New research overturns the conventional wisdom that mineral deposits interfere with microbial colonization of rapid sand filters that are used to treat groundwater for drinking.

Over time, the grains in rapid sand filters become coated with minerals. Much of this coating is periodically removed through backwashing. But in fact mineral coatings on the sand particles actually encourage microbial activity and density, the Danish study suggests.

Until now, little was known about the effect of such mineral coating on the activity, colonization, diversity and abundance of microbiota, according to the American Society for Microbiology, which has published the study in its journal Applied and Environmental Microbiology.

The research showed that the minerals form an abundant, honeycomb-like matrix around the sand particles, where bacterial cell density can be very high. With additional ammonium, this is boosted further.

The bacteria help remove ammonium, manganese and other impurities from the groundwater, and the investigation revealed that this ammonium-removal activity increased as the mineral deposits grew.

"These positive mineral-microbe interactions suggest protective and supportive roles of the deposits," commented corresponding author Barth F. Smets, from the Technical University of Denmark, Lyngby.

The researchers also measured a high diversity of ammonium- and nitrite-oxidizing species.

First author Arda Gülay said that the research raises the question of whether microbes influence the development of the microporosity, or simply take advantage of it. Either way, the mineralization could ultimately be steered to create micro-structures designed to house microbial cells to perform specific functions, Gülay concluded.