Nitrate-mediated biomigration and transformation of As/Fe in arsenic-bearing ferrihydrite

Reducing bacteria play a key role in the transformation and release of As/Fe in groundwater system. To investigate the influence of nitrate input on biological migration and transformation of As/Fe, anaerobic simulation experiments were used to study Fe(III) and As(V) reduction in liquid phase and arsenic-bearing ferrihydrite by metal-reducing bacteria D2201 with nitrate participation. The results indicated that nitrate input inhibited the biological reduction of Fe(III). The reduction rate of Fe(III) decreased by 68.3% and 90.2% when nitrate concentration increased from 0 to 1 and 3 mM, respectively. However, nitrate promoted the biological reduction of As(V) by enhancing bacterial growth. Compared with the experimental group without nitrate, the bacterial biomass of the experimental groups with 1 and 3 mM nitrate increased by 243% and 296%, respectively, and As(V) reduction rate increased by 102.1% and 276.9%, respectively. In addition, nitrate reduced arsenic release by inhibiting Fe(III) reduction on arsenic-bearing ferrihydrite. Scanning electron microscope (SEM) images show that Bacillus D2201 dissolved the ferrihydrite, and nitrate input restrained this process. Therefore, the existence of nitrate significantly inhibited arsenic pollution in groundwater, which indicated that nitrate concentration should be considered when studying the fate and migration of arsenic.