The differing physico-chemical properties of the RCs can explain the different removal performances observed. The high P removal at lower Fe:P ratios of 2.1:1 observed with ultrafiltered and acidified RC was due to the iron being available entirely in soluble form,thus giving a similar removal mechanism to FFS (Thistleton et al.,2002).
Lower removal with unfiltered, acidified RC compared with the ultrafiltered RC was due to the presence of more organic-
Fe complexes in the unfiltered RC as well as much higher proportions of insoluble Fe (55% compared with 99%