AWWA WQTC69446

Subsurface or in-situ iron removal involves the injection of aerated water into an anaerobic aquifer. Processes of adsorption, oxidation and precipitation result in reduced iron concentrations in the abstracted water. However, subsurface treatment has also an effect on arsenic and phosphate levels in the groundwater. Arsenic, phosphate and iron show a similar pattern during an injection-abstraction cycle. Once injection is stopped for a longer period, iron and arsenic concentrations increase significantly, the occurrence of arsenic remobilization is, however, not certain. The enhanced nitrification on the dry biofilters after subsurface treatment has been observed as another beneficial side effect. In this study ammonia oxidizing bacteria (AOB) and archaea (AOA), and G. ferruginea were identified to be present at higher levels in the subsurface aerated water than in reference (i.e., backgound) groundwater especially at the beginning of the abstraction period. G. ferruginea could influence iron oxidation and removal in biofilters in a similar way as was previously hypothesized for iron colloids. Includes 23 references, table, figures.