Variation in hydraulic conductivity with decreasing pH in a biologically-clogged porous medium

► Biofilm growth caused K to decrease significantly in porous medium columns. ► Acidification of the water entering the columns then caused K to increase slightly. ► Acidification killed and stressed cells in the columns more so at pH 4 than pH 5.7. ► Despite viability contrasts, reduced K was as persistent at pH 4 as pH 5.7.