Meanwhile, activated carbon filtration retained only 10 percent in the first 0.9 meters of the filter. As exciting as this news is, slow sand filtration is actually a pretty old technology.

Research Journal of the Water Pollution Control Federation, Vol. 62, No. 3 (May - Jun., 1990), pp. 239-245 (7 pages) The denitrification performance of a moving bed upflow sand filter with methanol ...