Evolution of the soil and vegetation cover on road embankments after the application of sewage sludge

Abstract

This research study used sewage sludge from urban wastewater treatment plants to restore road embankments. The results have been used to propose a series of basic principles for the application of sludge in this context. In the study, six experimental plots (each composed of one cut slope and one fill slope) were set up on a highway located in the province of Jaen (Spain). The soil and vegetation in the plots were restored by a conventional hydroseeding process, with each plot receiving a different sludge dosage. A control plot did not receive any treatment at all, whereas another plot was hydroseeded, but without any sludge added to the slurry mix. In the plots, soil evolution was controlled from the moment that the embankment was created and hydroseeded until the present. As part of the soil monitoring process, agronomic parameters and the heavy metal content of the soil were analyzed in the laboratory. Another parameter of analysis was the vegetation cover, which was studied on the basis of on- site visual inspections and the rasterization of images with a view to calculate the percentage of vegetation cover on each plot. Results showed the effectiveness of sewage sludge as an organic complement in the restoration of road embankments. Its viability is enhanced by the fact that the sludge can be applied with the same methods used in public highway construction. The results also showed the optimal sludge dosage to be used in the slurry mix during the hydroseeding process.