Alexander Szabo and Oscar Engle - Svenskt Vatten

accuracy (the accuracy of a single analysis is low) of the COD and TSS levels upstream and
downstream of the pond, more sampling is needed. The COD and TSS levels may also fluctuate
over the time, both upstream and downstream of the pond.
Another aspect that must be considered is the accuracy of the COD-reagents. The accuracy and
precision with Hach’s COD tests are around 5-10% and can be even higher if the sample contains
suspended solid (Boyles, 2007). It is possible that the sample analyzed from the stream contained
suspended solids (particle size of 1-100 µm).
7.
Sampling
and
analysis
methods
Sampling and flow measurements
The sampling procedure included filling plastic containers (each about 1 liter of volume) with
sample water from the influent chamber and one container with water from the effluent channel.
The samples were immediately transported to the laboratory where they were stored in a cooling
room (temperature between 10-13 °C).The following day the analyses of BOD and COD was
started. TSS analyses were usually carried out a few days after the sampling. The procedure for
flow measurements is described in Chapter 8.
COD
COD analyses have been undertaken with Hach standard procedure for colorimetric
determination. The Hach reagents used were capable of “high range” (0-1500 mg COD/l). The
digestions of the reagents were done in a Hach DRB 200 for 2 hours at 150 °C (see Figure 7.1).
The analysis has been done with single samples.
The reading of the Hach COD reagents was done in a Hach DR/4000 and a Hach DR/5000 (see
Figure 7.1). The average values from both machines were calculated.
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