max residual for water main disinfection

[CivilizedPE]

AWWA C651 requires minimum 25 ppm at beginning of disinfection and minimum 10 ppm of residual after 24 hours. Is there a maximum limit that should not be exceeded during the disinfection procedure?

 

[bimr]

No, there is not a maximum. Most attempt to minimize the chlorine residual because you have to pay for the chlorine and you also have to neutralize the chlorine prior to discharge.

 

[rconner]

While I’m not sure exactly what you are looking for, there are of course varied concerns regarding persistence of high residual concentrations of disinfectants. In addition to the aforementioned AWWA information a reading of the EPA guidance at

http://water.epa.gov/drink/contaminants/basicinformation/disinfectants.cfm,

as well as e.g. pages 63-66 of the Guidelines at

http://www.dipra.org/content/uploads/Guidelines-Installation-Guide.pdf

may be helpful to you.

 

[ch81pc]

I've used up to 100ppm, but that was in a known problem main with a history of quality issues. In 98% of cases there is no need to go above the 25ppm.

 

[adalinaabella]

No, as I know there is not any particular quantity which is specified as maximum limit.

However, if so , then please share what is the maximum limit.


Thanks!
magicrubbishclearanc

 

[rconner]

I noticed that for whatever reason some question was apparently left hanging on this thread. While I would certainly not profess to be an expert in many aspects of the disinfection and flushing processes (and I don't think there is any one answer), I nevertheless believe limits could be different on different jobs, in different locales, and with different considerations and regulations. While the general success of water disinfection in minimizing the proliferation of disease, and probably also increasing general life expectancy over more than a century is undeniable, with the same qualification I think at least from a health/safety/environment standpoint some overall caution is however likely in order when dealing with some quite powerful powerful disinfection chemicals, and maybe particularly in excess of concentrations mentioned in standards etc.
The previous EPA site I supplied link to of course explains e.g. they like no more than 4 ppm residual chlorine in drinking water. While it can be certainly be argued that much higher temporary concentrations are acceptable on at least some jobs when same are in theory are flushed rather quickly from the lines, anyone who has been around the field for long will realize that probably isn’t always done with 100% effectiveness or that isn’t all there necessarily is to it (notice bimr's mention of dechlorination issues etc.), and frankly even lower concentrations than what is mentioned on this thread or byproducts of same might not be good for some sensitive species etc.! After all, on a cellular level I have heard an action of some disinfectants is that they cause in effect sorts of “explosions” and/or shriveling up of living cells (in the best of worlds dangerous microbes etc.) Some appreciation for the complexity of this subject considering many of these angles may also be gained by reading the document e.g. now at

http://www.pollardwater.com/pdf/pdf_web_manuals/awwarf_dechlor_guides_pollard_dmb.pdf

.
That being said, I know there are also concerns of effects of some disinfectants on at least some sorts of piping materials. I am aware of a report that a new stainless steel water system in Denmark was subjected to a sodium hypochlorite solution with 40 L with 15% active chlorine contact per 1000 liters of water for only one day, apparently before it was diluted to 1500mg/L active chlorine content and flushed three days later with clean water. Through wall (not just at welds) and crevice (the latter at couplings) corrosion leaks/failures of the new stainless steel system reportedly occurred just three days after the flushing!
As also explained in many references, members of the “polyolefin” pipe family (i.e. polybutylene and polyethylene etc.) are clearly subject to varying extents to oxidation attack from the inside by disinfectants. The mechanism of these failures is reportedly the depletion/consumption of antioxidants from at least a thin layer on the inside of the pipe, resulting then in cracks. With plastic pipe materials with much less fracture toughness than e.g. steel and ductile iron, it then takes much smaller cracks or flaws (or critical crack length or depth, in fracture mechanics parlance) to result in propagation of failures under all manner of working stress etc. The former type of pipe is of course the subject of a billion dollar lawsuit due to quite premature (mostly plumbing) piping failures wherein I believe it was stated from experts disinfectants played a quite prominent role, and litigation and “ensuing litigation” have also been mentioned with regard to the latter type in different references including

http://www.thefreelibrary.com/Field+failure+mechanisms+in+HDPE+potable+water+pipe.-a0283705518

etc. I guess if one really wants to get into the nuts and bolts of this sort of attack, I have noticed this is examined in detail in the study, “EVALUATING THE COMPATIBILITY OF CHEMICAL DISINFECTANTS WITH PLASTIC PIPE MATERIALS USED FOR POTABLE WATER DISTRIBUTION TECHNICAL MEMORANDUM FINAL” dated August 2008 available now at

http://hdpeoxidation.com/Carollo Study on HDPE-PVC Pipe - Disinfectant Oxidation 8-08.pdf.

While I am not aware of like pipeline failures of pvc nor traditional cementlined iron or steel piping due to disinfection operations, I did hear a few years ago from an AWWARF report that some joint leaks in pvc piping (with whatever quality gaskets as had been furnished with same) had been blamed on disinfectants.
While I know what references I have provided here are probably not a final answer, I hope this information is at least of some help in understanding some potential concerns.