isn't sufficient that's why in an additional treatment step the bavarian team is also testing two different filter systems the first employed sound in bacteria. the second uses activated carbon granules in early trials it was much more effective that's because the compounds left over after the nation it here readily to their uneven surface but the system has a drawback after two years at the latest the activated carbon particles are covered completely they can't absorb anymore so the filters have to be swapped out and cleaned which is complicated and expensive. that's why the researchers have high hopes for a new activated carbon process that harnesses nature. as this underground is a kind of what's special about this granulated activated carbon is that when this