Complex sentence: It was based on the finding, made in the 50-th by the German engineer Karl Imhoff, who stated that the treatment efficiency of 60-80 percent could be achieved in highly loaded activated sludge basins.
Split into simpler sentences: It was based on the finding, made by the German engineer Karl Imhoff in the 50th. Imhoff stated that the treatment efficiency of 60-80 percent could be achieved in highly loaded activated sludge basins.