventually to be consumed or end up going to drain.
While closed-loop boiler systems technically do not qualify as TAC applications because there is no flow to drain, systems that incorporate a bottom blow-down with scheduled daily discharges have been successful in controlling scale while reducing or eliminating chemical additives.
TAC media (such as Watts’ OneFlow) is always used in an up-flow design so it is not subject to low-flow channeling or high-flow pressure drops. The pressure drop as measured at peak flow rate is less than 4 psi. Like other resins, the media is subject to water chemistry limitations, such as chlorine, iron, manganese, tannins and pH.
The effective life of the TAC media is three years and is independent of the volume and hardness level of water.
EIP. EIP is a physical water treatment process that uses an electric field to precipitate dissolved scale-forming particles in water. Precipitate forms on an electrode that must be cleaned periodically. The device tested in the ASU study required cleaning after treating 800 gal of water and reduced scale formation by approximately 50%.
MWT. MWT is a physical treatment in which water is subjected to a magnetic field to alter calcium carbonate adhesion properties. Most devices use a series of wires wrapped around a pipe, with a voltage transformer controlling the current through the pipe. By controlling the current, the magnetic field induced by it can be reversed, causing cations to move to the center of the pipe and anions to the wall of the pipe. MWT also achieved an approximate scale reduction of 50%.
CDI. CDI is a commercial electro-chemical water treatment process in which ions in water adsorb to charged electrodes that have a high surface area, effectively removing them from the water stream. Several CDI devices have been developed. They all include a forward-flow adsorption/regeneration process and a periodic backward-flow cleaning and recharging process. Due to its high upfront capital investment and relatively high energy requirement, CDI is currently only viable as a commercial PWT option.
Study Results
Because the total scale formed in the no-treatment controls was significantly different for each water source tested, the results for each water type were normalized to the no-treatment controls to show the relative reduction in scale formation.
According to the study, “TAC media was originally submitted to DVGW, the German Technical & Scientific Assn. for Water & Gas, whose standard [is] W512, [which] is considered the most rigorous and challenging accredited standard to certify PWT systems for scale reduction efficiency. The media achieved a scale prevention efficiency of more than 99% for both recirculation hot water (1998) and single-pass cold water (2006) protocols. In this most recent study, TAC reduced scale formation by greater than 88%.”
The results speak for themselves—all of the technologies tested have shown a reduction in scale formation in household water heaters to some degree, with some treatment methods pulling ahead of the rest. The emerging field of PWT and alternative methods of water conditioning is an exciting one and definitely worth looking into.
A copy of the ASU report can be found online at www.thescalesolution.com/resources.asp.
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