Effects of scrubber sludge on soil and dredged sediment aggregation and porosity

In a greenhouse experiment, we evaluated the effects of scrubber sludge on the aggregation and the porosity in various combinations of dredged sediments and topsoil in the presence of sudangrass roots. As expected, the water-stable aggregates increase with increasing percentage of topsoil. For all combinations, scrubber sludge decreased aggregation. The topsoil had a total porosity similar to the sediments at the completion of the study in the absence of scrubber sludge. The total porosity increased with additional quantities of scrubber sludge for all combinations of topsoil and sediments. Transmission (>50 μm), water storage (50 to 0.5 μm), and residual (<0.5 μm) pore volumes differed substantially between the sediments and topsoil, as well as with scrubber sludge treatments. The sediments had a higher water retention difference than the topsoil. The presence of scrubber sludge had little effect on topsoil, but reduced the water storage volumes for the sediments. With scrubber sludge addition, the residual pore volumes remained high for topsoil, but decreased substantially for sediments. For all combinations of topsoil and sediments, scrubber sludge dramatically increased transmission porosity. This increase in transmission pores within the sediments with scrubber sludge additions resulted in a higher rate of saturated flow of water than for the sediments without scrubber sludge. The pore-size distributions were estimated by water-release methods and verified by directly measuring soil pore-size distributions by Hg-intrusion porosimetry.