The importance of key attenuation factors for microbial and chemical contaminants during managed aquifer recharge: A review

There is increasing interest worldwide to utilize unconventional water resources such as reclaimed water, urban stormwater, or impaired surface water to augment drinking water supplies. Given the presence of traditional and emerging microbial and chemical contaminants (e.g., pathogens, trace organic chemicals, nutrients, trace metals) in these waters, efficient and reliable treatment processes are needed to assure a product water quality that is protective of public health. Natural treatment processes such as managed aquifer recharge (MAR) combine the benefits of efficient biological treatment for these contaminants with a low carbon footprint and a residual free operation. The drawbacks of MAR are the rather large space requirements and a lack of process understanding that can guide more efficient design and operation of these facilities. Among appropriate design and operational parameters as well as geochemical and hydrological conditions, retention time has been identified as a key parameter to achieve attenuation of microbial and chemical contaminants during MAR. Shorter retention time can result in significantly reduced footprints and thus facilitate the integration of MAR into urban and peri-urban water infrastructure. However, different minimum retention times are required to achieve reliable removal of microbial and chemical contaminants.