title: Use of polymer mats in series for sequential reactive barrier remediation of ammonium-contaminated groundwater: field evaluation.
abstract: A pilot-scale field trial was undertaken to evaluate the potential of in situ polymer mats (installed in series) as permeable reactive barriers within a treatment wall remediation system to induce sequential bioremediation of ammonium-contaminated groundwater. The treatment wall consisted of 10 m wide impermeable wings on either side of a 0.75 m wide permeable reactive zone flow-through box. Two polymer mats were positioned in the flow-through box. The upgradient polymer mat within the flow-through box was used to deliver oxygen to induce bacterial nitrification of the ammonium to nitrite/nitrate as the groundwater moved past. The downgradient polymer mat delivered ethanol to induce bacterial denitrification of the nitrite/nitrate to produce nitrogen gas. The field trial was carried out at a near-shore location. Initially the flow-through box was left open; however, this resulted in substantial groundwater mixing, which inhibited sequential remediation. Once the flow-through box was in-filled with gravel, groundwater mixing was reduced, achieving a greater than 90% reduction in total N. Estimated first-order half-lives for nitrification and denitrification rates were 1.2 and 0.4 d, respectively. Field nitrification half-lives were approximately an order of magnitude greater than rates determined in large-scale columns using soil and groundwater from the site, while denitrification half-lives were similar. The results of this pilot-scale field trial indicate that sequential bioremediation of ammonium-contaminated groundwater at field scale is feasible using in situ polymer mats as permeable reactive barriers, although hydraulic conditions can be complex in such barrier systems.
authors.affiliation: CSIRO Land and Water, Private Bag No. 5, Wembley, Western Australia 6913, Australia. bradley.patterson@csiro.au
authors.forename: B M
authors.initials: BM
authors.lastname: Patterson
authors.forename: M E
authors.initials: ME
authors.lastname: Grassi
authors.forename: B S
authors.initials: BS
authors.lastname: Robertson
authors.forename: G B
authors.initials: GB
authors.lastname: Davis
authors.forename: A J
authors.initials: AJ
authors.lastname: Smith
authors.forename: A J
authors.initials: AJ
authors.lastname: McKinley
mesh_terms: D001673:Biodegradation, Environmental; D011108:Polymers; D000644:Quaternary Ammonium Compounds / Q000302:isolation & purification* / Q000378:metabolism*; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000302:isolation & purification* / Q000378:metabolism*; D014872:Water Movements; D014873:Water Pollutants / Q000302:isolation & purification* / Q000378:metabolism*
chemical_list: D011108:Polymers; D000644:Quaternary Ammonium Compounds; D012989:Soil Pollutants; D014873:Water Pollutants