RBF_Cover (for eps) - National Water Research Institute

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experiments. Most of the hydrophilic compounds under investigation are industrial chemicals
with high production volumes and a broad range of applications; therefore, they are likely to enter
river water if they are not totally removed in industrial or municipal wastewater treatment plants.
In this paper, data on their fate during RBF will be presented, whereby the results of both lab-scale
experiments and long-time measurements of river water and bank-filtrated water will be given.
For the simulation of microbial degradation during RBF, a so-called “test filter” is used. This
closed-loop apparatus was developed and used by Sontheimer and Völker (1987) for the
characterization of fractions of surrogate parameters from wastewater effluents. In the last few
years, the method was adjusted and optimized to study the biodegradation of single compounds at
concentration levels relevant for the environment (Karrenbrock et al., 1999; Knepper at al.,
1999). Details of the experimental set-up are given elsewhere (Karrenbrock et al., 1999).
Several waterworks along the lower Rhine River were selected to measure the behavior of organic
micropollutants during RBF. All use bank-filtrated water from the Rhine River as raw water for
drinking-water production (Schubert, 2000; Denecke, 1997; Brauch et al., 2000), whereby their
wells are situated in a distance of 30 to 50 m from the Rhine River. In all cases, the raw water is a
mixture between bank-filtrated water and groundwater, whereby the groundwater fraction ranges
between 5 and 40 percent (i.e., the raw water is predominantly bank-filtrated water from the
Rhine River). Regular measurements were performed over a time period of several years to attain
reliable and significant data on the removal of organic compounds during underground passage
(Brauch et al., 2000).
Results
Complexing Agents
Aminopolycarbonic acids like nitrilotriacetic acid (NTA), EDTA, or diethylenetrinitrilopentaacetic
acid (DTPA) are used as chelating agents in detergents and industrial cleaners, as well as in the
photo, textile, and pulp- and paper-making industries. Due to their widespread use, NTA and
EDTA are permanently found in the Rhine River in concentration levels of more than 1 µg/L
(ARW and AWBR annual reports; Sacher et al., 1998). Besides these compounds, other
complexing agents like ß-alaninediacetic acid (ADA) or 1.3-propylenedinitrilotetraacetic acid
(PDTA) are used for special applications or as substitutes for EDTA. To test the biodegradation of
these synthetic compounds, test-filter experiments were performed in which water from the Rhine
River at Karlsruhe was spiked with NTA, EDTA, DTPA, PDTA, and ADA at a concentration
level of 10-µg/L each. These experiments showed that the concentration of NTA decreased quite
rapidly, indicating a fast microbial degradation of this complexing agent. The concentration of
ADA decreased much slower and, after 35 days, about 30 percent of the initial concentration was
still present. The concentrations of EDTA, PDTA, and DTPA seemed to be more or less constant,
indicating that these complexing agents are persistent under the conditions of the test-filter
experiment.
Looking at the concentrations of NTA, EDTA, and DTPA in the Rhine River and in the raw
water of the waterworks, which consists of at least 90-percent bank-filtrated water from the Rhine
River, it is clear that in correspondence to the results of the test-filter experiments, NTA is nearly
totally removed during RBF and is only sporadically found in raw water. On the other hand,
EDTA proved to be recalcitrant and was present in the raw water under investigation. DTPA was
found only once in raw water, but concentrations in the Rhine River are quite near to the limit
of determination (which was 2 µg/L until 1996 and is currently 1 µg/L), and mixing with some