Catalytic-iron filters for effective and low-cost treatment of odorous air

Several methods are available to remove hydrogen sulphide and volatile organic sulphides from ventilated air at sewage-treatment works. Some methods use alkaline and oxidative chemical scrubbers which may have high capital and operational costs. Other methods, such as bio-scrubbers and bio-filters, are used to biochemically oxidize sulphides. Biological scrubbers have the advantage of low operating costs, but their performance may be adversely affected by a high concentration of sulphide (>100 ml/m(3)). This paper describes the development of a novel, compact and low-cost 'rusty-iron' chemical filter which catalyzes the oxidation of hydrogen sulphide and organic sulphides to colloidal sulphur and water. Operating costs are relatively low with no need for routine maintenance. Full-scale demonstration of the effectiveness of such filters was carried out over two years at several treatment works, the results of which are described and discussed together with details of capital costs. The overall percentage removal of hydrogen sulphide by compact multistage filters was found to exceed 95%, irrespective of inlet sulphide concentrations which varied from 34 to 500 ml/m(3) (ppm).