The goal of this proposed research is to test the hypothesis that biochar is a rechargeable “geo-battery” that can promote microbial nitrate removal from stormwater.  This hypothesis is based on our recent laboratory and field results, as outlined below.

In a recently completed CAIT-funded project, we demonstrated that anaerobic bacteria can use reduced biochar as an electron source to degrade nitrate in water.  It was not clear, though, whether the “used” (i.e., oxidized) biochar can be rejuvenated to support further nitrate reduction.  In a parallel field study, recent data from a pilot scale bioretention cell offer interesting clues.  The pilot cell, located on the University of Delaware (UD) campus, consisted of a biochar-amended top layer (4% biochar) and a zero-valent iron-amended bottom layer (10% ZVI).  Both ZVI and biochar were added to provide the electrons needed for nitrate reduction, but their modes of action were different.  ZVI was a reducing agent that continuously supplied electrons for microbial nitrate removal.  In contrast, biochar, we hypothesized, acted as a “geo-battery” that would undergo reversible charging-discharging cycles and, when charged, it can provide electrons for nitrate degradation.