title: Feasibility of two low-cost organic substrates for inducing denitrification in artificial recharge ponds: Batch and flow-through experiments.
abstract: Anaerobic batch and flow-through experiments were performed to assess the capacity of two organic substrates to promote denitrification of nitrate-contaminated groundwater within managed artificial recharge systems (MAR) in arid or semi-arid regions. Denitrification in MAR systems can be achieved through artificial recharge ponds coupled with a permeable reactive barrier in the form of a reactive organic layer. In arid or semi-arid regions, short-term efficient organic substrates are required due to the short recharge periods. We examined the effectiveness of two low-cost, easily available and easily handled organic substrates, commercial plant-based compost and crushed palm tree leaves, to determine the feasibility of using them in these systems. Chemical and multi-isotopic monitoring (δ15NNO3, δ18ONO3, δ34SSO4, δ18OSO4) of the laboratory experiments confirmed that both organic substrates induced denitrification. Complete nitrate removal was achieved in all the experiments with a slight transient nitrite accumulation. In the flow-through experiments, ammonium release was observed at the beginning of both experiments and lasted longer for the experiment with palm tree leaves. Isotopic characterisation of the released ammonium suggested ammonium leaching from both organic substrates at the beginning of the experiments and pointed to ammonium production by DNRA for the palm tree leaves experiment, which would only account for a maximum of 15% of the nitrate attenuation. Sulphate reduction was achieved in both column experiments. The amount of organic carbon consumed during denitrification and sulphate reduction was 0.8‰ of the total organic carbon present in commercial compost and 4.4% for the palm tree leaves. The N and O isotopic fractionation values obtained (εNand εO) were -10.4‰ and -9.0‰ for the commercial compost (combining data from both batch and column experiments), and -9.9‰ and -8.6‰ for the palm tree column, respectively. Both materials showed a satisfactory capacity for denitrification, but the palm tree leaves gave a higher denitrification rate and yield (amount of nitrate consumed per amount of available C) than commercial compost.
authors.affiliation: Grup de Mineralogia Aplicada i Geoquímica de Fluids, Departament de Mineralogia, Petrologia i Geologia Aplicada, SIMGEO UB-CSIC, Facultat de Ciències de la Terra, Universitat de Barcelona (UB), C/ Martí i Franquès, s/n, 08028 Barcelona, Spain. Electronic address: albagrau@ub.edu.
authors.forename: Alba
authors.initials: A
authors.lastname: Grau-Martínez
authors.affiliation: Grup de Mineralogia Aplicada i Geoquímica de Fluids, Departament de Mineralogia, Petrologia i Geologia Aplicada, SIMGEO UB-CSIC, Facultat de Ciències de la Terra, Universitat de Barcelona (UB), C/ Martí i Franquès, s/n, 08028 Barcelona, Spain; Centre for Hydrogeology and Geothermics, University of Neuchâtel, Rue Emile-Argand 11, 2000 Neuchâtel, Switzerland.
authors.forename: Clara
authors.initials: C
authors.lastname: Torrentó
authors.affiliation: Grup de Mineralogia Aplicada i Geoquímica de Fluids, Departament de Mineralogia, Petrologia i Geologia Aplicada, SIMGEO UB-CSIC, Facultat de Ciències de la Terra, Universitat de Barcelona (UB), C/ Martí i Franquès, s/n, 08028 Barcelona, Spain.
authors.forename: Raúl
authors.initials: R
authors.lastname: Carrey
authors.affiliation: Hydrogeology Group (GHS), Department of Civil and Environmental Engineering, Universitat Politècnica de Catalunya (UPC), c/Jordi Girona 1-3, 08034 Barcelona, Spain.
authors.forename: Paula
authors.initials: P
authors.lastname: Rodríguez-Escales
authors.affiliation: Grup de Mineralogia Aplicada i Geoquímica de Fluids, Departament de Mineralogia, Petrologia i Geologia Aplicada, SIMGEO UB-CSIC, Facultat de Ciències de la Terra, Universitat de Barcelona (UB), C/ Martí i Franquès, s/n, 08028 Barcelona, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Domènech
authors.affiliation: Department of Chemical and Geological Sciences, University of Cagliari, Via Trentino 51, 09127 Cagliari, Italy; Desertification Research Center-NRD, University of Sassari, Viale Italia 39, 07100 Sassari, Italy.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Ghiglieri
authors.affiliation: Grup de Mineralogia Aplicada i Geoquímica de Fluids, Departament de Mineralogia, Petrologia i Geologia Aplicada, SIMGEO UB-CSIC, Facultat de Ciències de la Terra, Universitat de Barcelona (UB), C/ Martí i Franquès, s/n, 08028 Barcelona, Spain.
authors.forename: Albert
authors.initials: A
authors.lastname: Soler
authors.affiliation: Grup de Mineralogia Aplicada i Geoquímica de Fluids, Departament de Mineralogia, Petrologia i Geologia Aplicada, SIMGEO UB-CSIC, Facultat de Ciències de la Terra, Universitat de Barcelona (UB), C/ Martí i Franquès, s/n, 08028 Barcelona, Spain.
authors.forename: Neus
authors.initials: N
authors.lastname: Otero
mesh_terms: D000462:Algeria; D064751:Ammonium Compounds / Q000378:metabolism; D028023:Arecaceae / Q000737:chemistry*; D005591:Chemical Fractionation; D058440:Denitrification; D004784:Environmental Monitoring; D060587:Groundwater / Q000032:analysis*; D009566:Nitrates / Q000378:metabolism; D009587:Nitrogen Isotopes / Q000032:analysis; D010084:Oxidation-Reduction; D010103:Oxygen Isotopes / Q000032:analysis; D018515:Plant Leaves / Q000737:chemistry*; D061005:Ponds; D013030:Spain; D013431:Sulfates / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000378:metabolism*; D018508:Water Purification / Q000295:instrumentation / Q000379:methods*
chemical_list: D064751:Ammonium Compounds; D009566:Nitrates; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D013431:Sulfates; D014874:Water Pollutants, Chemical
keywords: Denitrification; Flow-through experiments; Monitored artificial recharge; Organic substrate; Permeable reactive barrier; Semi-arid region