What Is the Difference between Disinfection, Sanitization, and Sterilization?
Compiled by Mike Henley and James McDonald
(Editor’s note: This article is based on recent discussions in the LinkedIn Ultrapure Water and Industrial Water Treatment groups. This column seeks to accurately reflect comments from each contributor. On occasion, there may be the need to edit contributor comments for clarity or length. An important purpose of each group is to provide a forum for practical examination of issues facing endusers of high-purity and industrial water.)
Mike: How do you distinguish between disinfection, sanitization, and sterilization? What do you normally practice in your facility?
Pierre: “I use sodium hypochlorite to disinfect RO membranes, and peroxide to sterilize storage tanks and systems with loop recirculation and a combination microfilter/UV for TOC and endotoxins). Does sanitization mean a less microbiological impact by chemicals?”
Mike: “Group members, how would you define ‘sanitization’?”
Juzer: “Pierre, Are you sure you use sodium hypochlorite for RO membranes?”
Steven: “Sanitization is a process to reduce microorganisms by a minimum of 3-log reduction, disinfection to a level of greater than 6-log reduction, and sterilization is the absence of all microorganisms.”
Ian: “Steven is spot on. Precision in using these terms is unfortunately not common.”
Mike: “So, what determines whether to sterilize, sanitize, or disinfect a water system?”
Fritz: “Hi Steve, I also tried to find definitions for those words earlier, but I found different log reduction values: Sterilization in pharma is 6 log (https://en.wikipedia.org/wiki/Sterility_assurance_level) and absence of all MO, disinfection would be 3 to 5 log (depending on requirement, compare EN 13727); sanitization exceeds ‘cleaning’, but is not specified concerning the log reduction (e.g., see Roche lexicon). Do you have any references that support your values? I would like to find out what is correct now.”
Roberto: “Sanitization is the process to increase water to 80°C and clean some skid, including RO and CEDI systems. Sterilization up to 121°C is normally for cleaning loops. Disinfection refers to cleaning with chemicals as in an RO or softener.”
Sewer-to-Plant Source Water?
Mike: Do you feel comfortable using specially treated wastewater as one of the incoming feedwater sources at your facility? Why or why not?
Vinh: “I am uncomfortable except when I can visit in their treatment plant.”
Bala: “Reclaimed effluent has low ionic loads as feedwater. This leads to several operational benefits and cost savings.”
Jim: “This is already happening, although such reuse is not yet in the mainstream. Many companies are looking to wastewater refinement to reduce expenses. Cooling towers are one example of an application.”
Mike: “How do you overcome the fears some have of using a reclaimed effluent stream as part of the incoming plant feed?”
Sergio: “With good monitoring and intelligent deviation of bad quality to the drain. Good non-chemical antibacterial treatment is also a basic need along with good and quick monitoring.”
Benson: “The best way to overcome your fear is monitoring the reclaim water. Specific parameters are essential for safe operation in UPW plants.”
Industrial Water Treatment Discussions
Compiled by James McDonald, PE, Senior Corporate Engineer, Chem-Aqua
Cracked Softener Beads
James: What can cause water softener beads to crack?
Wouter: “One cause is a change of pressure in the complete system that causes ‘hammering’ of the water on the beads, cracking them over time (obviously, the old beads that are a bit weaker). The softener acts as a shock-absorber in the water-system. A second reason is a rinse that is too fast that causes the beads to swell and crack.”
François: “Point 1 of Wouter is correct (water hammer). I do not believe that Point 2 is in normal operation. The change in volume between regenerated (Na) and exhausted (Ca + Mg) resin is small. Only if the brine used for regeneration is— by accident— not diluted would the osmotic shock be sufficient to crack the resin beads. It is of course essential to purchase good quality resins. Although the manufacturing of softening resin is simple in principle, we have seen products with cracked beads when new, and products with insufficient osmotic stability.”
Keith: “Too high a salt concentration indeed can be a possible cause. The largest culprit we see, however, is excessive Delta P across the softener, resulting in premature resin failure. This usually occurs when discharging soft water to an atmospheric storage tank without flow limitations.”
Don: “High levels of chlorine cause softening of the beads so they are more subject to cracking.”
Vinod: “All the reasons cited earlier are good. Some other references on this topic can be found at: http://www.premierwatermn.com/hard-life-water-softener-resin/ and http://blog.klenzoid.com/blog/resin.”
Mohamed: “Dow has also explained the main reasons for resin cracking, including physical effect, excessive pressure, pressure drop, improper transfer, osmotic shock, and the oxidizing effect on the resin beads. This may be found at: http://www.desal.co.uk/pdfs/Technical%20Info/DOWEX_Ion_Exchange_Resins_-_A_Practical_Guide.pdf.”
Tracy: “From our experience, we see resin failure mostly related to chlorine exposure. We can usually double the life of resin by installing a carbon filter as pretreatment to the softener.”
Non-Oxidizing Biocide Method of Kill
James: How do non-oxidizing biocides kill microorganisms?
David: “Disrupt their cell walls?”
Romain: “Interactions with the cells’ membranes (permeabilization, osmotic pressure), inhibition of the transfer mechanisms through the cytoplasm, proteins coagulation and other interactions with proteins and/or enzymes disturbing the metabolism, cells’ divisions, energy transfers…”
Vashisth: “Non-oxidizing biocides function by interference with the metabolism of the organism in a variety of ways, by preventing normal processes to kill the organism.”
Francisco: “They work on the cell membrane or at the organelles.”
Jonathan: “It all depends on the biocide. Romain has nailed most of the major mechanisms.”
Siham: “Cell membranes disruption.”
Paul: “You could suspend inert macro-molecules of the right size, shape, modulus of elasticity, molecular weight and maybe a few other key dynamics ... and ... voilà cell wall disruption and a clean system. Oh, and a few other benefits, like improved pump efficiency, a degassed coolant, mitigation of crystalline and particulate fouling. You might even get a heat transfer coefficient higher than the clean state design parameters. It is truly amazing what you can do when you play on a micro scale. There is a disruptive technology out there if anyone cares to listen and learn.”
Andi: “There are so many ways for non-oxidizing biocides to kill micros, except oxidize it.”
The Ultrapure Water and Industrial Water interest groups may be accessed at www.linkedin.com.
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