Effect of low-impact development practices on the treatment of urban runoff

Abstract

The impact of a bioretention cell on the urban runoff (ur) quality was evaluated. The cell was constructed with the following stratification of materials (from the base): 20% coarse gravel, 40% gravel, hydrogel, 40% clinoptilolite, and succulent plants as cover. It was fed with real UR for 24 hours at constant speed to simulate 3.9 mm of precipitation. Samples were taken at the inlet and outlet of the cell, which were analyzed in terms of COD, N-NH4+, N-NO2-, N-NO3-, PO43- (total and dissolved), Escherichia coli density and various metals (Al, Fe, Cu, Mn, Pb, Zn, Cr, Cd and Ni) according to standard methods. To assess the effect of the cell on water quality, we proposed an index that we calculated for the aeu before and after receiving the treatment. The system removed several of the pollutants evaluated: COD (28.5%), N-NH4+ (84.3%), N-NO3- (49.4%), total PO43- (94.8%), and dissolved PO43- (86.2%). The metals were removed with efficiencies between 90 and 99%, with the exception of Ni (58.7%), while E. coli was completely removed. The index calculated for the water treated in the cell was considerably lower than the index calculated for the inlet aeu, which shows the bioretention effect on water quality.