Due to sudden changes in hydraulic regime the loose deposits in drinking water distribution
systems (DS) lead to discoloration events at the customers tap. About 1/3 of all customer
complaints about drinking water quality are due to the discoloration events. The loose deposits
may originate from insufficient treatment, microbiological regrowth or corrosion of the pipes.
Organic carbon (OC) influences the interaction and transport of many toxic organic or inorganic
chemicals found in the nature. The aim of this study was to investigate how the different factors
such as the raw water source and the material in the networks influence the concentration of OC in
the loose deposits. An OC isolation method for lake sediments was adapted to determine nonpurgeable
organic carbon (NPOC) in the loose deposits. The average NPOC amount in deposit
samples collected from DS supplied with groundwater varied from 0.18 mg/g to 21.01mg/g. In the
samples collected from DS supplied with surface water NPOC ranged from 1.21 to 18.99 mg/g. In
samples collected from different drinking water reservoirs in Latvia, NPOC ranged from 0.20 to
3.11mg/g. The pipe material was a single the only important factor influencing the concentration
of organic carbon in loose deposits. The smallest average NPOC amount was found in the samples
from polyvinyl chloride (PVC) pipes (0.48 mg/g of deposits), while the largest NPOC amount was
found in polyethylene (PE) pipes (14.29 mg/g). Samples collected from cast iron (CI) pipes
contained 4.64 mg/g. Iron was found to be the dominant material in sediments, followed by silica
and aluminum. Goethite and quartz were the minerals which were found in almost all the samples.
The OC isolation method was shown to be accurate and simple user-friendly for determination of
OC in loose deposits from drinking water
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