TECHNOLOGY
Treatment to oxidise iron and correct pH
passive systems can be deployed . These rely on naturally occurring processes to remove the metals and buffer the pH . For instance : oxidation of iron to insoluble ferric hydroxide using aerobic wetlands ; precipitation of metals as sulphide by means of sulphate reducing bacteria in anaerobic wetlands ; or the addition of alkalinity to the water by percolation through beds filled with crushed limestone
( anoxic limestone drains - ALD ).
Passive systems have a life of 10 to 20 years before they need to be replaced , during this period minimal maintenance is required .
For waters with either a very low pH and / or containing high concentrations of dissolved metals , active treatment using conventionally engineered treatment systems is required . These involve the continual input of reagents to remove the contaminants
20 December 2017