title: Breakthrough behavior of granular ferric hydroxide (GFH) fixed-bed adsorption filters: modeling and experimental approaches.
abstract: Breakthrough curves (BTC) for the adsorption of arsenate and salicylic acid onto granulated ferric hydroxide (GFH) in fixed-bed adsorbers were experimentally determined and modeled using the homogeneous surface diffusion model (HSDM). The input parameters for the HSDM, the Freundlich isotherm constants and mass transfer coefficients for film and surface diffusion, were experimentally determined. The BTC for salicylic acid revealed a shape typical for trace organic compound adsorption onto activated carbon, and model results agreed well with the experimental curves. Unlike salicylic acid, arsenate BTCs showed a non-ideal shape with a leveling off at c/c0 approximately 0.6. Model results based on the experimentally derived parameters over-predicted the point of arsenic breakthrough for all simulated curves, lab-scale or full-scale, and were unable to catch the shape of the curve. The use of a much lower surface diffusion coefficient D(S) for modeling led to an improved fit of the later stages of the BTC shape, pointing on a time-dependent D(S). The mechanism for this time dependence is still unknown. Surface precipitation was discussed as one possible removal mechanism for arsenate besides pure adsorption interfering the determination of Freundlich constants and D(S). Rapid small-scale column tests (RSSCT) proved to be a powerful experimental alternative to the modeling procedure for arsenic.
authors.affiliation: Department of Water Quality Control, Technical University of Berlin, Sekr. KF 4, Strasse des 17. Juni 135, 10623 Berlin, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Sperlich
authors.forename: Arne
authors.initials: A
authors.lastname: Werner
authors.forename: Arne
authors.initials: A
authors.lastname: Genz
authors.forename: Gary
authors.initials: G
authors.lastname: Amy
authors.forename: Eckhard
authors.initials: E
authors.lastname: Worch
authors.forename: Martin
authors.initials: M
authors.lastname: Jekel
mesh_terms: D000327:Adsorption; D001149:Arsenates / Q000302:isolation & purification; D001151:Arsenic / Q000302:isolation & purification; D002606:Charcoal / Q000737:chemistry; D011232:Chemical Precipitation; D004058:Diffusion; D005290:Ferric Compounds / Q000737:chemistry*; D005374:Filtration; D008956:Models, Chemical; D009930:Organic Chemicals / Q000302:isolation & purification; D020156:Salicylic Acid / Q000302:isolation & purification; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014873:Water Pollutants / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*
chemical_list: D001149:Arsenates; D005290:Ferric Compounds; D009930:Organic Chemicals; D014873:Water Pollutants; D002606:Charcoal; C021024:ferric hydroxide; D001151:Arsenic; D020156:Salicylic Acid