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Initial project plan

State of the art and preliminary work

Granular or powdered adsorbents are frequently used to remove specific pollutants from impacted sources for water supply and for advanced treatment of wastewaters to protect the receiving water bodies. Examples of such adsorbents are granular ferric hydroxides for removal of arsenic (Driehaus et al. 1998) and phosphate (Genz et al. 2004), activated alumina for fluoride adsorption, and activated carbons to separate non-polar to moderately polar organic micropollutants (Sontheimer et al. 1988). The adsorption step has been extensively studied, including the adsorption equilibria of single target substances, competitive adsorption in mixtures, external and internal mass transfer (Axe & Trivedi 2002, Badruzzaman et al. 2004, Worch 2008), regeneration by chemicals for oxides (Genz et al. 2008, Sperlich et al. 2005 and 2008), and thermal reactivation for activated carbon. However, there is only little knowledge of the extent and kinetics of desorption during operation with variable influent concentrations (especially during phases of lower concentrations) and the phenomenon of irreversible adsorption. Irreversible adsorption has to be distinguished from chemical elution during regeneration, and it is not a well-defined process as desorption depends on experimental conditions and may be determined by very slow kinetic steps. There are only a few studies on adsorption at hydroxide/oxide surfaces and they indicate a very significant effect of irreversible adsorption (Driehaus et al. 1998, Genz et al. 2008) which is interpreted as surface precipitation (Li & Stanforth 2000, Hongshao & Stanforth 2001, Loring et al. 2009). The mechanisms of irreversible adsorption are hardly known with regard to activated carbons, but they may be caused by absorptive uptake by the solid, similar to soil organic matter.

Aims and work steps

The aim of this doctoral thesis is to gain a better understanding of desorption processes and of irreversible adsorption in the applications of technical adsorbents such as hydroxides/oxides and activated carbon. The studies will use specific adsorption and desorption methods to derive the extent of these processes and phenomena. The work steps include: (i) Single solute adsorption studies will be performed on three selected and powdered adsorbents, followed by kinetic desorption experiments into the same solution without the target (“adsorption swing”). Solutes are arsenate-(V) for hydroxides and carbamazepine (a persistent pharmaceutical) for activated carbon. (ii) Two-step adsorption tests with two competing target compounds, added one after the other in equilibrium experiments, will be used to detect irreversible adsorption which is influenced by competition. The results will be compared with simultaneous adsorption of the binary mixtures and the single isotherms. (iii) Studies with differential adsorption filters will be designed for granular adsorbents, preloaded with single solutes or defined mixtures of target substances. These filters will allow determinations of kinetic desorption parameters, such as internal and external mass transport from the sorbent. As preloaded adsorbents from practical adsorption processes are available, these studies are extended to complex real systems, including desorption of organic background substances (Natural Organic Matter, NOM) from activated carbons.

Connections to interfaces and other doctoral theses

This doctoral thesis is directed to studies at technical interfaces of water with contaminants and selected solid adsorbents used in water treatment technologies. It will help to solve some scientific and technical aspects of desorption and of irreversible adsorption. A close collaboration on adsorption and desorption with T1 is planned to compare technical components such as activated carbon and iron oxides with anthropogenic dust components such as Black Carbon or organic matter in soils. There will be further collaboration with T6 on experimental work, namely the analysis of organic trace pollutants with a recent LC-MS-MS, and with N6 on adsorption/desorption.

 

References

Axe,L. & Trivedi,P. (2002): Intraparticle surface diffusion of metal contaminants and their attenuation in microporous amorphous Al, Fe, and Mn oxides. J. Colloid Interf. Sci., 247 (2), 259-265

Badruzzaman,M., Westerhoff,P. & Knappe,D.R.U. (2004): Intraparticle diffusion and adsorption of arsenate onto granular ferric hydroxide (GFH). Wat. Res., 38 (18), 4002-4012

Driehaus,W., Hildebrandt,U. & Jekel,M. (1998): Granular ferric hydroxide-A new adsorbent for the removal of arsenic from natural water. Journal of Water Supply Research and Technology-Aqua, 47 (1), 30-35

Genz,A., Baumgarten,B., Goernitz,M. & Jekel,M. (2008): NOM removal by adsorption onto granular ferric hydroxide: Equilibrium, kinetics, filter and regeneration studies. Wat. Res., 42 (1-2), 238-248

Genz,A., Kornmüller,A. & Jekel,M. (2004): Advanced phosphorus removal from membrane filtrates by adsorption on activated aluminium oxide and granulated ferric hydroxide. Wat. Res., 38 (16), 3523-3530

Hongshao,Z. & Stanforth,R. (2001): Competitive adsorption of phosphate and arsenate on goethite. Environ. Sci. Technol., 35, 4753-4757

Li,L. & Stanforth,R. (2000): Distinguishing adsorption and surface precipitation of phosphate on goethite (α-FeOOH). J. Colloid Interf. Sci., 230, 12-21 

Loring,J.S., Sandstrom,M.H., Noren,K. & Persson,P. (2009): Rethinking arsenate coordination at the surface of goethite. Chem. Eur. J., 15 (20), 5063-5072

Sontheimer,H., Crittenden,J.C. & Summers,R.S. (1988): Activated carbon for water treatment. DVGW-Forschungsstelle am Engler-Bunte-Institut der Uni. Karlsruhe, Karlsruhe 

Sperlich,A., Werner,A., Genz,A., Amy,G., Worch,E. & Jekel,M. (2005): Breakthrough behavior of granular ferric hydroxide (GFH) fixed-bed adsorption filters: modeling and experimental approaches. Wat. Res., 39 (6), 1190-1198

Sperlich,A., Schimmelpfennig,S., Baumgarten,B., Genz,A., Amy,G., Worch,E. & Jekel,M. (2008): Predicting anion breakthrough in granular ferric hydroxide (GFH) adsorption filters. Wat. Res., 42 (8-9), 2073-2082

Sperlich,A., Zheng,X., Ernst,M. & Jekel,M. (2008): An integrated wastewater reuse concept combining natural reclamation techniques, membrane filtration and metal oxide adsorption. Wat. Sci. Technol., 57 (6), 909-914

Worch,E. (2008): Fixed-bed adsorption in drinking water treatment: a critical review on models and parameter estimation. Journal of Water Supply: Research and Technology-AQUA, 57 (3), 171-183

 

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