Comparison of physicochemical iron removal mechanisms in filters

Water supply companies are continually seeking means to improve the process efficiency of iron removal from groundwater in order to minimize the depos ition of iron in distribution networks, backwash water use, and volume of t he sludge produced. It is expected that the process efficiency can be optim ized with a better understanding of the different mechanisms involved in th e iron removal process and their optimal utilization. in order to investiga te the options to improve the performance of an iron removal plant, pilot e xperiments were conducted with filters operating in two different iron remo val modes, namely floc filtration and adsorptive filtration. The results we re then compared with the performance of the full-scale plant Gilze, which operates mainly in the floc filtration mode. Results demonstrated that the performance of WTP Gilze in terms of ripening time, filter run time and fil trate quality (residual iron and turbidity) could be improved by operating the filters in (a) adsorptive mode With fine sand (0.5-0.8 mm) and low infl uent oxygen, or (b) in floc filtration mode with dual media (anthracite 0.8 -1.2 mm and sand 0.5-0.8 mm). In general, for a single media fine sand filt er, the adsorptive mode gave a longer run time than the floc filtration mod e with comparable filtrate quality. in the adsorptive mode, oxygen content and pre-oxidation time should be kept as low as possible. However, to ensur e sufficient removal of manganese and ammonium present in groundwater, a mi nimum oxygen concentration is required (about 2 mg l(-1) in case of WTP Gil ze). Experimental results suggested that filters with coarser single media or dual media operating mainly under adsorptive mode with short pre-oxidati on time could further improve filter performance and probably result in sig nificant cost savings.