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MERC ER02-10
5
Residual Chlorine
Analysis
- Levels of residual chlorine (or Total Residual Oxidants -
TRO) were below the permissible discharge limit of 0.10 ppm in all TF treated samples. Values
ranged from 0.06 ppm to below the method detection limit (MDL) of 0.02 ppm. A summary
table from the completed trial runs and the 24-hour dechlorination run is provided below. TRO
was immediately measured shipboard using the
DPD cholorimetric analysis method.
Note that Total Residual Chlorine (TRC) is not directly measured using
the
DPD
cholorimetric analysis method.
The analysis does not distinguish between various oxidants
(chlorine, bromine, ozone, etc). It reports TRO in chlorine equivalents (in other words, as if all
oxidant measured were chlorine). In freshwater, after introducing chlorine, we would be
comfortable calling the residual TRC. However, it is likely that in saltwater, while the majority
are chlorines, some portion may well be bromines. Thus, we only report TRO.
TRO as measured in the control and treated tanks.
Report ID
Run ID
Date
TRO Treated
Tank
TRO Control
Tank
Comment
Trial 1
SIE-03-10
4/27
0.06 ppm
Trial 2
SIE-05-10
5/18
0.08 ppm
0.01 ppm
Trial 3
SIE-06-10
5/25
0.09 ppm
0.03 ppm
Trial 4
SIE-07-10
6/1
ND
ND
Trial 5
SIE-08-10
6/8
0.06 ppm
0.04 ppm
24-Hour
Trial
SIE-09-10
6/10
0.59 ppm
0.06 ppm
Initial
0.20 ppm
Thiosulfate
0.21 ppm
Thiosulfate
0.22 ppm
Thiosulfate
0.04 ppm
Sulfite
0.04 ppm
Sulfite
0.02 ppm
Sulfite
0.03 ppm
Sulfite
0.06 ppm
Sulfite
0.03 ppm
Sulfite
Notes from dechlorination run.
1. Thiosulfate treatment did not result in adequate dechlorination at point of discharge.
2. Measured TRO levels in sodium sulfite treated samples were consistently below measured free (active)
chlorine levels, suggesting interference of sodium sulfite with DPD cholorimetric analysis.
Disinfection By-Products
-
A summaries of the results for DBP analyses for each trial are
in the results section below. Reporting detection limits are provided.
Twenty four-hour dechlorintation trial -
On June 9-10, 2010, MERC conducted one
additional trial that required the use of the Siemens dechlorination system. While TF water in all
5-day hold time trials had total chlorine levels below 0.1 ppm, a short 24-hour hold time resulted
in measurable levels of chlorine and the subsequent automate dechlorination of the treated water
upon discharge using Sodium Sulfite (Na
2
SO
3
,). For this added trial, total chlorine levels in
discharged treated water declined in from 0.59 ppm prior to dechlorination, to below 0.1 ppm