Prediction of iron and manganese release during riverbank filtration T. Grischek, S. Paufler 1
Outline Introduction Study area How much iron could be reduced? Conclusions 2
Processes during RBF Hiscock & Grischek 2002 3
RBF and iron (common expectation) River Groundwater portion 10 50 % Bank filtrate portion 50 90 % Oxygen depletion, Denitrification, Fe(II) release as result of degradation of DOC 4
RBF site Torgau, Germany Monitoring cross-section I 42 vertical wells Distance to river: about 300 m Monitoring cross-section II Depth of filters: 30-50 m bgl Abstraction rates: 150 m³/h/well Sandhu (2009) 5
Mean iron concentration 1993 Hochschule für Technik und Wirtschaft Dresden 0 MP 7/1: 20 MP 7/3: 18 Deich River Elbe Elbe 0,5 old branch Alte Elbe m a.s.l. 0,2 Up to 100 mg/l 90 65 Spremberger Schichten 41 0,09 MP 53 37 30 production Well Brunnen 33 33 borehole 33 Well 33 0,06 MP 43 14 24 0,7 9 5,7 26 0,4 MP 33 0,1 33 25 6,8 14,5 28 19 Around 30 mg/l Cross-section II 19 Meßprofil Torgau-Ost II 6
Decreasing iron concentration 1993-2008 100 90 Torgau-Ost: Monitoring cross-section II β(fe tot ) in mg/l 80 70 60 50 40 Well 33-50% in about 20 years 30 20 10 0 01.01.93 01.01.94 01.01.95 01.01.96 31.12.96 31.12.97 31.12.98 31.12.99 30.12.00 30.12.01 30.12.02 30.12.03 29.12.04 29.12.05 29.12.06 29.12.07 MP 33 MP 43 MP 53 Well 33 MP 53 Date 7
DOC removal in cross-section II Cross-section II MP 6 near well 33 sediment fraction < 2 mm Fe 2000-4800 mg/kg Sample Depth (m bgl) Fe (mg/kg) Mn (mg/kg) 1 1.8-2.5 3380 100 2 5.0-6.0 3910 33 3 9.0-10.0 1850 21 4 15.0-16.0 2390 16 5 21.0-22.0 2790 19 6 25.0-26.0 4310 28 7 27.0-28.0 4810 30 8 33.0-34.0 1950 15 9 37.0-38.0 2260 20 10 39.0-40.0 1890 20 11 42.0-43.0 2470 22 DOC in mg/l, 1995-1997 DOC in mg/l, 2005-2007 No change in DOC conc. = No change in Fe(II) conc.? 8
How much iron could be released? 9
Column experiment for extraction of total iron 3000 2500 >70% of total iron conc. extracted Fe tot 3550 mg/kg (Fe) in mg/kg 2000 1500 1000 500 0 0 100 200 300 400 500 600 700 800 900 Time Zeit in in ddays Fe tot 2470 mg/kg Hydroxylamine hydrochloride solution after Brand (1989) A1 A2 B1 B2 10
Well 2 Hochschule für Technik und Wirtschaft Dresden Hypothetical iron release along the flow path 150 m³/h River V = 800,000 m³ ρ = 1.8 10 3 kg/m³ Fe tot = 3,000 mg/kg 4,000,000 kg Fe pool in aquifer Well 1 Well 2 Well 3 Q well = 0.7*10 6 m³/a (50% bf) Fe(II) well = 20 mg/l River Fe removal = 14,000 kg/a > 250 years potential release of iron 11
Potential RBF site Embaba, Egypt 20m Potential RBF well 1,600,000 kg Fe pool in aquifer Q well = 1.2*10 6 m³/a (90% bf) Fe removal = 3,600 kg/a > 440 years potential release of iron Nile river Fraction < 2 mm Nile riverbed 11,000 mg/kg TOC 37,600 mg/kg Fe 780 mg/kg Mn Aquifer sediment 1,100 mg/kg TOC 11,100 mg/kg Fe 130 mg/kg Mn Groundwater: Fe > 3 mg/l Nile water: DOC < 5 mg/l, less degradable 12
RBF and iron (revised figure) Hochschule für Technik und Wirtschaft Dresden River Groundwater portion 10 50 % Anoxic conditions; low redox Generally substantial Fe(II) Low variation in water quality Bank filtrate portion 50 90 % Oxygen depletion, Denitrification, Fe(II) Dissolution/desorption of Fe(II) maximum permissible value for Fe in drinking water (0.2 mg/l) is usually exceeded at RBF sites Sandhu (2009) 13
Conclusions Fe(II) is a subject of concern for most RBF sites Check Fe(II) in land-side groundwater Fe(II) concentration can also decrease during RBF It takes decades to achieve steady-state conditions Prediction based on BDOC/TOC and Fe tot in sediment 14
Acknowledgements BMBF FHproUnt2012: Optimization of bank filtration and subsurface removal of iron and manganese (03FH042PX2). ESF grant (no. 200031585) Water company FWV Elbaue-Ostharz GmbH Contact Thomas Grischek (Mail: grischek@htw-dresden.de) Sebastian Paufler (Mail: paufler@htw-dresden.de) Faculty of Civil Engineering Division of Water Sciences 15
Mass balance approach DOM = (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 ) DOM + 138 O 2 106 CO 2 + 16 NO 3- + HPO 4 2- + 122 H 2 O + 18 H + DOM + 94,4 NO 3- + 92,4 H + 106 CO 2 + 55,2 N 2 + HPO 4 2- + 177,2 H 2 O NH 4+ + 2 O 2 2 H + + H 2 O + NO 3 - von Gunten et al. 1991 Observed removal: 2.9 mg/l DOC and 0.1 mg/l NH 4 + Oxidation requires only about 3.5 mg/l O 2 Along flowpath 10.4 mg/l O 2 and 22 mg/l NO 3- consumed 16
Decreasing Mn concentration 1995-2015 Mean manganese concentration Dresden Niederpoyritz -70% in about 20 years 17