Influence of fillers on the removal of rainwater runoff pollutants by a permeable brick system with a frame structure base

Understanding the removal of heavy metals from stormwater runoff in permeable pavement system

Understanding the removal of heavy metals (HMs) in permeable pavement systems is of great significance for controlling urban runoff pollution and optimizing structural design. However, few studies have systematically investigated the mechanism of permeable pavement systems in removing HMs from stormwater runoff. In this study, we adopted a hierarchical strategy to understand the efficiency of individual structural layers on HMs removal in a permeable interlocking concrete pavement (PICP) system. Experimental results illuminated that the surface layer exhibited the highest uptakes of HMs, which can remove up to 64 % of Pb2+, 50 % of Cu2+, 28 % of Cd2+ and 13 % of Zn2+. Meanwhile, as the rainfall return period increased, the removal rates of HMs in PICP was gradually decreased. In addition, batch experiments were conducted and the adsorption results were in accordance with the rainfall filtration experiments. More importantly, X-ray Photoelectron Spectroscopy (XPS) and leaching results were investigated to understand the HMs removal mechanism, which found that the ion exchange is the main mechanism in the surface layer to remove HMs, whereas the chemical adsorption play a crucial role in the base and sub-base layers. Overall, these findings provided new insights into the transport patterns of HMs in the internal structural layers of the PICP.

An Experimental Study of Clogging Recovery Measures for Ceramic Permeable Bricks

To explore the best clogging restoration measures for ceramic permeable bricks, ceramic permeable bricks were accurately clogged using a self-designed device by controlling the permeability, and different technical measures were adopted to restore the permeability. Then, the recovery effect, operating parameters and pore change inside the bricks using pressure washing were further discussed. The results showed that pressure washing was the best recovery measure, the joint methods was not recommended due to performance to price ratio. It was necessary to conduct pressure washing in relatively moist conditions, increase the cleaning frequency or prolong the cleaning time in the case of no serious blockage. Hydraulic cleaning can not only increase isolated pores but also remove the trapped solid particles, and increase the proportion of connected pores and dredges through water channels. This research offers some reference for the daily maintenance of permeable bricks.

Decontamination performance and cleaning characteristics of three common used paved permeable bricks

To investigate the effectiveness of different permeable bricks on the pollutants from urban rainfall runoff, three common used bricks (ceramic brick, cement brick, and steel slag brick) were selected and applied to study their decontamination performance. The influencing factors such as rainfall intensity and contaminant concentrations were investigated. Then the ultrapure water was used to wash the permeable brick to research the pollution status and cleaning characteristics by monitoring the water quality of the rinsing water. Suspended solids (SS), chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), total nitrogen (TN), total phosphorus (TP), and heavy metals (Cu, Zn, Pb, and Cd) in the influent and effluent were measured. The results showed the following: (I) The upper layer of the brick may play a more critical role in purification process; the uniform and dense pore distribution of ceramic permeable brick was instrumental in the retention of particulates. (II) Contaminant concentration and rainfall intensity had a great influence on pollutants with lower removal rate and had little effect on pollutants with higher removal rate. (III) Non-sintered bricks containing a certain amount of cement increased the pH after filtration. (IV) The removal performance of permeable brick for dissolved pollutants such as COD, NH₄-N, and TN was inferior to that for SS, TP, and heavy metals since the discrepancy in removal mechanism of pollutants. The study could offer a new perspective for the decontamination research of pervious bricks.

Risk of contamination of infiltrated water and underground soil by heavy metals within a ceramic permeable brick paving system

The risk of heavy metal contamination of infiltrated water and underground soil on a permeable brick paving system was investigated. The paving system was constructed as a frame structure base on top of a 1.0-m-thick clay layer with permeable ceramic brick at the surface. The concentrations of heavy metals (Zn, Cu, and Pb) in infiltrated water and soil at different underground depths under the paving system were measured. Speciation rates of Zn, Cu, and Pb at different clay depths were further determined to ascertain the probability of downward migration of the unstable forms. The results showed reduced risk of infiltrated water pollution by heavy metals due to underground soil acting as an effective trap. However, topsoil was more susceptible to heavy metal pollution, with the different pollution soil depths of Cu, Zn, and Pb mainly attributed to the different binding abilities between the heavy metals and soil. Soil Cu and Zn remained relatively stable, whereas there was a potentially high risk of Pb migration. The study found that topsoil could accumulate non-degradable heavy metals to unacceptable levels over a period of 30 years and that topsoil should therefore be replaced after 30 years to reduce the risk of soil pollution. This study fills a knowledge gap by both determining the risks of heavy metal pollution to underground soil and infiltrated water and exploring effective ways to reduce heavy metal pollution.