Information Bulletins
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Here is what appears in Volume 2 Number 2 of the Journal of the Swimming
Pool and Spa Industry:
General:
An Introduction to the Journal
Articles:
John A. Wojtowicz
Chemcon
Reevaluation of Chloroisocyanurate Hydrolysis Constants
In the course of correlating disinfection data with concentrations of
biocidal species in aqueous chlorisocyanurate media, it was necessary to
compare and assess the various published values of two of the more important
equilibrium constants and their temperature dependence, i.e., the hydrolysis
constants of mono- and dichloroisocyanurate ions (Wojtowicz 1996). Data
from four sources were analyzed, recalculated, or corrected. Three of these,
based on spectrophotometric measurements, gave reasonably consistent values
for the hydrolysis constants of mono- and dichloroisocyanurate ions (Brady
et al 1963, Gardner 1973, O’Brien et al 1974). Data obtained by polarographic
measurement of free available chlorine in aqueous sodium dichloroisocyanurate
(Pinsky and Hu 1981) was recalculated using more appropriate models resulting
in new values for the hydrolysis equilibrium constants and temperature dependence
for mono- and dichloroisocyanurate ions. However, the hydrolysis constants
are significantly higher than those reported by others. The reported equilibrium
constant for hydrolysis of the dichloroisocyanurate ion obtained by measurement
of free available chlorine in aqueous sodium dichlroisocyanurate with added
cyanuric acid (Pinsky and Hu 1981) was shown to be erroneous because an
incorrect model was employed. In addition, the data appear flawed.
John A. Wojtowicz
Chemcon
Swimming Pool Water Balance – Part 4: Calcium Carbonate Precipitation
Potential
Although the calcium carbonate saturation index is applicable to swimming
pool water balance calculations, it is only a qualitative indicator of calcium
carbonate precipitation since it does not indicate the extent of precipitation
that can occur at positive values of SI. Utilizing the mathematics of aqueous
carbonate and cyanurate equilibria allows calculation of the quantitative
calcium carbonate precipitation potential (CCPP), ie, the equivalent calcium
carbonate supersaturation. Precipitation of calcium carbonate is accompanied
by a drop in pH and a reduction in hardness of 1 mol and in total alkalinity
of 2 equivalents for each mol of calcium carbonate precipitated. The calcium
carbonate precipitation potential increases with saturation index and buffer
intensity. Buffer intensity in turn is a function of pH and total alkalinity.
Because buffer intensity decreases with increasing pH, the CCPP also decreases
as pH is increased. Cyanurate contributes to total alkalinity, thus it inreases
the CCPP for a given carbonate alkalinity. At constant pH, carbonate alkalinity,
and calcium hardness, the CCPP decreases with increasing TDS due to a decrease
in SI. In part 5 of this series, laboratory data on the precipitation of
calcium carbonate under different conditions will be presented and interpreted.
1996 Application Guidelines for Commercial Pools and Spa Pools - Corona
Discharge Systems
DEL Industries
To assist in the process of upgrading the general quality of ozonation
in commercial pools and spa pools, Del Industries has published an Application
Guideline for use by companies designing and installing ozone systems. At
the Sanitation Chemistry Symposium (Western Pool and Spa Show, Long Beach
CA, March 1996) Allen Clawson and Beth Hamil of DEL Industries presented
and described this document. With the permission of DEL Industries, portions
of the guideline are reprinted here. Please contact DEL Industries at 800–676–1335
for a copy of the complete document.
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