Reductive denitrification of nitrate by scrap iron filings

Reduction of nitrate by zero-valent iron is a highly exergonic reaction that has long been known to occur. Use of scrap iron filings (SIF) as the PRB (Permeable Reactive Barrier) material can be used to recycle certain by-products, and identify cheaper replacements for expensive conventional PRB materials, especially pure metallic iron. The feasibility of reductive denitrification of nitrate by SIF was studied by batch experiments. Operational parameters such as pH value, SIF dosage and initial concentration of nitrate were investigated. The removal efficiency of nitrate reached 80% under the conditions of pH of 2.5, nitrate initial con- centration of 45 mg/L and SIF dosage of 100 g/L within 4 h. Results indicated that nitrate removal is inversely related to pH. Low pH value condition favors for the nitrate transformation. Different from the results of others who studied nitrate reduction using iron powder, we found that there was a lag time before nitrate reduction occurs, even at low pH. Finally, the possible mechanism of nitrate reduction by Fe0 is discussed.

The Dynamic Experiment on Treating Acid Mine Drainage with Iron Scrap and Sulfate Reducing Bacteria Using Biomass Materials as Carbon Source

The study is aimed at the problem of high content of Cr^(6+),Cr^(3+)and SO_(4)^(2-)is high and low pH value in acid mine drainage(AMD).Moreover,treatment of AMD by sulfate reducing bacteria(SRB)requires the addition of carbon source,while the treating effectiveness is not good enough on its own.The sugarcane slag,the corn cob and the sunflower straw were selected as the SRB carbon source cooperating with iron scrap to construct the dynamic columns 1,2 and 3.The mechanism of removing Cr^(6+),Cr^(3+),SO_(4)^(2-)and H+and the regularity of sustained release of carbon source and TFe release was studied in AMD.The removal efficiency of heavy metal ions,the ability of sustained release of carbon source,and the ability of adjusting acid by the three dynamic columns were compared.The result shows that the average removal rates of Cr^(6+),Cr^(3+)and SO_(4)^(2-)in effluent of dynamic column 1,filled by sugarcane slag,iron scrap and SRB,were 96.9%,67.1%and 54.3%.The average release of TFe and chemical oxygen demand(COD)were 4.4 and 287.3 mg/L.Its average pH was 6.98.Compared with the performance of dynamic columns 1,2 and 3,dynamic column 1 performed best in removing Cr^(6+),Cr^(3+)and SO_(4)^(2-)from AMD and controlling the release of COD and TFe,adjusting the pH of the solution.The study is of significance in treatment of AMD by taking for biomass materials as SRB carbon source in cooperation with iron scrap.

Reduction of hexavalent chromium with scrap iron in a fixed bed reactor

The reduction of hexavalent chromium by scrap iron was investigated in continuous long-term fixed bed system. The effects of pH, empty bed contact time （EBCT）, and initial Cr（VI） concentration on Cr（VI） reduction were studied. The results showed that the pH, EBCT, and initial Cr（VI） concentration significantly affected the reduction capacity of scrap iron. The reduction capacity of scrap iron were 4.56, 1.51, and 0.57mg Cr（VI）-g1 Fe0 at pH 3, 5, and 7 （initial Cr（VI） concentration 4 mg.L 1, EBCT 2 min, and temperature 25℃）, 0.51, 1.51, and 2.85 mg Cr（VI）.g-I Fe0 at EBCTs of 0.5, 2.0, and 6.0rain （initial Cr（VI） concentration 4mg.L-1, pH 5, and temperature 25℃）, and 2.99, 1.51, and 1.01 mg Cr（VI）. gl Fe0 at influent concentrations of 1, 4, and 8 mg.L ^-1（EBCT 2 min, pH 5, and temperature 25℃）, respectively. Fe（total） concentration in the column effluent continuously decreased in time, due to a decrease in time of the iron corrosion rate. The fixed bed reactor can be readily used for the treatment of drinking water containing low amounts of Cr（VI） ions, although the hardness and humic acid in water may shorten the lifetime of the reactor, the reduction capacity of scrap iron still achieved 1.98 mg Cr6 ＋- g-~ Fe. Scanning electron micro- scope equipped with energy dispersion spectrometer and X-ray diffraction were conducted to examine the surface species of the scrap iron before and after its use. In addition to iron oxides and hydroxide species, iron-chromium complex was also observed on the reacted scrap iron.

Scrap Iron Filings assisted nitrate and phosphate removal in low C/N waters using mixed microbial culture

This study focuses on identifying the factors under which mixed microbial seeds assist bio-chemical denitrification when Scrap Iron Filings(SIF)are used as electron donors and adsorbents in low C/N ratio waters.Batch studies were conducted in abiotic and biotic reactors containing fresh and aged SIF under different dissolved oxygen concentrations with NO_(3)^(-)−N and/or PO_(4)^(3−)influent(s)and their nitrate/phosphate removal and by-product formations were studied.Batch reactors were seeded with a homogenized mixed microbial inoculum procured from natural sludges which were enriched over 6 months under denitrifying conditions in the presence of SIF.Results indicated that when influent containing 40 mg/L of NO_(3)^(-)−N was treated with 5 g SIF,79.9%nitrate reduction was observed in 8 days abiotically and 100%removal was accomplished in 20 days when the reactor was seeded.Both abiotic and seeded reactors removed more than 92%PO_(4)^(3−)under high DO conditions in 12 days.Abiotic and biochemical removal of NO_(3)^(-)−N and abiotic removal of PO_(4)^(3−)were higher under independent NO_(3)^(-)−N/PO_(4)^(3−)loading,while 99%PO_(4)^(3−)was removed biochemically under combined NO_(3)^(-)−N and PO_(4)^(3−)loading.This study furthers the understandings of nitrate and phosphate removal in Zero Valent Iron(ZVI)assisted mixed microbial systems to encourage the application of SIF-supported bio-chemical processes in the simultaneous removals of these pollutants.