Application of encapsulated and immobilized nano zero-valent iron for iron removal from roof-harvested rainwater

Abstract

Rainwater harvesting is a viable option for dealing with the global challenge of increasing water scarcity, but heavy metal contamination often prevents it from being widely used for drinking water purposes. Harvested rainwater collected from galvanized iron (GI) and tile roofs containing iron concentration of 0.46 and 0.38 mg/L respectively, were treated by two nano sorbents, CaCO3-nZVI and PUF/CaCO3-nZVI with the intention of making the iron concentration conform to drinking quality standards. The nano sorbents were synthesized and characterized using BET (Brunauer-–Emmett–Teller surface area), SEM-EDX (Scanning Electron Microscopy-Energy-Dispersive X-ray spectroscopy, and FTIR (Fourier Transform Infrared Spectroscopy). CaCO3-nZVI achieved iron removal efficacy of 88.69% and 89.21% for harvested rainwater from GI sheet roof and tiled roof respectively and the efficiency increased to 95.65% and 95.78% when treated with PUF/CaCO3-nZVI. In addition, the nano sorbents were found to have appreciable removal efficiency for other metals (Pb, Mn, Zn, Cu, Cd and Cr) present in the collected rainwater. The use of FTIR and EDX to characterise spent nano sorbents divulged that the iron was removed through sorption process. This study thus explored the potential of CaCO3-nZVI and PUF/CaCO3-nZVI for treating heavy metal contamination in roof-harvested rainwater. HIGHLIGHTS Developed a novel nanocomposite by impregnation and surface modification of nZVI.; PUF/CaCO3-nZVI reduced the iron concentration to acceptable limit for the potable water.; PUF/CaCO3-nZVI was able to simultaneously remove other heavy metals.; Novel nano composite reduced the turbidity of the samples to permissible limit.; PUF/CaCO3-nZVI outperformed conventional sorbents in iron removal.;

Keywords

• harvested rainwater
• immobilisation
• nano zero-valent iron
• polyurethane foam
• surface encapsulation