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One of the main difficulties in developing a universal neutralisation program suitable for pool chemicals is that most waste hypochlorite or halogenated organics (such as sodium dichloroisocyanurate [dichlor], trichloroisocyanuric acid [trichlor] and Bromochlorodimethylhydantoin [BCDMH]) will be contaminated in some way. These contaminants have the potential to react in an unknown manner relative to the pure hypochlorite or halogenated organic. It would be unwise to assign a specific procedure to general waste and not expect a deleterious reaction to result.

 

At its Conyers GA production facility, Bio-Lab has three large dissolution tanks specifically for the purpose of neutralising halogenated compounds. These tanks are partially filled with water. The waste material to be neutralised is added and allowed to dissolve. A reductant (anti-oxidant) is then added slowly to neutralise the free halogen present. As the waste is neutralised, pH balancing chemicals are added to ensure the reaction is kept at neutral pH (7.0). If this pH is not maintained as the waste is neutralised, hazardous gases, such as chlorine, bromine and sulfur dioxide, may be evolved. After all halogens are neutralised and the pH adjusted to 7, the neutralised wastewater is discharged to the municipal sewer. (1)

 

There are several reductants that can be used to neutralise oxidisers like hypochlorite. Two of the best are sodium sulfite and sodium bisulfite. Once again, when using these chemicals, care must be taken to maintain pH near neutrality. Bio-Lab's Technical Services Department at Decatur performed a series of stoichiometric calculations in order to determine the actual amount of sodium sulfite needed to neutralise a few of the more common chlorine-containing pool sanitisers. The data listed below was substantiated under laboratory conditions with small-scale samples. (1) Care must be taken when attempting this on a larger scale. The procedure cannot be rushed and the residual halogen level must be tested often.

 

 

The sodium sulfite should be added gradually to the neutralisation tank and the free halogen and pH levels tested regularly; the whole mass of sulfite should not be added in one dose. This method has been demonstrated successfully in Conyers, so should be applicable to halogenated waste disposal at other sites. Whilst adding sulfite in excess will not hinder the reaction, the use and/or discharge of excess sulfite may be undesirable and add unnecessary cost to the waste handling operations.

 

Sample Calculation (2)

The neutralisation reaction for lithium hypochlorite with sodium sulfite is:

Na2SO3 + LiOCl = Li+ + 2 Na+ + Cl- + 2 SO42-

From this, it can be seen that 1 mole of LiOCl will be neutralised by 1 mole of Na2SO3. However, since commercial lithium hypochlorite is only 29% pure, the mass of LiOCl that can be neutralised by 1 mole (126.0 grams) of sulfite is actually:

58.38 g/mol x (100/29) = 201.3 grams

 

Hence, 1 kg of LiOCl will require (126.0/201.3) = 0.626 kg of Na2SO3 for complete neutralisation.

 

Reference

1. C. Reed (Bio-Lab, Decatur GA), E-mail message to P. Jacobson, 11 December 1998.

2. C. Reed (Bio-Lab, Decatur GA), E-mail message to G. O'Connell, 30 December 1998.

 

The above information is supplied by Bio-Lab and represents its best interpretation of available technical information at the time of preparation. The sole purpose is to supply factual information to Bio-Lab customers. It is not to be taken out of context nor used as support for any other claim not made herein.