Release of aluminium during installation of granular activated carbon adsorbers (Alu-Carbon)

Against the background of the discussion on the introduction of a parameter value for aluminium as a purity requirement for granulated activated carbons, a data basis was developed within the framework of the research project that enables an assessment of the aluminium discharge.

Aluminium is a component of coal, so that especially when using activated carbons based on raw materials such as hard coal and lignite, there is a release into the water to be treated.

In order to generally achieve a site-independent evaluation of the purity of granulated activated carbons, the existing DIN EN 12902 method for determining the water-extractable substances was modified to the effect that a model water (extraction water) is used for all process steps. Due to the fact that the solubility of aluminium is essentially determined by the pH value of the water, which briefly rises into the basic range when activated carbon filters are put into operation, a certain buffering is achieved by specifying a hardness of 11 °dH for the model water.

According to the results, almost all activated carbons based on hard coal and lignite as well as the activated carbons with an unknown raw material base release aluminium, whereby the limit value of 200 µg/L of the Drinking Water Ordinance is exceeded in five of the 14 tested activated carbons. If the conditions in the waterworks with regard to buffering the water are similar or lower, the run-in phase is usually extended in the waterworks by an initial filtrate reduction until the limit value is not exceeded. In conclusion, it is therefore recommended not to regulate the aluminium concentration in the extraction water and, for example, to formulate instructions in DVGW Code of Practice W 239 A, such as providing for the possibility of an initial filtrate cut-off.

Furthermore, high aluminium concentrations in the filtrates are noticeable when reactivates are used. For the water supply companies, this may mean long periods of rejection. According to information from the practice, this requirement is costly for the company, but taking into account the lower costs of the reactivates compared to fresh carbon, this operational expense is considered justifiable. In connection with the discussion on the standardisation of purity requirements for fresh coal and reactates, it can also be concluded from the data that a parameter value regarding aluminium should not be specified. Given the current market situation (poor availability of activated carbons based on hard coal) and the lower carbon footprint, the future use of reactivates should be aimed for.

Publication:

Haist-Gulde, B.; Schäfer, R.; Riegel, M.: Aluminiumabgabe von granulierten Aktivkohlen. DVGW energie | wasser-praxis 11/2022, 42-47 (2022)