New biofilter can remove toxic elements

Nitrogen and phosphorus are two of the most common elements found in industrial and agricultural wastewater today. Because these elements are causing environmental problems, there is a need for technologies that can reclaim them from waste streams.

The EU-funded PSNOP project thus set out to develop and test a natural pyrrhotite (a type of mineral) simultaneous nitrogen and phosphorus (PSNOP) biofilter. It works by colonising pyrrhotite particles with bacteria that can remove nitrogen from wastewater.

The project began by culturing denitrifying (nitrate-reducing) bacteria from anaerobic sludge of a wastewater treatment plant. Over several days, this process produced a thriving colony of denitrifying bacteria that could be used to 'seed' pyrrhotite particles.

Researchers also showed that pyrrhotite (without a bacterial biofilm) naturally removed up to 99 % of phosphorus from wastewater over 24 hours. This worked effectively in different acidity conditions (pH 4–12), and the efficiency improved as the temperature increased.

PSNOP then created several biofilters by allowing the denitrifying bacteria to colonise pyrrhotite and limestone, or a combination of the two. These were tested for their ability to remove phosphorus and nitrogen simultaneously from wastewater.

Overall, the pyrrhotite-only biofilter performed best. The limestone-only biofilter could not remove nitrogen, and the mixed biofilter had limited capacity to remove both elements. A major success is that the PSNOP biofilter could remove 85–90 % of phosphorus and nitrogen when operating continuously.

This new technology could find application as a tertiary treatment process in wastewater treatment plants.