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 certai...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.展开更多
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 ...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.展开更多
基金Project (No. 20407015) supported by the National Natural Sci-ence Foundation of China
文摘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.
基金We are grateful for the project grants supported by the Major Science and Technology Programs for Water Pollution Control and Management of China(Nos.2012ZX07205-001 and 2017ZX7103-007).
文摘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.
