Metals removal from automobile workshop stormwater runoff using rice husk, GAC and gravel filtration

The efficiency of combined filtration media consisting of rice husk (RH), granular activated carbon (GAC) and gravel (GR) for the removal of metals cadmium, copper, lead and iron from stormwater runoff emanating from automobile workshops in Nigeria was investigated. Stormwater runoff samples were collected from five sites over a period of nine (9) weeks and filtered using two filter combinations, GAC - RH, GR - GAC as well as a RH-only filter. All the filters removed metals. Highest average singular metals removals were: approximately 74% copper for GR - GAC; 70% lead for RH, 67% iron for GAC - RH and 46% cadmium for GAC - RH. Average metals removal efficiencies (all metals combined) were GAC - RH 61%, GR - GAC 52% and RH-only 46%. The combined filter materials therefore showed better metals removal efficiencies than the RH-only filter. Further filtration of metals polluted stormwater would be required to lower the average metals concentration to meet local and international discharge standards. Future research into low cost modifications towards optimising the filter materials to improve metals removal efficiencies is recommended.