In the rush to move away from gaseous chlorine for disinfection, many industrial applications have quickly run to sodium hypochlorite. Bleach, the common name for sodium hypochlorite, is not the be-all-end-all to replace gas. With growing concerns over gas leaks, operator safety, and the well-being of those within the kill zones of gas cylinders, sodium hypochlorite may be the best and safest solution to meet our disinfection needs. As a result, the use of bleach has taught industrial users several things.
First, even if delivered to your site, bleach is very difficult to handle. It is not an easy chemical to have on site because it is very corrosive, highly toxic and potentially hazardous to personnel. Bleach at its best, is toxic and must be labeled as a hazardous chemical.
Second, bleach wreaks havoc on pumps, nearby electrical panels and clogs valves regularly. I have entered chlorine feed buildings before with corroded doors barely hanging on their hinges as well as green panels that give evidence that bleach had been used. The latest pump designs have sought to overcome the inherent weaknesses of bleach. The result of these pump design changes has been much like dressing up a pig to take to the Presidential Ball...This is in no way a reflection on the engineers’ efforts to upgrade their pumps, but more so a reflection of the difficulty in handling bleach.
Finally, we should keep in mind the propensity of bleach to degrade rapidly. When affected by time and temperature, bleach degrades quickly leaving the majority of disinfectant liquid useless. As a result, the treated water may not be appropriately disinfected. Although, bleach or sodium hypochlorite has a lower price point, it does not often deliver the needed results.
Safe Alternative
There are several questions to ask:
Is there a safe alternative? And the answer is yes, absolutely. When asked, “Which disinfectant do you believe to be the safest: a) Bleach; b) Chlorine gas; or c) Solid chlorine tablets?” Most water treatment professionals would agree that chlorine tablets, although still chlorine, are the safest type of chlorine available. The substantiation for this revolves around the fact that as tablets, the chlorine is in a solid form and it remains that way until dissolved into liquid.
There is a vast difference between a chlorine gas leak, a bleach spill and knocking over a bucket of tablets. A Chlorine gas leak has potentially deadly consequences. A bleach spill requires a hazmat response team, and a spill of chlorine tablets requires an operator with gloves, a dust mask and goggles to pick up the tablets and place them back into the bucket. Therefore, the question of safety in response to a spill leaves one leaning toward the use of chlorine in solid form. However, the major question now becomes “can tablets go into solution safely and then be fed back into your process accurately?” Again, the answer is yes.
Not Your Fathers Chlorinator
Like all technology, tablet chlorinators have continually evolved. This evolution has been enhanced by the need to find safe alternatives to gas and bleach.
Tablet chlorinators started out as nothing more than a bucket with water running over the tablets. This leaves much to be desired when trying to make consistent solution strength as well as feed it accurately. Tablet technology today can be just as accurate as traditional gas feeders. The goal is to find a system that makes solution on demand as well as uses some type of positive displacement metering pump. There are several systems on the market that make batches of chlorine solution on demand and then feed the solution via a variable speed metering pump. Anything other than a positive displacement metering pump on a tablet system may lead to accuracy problems. It is unlikely that an industrial user would choose a centrifugal pump over a metering pump to inject a chlorine solution. Centrifugal pumps are not intended for use in precise applications requiring accurate solution injection. When it comes to something as critical as disinfecting water, precise volumetric accuracy is a must. In addition, spare parts must be taken into consideration.
Final Thoughts
Because disinfecting water is a critical application, the fact should not be overlooked that at some point, the equipment in use may fail. Ask your manufacturer or representative for a spare parts list and then stock up on the critical parts that will keep your system running. When considering the evolution of tablet feeders, the safety of water treatment operators and nearby neighbors, tablet chlorination is a safe and wise alternative to gas and bleach.
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