Research on enhancement of zero-valent iron on dissimilatory nitrate/nitrite reduction to ammonium of Desulfovibrio sp. CMX

Iron-Activated Carbon Systems to Enhance Aboriginal Aerobic Denitrifying Bacterial Consortium for Improved Treatment of Micro-Polluted Reservoir Water: Performances, Mechanisms, and Implications

“…Methylotenera almost only presented in iron-modified systems; this result was consistent with the previous study that ZVI increased the abundance of Methylotenera in a biological nitrate removal system . The relative abundance of Methyloversatilis was significantly improved in the ACSI system, which has been proved to “switch” from heterotrophy to autotrophy by using inorganic electron donors (hydrogen or iron) when organic matter is insufficient. , In addition, Hydrogenophaga are facultative aerobic autotrophic denitrifying bacteria using [H] or H 2 as electron donors. , Hydrogenophaga almost only presented in the ACSI system but were absent in others, which is consistent with the previous study . In the ZVI-modified system, the produced ferrous ions and hydrogen were released by immersed iron and used by Hydrogenophaga, which could explain this phenomenon .…”

“…In recent years, many strains of aerobic denitrifiers have been found to have a high nitrate removal capacity in media with high nitrate concentrations. − However, they have an unsatisfactory capacity to treat raw water because of their weak resistance to environmental loads and insufficient nutrients . Previous studies found that a mixed-aerobic denitrifying consortium presented significantly higher NO 3 – -N removal efficiency and better response to environmental changes than that of a single strain, which might be attributed to an efficient and complete nitrogen cycle caused by interspecies interactions. , Thus, in contrast to previous investigations, this study added iron as inorganic electron donors directly into the raw water to enhance the nitrogen removal ability of the aboriginal mixed bacteria consortium without using an artificial denitrification medium.…”

“…During the first 6 days, the alkalinity in the three systems increased owing to the production of hydroxide ions during denitrification (eqs –). , The pH value was about 8.06 in the iron-containing systems after the 6th day, while the AC system showed a more alkaline environment. It was reported that ZVI and Fe 2+ can reduce the pH of alkaline systems due to the reaction between OH – and iron ions, which also theoretically explains the low total iron concentration (<0.030 mg/L and mean value of 0.014 mg/L) during the experiment. …”

“…The nitrate concentration decreased by 0.81 mg/L, and the ammonia concentration increased by 0.64 mg/L at this stage. ZVI could hardly react with nitrate but could promote the chemical reaction of nitrite to ammonium under a neutral pH condition . However, Fe/AC showed a wilder pH range for the chemical reaction of ZVI with nitrate that TN removal efficiency kept higher than 35% with pH lower than 9.0 with main production of ammonia .…”

“…(2) During 3–24 days nitrate was mainly reduced by the biological denitrification promoted by ZVI; ammonia, nitrite, and nitrate nitrogen concentrations showed a slow decreasing trend. In addition to the improvement in chemical denitrification, ZVI also promotes the biological denitrification by rendering additional electron sources . Ferrous ions and hydrogen produced by immersed iron can also be used by biotic denitrifiers to remove NO 3 – -N .…”