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  Scott Tarr August 28, 2011 at 6:49pm

  Thanks for the input guys!!
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  Michael Aschenbrenner July 22, 2011 at 10:46am

  Considering the rate at which chlorine disapates in water exposed to the atmosphere, I would think that a holding pond, that would have a valve to empty the backwash water once it achieves a low enough chlorine reading would fit the bill nicely. Kind of like a kiddie pool with no kiddies allowed. Test it once a day until the levels are low enough, then open the valve and let the water out.If you had a flood irrigation area at a lower level, or an irrigation system that used grey water, you could even reuse this water for that purpose.
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  Bob Baer May 18, 2011 at 5:42am

  Our set-up uses a Blue-White FlexFlo peristaltic pump that is wired into the auto-backwash panel. When we're backwashing, it activates the pump, which draws thiosulfate dissolved in a 5 gallon bucket of water and injects it into the outgoing water stream.
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  Richard A. Falk May 14, 2011 at 11:57am

  Sodium metabisulfite added to water produces sulfur dioxide which is smelly and is the reducing agent.  It is not non-toxic.  Food-grade just means that it is pure enough for use in foods, but only at low enough concentrations to not be toxic, most typically used as a preservative in seafood, especially in shrimp to retard Melanosis, or black spot.  It has an oral toxicity in rats and guinea pigs of around 1000 mg/kg so that's 1 gram per kilogram of weight and has dermal toxicity as well so be careful when handling it.  It may be mutagenic though that is not clear.  In concentrated form it can be hazardous as noted in this paper.

   

  I should clarify that when I wrote before that sulfur based compounds would not be as good to release into downstream water (i.e. rivers, lakes, ocean), the sulfur in sodium metabisuflite doesn't remain in the water because the sulfur dioxide will eventually outgas to the air if it doesn't find any oxidizers to reduce.  So care should be taken when using this product, but its fate in the water is not as problematic as with sodium thiosulfate.
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  Bruce Wettstein May 14, 2011 at 7:08am

  Hi Wes-

   

  We buy it locally at Gallade Chemical.  They have a website  (www.galladechem.com) and it looks like you can order direct from them.  We pay about $40.00 for a 50 pound bag (we go through a bag every month or so, so we don't purchase in larger quantities, but I think they have larger sizes).

   

  Hope this helps!  We like that it is food grade quality, and it does a great job of neutralizing chlorine rapidly!

   

  -Bruce

  

  Gallade Chemical - Chemical Distributor

  15,000+ rare and fine chemicals in our continually updated searchable online catalog. If we don't have it we'll find it for you. Gallade Chemical is…
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  Wes Burdine May 13, 2011 at 7:44pm

  Bruce,

  Where to you buy SMBS?
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  Bruce Wettstein May 9, 2011 at 3:01pm

  We inject sodium meta bisulfite via injection pumps prior to our membranes to remove the chlorine.  SMBS is a food grade additive, and relatively cheap and fast acting.  If we come upon a pool with a high FC residual that may not be addressed by the injection pumps, then we broadcast the SMBS directly into the pool.

   

  Hope that helps some!
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  Ben Madison May 5, 2011 at 11:14am

  It seems like there are 2 separate questions here, that are getting mingled.

  
  The first is, "How do you effectively dechlorinate filter backwash or other pool outflows? That's not necessarily the question anyone really needs an answer to.

  
  The second, more relevant, question is, "How can you comply with state mandated dechlorination requirements?". It is this question that most need to answer. It's entirely possible to answer #1 in ways that probably do NOT satisfy #2.

  
  There is a third implicit question most operators will want to answer, "What is the right thing to do here, and how do I do. it?" In this particular case, I don't actually know. To the best of my knowledge, I've never created a fish kill from all the pools I've pumped and / or backwashed over the years. But I don't actually know for sure how toxic filter backwash effluent might be, NOR whether any such toxicity would be a result of chlorine, or from other chemicals present. (I do know that copper and some algaecides ARE a problem!)

   

  In my own experience with commercial pools, trying to do the "right thing" isn't adequately answered by "complying with code". So, I've tried to do the "right thing" and "comply with code". Over the years, this has many times led my doing MORE than code required. But there have also been a number of 'dummy' installations or actions that 'complied with code' without messing up an already successful and sanitary operation. I've even  had experienced inspectors, who knew my track record, deliberately 'look without seeing', so they wouldn't have to mess up the pool in question!

   

  In this case, of dechlorinating effluent,, "doing the right thing" might be --- assuming actual backwash effluent toxicity is low --- to use an ineffective system, like sodium thiosulfate tabs, that complies with code, without introducing unnecessary expense OR downstream toxicity.
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  Richard A. Falk March 30, 2011 at 12:38am

  The pH neutral version is sodium ascorbate and in this link costs from $14 to $19 per pound that would neutralize 1 ppm FC in 50,000 gallons.  Sodium thiosulfate in this link is $1.35 to $2 per pound that would neutralize 1 ppm FC in 117,600 gallons so is far less expensive, but more toxic to fish.
  
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  Lester Eric Brehm March 29, 2011 at 7:45pm

  This system uses ascorbic acid as Richard has mentioned to dechlorinate municipal water when flushing lines. http://www.vita-d-chlor.com/