The aluminium release of granular activated carbons (GAC) – virgin and reactivated carbons – will be determined with the incentive to establish requirements for the impurity. Furthermore, for drinking water treatment plants recommendations are derived for GAC selection and the initial launch. The existing testing procedure for the impurities will be modified.
According to §11 of the Drinking Water Ordinance in Germany GAC for drinking water treatment may only be used if the impurity requirements according to DIN EN 12915-1 are met. These include among others limit values for water-extractable trace metals. Water suppliers are currently reporting that the duration of the initial filtrate discharge is determined by increased aluminium filtrate concentrations.
There is currently no limit value for aluminum as a water extractable element. A limit value for aluminum can only be set if a reliable database is available about the filtrate concentrations that are achieved when using the currently available GAC types. Such data do not yet exist. However, only with knowledge of the fluctuation range for GAC, it can be avoided that by setting a limit value GAC, which contain aluminum due to raw material (e. g. bituminous coal based types), are completely excluded from use in waterworks. The relevance of the topic for powdered activated carbons is not known as well.
If GAC is used in an adsorber, trace metals are only released in the initial phase of operating. In practical operation in the waterworks an exceeding of limit values in drinking water is avoided by an initial filtrate discharge or by mixing with the filtrates of several adsorbers operated in parallel. In addition, the course of the concentration in the filtrate is of decisive importance. Such values are not taken into account in the test procedure implemented by the DIN EN 12902.
Furthermore, due to this test procedure with partly different water matrices, location-dependent differences in the assessment of activated carbons may result. Thus, the currently valid requirements for the impurities do not provide the desired safety for the use of GAC and lead to uncertainty when interpreting the list of treatment materials and disinfection methods published by the UBA.
As part of the research project, the release of aluminum from virgin GAC and reactivates is determined and evaluated. Furthermore, the relevance of the topic for powdered activated carbon is examined. First, a suitable test method has to be developed that delivers location-independent results for aluminum as well as for the already regulated trace metals (e.g. As, Sb, Ni ...). In addition to the fluctuation range of the aluminum concentrations that occur, the evaluation of the results should examine to what extent the aluminum release depends on the raw material of the GAC or to what extent the aluminum release is determined by the manufacturing processes (directly activated and agglomerated) and the country of origin (USA and China).
The aim of the research project is to establish the limit values for the extractable trace metals and aluminum for GAC. Besides, recommendations for water supply companies are derived for selecting GAC types and setting GAC adsorbers into operation. The corresponding DIN EN standards should be adapted.