Aqua Ionic – Reduce Water Use Eliminate Scale and Legionnella
Aqua Ionic Benefits
- Large reduction in fresh makeup water use
- Large reduction in blowdown discharge to sewer
- Elimination of energy wasting scale
- Reduced chemical and biocide use
- Eliminate risk of Legionnaires’ Disease
- Low corrosion rates
- Reduced operating costs for water, sewer, energy, treatment chemicals, and maintenance
- Reduced environmental impact due to lower water and energy use
Background
Shortages of fresh water and increased costs for both makeup water and blowdown disposal have created a need to increase the cycles of concentration (COC) in cooling tower systems, which decreases both fresh water makeup and blowdown to sewer. Unfortunately, increased COC also increases the concentration of hardness ions in the cooling water, making the cycled waters highly scale forming. Formation of hardness scale in heat exchangers is unwanted, as even a small amount of scale will decrease the efficiency of heat transfer, resulting in increased power consumption for chiller operation and decreased productivity in industrial processes. In severe cases, scale can completely plug heat exchangers and piping.
Many facilities have always confronted the problem of scale control. Typically, hardness scale has been controlled via use of chemical inhibitors, with or without acid addition for pH adjustment. This technology is not always effective, can be extremely costly, risks severe equipment corrosion damage with loss of pH control, and acid is an EHS hazard.
Cooling tower blowdown is often the major water use in many facilities as blowdown from cooling tower operation must be replaced with fresh makeup water. It is costly as blowdown has three costs: purchase price of the water, a sewerage charge for disposal, and cost of water treatment chemicals. The volumes can be substantial, for instance, a 1,000 ton annual thermal load cooling tower running at COC of 2 will evaporate 26,550 gallons per day (gpd) with a blowdown of 26,550 gpd. If the COC is increased to 4, the blowdown decreases to 8,867 gpd.
The equations are:
- evaporation = tons cooling x 26.55 gpd
- blowdown = evaporation/COC-1
Cooling towers can generally be operated at maximum COC levels between 2 and 4 based on the makeup water quality due to scale formation if these COC levels are exceeded.
A proven technology, which addresses the need for increased COC while avoiding scale formation, is to remove the scale forming ions by water softening prior to use as makeup water. The problem most often cited in opposition to use of this technology is the increased corrosivity of cycled, soft water.
Aqua Ionic Technology
Operation of cooling towers with softened makeup water was started in 1984 at Brockway Glass Company in a successful program, directed by Timothy Keister, to control scale in extremely high heat flux furnace electrode cooling jackets. ProChemTech International has since developed and refined this ground breaking technology into a complete patented* water management technology, Aqua Ionic, which addresses the need for increased COC while maintaining control of scale, deposition, and corrosion.
The benefits of this technology are immediately obvious to facilities that have suffered from the problems caused by scale formation in cooling systems or the corrosion damage resultant from upsets in acid feed pH control systems. Use of softened water immediately eliminates the scale potential of the cooling water, rendering it non-scale forming, while completely eliminating any further need for pH control via feed of corrosive, dangerous to handle acids.
With elimination of the potential for scale formation, cooling towers can be operated at much higher COC, generally 8 to 10, limited mainly by the potential for deposition from solids in the cooling tower air intake. Water savings are substantial; using our previous example of a 1,000 ton thermal load cooling tower operating at a COC of 3, blowdown would be 13,275 gpd. Going to an Aqua Ionic program operating at a COC of 8 will reduce the blowdown to just 3,793 gpd, annual reduction in water use of 3,460,930 gallons.
Corrosion Control
Cycled soft water is much more corrosive than hard water and the water management program must provide superior corrosion control. ProChemTech has developed an entire family of effective Aqua Ionic products that control corrosion of ferrous, galvanize, aluminum, zinc, and yellow metals in a cycled, soft water environment. Cooling towers using soft makeup water and Aqua Ionic technology routinely operate at steel corrosion rates below 2 mil/yr, often attaining rates between 0.25 and 0.5 mil/yr. This is better performance than can be achieved using conventional technology with hard water makeup.
“White Rust”, an accelerated corrosion of zinc (galvanize), and its alloys, due to chemical attack by high pH/high alkalinity waters, is recognized as a major problem with high COC operation of cooling systems in any area with alkaline makeup waters. Softening of hard water actually makes the problem worse; replacing hardness ions with sodium ions makes the water substantially more corrosive to zinc and its alloys.
Our discovery of a proprietary chemical inhibitor to control white rust, “GalvaGard”, allows use of softened, high alkalinity waters as makeup water in galvanized cooling towers.
Deposition Control
Aqua Ionic products incorporate the latest developments in deposition control, being formulated with dispersant surfactants and terpolymer. Operation of many cooling systems, using soft makeup water since 2007, has shown operation at COC from 8 to 15 as optimum for control of deposition via dispersants and blowdown.
For operation of cooling towers at COC higher than 10, up to zero blowdown, we utilize multimedia pressure filters, operated in a side stream mode, to remove by filtration the suspended solids that cause deposition. These automatic backwashing units are typically designed to turn over the volume of cooling water in the cooling tower every 12 hours.
Microorganism and Legionella Control
Routine testing for the presence of Legionella bacteria in seventeen (17) cooling systems using Aqua Ionic water treatment programs resulted in “none detected” results. These results prompted review of the scientific literature and discovery of a published report1. This report clearly shows that growth of Legionella bacteria in cooling tower water is inversely correlated with increases in pH and alkalinity. Given the reported pH tolerance range for Legionella bacteria of 5.5 to 9.2, operation of cooling towers with cooling water pH values above 9.2 with high alkalinity is an effective means for controlling Legionella bacteria in cooling towers.
A paper at the International Water Conference2 and article in the AWT Analyst3 both note that higher pH and alkalinity values not only curtail growth of Legionella bacteria, but also have an adverse effect on other microorganisms. Additional comments on the control of microorganisms are also found in the Analyst article where it is theorized that high pH and alkalinity combined with the high dissolved solids typically found in cooling towers operating with ion exchanged makeup water is biostatic to all microorganisms. Our own research into controlling Legionella via use of Aqua Ionic technology was reported in a Water Conditioning & Purification article4 where a cooling tower was operated without any biocide addition for a period of six months with nine Legionella samples obtained. All of the Legionella test results were “not detected”.
Aqua Ionic water treatment programs generally operate at a pH of 9.2 to 10.0 with high alkalinity and dissolved solids and thus the cooling water has an adverse effect on all microorganisms, including Legionella bacteria. This documented effect reduces, or even eliminates, the need for biocides to control microorganism growth and the potential for a Legionnaires’ disease outbreak.
While an Aqua Ionic program minimizes, or eliminates, the need for biocides, best practice suggests that a biocide be utilized to ensure complete control. We have found that a single oxidizing biocide is sufficient to establish excellent control of microorganisms in almost all cooling tower systems. As cooling tower waters using ion exchanged makeup are generally high pH, the oxidizing biocide of choice is bromine. Bromine is an economical biocide delivered either as liquid “stabilized bromine” or generated on-site as electrolytic bromine.
System Control
Makeup water that has been ion exchanged is chemically constant so the low cost, high reliability makeup proportional method to control blowdown and inhibitor feed can be used in place of higher cost, maintenance intensive conductivity controllers. Biocide addition is generally on a timed feed basis.
If remote monitoring is desired in areas where the makeup water conductivity is known to vary, conductivity of the makeup and cooling waters can be monitored and blowdown controlled based upon the actual cycles of concentration desired.
Softening Technologies
ProChemTech builds water softener units suitable for treating cooling tower makeup water for any size cooling tower. As several areas of the country are either restricting, or have proposed a restriction, on the discharge of regeneration brine wastewater from ion exchange units, ProChemTech has developed both nano filtration and chemical process/inclined plate clarifier technologies to remove hardness ions.
Proven Process
Aqua Ionic is a proven process having been used since 2007 in many casino and commercial building HVAC systems, glass container plants, plastic molding plants, sintered metal plants, electronic component plants, chemical plants, non-ferrous metal plants, and die casting plants.
ProChemTech International, Inc.
Innovation in Water Management
Apache Junction, AZ and Brockway, PA 15824
480-983-5385 www.prochemtech.com 814-265-0959
* Aqua-Ionic patents # 7,595,000 and 8,128,841
1“An Alkaline Approach to Treating Cooling Towers for Control of Legionella Pneumophila”, States et. al., Applied and Environmental Microbiology, Aug, 1987, p. 1775-1779.
2“Benefits of Soft Water Makeup for Cooling Tower Operation”, Harfst, IWC Paper 07-01, 2007
3“Legionella Outbreak Prevention for Cooling Towers”, Rahimian-Pour and Anderson, The Analyst, Vol. 23, No. 3, summer 2016
4 “Eliminating Legionella via Softened Makeup and High Cycle Operation of Cooling Towers”, Keister, Water Conditioning & Purification, April, 2021.