Iron hydroxide-coated sand filter for household drinking water from roof-harvested rainwater

This paper reports the performance of iron hydroxide-coated sand medium in removing bacteria and heavy metals from roof-harvested rainwater. In long-duration column tests (15 cm × 2.5 cm ID columns; empty bed contact time 15 min) employing roof-harvested rainwater, total coliform and faecal coliform removal ranged from 97% to >99%, and effluent turbidity remained below 2.0 NTU up to 500 bed volumes (BV). In comparison, bacterial removal by uncoated sand medium was always below 21%. Further column tests duplicating the use pattern of household water purification devices (daily input of 10 BV) indicated that intermittent use of the medium did not affect its performance, with bacterial removal remaining in the same range of 97–99% for 500 BV (50 d). Long-duration column tests conducted using a roof runoff (galvanised iron roof) with elevated levels of heavy metals, lead and zinc, showed that the medium is capable of effectively removing bacteria and heavy metals simultaneously for 600 BV, with effluent lead and zinc levels below the WHO guideline values for drinking water. Influent pH did not affect the bacterial removal in the pH range studied (pH 6.0–9.0). No leaching of iron from the sand was noticed for this pH range. The study showed the potential of iron hydroxide-coated sand as a sorptive filter medium for use in simple home water purification devices for treatment of roof-harvested rainwater which is generally contaminated by microorganisms and heavy metals.