Date: 05 August 1998 16:25
To: aqua-l@killick.ifmt.nf.ca
QUESTION:
I am trying to confirm the amount of sodium thiosulfate needed to
neutralize sodium hypochlorite (20ppm solution)? Also, what amount of residual chlorine in the culture water is acceptable (<0.1ppm)?
Jeanette Chavez
Hubbs-Sea World Research Institute
4200 Garfield St.
Carlsbad, CA 92008
(760) 434-9501
(760) 434-9502 (fax)
jchavez@hswri.org
***************
COMMENTS 1:
It is my understanding that 7mg/l sodium thiosulfate is required to
neutralize 1mg/l sodium hypochlorite. As for acceptable levels, I am not comfortable with anything greater than zero but this is debateable,
depending on other water quality parameters such as ammonia concentration and pH.
Nancy Lightowler
Water quality Tech
Long Beach Aquarium of the Pacific
<nlightowler@lbaop.org>
***************
COMMENTS 2:
I use 1 gram of sodium thiosulfate for each 10ml of liquid household bleach (5.4% sodium hypochlorite) I had used in chlorinating. The strength of solution (ppm chlorine) is not really important, it is the total amount of chlorine you need to neutralize. For invertebrates or phytoplankton, there should be no residual. I have seen phytoplankton killed when there was no measurable chlorine residual. Oyster larvae are sensitive to 1 ppb.
Nancy Hadley
SC DNR
Marine Resources Research Institute
PO Box 12559
Charleston, SC 29422-2559
hadleyn@mrd.dnr.state.sc.us
(843) 762-5022
***************
COMMENTS 3:
I am not sure about the thiosulfate concentrations you will need but any general chemistry text should be able to help you out.
As far as residual chlorine levels go, the recommended min concentration is usually 0.03 mg/L. I have published on the effects of 0.45 mg/L and 0.2 mg/L in rainbow trout. Even at 0.2 mg/L there were ionic flux disturbances presumably across the gills (all work was done at 10 C). Here we do not dechlorinate but allow our water to sit aerated for a couple of days and then use it without any real problems. I prefer this method since it cuts down the problems of having other chemicals in the water!
Dr. Mark Powell
Lecturer, School of Aquaculture
University of Tasmania,
P.O. Box 1214
Launceston, Tasmania
Australia 7250
Tel: +61 3 63243813 Fax: 03 63243804
E mail: Mark.Powell@utas.edu.au
***************
COMMENTS 4:
The primary equation would be:
2Na2S2O3 + NaOCl + H2O = Na2S4O6 + NaCl + 2NaOH
If you work through the calculations then it takes 4.2 mg of thio to react with 1 mg of hypochlorite. I have heard that excess thiosulfate can be toxic to some invertebrates, does anyone know if this is true?
Michael Payne
Research Student
School of Environmental Biology,
Curtin University of Technology,
GPO BOX U1987,
Perth 6845
Western Australia
E-mail : epayne2@cc.curtin.edu.au
Ph : (08) 9266 7915 or 9266 7311
Fax : (08) 9266 2495
International prefix +61 8
***************
COMMENTS 5:
For dechlorination I use 0.05g sodium thiosulfate/l of water I am
dechlorinating. I use chlorine for saltwater sterilization for algal
culture and will add 0.5ml/l of water I am sterilizing and then
dechlorinate with 0.05g/l. Using a simple hatch kit I have found
chlorine to be neutralized within 45 minutes after sodium thiosulfate
addition. I understand every situation is different though.
Ken La Valley
Technical Manager
Spinney Creek Shellfish
scs.shells@rscs.net
***************
COMMENTS 6:
I know that bivalve larvae (at least hard clams and oysters) will not live in chlorinate-dechlorinated water. I have always taken this to be because of byproducts of the dechlorination. I suspect it could be removed with activated carbon but have never tried - just don't use chlorinated water for them!
Dechlorination by using 0.05g Na2S2O3/l water is the same rate as I use, but I use almost twice the chlorine (of course I am only using household bleach). I use 120 ml of bleach for 150 liters of seawater (0.8 ml/l). I dechlorinate with 12 g of sodium thiosulfate (0.08 g/l). I find that the dechlorination is much more reliable if you predissolve the sodium thiosulfate in fresh water. I make up a stock solution. Before I started doing this I sometimes had incomplete dechlorination even after an hour. Although the test kit would not pick up any chlorine there was enough in there to kill my algal culture. I still allow an hour for dechlorination although I am pretty sure it is complete within about 30 minutes.
Nancy Hadley
SC DNR
Marine Resources Research Institute
PO Box 12559
Charleston, SC 29422-2559
hadleyn@mrd.dnr.state.sc.us
(843) 762-5022
***************
COMMENTS 7:
The problem with aerating to get rid of the chlorine is that some
household bleach has a chemical added slowing down the breakdown of the chlorine, thus lengthening the shelf life of the product. Whatever method is used to dechlorinate you should always test for chlorine before the water is used.
Dena Wiseman
Maritime Mariculture, Inc.
c/o Ocean Sciences Centre
Memorial University of Newfoundland
St. John's, NF
Canada A1C 5S7
Tel (709)737-3794
fax (709)737-3220
email dena@morgan.ucs.mun.ca
***************
COMMENTS 8:
I find pasteurization to be a much more reliable and safe way to prepare seawater for culture of phytoplankton to be fed to bivalve larvae, than the bleach/debleach technique. Using a titanium plate/frame heat exchanger I bring the filtered seawater up to at least 70 C, then let it cool to culture temperature and inoculate. Crashes with this technique are extremely rare, and there are no strange chemical residuals to worry about.
Will Borgeson
Bodega Marine Lab
P.O. Box 247
Bodega Bay, CA 94923, USA
<wdborgeson@ucdavis.edu>
***************
COMMENTS 9:
I strongly support Will Borgeson's comments on the use of pasteurisation in the preparation of algal culture media. I used it in a number of facilities in the early days of commercial shellfish hatchery development (1960's). My inspiration came from a publication by B. Wisely with C.S.I.R.O. in New South Wales, Australia. It is not only inexpensive and low-tech, but it avoids the chemical changes we experienced with autoclaving, chlorination and ozonation, all of which we tested. We found it extremely effective and it became our standard technology. For routine cultures in large glass carboys, after filling with filtered enriched seawater these were stood on electric heaters and equipped with strap-on thermostats (from domestic water
heaters). Controlled by timer they were processed overnight and ready for setup and inoculation next morning. The technique was used for both batch and continuously harvested cultures.
Roy Drinnan
<rdrinnan@netcom.ca>
**************
COMMENTS 10:
How do you handle larger volumes such as 200 liter kalwalls or tank
cultures?
Is there a way to (inexpensively) pasteurize large volumes and then hold it until needed for filling carboys or kalwalls? My carboys are plastic - they autoclave OK but they cannot be placed on an electric heater!
Nancy Hadley
SC DNR
Marine Resources Research Institute
PO Box 12559
Charleston, SC 29422-2559
hadleyn@mrd.dnr.state.sc.us
(843) 762-5022
***************
COMMENTS 11:
I haven't operated a shellfish hatchery in 25 years. My experience was all in the Early Plastic Age. I worked only with batch treatment using glass carboys but can see no problems developing a flow-through system. Will Borgeson's reference to a plate heat exchanger suggests that he has done so. I suggest that you enquire into the pasteurisation technology used by dairy or brewing operations. The microbreweries so common these days may well have appropriately sized equipment or technology which might be copied.
Roy Drinnan
<rdrinnan@netcom.ca>