Lee WH, Wahman DG, Bishop PL, Pressman JG. Free chlorine and monochloramine application to nitrifying biofilm: comparison of biofilm penetration, activity, and viability. Environ Sci Technol. 2011 Feb 15;45(4):1412-9. doi: 10.1021/es1035305. Epub 2011 Jan 12. PMID: 21226531.
ABSTRACT
Biofilm in drinking water systems is undesirable. Free chlorine and monochloramine are commonly used as secondary drinking water disinfectants, but monochloramine is perceived to penetrate biofilm better than free chlorine. However, this hypothesis remains unconfirmed by direct biofilm monochloramine measurement. This study compared free chlorine and monochloramine biofilm penetration into an undefined mixed-culture nitrifying biofilm by use of microelectrodes and assessed the subsequent effect on biofilm activity and viability by use of dissolved oxygen (DO) microelectrodes and confocal laser scanning microscopy (CLSM) with LIVE/DEAD BacLight. For equivalent chlorine concentrations, monochloramine initially penetrated biofilm 170 times faster than free chlorine, and even after subsequent application to a monochloramine penetrated biofilm, free chlorine penetration was limited. DO profiles paralleled monochloramine profiles, providing evidence that either the biofilm was inactivated with monochloramine's penetration or its persistence reduced available substrate (free ammonia). While this research clearly demonstrated monochloramine's greater penetration, this penetration did not necessarily translate to immediate viability loss. Even though free chlorine's penetration was limited compared to that of monochloramine, it more effectively (on a cell membrane integrity basis) inactivated microorganisms near the biofilm surface. Limited free chlorine penetration has implications when converting to free chlorine in full-scale chloraminated systems in response to nitrification episodes.
To read the full paper you need institutional access.
Here is a quote from another paper. What is important in the below is that chlorine kills better but takes a lot longer to penetrate the biofilm. The level of chlorine
With the same biofilm thicknesses (2,000 μm) and equivalent bulk water chlorine concentrations (10 mg Cl2 L−1), monochloramine required approximately 2 days for 90% biofilm penetration while free chlorine took over 16 days for 84% biofilm penetration regardless of whether the biofilm was previously fully penetrated by monochloramine. However, monochloramine’s faster penetration did not correlate with an immediate viability and aerobic activity loss whereas free chlorine’s slower biofilm penetration corresponded directly with a loss in viability and aerobic activity.
The above is from here
Lee WH, Pressman JG, Wahman DG. Three-Dimensional Free Chlorine and Monochloramine Biofilm Penetration: Correlating Penetration with Biofilm Activity and Viability. Environ Sci Technol. 2018 Feb 20;52(4):1889-1898. doi: 10.1021/acs.est.7b05215. Epub 2018 Feb 8. PMID: 29376332; PMCID: PMC6056003.
They used 10 ppm concentration of chlorine: "Two experiments consisting of a total of three biofilm application scenarios (
Table 1) were conducted under the same conditions: pH 8.0, 8.3 mg O2 L−1, 23 °C, equivalent 10 mg Cl2 L−1" 1 mg/L = 1 ppm.
The reasons one can rinse media under chlorinated tap water and not harm their biofilter is thayt the residual level of chlorine of chloramine in water is pretty minimal. Then the actual exposure is a matter of seconds or maybe minutes and not a day or longer. Finally, if one uses dechlor, and especially if one is doing a water change after cleaning filter media, then there is a decent dose of dechlor in the water that will soon be going through the media.
However, fish gills are a lot more senstive in terms of chlorine and chlorlamine than the bacteria protected by a biofilm.
I should also mention that I have well water and have ne need to use dechlor. However, I do have some as I have to bleach dip planys if alage gets ahaed of me and I will use dechlor for this process. Also, I used to sell fish at weekend events and I often had to use some amount of hotel water which did need dechlorinating.
There are more papers onthis subject. If you want to read them here is a list of 100 papers mmany of which will help but not all are ideal. I got the liste frome papers cponsidered to the one with the abstract above.
https://scholar.google.com/scholar?...n,+activity,+and+viability+&hl=en&as_sdt=0,33
I rinse & squeeze the heck out sponges in running tap. I have chloramines in my tap here so I add Prime to the filter box refill water to restart. No problem, ever.
