Laboratory studies on ochre formation and removal from geotextile filters

The clogging of drainage systems due to the formation of ochre is considered a major threat to the performance of filters and drainage systems. Aiming to understand the factors leading to clogging, column tests were conducted using geotextile filters under three different filter submersion conditions and ferric citrate percolation to stimulate ochre production. After 76 days, in half of the column tests, the ferric citrate was changed to D-glucose in the percolation fluid to remove the ochre by the reductive dissolution of iron. The concentrations of dissolved oxygen (DO), Fe(II), Fe(III), and pH were monitored as a function of time. Ochre-clogged geotextile filters and the effects of reductive dissolution were observed by scanning electron microscopy coupled to energy-dispersive spectroscopy. The results indicated that ochre formation decreased substantially in the submerged filters due to the lower availability of oxygen for microbial aerobic activities. Percolation with D-glucose led to low DO content, reduced pH in the percolation fluid, and stimulation of a pre-existing population of iron-reducing bacteria, which reduced the Fe(III) to soluble Fe(II), reversing clogging in geotextile filters. This fundamental research may indicate a path for a new procedure for mitigation and removal of ochre of drainage systems.