The topic of this study is flow properties of novel stormwater filter media prepared from various construction and demolition waste (CDW) materials. The main objective of the study is to find out the effect of filter media, including particle size and layer height, on the flow of water through the bed. It is important to recognize the most important parameters with laboratory experiments, to be able to produce stormwater filter media for long-term use in wetlands, where urban stormwaters are treated before their discharge to natural waters. In this study, hydrostatic pressure was used as the driving force and water was filtered through various bed layers made from CDW in a vertical column, where the pressure, i.e., the head, was kept constant during each experiment. The data was compared to theoretical values obtained by Darcy-Weissbach, Ergun, and Kozeny-Carman equations.

Different size fractions of two types of CDW concrete and brick waste materials were used in the column experiments. The results revealed that particles larger than 800 µm and smaller than 300 µm are unsuitable for the specific filter column used for the experiment. When particles are coarser than 800 µm, the superficial velocities become unrealistically high for a deep bed filter. Conversely, when particles are finer than 300 µm, superficial velocities are low, and probably not applicable in full-scale stormwater filters. Therefore, a series of experiments was carried out using two fractions of two different bed materials separately: 0.3 mm- 0.5 mm and 0.5 mm- 0.8 mm, and each fraction had four different bed heights: 30 cm, 40 cm, 50 cm, and 60 cm.

Morphology analysis of bed materials developed using CDW concrete waste revealed that the finer the particles, the more their shape deviated from the regular spherical particles, which is an important factor, when the results are evaluated against the theory. The particle sphericity was calculated using the Sauter diameter and the mean volume diameter of particles. The particle sphericity of both types of samples ranged from 0.5 to 0.9. In terms of two-dimensional determination of particle shapes, the circularities of the two samples ranged from 0.6 to 0.8 and 0.7 to 0.8, respectively. Microscope images of these two C&D concrete waste types revealed that the finer the particle size range, the higher the number of particles attached to each other, as usual.

The experimental data were used to calculate theoretical pressure drops using the Darcy-Weisbach, Ergun, and Kozeny-Carman equations. The calculated pressure drops across the bed materials indicated that the Kozeny- Carman equation gives the most reliable values in this case, close to the experimental pressure drops, followed by the Ergun equation. Moreover, the modified Ergun equation, which includes the particle shape factor, provides even more accurate pressure drops than the original Ergun’s equation. However, the calculated pressure drops via the Darcy-Weisbach equation are far lower than the actual experimental pressure drops. The most probable reasons for this could be that the Darcy-Weisbach equation does not consider the porosity, and the hydraulic particle diameter used to calculate Reynold’s number is not a fair representation of all particles in the actual particle size distribution range. These results highlighted that ...