Water Efficiency June 2012 : Page 45
VOCs within hours. Dollar-wise, says Smith, “Th ey’re all very cost eff ective because the system uses no chemicals or carbon, and very little energy.” Payback periods will vary, but the company claims norms ranging from one to fi ve years. FINAL THOUGHTS GE’s Shuler offers a take on these developments that pegs the driving force for all these innovations—espe-cially those now flourishing abroad— on a new reality. “From global perspective,” he says, “North America’s water treatment stan-dards and practices have been shaped by our abundant water and cheap energy. But we are spoiled—and that abundance is not going to continue for the remainder of our lifetimes. We need to look to places where water quality and quantity are limited and the cost of energy is high—like Asia or Africa. New technologies are being accepted there, and those places are bringing practices, work processes, and technologies to North America to make us better.” THE IMPORTANCE OF PLANT DESIGN Simply changing chemicals without altering structure underscores another topic to consider, regarding capital cost-saving opportunities in plant designs or redesigns. This often results when decisions are driven by well-inte-grated, gentle, and efficient chemical treatment strategies. An added benefit is the operational savings. This applies across the spectrum of water and wastewater issues. Harold Aronovitch, who is an H&T vice president and its technical director, advises many consulting engineers and water agencies on plant designs. On this he points out that while selection and application of chemicals will either save on, or add to, overall costs, the primary driver is always the water itself that’s be-ing treated, and local water conditions always seem to dictate unique analysis. Within this mandate, then, various cost-saving alternatives can usually be weighed and compared. An interplay between material cost, labor, time, and consequences oft en results. Aronovitch illustrates: “Suppose water requires [pH] neu-BORD NA MÓNA Chemical feeder tralization, and someone asks, ‘Should we use sodium hydroxide or potassium hydroxide?’ Th e fi rst thing I would say is that potassium hydroxide costs more. I would then ask, ‘Do you have an is-sue with sodium in your water so that you’d have to use something that would be more expensive? Otherwise, use sodium hydroxide.’ ” Another example: “Potassium permanganate comes in dry crystals, which you have to dis-solve,” he says. “It has limited solubility so that you have to have a mix tank. And you have to add limited amounts. If you add too much, it will start drop-ping out on you and you end up with solids on the bottom of your tank. “As an alternative, and more expen-sive, of course, you buy something like sodium permanganate, which is also an oxidant,” he adds. “Buy it in 20% or 40% concentration—and that would cut down on the labor involved. But you’d have a higher . . . operating cost, buying that chemical.” Aronovitch continues: “Rather than using potassium permanganate or sodium permanganate, if you could end up using bleach —sodium hypochlo-rite—that would be even less expensive.” In one recent design conference with consulting engineers, he recalls, the decision was made to go with costlier potassium permanganate over chlorine in a new municipal plant, “be-cause the client had been using it in the past—and they have an older workforce. Rather than try and pull something new on them, they decided to stick with something that everyone already knew. Also, they were a fairly small utility, and the cost saving would not amount to that much of a diff erence.” Th is anecdote illustrates the obvious real-world fact that chemical choices can’t always be reduced to pure cost factors; human resource issues sometimes trump costs. Likewise, po-litical, perceptual, and regulatory forces come to bear, and not infrequently, pro-prietary commercial patents or trade secrets also impose constraints. In another illustrative case, a water plant opted to use hydrochloric acid as a regenerative medium, as opposed to cheaper sulfuric acid. Th e sole reason was that the water agency balked when contemplating a potential public rela-tions nightmare if it was perceived to be routinely transporting truckloads of sulfuric acid through town. Another real-world factor is that, due to sometime complex local vari-ables in water conditions, and the steady advent of product innovations, there’s oft en no true expert consensus on what is “best available practice.” Hence, a need for experimentation and testing arises. Example: One engineer came along with a design proposal “for putting in a clarifi er and fi lters in order to treat a water which had hardness and lots of iron,” for a textile plant. Aronovitch suggested instead an ion exchange pro-cess using acid regeneration. It was a method that, he says, “to my knowledge had never been done, with that much iron in the water.” When it succeeded, the eventual savings easily justifi ed the expense of the pilot test. Lastly, Aronovitch notes, steadily rising costs of wastewater disposal tend to alter economics over time. What was right a decade ago may no longer be. In such cases, he says, “Any water that [agencies] could reuse or cut down on, using an alternative process, could bring tremendous saving.” He sums up, “Th e tools are already there. It’s how you apply them that can be innovative.” WE Writer David Engle specializes in construction-related topics. Scan here to share this article or read later. Get the app at http://gettag.mobi JUNE 2012 WATER EFFICIENCY 45
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