Abstract: The densities D of normally growing heterogeneous biofilms changed with biofilm depths d.There was a highly positive correlation of double natural logarithm between D and d,which could be expressed as lnd=DflnD+lnm or d=m·D-Df,the correlation coefficients decreased with the increase of d.The formula d=m·D-Df indicates that the spatial changes of D present fractal features,the fractal dimensions represented with Df defined as Hausdorff dimension,which values reflected fractal characteristics of the spatial d...