The effect of granular ferric hydroxide amendment on the reduction of nitrate in groundwater by zero-valent iron

• Granular ferric hydroxide (GFH) was used as an amendment material in Fe(0) reaction.
• GFH amendment enhanced nitrate reduction rate and capacity.
• The overall effect of GFH stems from pH buffering and magnetite formation.
• Potential utility of Fe(0)/GFH as a viable technology for contaminant removal.

The feasibility of using granular ferric hydroxide (GFH) with zero-valent iron (Fe(0)) for its potential utility in enhancing nitrate reduction was investigated. The addition of 10 g L−1 GFH to 25 g L−1 Fe(0) significantly enhanced nitrate removal, resulting in 93% removal of 52.2 mg-N L−1 in 36-h as compared to 23% removal with Fe(0) alone. Surface analyses of the reacted Fe(0)/GFH revealed the presence of magnetite on the Fe(0) surface, which probably served as an electron mediator for nitrate reduction. Addition of GFH to Fe(0) also resulted in lower solution pH compared to Fe(0). The rate enhancing effect of GFH on nitrate reduction was attributed to the combined effects of magnetite formation and pH buffering by GFH. GFH amendment (100 g L−1) significantly increased reduction capacity and longevity of Fe(0) to complete several nitrate reduction cycles before inactivation, giving a total nitrate removal of 205 mg-N L−1, while unamended Fe(0) gave only 20 mg-N L−1 before inactivation during the first reduction cycle. The overall result demonstrated the potential utility of Fe(0)/GFH system that may be developed into a viable technology for removal of nitrate from groundwater.