Abstract
The impact of structural properties of three commercial PACs as well as two mechanically ground PACs on their efficiency in NOM removal and fouling reduction in combined adsorption-ultrafiltration (PAC-UF) of northern German groundwater was investigated. All PACs showed highest adsorption affinity for medium molecular weight NOM fractions. The meso-pore surface area rather than the total surface area (B.E.T.) mainly governed the extent of NOM removal. However, adsorption of macromolecular NOM fractions, which were found to be the main contributor to total and irreversible fouling, was limited by tested commercial carbons, and no significant mitigation of fouling was achieved by any tested PAC concentration. Lowering the particle size by grinding of the PAC, however, enhanced removal of macromolecular NOM fractions considerably, and fouling mitigation occurred at substantially lower PAC concentrations compared to raw carbons. A larger external surface area probably let to more shell adsorption, a more homogeneous particle distribution on the membrane surface and a better mass transport. In addition, comparison of the adsorption isotherms of raw and milled PACs showed that, due to the grinding of PAC particles, additional inner pores structures became available for NOM adsorption. Results of this study point out that structural properties of PAC dramatically influence the efficiency of combined PAC-UF, which needs to be considered during PAC selection and process design.
Highlights
Natural organic matter (NOM) is ubiquitous in drinking water sources
NOM originates from degradation of aqueous and terrestrial plants as well as from microbial excretion
2) and provide larger surface provide for adsorption. These results suggest that a higher inner surface area does not necessarily lead to a higher
Summary
Natural organic matter (NOM) is ubiquitous in drinking water sources. The term “NOM” is used to designate all organic material in an aqueous ecosystem other than living organism and compounds of anthropogenic origin [1]. NOM originates from degradation of aqueous and terrestrial plants as well as from microbial excretion. It is a complex mixture of highly heterogeneous compounds including an infinite number of single compounds extremely difficult to identify. It is common practice to classify groups of substances with similar properties, related to, e.g., size, hydrophobicity, and reactivity. NOM contains substances with a broad range of molecular weight, including macromolecular humic substances, polysaccharides and proteins, medium molecular amino sugars, peptides, lipids as well as small hydrophilic acids and neutrals
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