Phosphorus removal from stormwater using zero-valent iron
Date
2016
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Nutrient removal from water sources is becoming increasingly important, as nutrient pollution is emerging as a challenging and critical environmental issue. Nutrient pollution (excess nitrogen and phosphorus) can cause algal blooms, human health issues, and ecological and economic losses. Stormwater runoff can aggravate this issue, because it easily carries pollutants from surfaces into storm sewer systems and is discharged, untreated, to water sources. More recently, transportation agencies have become interested in treating stormwater runoff, particularly which comes off of road surfaces. There have been efforts by these agencies, along with the U.S. EPA to efficiently treat runoff. This work focuses on removal of phosphorus using scrap iron, or, zero-valent iron (ZVI). ZVI has numerous applications in removal technologies, and in this case, can be used as an amendment into a bioretention system to treat stormwater. By using several phosphorus pulse tests on flow-through columns, on both columns with and without ZVI, we were able to assess the removal efficiency of phosphorus by ZVI, by using the advection-dispersion-reaction equation to confirm our observational data. It was determined that ZVI can remove up to 98% of influent phosphorus at the lowest concentration of phosphorus (1.6 ppm PO4-P) used. At the highest concentration (16 ppm PO4-P), ZVI was shown to still remove up to 36% of incoming phosphorus. Through several phosphorus extractions, it was also determined that the phosphorus retained in the column is mostly iron-bound (strongly-bound) phosphorus, accounting for over 50% of the total phosphorus extracted. Iron-bound phosphorus will not be easily leached out of the system, since it is very stable, and only extractable with an acid. This has great promise as an amendment into the field for the treatment of excess phosphorus in stormwater. For future research, it would be advisable to study the effect that pH and flow rate has on the removal efficiency of phosphate by ZVI, as well as conduct a long-term study to determine the physical changes ZVI undergoes, and to determine potential iron-phosphate mineral formation.