Due to rapid industrialisation, the disposal of lead (heavy metal) from the industries (battery and paint manufacturing, electroplating, galvanizing and rubber processing) into the aquatic environment is increasing substantially. The untreated water on consumption causes lung and kidney failure, damage to the central nervous system, including death. Porous concrete is a special type of concrete that allows the water to percolate through the interconnected voids. Its application as pavement reduces the stormwater volume and additionally traps the runoff contaminants including heavy metals (lead, copper, zinc, and cadmium), hydrocarbons, motor oil, and so on. The present study at the Department of Civil Engineering, IIT Madras developed a porous concrete water filter to remove the Pb metal ions efficiently from aqueous solutions, which is schematically illustrated in Figure 1.
Characteristics of Porous Concrete
The porous concrete filter was designed with the controlled levels of permeability which is similar to the sand filters used in water treatment. The permeability and compressive strength of the porous concrete water filter was 7.98 ± 3.83 cm/min and 22.96 ± 1.76 MPa, respectively. The proposed concrete section was scanned using 3-dimensional computed tomography and the resultant images were analysed using image analysis software to determine the size of voids in the filter and thus, it was found to be 1.84 ± 1.39 mm (127 µm to 16.2 mm). Figure 2 shows the interconnected voids in the concrete filter.
Influence of Hydraulic Retention Time
After several trials to assess the influence of hydraulic retention time (HRT) on the efficiency of the filtration process, a filtration system with porous concrete was developed. In this system, three individual cylindrical specimens of size 100 × 150 mm (ø × H) were arranged in series with progressively decreasing levels of hydraulic head (30 cm, 7.5 cm and 0 cm). Pb containing solution of concentration 8 mg/L was passed through these concretes under continuous flow for sixty minutes. This filtration arrangement removed nearly 98% of Pb2+ ions from the acidic aqueous media by sorption and co-precipitation (Murugan 2017). A comparison of the costs of the newly developed system with the conventional methods for Pb removal was also performed, and thus clearly indicated the porous concrete system presents a cost-effective alternative to the current methods. The easy availability of concrete making materials, as well as the ease of fabrication of such filters makes them a viable solution to the needs of water filtration systems especially in rural areas.